Ventilator

Architectural Frameworks to Leverage Ventilation Protocols into Software

Quick and Easy Guide to Initial Ventilator Settings and Rapid Diagnostics

Magical VC Setting FiO2 100-PEEP 5-RR 15-TV 400: In Volume Control (VC) mode, initial settings such as FiO2 at 100%, PEEP at 5 cm H2O, a respiratory rate of 15 breaths per minute, and a tidal volume of 400 mL provide a foundational approach for the management of mechanically ventilated patients. These parameters serve as starting points and must be finely adjusted based on the patient's specific needs and responses, with ongoing monitoring to ensure optimal outcomes.

MV without Referring to PBW: While minute ventilation (MV) calculations ideally utilize predicted body weight (PBW) for accuracy, emergency clinical scenarios might necessitate quick estimations without immediate access to detailed PBW tables. Under such circumstances, a rough MV can be quickly calculated based on the patient's weight: approximately 5 liters per minute for a 50 kg patient, 6 liters for a 60 kg patient, and 7 liters for a 70 kg patient. These preliminary estimates are vital for initial ventilator setup, requiring subsequent adjustments as more information becomes available or as the patient's condition evolves.

Lung Condition Without C_dyn but Quickly Using Plateau Pressure: Dynamic compliance (C_dyn), a detailed measure of lung condition, typically considers values greater than 50 mL/cm H2O as normal, while lower values suggest potential ARDS, necessitating further diagnostics like chest X-rays. However, measuring C_dyn involves time-consuming inspiratory and expiratory holds. A quicker clinical alternative is to observe the plateau pressure. If the plateau pressure, based on an accurate MV computation per PBW, remains below 30 cm H2O, it suggests that the lungs are likely not severely compromised, indicating that the current ventilatory support is within safe limits and avoiding undue lung stress. If the difference between the peak pressure and plateau pressure is less than 5 cm H2O, it may indicate that the lung condition is within an acceptable range.

PEEP Setting Adjustments Based on Chest X-ray Findings: A clear chest X-ray typically warrants a PEEP of 5 cm H2O, while mild, moderate, and severe infiltrations might necessitate settings of 10, 15, and 20 cm H2O, respectively. However, maintaining PEEP below 12 cm H2O is generally advisable to avoid decreasing cardiac output and blood pressure:

Monitoring with Trend Feature - Airway Resistance Associated with Peak Pressure and Lung Condition with Plateau Pressure: When airway resistance increases, it is typically observed as a rise in peak pressure in the ventilator, while plateau pressure remains stable, particularly noticeable in Volume Control (VC) mode. Absence of an upper limit for peak pressure can cause significant increases. Conditions like pneumonia can escalate both peak and plateau pressures, necessitating rigorous monitoring. Utilizing the "Trend" feature of ventilators is crucial as it helps monitor these pressures over 24 hours, facilitating informed clinical decisions. If peak pressure rises while plateau pressure remains stable, this suggests increased airway resistance. Conversely, an increase in both peak and plateau pressures, or just plateau pressure, can indicate deteriorating lung compliance, potentially requiring further assessments such as a chest X-ray.

Use of Ventilator Loop Features: In ventilator management, the loop feature is an invaluable tool for comparing the current respiratory status against specific points in the past, helping identify changes and trends in a patient's condition. Modern ventilators, such as Servo ventilators, often feature a button labeled "Freeze," "Reference," or "Hold" that allows clinicians to compare the current loop with those from previous time points. By pressing this button, you can capture the current graph and overlay it with a graph from a previous time, facilitating a visual comparison of respiratory mechanics. This is particularly useful for evaluating changes when symptoms like sputum obstruction are present.

Note: It is crucial to customize all ventilator settings to the individual needs of the patient, considering their specific medical conditions, responsiveness to initial settings, and changes in their clinical status. This guide provides a foundational framework and should be utilized in conjunction with the latest clinical guidelines and under the supervision of experienced clinicians.

PBW (kg) = 50 + 0.91 × (Height in cm − 152.4)

PBW (kg) = 45.5 + 0.91 × (Height in cm − 152.4)

VT = PBW (kg) × Desired Tidal Volume per kg

f = V̇E / VT

BSA (m²) = sqrt(Height (cm) × Weight (kg) / 3600)

BSA (m²) = 0.007184 × Height (cm)0.725 × Weight (kg)0.425

Lung Protection Strategies

Effective lung protection strategies are essential in mechanical ventilation, particularly when managing conditions such as Acute Respiratory Distress Syndrome (ARDS) and Chronic Obstructive Pulmonary Disease (COPD).

Plateau Pressure Management: It is crucial to keep the peak inspiratory pressure (PIP) below 40 cm H2O to mitigate the risk of barotrauma and volutrauma. For ARDS patients, ensuring the plateau pressure remains at or below 30 cm H2O is imperative. The driving pressure — defined as the difference between plateau pressure and Positive End-Expiratory Pressure (PEEP), also known as 'Pressure above PEEP' — should not exceed 15 cm H2O to prevent lung injury. This approach, supported by findings from Marcelo B.P. Amato et al. (NEJM, 2015), demonstrates that maintaining the driving pressure below 15 cm H2O significantly enhances survival outcomes by minimizing lung stress and reducing the risk of ventilator-induced lung injury (VILI).

Considerations for Managing Airflow Obstruction in COPD and Complicated Cases: In conditions like COPD where severe airflow obstruction is prevalent, it may be necessary to maintain a peak inspiratory pressure above 50 cm H2O to ensure adequate ventilation, especially since the plateau pressure is likely to stay below 30 cm H2O. This helps prevent hypoventilation and maintains sufficient oxygen delivery. However, special caution is necessary when COPD is complicated by conditions like new onset pneumonia, where unrestricted peak pressures can significantly increase plateau pressures, elevating the risk of lung injury. It is essential to meticulously monitor and adjust ventilator settings to keep the plateau pressure within safe limits.

Tidal Volume Adjustment: To prevent lung overdistension and minimize the risk of VILI, a lower tidal volume of 4 to 6 mL/kg of predicted body weight (PBW) is recommended for ARDS patients. Patients without ARDS can typically tolerate a standard tidal volume ranging from 6 to 8 mL/kg of PBW. (Generally, a lung condition is considered stable if the plateau pressure remains below 30 cm H2O, even when a tidal volume of 400 mL is used. This stability indicates that the lungs are not being overdistended and that the mechanical ventilation is within safe limits to support the patient's respiratory needs without causing additional harm.)

Ventilator Modes and Required Variable Settings

The table below provides a structured overview of common ventilator modes, arranged from those relying primarily on machine-driven parameters to those granting greater patient autonomy. Each mode lists the primary control variable, mandatory settings (with typical ranges where applicable), and additional adjustable parameters. The ranges and values are considered guidelines and may vary depending on clinical judgment and individual patient needs.

Written on December 12th, 2024

Control Mode

Operational Differences and Patient Outcomes between VC and PC Ventilation

Practically speaking, a significant advantage of Volume Control (VC) ventilation is its ability to allow a single clinician to manage multiple patients simultaneously, especially in scenarios that require interventions like sputum suction, which can decrease minute ventilation (MV). In such situations, VC automatically increases the peak pressure to maintain the predetermined tidal volume (TV), giving clinicians additional flexibility and time to manage other tasks. Conversely, Pressure Control (PC) ventilation maintains a fixed pressure, which does not automatically adjust in response to changes in patient conditions, such as diminished TV due to airway obstruction. This characteristic necessitates a more immediate and direct response from clinical staff to ensure patient safety and effective ventilation.

Pressure Control (PC) ventilation offers several significant benefits due to its decelerating flow characteristics. Firstly, it is highly recommended for neonates because it reduces the risk of complications. Secondly, PC ventilation typically results in lower peak inspiratory pressures (PIP), which can minimize the risk of lung injury. The decelerating flow pattern in PC ventilation results in lower PIP because it better accommodates the natural compliance and resistance of the lungs. In contrast, the constant flow pattern in Volume Control (VC) ventilation can lead to higher PIP due to the inability to adjust to varying airway resistance dynamically. Additionally, an increase in mean airway pressure (MAP) can reduce dead space and enhance oxygenation. Furthermore, PC improves patient-ventilator synchrony and reduces the work of breathing (WOB), thereby decreasing the likelihood of the patient 'fighting' the ventilator. This is particularly advantageous as PC allows for flexible adjustment of the inspiration time, contributing to more natural breathing patterns that better meet the dynamic needs of the patient.

Plateau Pressure: In Volume Control (VC) mode, plateau pressure is not directly visible during regular ventilation cycles. It must be measured using an inspiratory pause, where airflow is briefly halted at the end of inspiration to allow pressures within the lung to equalize, giving a true measure of plateau pressure. Also, during the T-pause, which is the pause time during VC mode, the plateau pressure is estimated effectively due to the cessation of airflow, which allows for pressure equilibration across the pulmonary system, reflecting the pressure exerted by the ventilator against the lung compliance. In Pressure Control (PC) mode, since the ventilator delivers a preset pressure and maintains it throughout the inspiratory phase, the peak pressure is effectively the plateau pressure.

A Hybrid Approach of Volume Control and Pressure Modulation in PRVC

Pressure Regulated Volume Control (PRVC) integrates the precision of Volume Control (VC) with the protective features of Pressure Control (PC), forming a unique and dynamic approach to mechanical ventilation. In this mode, a preset tidal volume is targeted, much like in VC, but the delivery method adapts characteristics of PC by adjusting the inspiratory pressure automatically on a breath-to-breath basis. This adaptability ensures the set volume is delivered with the minimum necessary pressure, enhancing patient safety by reducing the risk of barotrauma. The key settings include not only the tidal volume but also an adjustable inspiratory pressure (capped at an upper limit to prevent lung injury), respiratory rate, inspiratory time, and positive end-expiratory pressure (PEEP), which aids in maintaining alveolar stability and improving oxygenation.

The operational flexibility of PRVC becomes particularly advantageous when managing patients with variable lung mechanics. If a drop in the delivered tidal volume is detected, the system initially applies a volume-type strategy, automatically adjusting to a pressure-type mode if the volume shortfall persists. This ensures the intended tidal volume is maintained even under changing physiological conditions. As the patient's lung mechanics stabilize and tidal volume recovers, the system responsively lowers the peak pressure. This dynamic adjustment not only optimizes gas exchange and lung protection but also minimizes the risk of ventilator-induced lung injuries, making PRVC an essential tool in modern respiratory care, particularly in scenarios where both volume consistency and pressure mitigation are critical. (Additionally, PRVC employs a decelerating flow waveform, similar to PC, enhancing gas exchange and matching ventilation closely to the patient's needs.)

Drawbacks: If the patient's airway resistance increases, the peak pressure cannot rise as rapidly or effectively as in PC mode due to the inherent limitations of PRVC. PRVC adjusts pressure gradually, both increasing and decreasing it slowly. This slower adjustment can lead to delays in reaching the necessary inspiratory pressure during sudden changes in the patient's airway resistance or compliance, making PRVC less responsive in acute situations where rapid pressure adjustments are necessary. Additionally, PRVC's dependence on accurate real-time respiratory data means that sudden changes in the patient's condition or data errors might prevent timely adjustments, potentially leading to inappropriate ventilatory support. Noteworthily, during procedures such as sputum suctioning, the removal of airway obstructions can suddenly reduce airway resistance. PRVC might respond by delivering a higher tidal volume than intended before recalibrating, risking overdistension of the lungs. This potential for increased tidal volume underscores the importance of careful monitoring during such procedures.

Dynamics of Pressure-Driven Ventilation

(A) Understanding PC and PS Mode

Ventilator pressure modes are categorized into controlled and support modes, each tailored to different patient needs. In controlled mode, the ventilator autonomously delivers breaths at preset times and volumes, which is essential for patients who are unconscious or unable to breathe voluntarily. This mode ensures that the patient receives adequate ventilation without relying on their respiratory effort, leading to generally seamless synchrony between the patient and the ventilator due to the absence of patient-initiated breathing efforts.

Conversely, support mode is designed to work in harmony with the patient's own respiratory efforts. It dynamically adjusts variables such as the inspiratory to expiratory (I:E) ratio, inspiratory time, tidal volume, and trigger sensitivity based on the patient's initiated breaths. This mode is particularly beneficial for conscious patients who are capable of voluntary breathing but still require assistance to maintain adequate ventilation. However, achieving synchrony in support mode can be challenging, as the ventilator must finely tune its responses to closely match the timing and intensity of the patient's spontaneous breaths.

Specific considerations arise within these modes, especially concerning Pressure Control (PC) and Pressure Support (PS) ventilation. In PC mode, patients with conscious and voluntary breathing may face synchrony challenges because the fixed pressure delivery might not align perfectly with their natural breathing patterns. This misalignment can lead to discomfort or inefficiency in ventilation support.

In contrast, PS mode often proves more suitable for conscious patients who can initiate breaths. This mode allows for a more natural interaction with the ventilator, which can significantly improve both synchrony and comfort by adapting the ventilation support more closely to the patient's actual respiratory needs. The inspiratory time in PS mode isn't set by the clinician but is instead determined by the patient's inspiratory effort and the cycle-off criteria, typically based on a percentage of peak inspiratory flow. This approach makes the inspiration time more dynamic and patient-driven, reflecting their current respiratory status and contributing to a more personalized ventilation strategy.

Overall, support mode is crucial for patients who are capable of participating in their own breathing yet require assistance to achieve or maintain adequate ventilation. This mode's flexibility helps accommodate individual respiratory patterns and reduces the work of breathing, making it a preferred option for patients in the process of recovering respiratory function.

(B) Adjusting Inspiratory Settings

Adjusting inspiratory settings for better outcomes in mechanical ventilation involves meticulous management of the dynamics between Pressure Control (PC) and Pressure Support (PS) ventilation modes. In PC ventilation, manual adjustment of the inspiratory time (Ti) is crucial to maintain patient-ventilator synchrony. Typically, longer Ti settings are well-tolerated during sleep, but adjustments may be necessary when a patient awakens and becomes more active. Changes in the breathing pattern, often observable on the pressure graph as an upward trend at the end of inspiration, indicate the patient's attempt to exhale while the ventilator continues to deliver air. Reducing Ti in these instances helps align the ventilator support with the patient's natural desire to breathe more shallowly or exhale, thereby reducing the risk of patient-ventilator asynchrony, often referred to as "fighting the ventilator."

In PS ventilation, the inspiratory cycle-off setting is critical. This setting determines when the ventilator ceases inspiratory pressure support and transitions to expiration, based on a predefined percentage of peak inspiratory flow. Typically, the inspiratory cycle-off is set to terminate inspiration at about 25% of the peak inspiratory flow. Adjustments to this setting are necessary when patients exhibit signs of discomfort or asynchrony, such as trying to exhale while still in the inspiratory phase. Decreasing this percentage to around 15% can allow the ventilator to switch to the expiratory phase sooner, thus reducing the risk of breath stacking and enhancing comfort. This adjustment better synchronizes the ventilator with the patient's breathing efforts, particularly if the patient completes their inhalation quickly or feels that the breaths are too long. Conversely, increasing the cycle-off percentage to around 50% prolongs the time the ventilator provides support during inhalation. This can be beneficial if the patient feels they are not getting enough air before the ventilator cycles off, as it allows more complete inhalation according to the patient's needs.

However, in PS mode, adjusting Ti is not an option since it is inherently designed to be patient-driven. The duration of inspiration is determined by the patient's inspiratory effort and the cycle-off setting, rather than a fixed time set by the clinician. This design emphasizes the supportive nature of PS ventilation, giving patients greater control over their breathing patterns, which is especially vital for those with varying levels of respiratory drive. This approach allows inspiration time to be more dynamic and patient-driven, reflecting their current respiratory needs and efforts, and enhances overall patient comfort and ventilator efficiency.

(C) Understanding and Managing Double Triggering in Mechanical Ventilation

Double triggering is a significant issue in mechanical ventilation, particularly in Pressure Support (PS) and Pressure Control (PC) modes, with a higher occurrence in PS. This phenomenon arises when the ventilator's sensitivity settings fail to align with the patient's actual respiratory demands, or if the inspiratory time set by the device does not synchronize with the patient's natural breathing pattern. Such misalignments can lead to a scenario where a patient initiates a second breath while the first is still being completed, potentially disrupting both patient comfort and the efficiency of the ventilation process.

In PS mode, the ventilator responds to the patient's breathing efforts, and if these efforts trigger the ventilator prematurely during the inspiratory cycle, double triggering may occur. This typically happens if the patient attempts to breathe in again before the machine has completed the cycle, which ideally should transition into expiration. In PC mode, although the ventilators are programmed with preset inspiratory times to mitigate this issue by strictly controlling the breathing cycles, mismatches with the patient's natural respiratory rhythm can still lead to synchronization problems and subsequent double triggering.

To manage and prevent double triggering effectively, it is crucial to ensure that the ventilator settings are meticulously adjusted to the patient's current respiratory status. This includes fine-tuning the sensitivity settings and inspiratory times to better match the patient's natural breathing patterns, thus minimizing the risk of premature initiation of a second breath.

(D) Adjusting Trigger Sensitivity for Improved Patient-Ventilator Synchrony

Effective management of ventilator settings, particularly trigger sensitivity, is essential, especially in the presence of leaks. The default setting for flow trigger sensitivity is typically +2, which detects changes in flow rate to initiate ventilation in response to patient-initiated respiratory efforts. To minimize the risk of auto-triggering due to a leak, it may be necessary to adjust this setting to -2 or lower. Settings in negative values use pressure triggers, which are more precise in detecting actual decreases in pressure, thus ensuring a more accurate response to genuine respiratory efforts and reducing false triggers.

For neonatal patients, who exhibit unique respiratory dynamics, a higher sensitivity setting of +5 may be required. This adjustment ensures that the ventilator can effectively detect the subtle respiratory efforts typical in neonates, which might not activate standard sensitivity settings.

(E) Challenges in ARDS Patients

In scenarios involving patients with Acute Respiratory Distress Syndrome (ARDS), the severely compromised lung function results in rapid exhalation phases, making Pressure Support Ventilation (PSV) unsuitable. PSV depends heavily on the patient's spontaneous breathing, which may be insufficient or unstable in ARDS cases. Consequently, Pressure Control Ventilation (PCV) is generally preferred as it provides better control over the breathing cycle with fixed pressure delivery, aiding in synchronizing ventilation with the patient's respiratory needs.

However, even in PCV, mismatches between the set inspiratory times and the patient's natural breathing rhythm can lead to double triggering — where the ventilator delivers two breaths in rapid succession without allowing for a full exhalation in between. Managing these cases may necessitate clinicians to adjust the trigger sensitivity to make the ventilator less responsive to minor respiratory efforts, increase the volume settings for more complete breaths, or use sedation to moderate the patient's spontaneous breathing efforts, thereby enhancing overall control over ventilation.

(F) Optimizing Pressure Rise Settings

In Pressure Control (PC) mode, rapid increases in pressure at the onset of inspiration can sometimes lead to disruptions in the ventilator's pressure graph, which may appear as abrupt changes or instabilities. Such occurrences can compromise the smooth delivery of ventilation and potentially affect patient comfort. To address this issue, it's essential to adjust the 'T insp rise' setting, which controls the rate at which pressure increases during the inspiratory phase.

Typically, if this setting is at zero (or off), the pressure rise is immediate and steep, leading to what might be perceived as an abrupt start to inspiration. Incrementally adjusting this setting by 5% or 10% allows for a more gradual and controlled pressure increase. This modification helps smooth out the initial pressure transition, thereby stabilizing the pressure graph at the beginning of inspiration. Such adjustments not only enhance the mechanical performance of the ventilator but also improve patient-ventilator synchrony and reduce potential stress on the patient's respiratory system.

(G) "PC above PEEP" and Driving Pressure: Insights from Marcelo B.P. Amato et al. (NEJM, 2015)

In Pressure Control (PC) mode, "PC above PEEP" refers to the pressure set above the baseline Positive End-Expiratory Pressure (PEEP) during the inspiratory phase, and this value is equivalent to the driving pressure. According to the study by Marcelo B.P. Amato et al. (NEJM, 2015), driving pressure (ΔP) is a critical factor associated with survival in patients with acute respiratory distress syndrome (ARDS). The study found that lower driving pressures, achieved by adjusting ventilator settings to avoid increases in peak inspiratory pressure (PIP) while optimizing PEEP, were strongly linked to improved survival rates.

Ventilator Asynchrony

Strategies for Managing Patient-Ventilator Asynchrony

Active Inspiration: Protecting lung integrity is critical, as highlighted by studies such as "Driving Pressure and Survival in the Acute Respiratory Distress Syndrome" by Marcelo B.P. Amato et al. (NEJM, 2015) and "Ventilation with Lower Tidal Volumes as Compared with Traditional Tidal Volumes for Acute Lung Injury and the Acute Respiratory Distress Syndrome" by The Acute Respiratory Distress Syndrome Network (NEJM, 2000). However, strict adherence to these guidelines might lead to insufficient breathing, potentially causing double triggering if patients inhale more than the set tidal volume. To mitigate this, clinicians may consider increasing the tidal volume, adjusting trigger sensitivity, or sedating the patient to decrease spontaneous efforts. Raising the trigger level can enhance ventilator response to patient-initiated breaths, while reducing it helps prevent double triggering. Modifications to ventilator alarm settings, such as the low PEEP alarm, are also often necessary. In Pressure Control (PC) mode, inspiratory time (Ti) is generally set between 0.8 to 1.25 seconds but may be shortened to minimize ventilator conflict. Unlike PC mode, Pressure Support (PS) mode does not allow direct control over Ti, thus incrementally adjusting the "End Inspiration" or "Esens" settings from 30% to 50% can assist in better managing breath termination timing.

Active Expiration: Challenges during expiration, particularly with high Positive End-Expiratory Pressure (PEEP) settings, increase work of breathing (WOB), potentially causing discomfort and leading to non-compliance with ventilation. Shortening the expiratory time in PC mode can effectively address these issues. In PC mode, adjusting the expiratory time primarily involves altering the inspiratory time (Ti) and the respiratory rate (RR), as these settings will indirectly affect how long the expiratory phase lasts. For example, decreasing the Ti from 1.2 seconds to 0.8 seconds and maintaining a consistent respiratory rate will naturally extend the expiratory phase. In Pressure Support (PS) mode, expiratory time adjustment differs since inspiratory time is typically patient-driven. Adjusting the "cycling off" criteria, for instance, setting it to terminate inspiration when the flow decreases to 25% of the peak flow rate, will typically shorten the inspiratory phase and potentially increase the expiratory time.

Managing Leaks: Leaks in Volume Control (VC) mode particularly pose challenges, as they can prevent the ventilator from delivering the set tidal volume accurately. This shortfall in delivered volume can destabilize vital signs and may prompt incorrect ventilator adjustments. "End Inspiration" settings may need to be adjusted upwards (e.g., from 30% to 50%), and "Trigger Pressure" should be set to a less sensitive level (ranging from -10 to -20). Regular checks, such as ensuring proper ET tube cuff pressurization and verifying ventilator integrity with a test lung, are essential for identifying equipment-related issues. If leaks persist, increasing minute ventilation (MV) may temporarily resolve issues until more definitive solutions like reintubation or manual bagging are executed.

Biased Flow: Biased flow maintains a continuous stream of air through the mechanical ventilation system, aiding in keeping airways open and detecting spontaneous breathing efforts. Typically set at 2 liters per minute, biased flow comprises a significant part of the total ventilation volume. For example, out of a total of 9 liters, 7 liters are ventilator-delivered, and 2 liters are biased flow. An active inhalation of 1.6 liters (or 80% of the biased flow) by a patient indicates effective inspiration. For smaller or weaker patients, increasing the biased flow (from 2L to 3L or 4L) ensures even minimal efforts are recognized, thus easing their breathing work. However, too high a setting may induce auto-triggering, where minor disturbances are mistakenly interpreted as breathing attempts. Adjusting sensitivity settings can help mitigate auto-triggering, ensuring the ventilator supports only genuine respiratory efforts.

Improving Patient-Ventilator Synchrony Through Neurally Adjusted Ventilatory Assist (NAVA)

Neurally Adjusted Ventilatory Assist (NAVA) represents a progressive form of mechanical ventilation that optimizes the synchronization between the ventilator and the patient by leveraging the electrical activity of the diaphragm (EAdi). This technology allows the ventilator to respond dynamically to the patient's breathing needs, ensuring that assistance is provided in direct correlation with their respiratory effort. This method not only enhances comfort but also aligns precisely with the patient's natural respiratory drive, crucial for those who can breathe spontaneously but require additional support due to conditions like respiratory failure or challenges in weaning from mechanical support.

The functionality of NAVA hinges on the continuous monitoring of Edi, which acts as the primary trigger for ventilatory assistance. When a patient initiates a breath, the resulting electrical activity of the diaphragm prompts the ventilator to deliver pressure proportionate to this signal, ceasing as the signal diminishes. This responsive system adapts to the patient's breathing needs in real-time, offering a level of support directly correlated to their respiratory muscle effort, thereby mitigating the risks of over- or under-ventilation and enhancing comfort.

The principle of NAVA lies in its ability to detect and utilize the diaphragm's electrical signals as the direct driver for ventilatory assistance. The ventilator adjusts its support based on real-time changes in EAdi, providing a tailored respiratory aid that prevents the common pitfalls of conventional ventilation, such as asynchrony or mismatched timing and intensity of support. This responsiveness to the patient's own respiratory signals makes NAVA particularly advantageous for patients with varying respiratory drive and those susceptible to discomfort with traditional mechanical ventilation methods. However, the efficacy of NAVA can be compromised in patients with conditions that impede the generation or detection of accurate EAdi signals, such as severe diaphragmatic dysfunction, certain neuromuscular disorders, or obstructive esophageal pathologies that prevent proper catheter placement.

NAVA is particularly beneficial in conditions like Acute Respiratory Distress Syndrome (ARDS) in adults and Respiratory Distress Syndrome (RDS) in neonates. It's also indicated in cases of pulmonary hypertension and scenarios requiring detailed assessment of respiratory activity, such as in central hypoventilation syndrome. However, its application is limited by conditions that affect the diaphragm's ability to generate reliable Edi signals, such as neuromuscular disorders, severe diaphragmatic dysfunction, or esophageal anomalies, which might impede the placement or function of the necessary esophageal catheter.

Setting up a NAVA system requires meticulous initial adjustments to ensure optimal patient support. These settings include establishing the NAVA level, which is calculated by the formula NAVA level x (Edi max - Edi min) + PEEP, and determining the trigger sensitivity. The chosen NAVA level, expressed in cmH₂OμV, should aim for a target Edi range of 5-20 μV, adjusted based on observed Edi max values to either enhance or reduce ventilatory support.

Clinically, NAVA has shown to significantly improve patient-ventilator synchrony, reducing the risks associated with mechanical ventilation such as ventilator-induced lung injury. By supporting the natural breathing pattern of the patient rather than overriding it, NAVA facilitates a more physiological form of respiratory support, which can lead to better outcomes in the weaning process and overall patient comfort. Its capability to adjust support based on the patient's immediate respiratory muscle output distinguishes it from other assisted modes like Pressure Support Ventilation (PSV), which may not accurately align support with patient effort.

The real-world application of NAVA, especially in complex clinical scenarios, underscores its significant benefits. Studies have documented improved outcomes in diverse patient populations, including adults with acute respiratory conditions and neonates experiencing respiratory distress (Beck et al., 2009; Breatnach et al., 2010). The ability to maintain effective ventilation despite challenges such as air leaks — common in both invasive and non-invasive forms of ventilation — further demonstrates NAVA's robustness (Beck et al., 2009). Its adaptability extends to non-invasive applications, where it can be used with nasal prongs or masks, allowing for a smoother transition from invasive to non-invasive support and potentially reducing the need for higher pressures typically required in conventional ventilation settings (Makker et al., 2020).

• Shah, S. D., & Anjum, F. (2024). Neurally Adjusted Ventilatory Assist (NAVA). In StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK572111/
Beck, J., Reilly, M., Grasselli, G., Mirabella, L., Slutsky, A. S., Dunn, M. S., & Sinderby, C. (2009). Patient-ventilator interaction during neurally adjusted ventilatory assist in low birth weight infants. Pediatric Research, 65(6), 663-668. https://doi.org/10.1203/PDR.0b013e31819e72ab
• Breatnach, C., Conlon, N. P., Stack, M., Healy, M., O'Hare, B. P. (2010). A prospective crossover comparison of neurally adjusted ventilatory assist and pressure-support ventilation in a pediatric and neonatal intensive care unit population. Pediatric Critical Care Medicine, 11(1), 7-11. https://doi.org/10.1097/PCC.0b013e3181b0630f
• Makker, K., Cortez, J., Jha, K., Shah, S., Nandula, P., Lowrie, D., Smotherman, C., Gautam, S., & Hudak, M. L. (2020). Comparison of extubation success using noninvasive positive pressure ventilation (NIPPV) versus noninvasive neurally adjusted ventilatory assist (NI-NAVA). Journal of Perinatology, 40(8), 1202-1210. https://doi.org/10.1038/s41372-019-0578-4

Spontaneous Breathing and Ventilator Weaning

A Comparative Analysis of Ventilation Modes for Patients with Spontaneous Breathing

When considering the various modes of mechanical ventilation with spontaneous patient breathing — Spontaneous Timed (ST), BiPAP (Bilevel Positive Airway Pressure), BiVent/APRV (Airway Pressure Release Ventilation), Volume Support (VS), Pressure Support (PS), and CPAP (Continuous Positive Airway Pressure) — it's essential to understand both their operational characteristics and the freedom they afford to patients. Each mode requires specific parameters to be set, ensuring optimal ventilation and patient comfort during respiratory support:

• ST: EPAP/IPAP, RR, FiO2, and Ti
• BiPAP: EPAP/IPAP, RR, FiO2 (, and Ti as the maximum duration of inspiration allowed by the ventilator)
• PS: FiO2, PEEP, and PS above PEEP
• CPAP: FiO2, CPAP, and trigger sensitivity

In understanding these modes, it's crucial to note that PS mode with 'PS above PEEP' set at zero essentially functions as CPAP, offering continuous positive airway pressure without additional support during inspiration. This equivalence underscores the versatility of PS mode, adapting its function based on settings to meet patient needs. BiPAP, on the other hand, provides variable pressure support during both inhalation and exhalation, offering enhanced ventilation assistance compared to CPAP or PS alone. However, despite its efficacy, BiPAP may feel more restrictive to patients due to its dual-pressure levels. Conversely, CPAP, whether delivered independently or through PS mode, offers continuous support with less complexity, potentially affording patients a greater sense of freedom in their breathing.

When considering freedom to breathe, PS mode stands out as it allows patients to initiate breaths spontaneously and breathe at their own pace. This mode synchronizes with the patient's respiratory effort, providing additional support when needed, while still allowing for variability in breathing rates and patterns. ST mode, while offering partial ventilatory support, imposes fixed intervals for mandatory breaths, which may feel somewhat restrictive compared to the flexibility of PS mode. BiPAP, with its dual-pressure levels, offers tailored support during both inspiration and expiration but may feel more constraining due to its preset parameters. CPAP, whether provided independently or through PS mode, offers continuous positive airway pressure without additional support during inspiration, providing a stable environment for breathing but potentially lacking the adaptability of PS mode.

BiVent/APRV is notable for its innovative ventilation strategy that emphasizes spontaneous breathing across the entire respiratory cycle. This mode operates by maintaining a high baseline airway pressure to optimize oxygenation and alveolar recruitment, while periodically dropping to a lower pressure to allow for CO2 elimination without disrupting the patient's natural breathing attempts. The high pressure phase supports the alveoli continuously, which is critical for patients experiencing severe respiratory distress. In contrast, the brief, controlled lower pressure phase acts like a sigh, aiding in more effective CO2 removal. This mode's ability to allow spontaneous breathing throughout its cycle offers a significant improvement in patient comfort compared to more traditional, restrictive methods.

Volume Support (VS), on the other hand, provides a blend of controlled and supportive ventilation, ideal for patients who are capable of initiating breaths but require assistance in achieving consistent tidal volumes due to varying respiratory muscle strength or lung compliance. Once a patient initiates a breath in VS mode, the ventilator adjusts the pressure dynamically to deliver a predetermined tidal volume. This adaptability ensures adequate ventilation while permitting the patient to control the timing and frequency of breaths, thereby reducing fatigue and promoting a more natural breathing pattern. Unlike modes such as Pressure Support (PS) or BiPAP, VS not only supports the breath initiated by the patient but also guarantees the delivery of a specific volume, adjusting pressure as needed on a breath-by-breath basis to maintain consistent minute ventilation.

Ventilation Settings and Their Role in Effective Weaning

Weaning patients from mechanical ventilation is a critical step in their recovery, marking the transition from artificial support back to natural breathing patterns. Typically, humans breathe using negative pressure, where the diaphragm creates a vacuum that draws air into the lungs. In contrast, mechanical ventilation employs positive pressure to push air into the lungs, which can lead to complications such as barotrauma from excessive air pressure and inadequate gas exchange due to low tidal volumes. To mitigate these issues, sedation often facilitates controlled mechanical ventilation with two primary modes: Volume Control (VC), where tidal volume is precisely regulated, and Pressure Control (PC), which adjusts "PC above PEEP" to ensure consistent lung inflation.

As patients stabilize, ventilator settings transition to support modes that allow more spontaneous breathing efforts. Pressure Support (PS) aids each breath initiated by the patient by maintaining "PS above PEEP," while Continuous Positive Airway Pressure (CPAP) maintains a constant pressure to keep the alveoli open, supporting natural lung function but not directly assisting the breathing effort. A notable challenge with support modes like PS is their inability to control the respiratory rate (RR), which can result in apnea if the patient's spontaneous efforts are insufficient.

Transitioning from Controlled Mandatory Ventilation (CMV) to Assisted/Control Mandatory Ventilation (ACMV) is significant, allowing the start of inspiration to be patient-initiated rather than ventilator-initiated, granting more autonomy in the breathing process. For patients requiring intermittent assistance, Synchronized Intermittent Mandatory Ventilation (SIMV) provides mandatory breaths as a backup, set by the SIMV rate, which defines the frequency of controlled breathing. Crucially, if there is an absence of spontaneous patient breathing, the system reverts from ACMV to CMV, ensuring continuous ventilation. However, between controlled breaths, PS can be activated to provide necessary support.

Moreover, transitioning from PS to CPAP involves shifting the control from "PS above PEEP" to a mode where only PEEP is provided, allowing patients under CPAP to utilize negative pressure for breathing. Significantly, if the inspiration strength in PS is set to zero, it effectively transitions the operation to CPAP, emphasizing passive support through maintained PEEP without additional pressure support. This phase is critical as it encourages patients to engage their respiratory muscles more actively, vital for successful weaning.

Assessing Readiness for Ventilator Weaning Using RSBI and P 0.1: To determine if a patient is ready for weaning from mechanical ventilation, two key measures are often evaluated: the Rapid Shallow Breathing Index (RSBI) and the P 0.1 or Occlusion Pressure. The RSBI is calculated by dividing the respiratory rate (RR) by the expiratory tidal volume (VTe) measured in liters. An RSBI value less than 105 breaths per minute per liter is considered indicative of a patient's readiness for weaning. This index, measured during a spontaneous breathing trial, helps assess the patient's workload of breathing, providing a quantitative basis for evaluating their ability to breathe independently.

Additionally, the P 0.1, which is the negative pressure exerted by the patient in the first 100 milliseconds of an occluded airway, is another crucial measure. A P 0.1 value between 1 to 2 cm H2O suggests a lower respiratory drive, which can indicate that the patient may be ready for weaning. This measure provides insight into the patient's respiratory effort and capacity to maintain adequate breathing without ventilatory support. Both the RSBI and P0.1 are essential in providing a comprehensive assessment of a patient's potential to successfully transition off mechanical ventilation.

Rapid Shallow Breathing Index (RSBI) Calculator

Predicts the success of weaning from mechanical ventilation. An RSBI ≤ 105 breaths/min/L is considered an indicator of readiness for weaning.

RSBI = f / VT

Clinical Case Study

Case1: Managing Dyspnea in an ALS Patient with ST Mode Ventilation

Managing a patient with ALS experiencing dyspnea necessitates a nuanced approach to both immediate and long-term respiratory support strategies. An effective initial strategy often includes adjusting the Inspiratory Positive Airway Pressure (IPAP) in Spontaneous/Timed (ST) mode, for example, increasing it from 13 to 15 cm H2O. This adjustment can enhance alveolar ventilation by increasing the tidal volume, potentially alleviating symptoms of dyspnea and reducing the patient's respiratory effort. Such strategic management is essential in addressing progressive neuromuscular conditions like ALS, where muscle weakness can intensify over time, escalating the patient's respiratory workload.

If the patient's dyspnea persists and there is an inclination to remove the ventilator, it might indicate a conflict during inspiration when the patient attempts to exhale. In such scenarios, it is crucial to consider adjusting or increasing the "Cycle" setting of the ST mode from the current 25% gradually upwards. This adjustment can help synchronize the ventilator more closely with the patient's natural breathing cycle, potentially reducing the sensation of fighting the ventilator and improving comfort.

Continuous assessment is crucial to determine if further adjustments or a switch in ventilation mode might offer additional benefits. In cases where adjustments to IPAP alone are insufficient for managing symptoms effectively, or when concerns arise regarding patient comfort and ventilator synchrony, exploring other modes such as BiPAP or CPAP may be warranted.

BiPAP is particularly beneficial due to its capability to independently control both IPAP and EPAP, allowing for customized support during both inhalation and exhalation phases. Unlike ST mode, which primarily focuses on maintaining a minimum number of breaths per minute with less flexibility, BiPAP facilitates dynamic adjustments that can more precisely respond to the patient's varying respiratory needs throughout the day or as their condition changes. This refined approach to respiratory support is especially advantageous in ALS, where patients may experience fluctuating respiratory efforts.

Furthermore, BiPAP can enhance patient-ventilator synchrony by independently and precisely adjusting IPAP and EPAP. This adjustment improves synchrony with the patient's natural breathing cycle, potentially reducing asynchrony and increasing comfort — critical factors for patients who can still initiate breaths but whose respiratory strength may vary. The versatility of BiPAP extends to periods of sleep or varying levels of respiratory muscle fatigue, making it an optimal choice for maintaining comfort and effective ventilation across different states of patient activity and rest.

Pressure Support (PS) mode offers another viable option for patients capable of initiating breaths independently but who require assistance to maintain adequate ventilation. PS mode supports the patient's breathing effort by providing a preset level of pressure support during inhalation, terminated based on the patient's inspiratory flow, thus facilitating a more natural breathing pattern. This mode significantly enhances patient-ventilator synchrony and comfort, particularly beneficial for conscious patients with fluctuating respiratory drive.

Conversely, Continuous Positive Airway Pressure (CPAP) maintains a constant pressure throughout the respiratory cycle. This mode might not suit ALS patients requiring active assistance with inhalation due to muscle weakness. CPAP is generally more appropriate for patients who can maintain adequate spontaneous breathing efforts and primarily need support in keeping their airways open.

Ultimately, the decision to adjust IPAP within ST mode or to transition to another mode such as BiPAP or PS should be driven by ongoing evaluations of the patient's respiratory status, including blood gas analyses and symptom assessment. Regular re-evaluation and close monitoring are essential to ensure that the ventilatory support continues to meet the evolving needs of the ALS patient, striving to achieve an optimal balance of adequate ventilation, patient comfort, and minimal respiratory effort. This comprehensive approach ensures that respiratory management is both effective and adaptable, providing tailored support that evolves with the patient's condition.

Guardian consent obtained for IRB-approved clinical research aimed at disseminating better clinical practices in hemodynamics.

Case2: Tailoring BiPAP Settings for Managing Respiratory Distress with CO2 Retention

In managing respiratory distress in patients using BiPAP ventilation, specific adjustments are essential for those showing signs of hypoventilation and CO2 retention. Typically, these patients demonstrate reduced tidal volumes (Vt) of 150-250 mL, with arterial blood gas (ABGA) analyses indicative of mild respiratory acidosis, typically with a pH slightly below the normal range of 7.35-7.45, and elevated PCO2 slightly above the normal range of 35-45 mmHg. Bicarbonate levels may also be at the upper end of the normal range (22-28 mEq/L), indicating renal compensation. Additionally, an elevated PO2 well above the normal range for room air (75-100 mmHg) suggests the use of supplemental oxygen therapy, which is crucial for managing hypoxemia but requires careful monitoring to avoid complications associated with hyperoxia.

Rationale for Increasing IPAP: An increase in IPAP, for example from 13 to 15 cm H2O, is strategically implemented to enhance alveolar ventilation and improve CO2 clearance. This intervention is essential as it directly increases tidal volume, promoting deeper breaths that not only help in recruiting more alveoli for gas exchange but also effectively eliminate excess CO2.

Reasoning for Lowering Oxygen Supply: Even with stable SpO2 levels above 92%, reducing supplemental oxygen is crucial to prevent oxygen toxicity and hyperoxia, which could suppress respiratory drive — particularly harmful in conditions predisposing to CO2 retention. Adjusting oxygen delivery to maintain SpO2 just above 92% ensures sufficient oxygenation without compromising the patient's inherent respiratory efforts, thereby supporting natural respiratory mechanisms and enhancing overall respiratory function.

Necessity of Manual Adjustment of IPAP: Despite the dynamic capabilities of BiPAP machines to adjust IPAP and EPAP, manual intervention is often required. Automatic adjustments might not always perfectly align with rapidly changing or unique clinical situations due to limitations in preset algorithms. Manually increasing IPAP allows healthcare providers to fine-tune ventilatory settings based on real-time patient responses and specific ventilation goals, ensuring that the therapeutic approach is precisely tailored to achieve optimal outcomes. This level of customization is crucial for effectively managing acute respiratory distress and provides significant advantages over more rigid modes like ST, which are less adaptable to patient-specific needs.

Guardian consent obtained for IRB-approved clinical research aimed at disseminating better clinical practices in hemodynamics.

Case3: Longitudinal Analysis of Ventilator Management in a Patient With Chronic Respiratory Failure

Home Ventilator Application Status
- Chronic CO2 retention and respiratory acidosis
- Compensatory metabolic alkalosis
  
- December 22, 2023: BiPAP initiated
  
- December 29, 2023: Due to diaphragmatic dysfunction, home ventilator initiated in SIMV-PS mode
     Tidal Volume (TV): 300–350 mL
     Inspiratory Pressure (Pi): 10–15 cmH2O
     Respiratory Rate (RR): 16 breaths/min
    
- February 2024: Home ventilator adjusted (SIMV mode)
     Pressure (Pr): 13 cmH2O
     PEEP: 5 cmH2O
     RR: 15 breaths/min
     O2: 1 L/min
    
- March 25, 2024: Changed to PSV mode
     Measured TV: ~300 mL
     Pressure Support (Pr): 12 cmH2O
     PEEP: 5 cmH2O
     RR: 15 → 14 breaths/min

- November 8, 2024: PSV mode continued
     Measured TV: ~300 mL
     Pr: 12 cmH2O
     PEEP: 5 cmH2O
     RR: 14 breaths/min

The patient has chronic CO2 retention and a compensatory metabolic alkalosis, indicating a long-term respiratory failure scenario. Initial noninvasive management (BiPAP) was followed by a transition to a home ventilator setup due to diaphragmatic dysfunction. Over time, the ventilator mode evolved from SIMV with pressure support to PSV, reflecting changes in clinical strategy and attempts to balance stable support with partial patient-driven ventilation. Ultimately, the patient has maintained stability on a PSV configuration without further reductions in pressure support.

Chronological Overview of Ventilator Management

1. December 22, 2023 (BiPAP Initiation)

   Documented Settings: BiPAP (Bilevel Positive Airway Pressure) initiated, but no exact pressures recorded.

   Typical Variables Required:

   • IPAP (Inspiratory Positive Airway Pressure)
   • EPAP (Expiratory Positive Airway Pressure)
   • FiO2 or O2 flow as needed

   Commentary: BiPAP provides two distinct pressure levels. At this stage, it was likely chosen to noninvasively support ventilation, reduce CO2 levels, and alleviate work of breathing. Precise IPAP and EPAP values would be necessary to fully reproduce the initial setup. The missing data here—such as exact pressure levels and O2—suggests incomplete information.

2. December 29, 2023 (Transition to SIMV-PS)

   Documented Settings: SIMV-PS mode: TV ~300–350 mL, Pi 10–15 cmH2O, RR 16 (PEEP and exact FiO2/O2 unknown)

   Typical Variables Required for SIMV-PS:

   • For Volume-Controlled SIMV: Set Tidal Volume, RR, FiO2/O2, PEEP
   • For Pressure-Controlled SIMV: Set Inspiratory Pressure, RR, FiO2/O2, PEEP, and inspiratory time
   • Pressure Support (PS) level for spontaneous breaths above PEEP

   Commentary: Transitioning to SIMV suggests a need for more structured ventilatory support. Some parameters (PEEP, FiO2) are not documented here, making it hard to fully replicate the initial SIMV setup. The mention of Pi (Inspiratory Pressure) suggests a pressure-limited or pressure-supported component for spontaneous breaths.

3. February 2024 (Adjusted SIMV Settings)

   Documented Settings: SIMV: Pr 13 cmH2O, PEEP 5 cmH2O, RR 15, O2 1 L/min

   Typical Variables for SIMV-PS:

   • Pressure Support level (Pr)
   • PEEP
   • Mandatory RR
   • FiO2 or O2 flow

   Commentary: By February, the documentation is more complete: a defined pressure support level (Pr 13 cmH2O) and PEEP (5 cmH2O) are stated, along with RR and O2 flow. This reflects a refinement in the ventilation strategy. The patient is still receiving partial mandatory support (SIMV) along with pressure support for spontaneous breaths. Although O2 is given as 1 L/min, the exact FiO2 remains unreported; still, this information is more sufficient for reproduction compared to December 29, 2023.

4. March 25, 2024 (PSV Mode Initiation)

   Documented Settings: PSV mode: Measured TV ~300 mL, Pr 12 cmH2O, PEEP 5 cmH2O, RR from 15 to 14

   Typical Variables Required for PSV:

   • Pressure Support level (above PEEP)
   • PEEP
   • FiO2/O2 flow
   • The tidal volume and RR are patient-dependent (not “set” but “achieved”)

   Commentary: Switching to PSV reduces mandatory breaths, relying on the patient’s inspiratory effort. Pressure Support (12 cmH2O) and PEEP (5 cmH2O) remain key settings. The measured tidal volume (~300 mL) and recorded RR (14) show patient-driven ventilation within supported parameters. Additional variables (exact FiO2, alarm settings) are not specified, but enough information is present to approximate the scenario.

5. November 8, 2024 (Continued PSV Mode)

   Documented Settings: PSV mode: TV ~300 mL, Pr 12 cmH2O, PEEP 5 cmH2O, RR 14

   Commentary: No change in support parameters since March 25, 2024. This long-term stability suggests the patient’s condition is neither deteriorating nor significantly improving toward lower support. The ventilator settings remain consistent, likely indicating chronic stable respiratory failure management.

Comparing Noninvasive and Invasive Modes, Including CPAP

• BiPAP vs. PSV as Final Steps:
  • BiPAP (Noninvasive): Often considered for patients who do not require intubation, or as a step down from invasive ventilation to noninvasive support at home. It is suitable as a “final step” in noninvasive respiratory support for stable chronic patients.
  • PSV (Invasive): Commonly used as a final step in weaning from invasive mechanical ventilation. Once a patient can maintain adequate ventilation and oxygenation on low levels of PSV, clinicians may consider extubation.
• What About CPAP?
  • CPAP (Continuous Positive Airway Pressure): Provides a single constant pressure level. It improves oxygenation by preventing alveolar collapse but does not offer additional inspiratory support.
  • BiPAP: Offers two pressure levels—IPAP and EPAP. IPAP assists inspiration, while EPAP (similar to PEEP) keeps alveoli open. This dual-level support can augment ventilation and reduce CO2 more effectively than CPAP alone.
• Naming and Variables:
  • BiPAP: "Bi" stands for “Bilevel Positive Airway Pressure,” reflecting the provision of two distinct pressure levels—one for inhalation and one for exhalation.
  • CPAP: "C" stands for “Continuous Positive Airway Pressure,” signifying a single (continuous) level of pressure throughout breathing cycles.
• Required Variables:
  • CPAP: CPAP pressure level, FiO2
  • BiPAP: IPAP, EPAP, FiO2 (or O2 flow)

Weaning Criteria and Advanced Indices

Weaning from mechanical ventilation—whether invasive (via PSV reduction) or noninvasive (gradual reduction in IPAP/EPAP)—typically requires objective and subjective assessments. Common criteria and indices include:

• Respiratory Mechanics and Gas Exchange:
  • Adequate oxygenation (e.g., PaO2 ≥ 60 mmHg on FiO2 ≤ 0.4 and PEEP ≤ 5–8 cmH2O)
  • Stable ventilation with near-normal PaCO2 and pH
• Hemodynamic Stability:
  • No significant hypotension, shock states, or significant arrhythmias
• Spontaneous Breathing Indicators:
  • RSBI (Rapid Shallow Breathing Index):
    • RSBI = (Respiratory Rate) ÷ (Tidal Volume in liters)
    • A value <105 suggests a higher likelihood of successful weaning.
  • Pressure support requirements: Lowering pressure support to 8–10 cmH2O or below without respiratory distress is favorable.
• Other Considerations:
  • Adequate airway protection
  • Mental status allowing cooperation
  • Absence of excessive secretions or severe metabolic derangements

Assessing Future Weaning Potential

By November 8, 2024, the patient remains stable on PSV at Pr 12 cmH2O and PEEP 5 cmH2O, with a tidal volume around 300 mL. To assess further weaning potential, it would be advisable to:

1. Gradually reduce the Pressure Support and observe if the patient can maintain adequate ventilation and comfort at lower levels (e.g., PSV 10 cmH2O).
2. Check RSBI or other parameters under these lowered support conditions.
3. Monitor arterial blood gases, ensure stable hemodynamics, and assess secretion management.

No attempts since March 2024 have been documented to reduce support from PSV 12 cmH2O to a lower level or to shift to a simpler mode (e.g., CPAP only) as a step toward extubation or liberation from mechanical ventilation.

For future monitoring, it would be prudent to consider:

• Trying lower pressure support levels to see if the patient can maintain adequate ventilation and oxygenation.
• Evaluating RSBI and other indexes when spontaneously breathing at lower support levels.
• Assessing cough strength, secretion management, and patient comfort.
• Monitoring arterial blood gases and overall clinical stability during any trial of reduced support.

If the patient tolerates reduced support (e.g., PSV 10 cmH2O or even transitioning to CPAP or minimal support), it may indicate readiness to attempt complete weaning or prolonged noninvasive support only (e.g., BiPAP at home if considered appropriate).

Rapid Shallow Breathing Index (RSBI) Computation

The Rapid Shallow Breathing Index (RSBI) is a clinical parameter used to assess the likelihood of successful weaning from mechanical ventilation. It relates a patient’s respiratory rate (RR) to their tidal volume (Vt), providing insight into respiratory efficiency and effort.

\[ \text{RSBI} = \frac{\text{Respiratory Rate (RR)}}{\text{Tidal Volume (Vt in liters)}} \]

• RR (Respiratory Rate): Measured in breaths per minute.
• Vt (Tidal Volume): Measured in liters. If Vt is given in milliliters (mL), convert it to liters by dividing by 1000.

Choosing the Appropriate Tidal Volume for RSBI

• VTe (Exhaled Tidal Volume): Preferred for RSBI calculations, VTe reflects the actual volume of air the patient exhales. It is less influenced by system compliance or leaks, making it more reliable for evaluating the patient’s respiratory effort and efficiency.
• VTi (Inspiratory Tidal Volume): Can be used if VTe is not available, but it may be less accurate. VTi can be influenced by factors like gas compression or leaks, potentially distorting the true measure of the patient’s respiratory effort.

Why VTe is Preferred

1. Reflects Effective Ventilation: VTe directly measures the patient’s exhaled volume.
2. Reduces External Influences: VTe is less affected by system compliance or leaks, ensuring more reliable RSBI values.

Using VTi If Necessary

If you must use VTi:

• Clearly document that VTi was used instead of VTe.
• Interpret the RSBI values with caution, keeping in mind the potential inaccuracies due to ventilator-related factors.

Example Calculation

• Given:
  • RR = 15 breaths/min
  • Vt = 350 mL = 350 ÷ 1000 = 0.35 L

\[ \text{RSBI} = \frac{15}{0.35} \approx 42.9 \]

An RSBI of about 42.9 is well below the commonly accepted threshold of 105, suggesting that the patient may be ready to begin weaning from mechanical ventilation.

Guardian consent obtained for IRB-approved clinical research aimed at disseminating better clinical practices in hemodynamics.

Written on Decmeber 11, 2024

Case4: An Explanation of SIMV Ventilator Settings: Understanding "IP" and "SP"

Mechanical ventilation modes such as Synchronized Intermittent Mandatory Ventilation (SIMV) allow both mandatory (ventilator-driven) and spontaneous (patient-driven) breaths. Clinicians often use pressure-based settings to control or support these breaths. However, handwritten and device-displayed ventilator settings can sometimes differ in terminology, causing confusion about parameters like IP (Inspiratory Pressure) and SP (Pressure Support). This document clarifies these terms and illustrates how they translate across different devices.

Handwritten Ventilator Settings from the Transfer Request Form

A frequently encountered example is a handwritten note reading:

SIMV | O2 2L | RR 16 | IP 8 | SP 8 | PEEP 5

1. SIMV
Synchronized Intermittent Mandatory Ventilation, a mode where a set number of breaths are delivered by the ventilator at a preset level, while allowing spontaneous breathing in between.

2. O2 2L
Represents an oxygen flow of 2 L/min. Depending on the ventilator model, this may correlate to a specific FiO₂ (Fraction of Inspired Oxygen).

3. RR 16
A mandatory breath rate of 16 breaths per minute.

4. IP 8 → "P control"
Often shorthand for Inspiratory Pressure (in pressure-controlled or assisted modes). In many SIMV modes, “IP” may be the pressure above PEEP delivered during each mandatory breath.

5. SP 8 → "PS"
Common shorthand for Pressure Support for spontaneous breaths. Helps reduce work of breathing by assisting patient-initiated breaths with an additional 8 cmH₂O of pressure.

6. PEEP 5
Positive End-Expiratory Pressure of 5 cmH₂O, preventing alveolar collapse at end-expiration and improving oxygenation.

In this handwritten example, both the mandatory breaths (IP 8) and spontaneous breaths (SP 8) receive a similar pressure level (8 cmH₂O above PEEP).

Confirming IP and SP on a ResMed Device

Later, the ventilator settings were checked on a ResMed device, which displayed:

In this scenario:

• IP (Inspiratory Pressure) in the handwritten note correlates with PC (Pressure Control) on the ResMed device.
• SP (Pressure Support) in the handwritten note is labeled simply as PS on the ResMed device.

Clarifying IP vs. PS

Inspiratory Pressure (IP) / Pressure Control (PC)
Refers to the preset pressure for mandatory breaths. In pressure-controlled SIMV, the ventilator ensures each mandatory breath reaches this target pressure above PEEP.

Pressure Support (PS)
Augments spontaneous breaths initiated by the patient. Eases the patient’s work of breathing by providing extra pressure, helping overcome airway resistance and ventilator circuit resistance.

Typical Ranges for Adult Ventilator Parameters

Ventilator settings vary based on patient condition, but the following ranges serve as general guidelines:

Clinical Implications

1. Balancing Mandatory and Spontaneous Support
   In P-SIMV, maintaining appropriate Inspiratory Pressure (PC/IP) for mandatory breaths and sufficient Pressure Support (PS) for spontaneous breaths is crucial for optimal ventilation and patient comfort.
2. Weaning Strategy
   During weaning, the mandatory breath rate (RR) may be decreased, and Pressure Support (PS) may be gradually reduced to encourage spontaneous breathing. Close monitoring of respiratory effort, arterial blood gases (ABGs), and vital signs guides this process.
3. Customization and Monitoring
   Since no two patients present identically, constant reevaluation of airway pressures, blood gases, and clinical feedback is essential. Adjustments to PEEP, IP/PC, PS, and RR must be made to balance oxygenation, CO₂ removal, and patient comfort.

Guardian consent obtained for IRB-approved clinical research aimed at disseminating better clinical practices in hemodynamics.

Written on February 25, 2025

Case5: Ventilator Weaning in a Neurologically Impaired Patient

A patient with a prior stroke secondary to arrhythmia initially received anticoagulant therapy, followed by a hemorrhagic stroke, which required neurosurgical intervention. After an extended hospitalization (~140 days) with persistent deep drowsiness, the patient was transferred to the current facility on March 21, 2025 for continued neurological care, infection control, and ventilator weaning.

• High secretion burden (requiring frequent suctioning).
• Recurrent pneumonia; currently improved on meropenem.
• Vancomycin-resistant Enterococcus (VRE) necessitating isolation precautions.

Tracheostomy and Auto-Suction Line

The patient has a tracheostomy with a T-tube (size 7.0). An auto-suction line—a specialized, often closed, suction system designed to reduce circuit breaks and minimize infection risk—is available. However, it is not currently used because previous episodes of aspiration pneumonia coincided with mealtime and feeding, leading the care team to opt for manual suctioning and more controlled airway management techniques.

Current Ventilator Management

1. Ventilator Mode (ResMed PSIMV)

   The patient is managed using PSIMV (Pressure Synchronized Intermittent Mandatory Ventilation) with Pressure Support (PS) for spontaneous breaths. A Pressure Control (PC) backup ensures a minimum mandatory ventilation if the patient’s spontaneous rate or effort becomes insufficient.

   Weaning Approach: In this mode, the focus is on gradually reducing Pressure Support. For example, from 10 cmH₂O to 8 cmH₂O, and then to 5 cmH₂O, provided the patient maintains adequate ventilation and stable vital signs.

2. Ventilator Settings Table

   

   Parameter	Current Setting	Typical/Normal Range	Target / Rationale
   Ventilator Mode	PSIMV (ResMed)	N/A	Main mode for partial support; PC acts as backup
   Pressure Control (backup)	10 cmH₂O	8–20 cmH₂O (varies by lung condition)	Reduce if the patient consistently meets spontaneous ventilation
   Pressure Support (PS)	10 cmH₂O	5–15 cmH₂O	Key for weaning; decrement as tolerated
   PEEP	5 cmH₂O	5–10 cmH₂O	Maintain end-expiratory lung volume; can adjust for oxygenation
   Set Respiratory Rate	12 breaths/min	12–20 breaths/min (adult)	Ensures a minimal backup rate
   Measured Tidal Volume (Vti)	~360 mL (0.36 L)	~6–8 mL/kg PBW1 (≈400–600 mL)	Monitor for adequate alveolar ventilation
   Supplemental O₂	3 L/min (nasal cannula)	1–6 L/min	Aim for SpO₂ ≥ 92%

   ¹ PBW = Predicted Body Weight

Challenges in Weaning

1. Neurological Limitation
   • Deep drowsiness complicates spontaneous breathing trials (SBTs) and patient cooperation.
2. Infection Control
   • High risk of recurrent pneumonia; meropenem therapy shows improvement but requires continued vigilance.
   • VRE isolation and strict aseptic techniques needed during tracheostomy care.
3. Secretion Burden
   • Frequent manual suctioning is necessary, especially in the absence of auto-suction line usage.
4. Assessment and Monitoring
   • Rapid Shallow Breathing Index (RSBI) = Respiratory Rate / Tidal Volume (L). With RR ≈ 20 and Vti 0.36 L, RSBI ≈ 55.6—below the usual cutoff of 105, suggesting potential readiness for progressive weaning.

Weaning Strategy

1. Stepwise Reduction in Pressure Support

   Lower PS from 10 cmH₂O to 8 cmH₂O, and subsequently to 5 cmH₂O if tolerated. Evaluate respiratory rate, tidal volume, oxygen saturation, and overall work of breathing.

2. Monitoring Gas Exchange

   Arterial Blood Gas Analysis (ABGA) remains the gold standard for assessing PaCO₂, PaO₂, and pH during weaning trials. If ABGA is not immediately available, rely on:

   • SpO₂ (pulse oximetry) to monitor oxygenation.
   • Heart rate and blood pressure.
   • Capnography (end-tidal CO₂), if accessible, to approximate ventilation status.
3. Infection and Nutrition

   Continue the antibiotic regimen until clinical and radiological resolution of pneumonia. Optimize enteral feeding (600–900 mL/day) to maintain adequate nutrition without exacerbating respiratory effort or aspiration risk.

4. Family Communication

   The patient’s husband remains the primary caregiver. Ongoing discussions about the risks, benefits, and timeline of ventilator weaning are essential to maintain trust and realistic expectations.

Guardian consent obtained for IRB-approved clinical research aimed at disseminating better clinical practices in hemodynamics.

Written on March 21, 2025

Case6: ACMV-PC Mode and Its Relationship to ResMed’s P(A)CV and P(A)C

A patient has been transferred with a ventilator set to ACMV-PC (Assist-Control Mandatory Ventilation in Pressure Control) mode. The transfer document lists specific settings—PEEP 6 cmH₂O, Pi 10 cmH₂O, Rate 14 breaths/min, Ti 1.1 seconds, and a High Trigger—which invite a detailed examination of each parameter and a broader discussion comparing ACMV-PC to ResMed’s P(A)CV and P(A)C modes. The following sections provide a structured overview of these settings, their typical clinical ranges, and the rationale behind assist-control ventilation.

1. Mode Overview: ACMV-PC vs. P(A)CV and P(A)C

1. ACMV-PC (Assist-Control Mandatory Ventilation – Pressure Control)

   • Guarantees a minimum number of mandatory breaths per minute at a preset pressure (Pi).
   • Allows the patient to trigger additional breaths; each triggered breath receives the same preset pressure.
   • The ventilator is not in total control: if a patient initiates a breath, it is fully supported (“assist”). If the patient does not initiate, the ventilator provides time-triggered mandatory breaths (“control”).

2. P(A)CV in ResMed Devices

   • Often referred to as Pressure (Assisted) Controlled Ventilation.
   • Involves setting PC (pressure), PEEP, RR, Ti, Rise Time, Safety Vt, and Trigger.
   • Conceptually similar to ACMV-PC because both modes deliver pressure-controlled breaths at a defined rate and fully support patient-initiated breaths.

3. P(A)C in ResMed Devices

   • Sometimes termed Pressure (Assisted) Control in a bi-level format.
   • Utilizes IPAP (Inspiratory Positive Airway Pressure) and EPAP (Expiratory Positive Airway Pressure) instead of a single target pressure plus PEEP.
   • Other adjustable features are similar (RR, Ti, Rise Time, Safety Vt, Trigger), but the presence of IPAP/EPAP is a key differentiator, especially in noninvasive ventilation contexts.

2. Parameters in ACMV-PC: Provided Settings and Typical Ranges

The table below aligns the provided settings from the transfer document with typical clinical ranges used in practice. While these values are generally appropriate for many adult patients, they must be adjusted based on individual factors such as lung compliance, oxygenation requirements, and the patient’s spontaneous breathing effort.

3. The Meaning of “Assist-Control”

• Assist Component: If the patient makes an inspiratory effort above the set rate, the ventilator provides a full pressure-controlled breath (identical to the mandatory setting).
• Control Component: A guaranteed number of breaths (e.g., RR = 14) is delivered if the patient does not initiate inspiration.
• This mode is not purely “controlled”; instead, it “assists” when the patient attempts to breathe. Hence, the term “assist-control” emphasizes that the patient has room to breathe spontaneously but still receives full support with each breath.

4. Detailed Examination of Ti and Trigger

1. Inspiratory Time (Ti)

   • Duration of Pressure Application: In pressure-control modes, the ventilator applies a set inspiratory pressure (Pi) for the entirety of Ti.
   • Impact on Gas Exchange: A longer Ti can potentially improve oxygenation by allowing more time for gas distribution but may risk air trapping if expiration is insufficient or the respiratory rate is high.
   • Advanced Settings: Some ventilators offer adaptive Ti features that can adjust cycle-off criteria based on patient flow or effort, though many standard modes utilize a fixed Ti.

2. Trigger Sensitivity

   • Definition: Governs how easily the ventilator detects and responds to a patient’s spontaneous effort, typically via a flow or pressure trigger.
   • Clinical Adjustments:
     • High Trigger Threshold: Prevents auto-triggering (common if the patient is hemodynamically unstable or if circuit vibrations occur), yet demands a stronger inspiratory effort.
     • Low Trigger Threshold: Increases sensitivity, making it easier for patients to trigger a breath but risking false triggers.
   • Effect on Patient-Ventilator Synchrony: Proper trigger settings are essential to match patient effort closely with ventilator-delivered breaths, promoting comfort and reducing work of breathing.

5. Clinical Perspective and Mode Selection

1. Comparing ACMV-PC to ResMed’s P(A)CV: Both deliver pressure-controlled breaths at a preset rate, with the capacity for patient-triggered support. The main difference often lies in ventilator-specific nomenclature and additional features (e.g., Safety Vt, Rise Time).
2. Comparing ACMV-PC to ResMed’s P(A)C: In P(A)C modes, separate inspiratory and expiratory pressures (IPAP/EPAP) are set, typically in bi-level ventilation or specific noninvasive applications.
3. Personalizing Settings: Optimal PEEP, Pi, Rate, Ti, and Trigger must be regularly evaluated using clinical signs, blood gas analyses, and pulmonary mechanics. Adjustments are made to maintain adequate oxygenation/ventilation and reduce the risk of volutrauma or barotrauma.
4. Safety Net: Some advanced modes include a “Safety Vt” or other alarms to ensure that tidal volume remains within acceptable limits, preventing underventilation or inadvertent excessive volumes.

Guardian consent obtained for IRB-approved clinical research aimed at disseminating better clinical practices in hemodynamics.

Written on March 27, 2025

Case7: Management of a 90-year-old patient on mechanical ventilation using a ResMed device

A 90-year-old male patient was transferred with the following ventilator document entry:

Ventilator Transfer Document

• PC/AC → P(A)CV
• Frequency (set): 26 → RR
• Tidal Volume: 400 mL
• PEEP: 4 cmH₂O
• I:E Ratio: 1:1.9
• Inspiration Time: 0.8 seconds

↑ Settings ↑

---

↓ Measurements ↓

• VTi: 403 mL
• Minute Volume: 11.2 L/min
• Peak Pressure (Ppeak): 22.4 cmH₂O

The document includes both settings (e.g., pressure control, respiratory rate, PEEP) and monitored values (e.g., measured tidal volume, minute volume, peak pressure). The following outline explains each parameter, discusses the equivalent mode on a ResMed ventilator, and provides a table of typical normal ranges to guide clinical decision-making.

1. Ventilator mode: PC/AC

• Definition: “PC/AC” typically denotes Pressure Control in Assist/Control mode. In this mode, the ventilator delivers each breath at a preset inspiratory pressure while also supporting breaths initiated by the patient.
• Equivalent ResMed mode: On a ResMed ventilator, this is usually referred to as Pressure Control Ventilation (PCV) or another pressure-targeted mode with assist/control functionality. Although naming conventions may differ, the clinical approach remains consistent: maintain a desired pressure level while delivering a set minimum rate.

2. Clarification of “frequency”

• Frequency (set) 26: “Frequency” describes the respiratory rate in breaths per minute. A set rate of 26 indicates a relatively high ventilation frequency, which may be necessary to maintain adequate alveolar ventilation in this 90-year-old patient, depending on blood gas results and clinical status.

3. Settings vs. monitored values

The list includes both configuration settings and measurements:

• Settings: Pressure Control level, frequency (respiratory rate), tidal volume (if in volume-control or target-based in pressure-control), PEEP, I:E ratio, and inspiratory time.
• Measurements: VTi (delivered tidal volume), minute volume, and peak pressure (Ppeak).

4. Typical normal ranges for ventilator settings

The following table provides general reference ranges. Actual targets must be tailored to each patient’s clinical condition, including lung mechanics, gas exchange requirements, and comorbidities.

5. Patient’s parameters in context

• PC/AC: Each breath is delivered at a targeted pressure, ensuring a minimum set rate of ventilation.
• Frequency (26 breaths/min): A relatively high rate, likely to support sufficient CO₂ clearance in a 90-year-old with possible compromised lung function.
• Tidal Volume (400 mL): Near the lower end of the lung-protective strategy range, depending on the patient’s predicted body weight.
• PEEP (4 cmH₂O): Slightly below the typical 5 cmH₂O starting point; may be appropriate if the patient tolerates lower PEEP without negative effects on oxygenation.
• I:E Ratio (1:1.9): Allows roughly 0.8 seconds of inspiration and about 1.5 seconds of expiration. Adequate for most adult lungs if no obstructive pattern is present.
• VTi (403 mL): Measured tidal volume aligns well with the set tidal volume of 400 mL.
• Minute Volume (11.2 L/min): Slightly above standard reference, which may be necessary to meet increased metabolic or clearance demands in this elderly patient.
• Ppeak (22.4 cmH₂O): Within a safe range; continued monitoring is crucial to ensure there is no upward trend suggestive of increasing airway resistance or decreased compliance.

6. Application on a ResMed ventilator

When transferring these parameters to a ResMed ventilator, the following approach is recommended:

1. Mode Selection: Choose Pressure Control Ventilation (PCV) or a similar pressure-targeted, assist/control setting to replicate PC/AC.
2. Respiratory Rate: Enter 26 breaths/min as the base rate, adjusting to maintain appropriate PaCO₂ levels as indicated by arterial blood gases.
3. Inspiratory Pressure / Tidal Volume: In pressure control, fine-tune the inspiratory pressure to achieve the target tidal volume (~400 mL). Monitor the exhaled tidal volume (VTi) to ensure lung-protective ventilation.
4. PEEP: Set at 4 cmH₂O initially, then adjust according to oxygenation requirements, end-expiratory lung volume, and hemodynamic tolerance.
5. I:E Ratio and Inspiratory Time: Configure the inspiratory time of 0.8 seconds to achieve approximately 1:1.9. Reassess if changes in airway mechanics arise (e.g., obstructive pathologies).
6. Monitor Trends:
   • VTi: Verify effective tidal volume delivery.
   • Peak Pressure: Watch for elevations that might indicate increasing airway resistance or decreased compliance.
   • Minute Ventilation: Ensure adequate CO₂ clearance without causing excessive inflation pressures.

Guardian consent obtained for IRB-approved clinical research aimed at disseminating better clinical practices in hemodynamics.

Written on March 27, 2025

Case8: A Patient with Hypoxic Encephalopathy, Myoclonic Seizures, and Ventilatory Considerations

This case details a patient diagnosed with hypoxic encephalopathy who presented with myoclonic seizures. Pharmacological management included valproate, levetiracetam, and clonazepam, alongside sedative agents. While overt seizure activity subsided, persistent spasticity and a stuporous mental status remained.

Although the patient could initiate spontaneous breathing, intermittent apnea necessitated prolonged ventilatory support. Consequently, a tracheostomy was performed to secure the airway, maintain adequate ventilation, and mitigate the risk of aspiration. The discussion below concentrates on the ventilator settings reported, the indications for mechanical ventilation, and the rationale behind choosing Pressure Support Ventilation (PSV) over other modes.

Patient Presentation

Diagnosis

• Hypoxic encephalopathy
• Myoclonic seizures (controlled with antiepileptic and sedative medications)
• Spasticity
• Stuporous mental status

Respiratory Status

• Intermittent apnea
• Some spontaneous respiratory drive

Airway Access

• Tracheostomy for prolonged mechanical ventilation and airway protection

Ventilatory Management

1. Reported Settings

   The ventilator settings are reported as:

   “PSV, Above PEEP 9, PEEP 7, FiO₂ 25%”

   The notation “Above PEEP 9, PEEP 7” indicates that the patient receives 9 cm H₂O of Pressure Support (PS) in addition to a Positive End-Expiratory Pressure (PEEP) of 7 cm H₂O. Hence, each inspiratory effort is assisted by 9 cm H₂O on top of the 7 cm H₂O baseline. The fraction of inspired oxygen (FiO₂) is set at 25%, suggesting a comparatively low supplemental oxygen requirement.

   Patient’s Ventilator Settings	Value	Approximate Range
   Ventilation Mode	PSV
   Pressure Support (Above PEEP)	9 cm H₂O	5–20 cm H₂O
   PEEP	7 cm H₂O	5–10 cm H₂O
   FiO₂	25%	21–100% (adjusted per ABG results)

2. Indications for Mechanical Ventilation

   Mechanical ventilation was mandated based on neurologic compromise and respiratory insufficiency. In general, mechanical ventilation is considered when specific clinical or numerical thresholds are met:

   Indication	Typical Criteria/Threshold
   Apnea or Impending Respiratory Arrest	Absent or severely depressed respiratory drive
   Hypoxemia	PaO₂ < 60 mmHg on FiO₂ ≥ 0.50
   Hypercapnia with Respiratory Acidosis	PaCO₂ > 50 mmHg and pH < 7.25
   Inability to Protect the Airway	Diminished consciousness, high risk of aspiration
   Ventilatory Muscle Fatigue & Elevated Work of Breathing	RR > 35 breaths/min, rapidly rising PaCO₂
   Neurological Factors	Severe stupor, inability to maintain consistent ventilatory effort (e.g., GCS < 8, repeated apnea episodes)

   In this patient:

   • Intermittent Apnea and Reduced Respiratory Drive necessitated mandatory ventilatory support.
   • Stupor and a high aspiration risk indicated the need for a secure airway (tracheostomy).
   • Hypoxic Encephalopathy and sedation further compromised reliable spontaneous ventilation.

3. Rationale for Selecting Pressure Support Ventilation (PSV)

   A variety of modes—such as SIMV (Synchronized Intermittent Mandatory Ventilation) PC + PS, PSV, and BiPAP (Bilevel Positive Airway Pressure)—were assessed. Each mode differs in its level of control, synchronization, patient comfort, and reliance on spontaneous effort.

   Parameter	SIMV PC + PS	PSV	BiPAP
   Level of Control	Mandatory PC breaths + partial support	Patient-driven, pressure-supported breaths	Two-level (inspiratory/expiratory) pressure
   Backup Ventilation	Yes (preset mandatory rate)	No guaranteed rate	Limited (usually noninvasive)
   Patient Effort Required	Moderate	High (patient determines RR & VT)	Moderate to high (depends on mask seal)
   Weaning Potential	Good (can gradually reduce mandatory rate)	Very good (encourages spontaneous effort)	Generally used for noninvasive or mild cases
   Suitability for Altered Mental Status	Moderate (requires patient triggering for additional breaths)	Good if patient can trigger consistently	Less optimal if severe alteration or tracheostomy needed
   Key Advantages	Guarantees a minimum ventilation	Excellent synchrony & comfort, easier weaning	Noninvasive option for less severe cases
   Key Limitations	Possible dyssynchrony if sedation is off	No mandatory minimum ventilation	Not suitable for high apnea risk or severe consciousness depression

   Why PSV for This Patient?

   • The patient retains some spontaneous respiratory drive but is prone to intermittent apnea.
   • PSV affords augmented support during each spontaneous inspiration, reducing the work of breathing and improving comfort.
   • A guaranteed rate (as in SIMV) is less essential if close monitoring is feasible, and the sedation plus intermittent apnea can be managed by adjusting the support level.
   • BiPAP, typically noninvasive, is unsuitable here due to the tracheostomy and high apnea risk, necessitating a more invasive approach.

Guardian consent obtained for IRB-approved clinical research aimed at disseminating better clinical practices in hemodynamics.

Written on March 28, 2025

Case9: Ventilator asynchrony in a patient with stage IV cerebral cancer

A 47-year-old woman with metastatic cerebral carcinoma developed marked tachypnoea (43–48 breaths min⁻¹) and apparent ventilator asynchrony after an episode of regurgitation while receiving pressure-controlled ventilation. This report summarises the clinical findings, analyses the potential mechanisms of patient–ventilator dyssynchrony, and proposes a structured, evidence-based management algorithm. The discussion emphasises protective ventilation, airway protection, neurocritical-care goals, and the importance of waveform analysis.

Case presentation

The bar chart below illustrates the disparity between the programmed and observed respiratory rates, highlighting probable trigger asynchrony.

Problem list

1. Patient–ventilator asynchrony (high spontaneous RR vs mandatory RR).
2. Post-regurgitation aspiration risk with possible airway obstruction.
3. Uncertain gas exchange (ABG pending) in a neuro-oncology patient where normoxia and normocapnia are critical.
4. Mild hyperthermia and potential sepsis.
5. Stage IV cerebral cancer with high intracranial pressure (ICP) risk.

Pathophysiological analysis

1. Types of dyssynchrony suspected

   • Ineffective triggering: Occurs when patient’s inspiratory effort fails to meet the ventilator’s trigger threshold, so no assisted breath is delivered despite diaphragmatic contraction.
     • Waveform clues: Small negative deflection on the pressure–time curve without corresponding flow delivery; “missed” dips on the flow–time curve.
     • Contributing factors: Too high trigger sensitivity setting, presence of auto-PEEP, weak respiratory drive or muscle fatigue, inadequate sedation level.
     • Clinical impact: Increased work of breathing, patient fatigue, risk of respiratory muscle exhaustion.
     • Interventions: Lower trigger threshold (flow or pressure), reduce PEEP or intrinsic PEEP, optimise sedation to balance comfort and drive.
   • Double-triggering / breath-stacking: Occurs when a spontaneous effort outlasts the set inspiratory time, prompting a second ventilator cycle before full exhalation.
     • Waveform clues: Two consecutive pressure pulses with minimal expiratory phase between; truncated expiratory flow in the flow–time curve.
     • Contributing factors: Inspiratory time too short, high patient drive, mismatched cycling criteria, inadequate tidal volume delivery.
     • Clinical impact: Excessive tidal volumes, risk of volutrauma or barotrauma, elevated mean airway pressure.
     • Interventions: Lengthen inspiratory time or switch to pressure-controlled assist/control, adjust cycling sensitivity (flow or time), consider slight increase in tidal volume target.
   • Reverse triggering: A form of entrainment in which controlled ventilator breaths provoke a reflex diaphragmatic contraction, effectively triggering a patient effort after the mandatory breath.
     • Waveform clues: Regular, time-locked patient efforts following each ventilator-delivered breath; visible deflections after mandatory cycles.
     • Contributing factors: Deep sedation or neuromuscular blockade reducing spontaneous initiation, high respiratory drive.
     • Clinical impact: Breath stacking, increased minute ventilation without true spontaneous effort, potential for lung injury.
     • Interventions: Reduce sedation depth to restore spontaneous rhythm, adjust ventilator rate to avoid entrainment, consider spontaneous modes (e.g., PSV) or temporary neuromuscular blockade for refractory cases.

2. Contributing factors

   • Insufficient P_control (8 cmH₂O) leading to low delivered tidal volume (Vᴛ), stimulating respiratory drive.
   • Anxiety, pain, or inadequate sedation.
   • Aspiration-induced hypoxaemia and airway irritation.
   • Possible metabolic acidosis from sepsis or tumour lysis.

Immediate bedside assessment checklist

1. Airway reassessment
   • Confirm ETT position and cuff pressure.
   • Perform oropharyngeal and subglottic suctioning; consider bronchoscopy if large particulate matter is suspected.
2. Ventilator waveform review
   • Inspect flow-time and pressure-time curves for ineffective efforts or double-triggers.
   • Measure Vᴛ and peak / plateau pressures.
3. ABG + lactate within 15 min.
4. Chest imaging (portable radiograph) for aspiration pneumonitis / ARDS.
5. Neurological status and pupillary size; ensure head-of-bed elevated ≥ 30 °.

Stepwise management algorithm

Trigger sensitivity and inspiratory time guidance

1. Normal trigger sensitivity

   Trigger type	Recommended range	Typical setting
   Flow trigger	1–3 L/min	2 L/min
   Pressure trigger	–0.5 to –2 cmH₂O	–1 cmH₂O

2. Normal inspiratory time (Tᵢ)

   Ventilator mode	Absolute Tᵢ	I:E ratio
   Volume-controlled	0.8–1.2 s	1:2 to 1:3 (≈25–33%)
   Pressure-controlled	0.8–1.0 s	Ti% ≈ 30–35%

3. Adjustment recommendation

   Setting	Adjustment	Purpose
   Trigger sensitivity	Lower threshold (↑ sensitivity) Flow: 1 L/min Pressure: –1 cmH₂O	Ensures patient efforts reliably trigger breaths Reduces work of breathing Aligns spontaneous and mandatory rates
   Inspiratory time	Maintain within above ranges; adjust Ti% based on drive and mechanics	Prevents double-triggering Enables adequate tidal volume delivery

4. Key rationale

   • Work of breathing is decreased when even modest inspiratory efforts are supported.
   • Respiratory drive is dampened, helping to normalize spontaneous rate.
   • Muscle fatigue risk is minimized, preserving respiratory muscle strength.

   |<--- Insp. (30%) --->|<------ Exp. (70%) ------>|
   

   Note: Excessive sensitivity may lead to auto-triggering (e.g., from circuit noise or cardiac oscillations). Fine adjustments guided by waveform inspection are advised.

Discussion

Protective ventilation in brain-injured oncology patients requires a balance between minimising ventilator-induced lung injury and avoiding secondary cerebral insults. Hypoxaemia and hypercapnia both augment cerebral blood flow and raise ICP; conversely, excessive hyperventilation may cause cerebral vasoconstriction and ischaemia. The observed tachypnoea likely reflects inadequate tidal volume delivery and a strong central drive, compounded by agitation and airway irritation after regurgitation.

Pressure control of 8 cmH₂O typically yields Vᴛ < 4 ml kg⁻¹ in most adults, insufficient for CO₂ clearance. Gradual increments, combined with careful waveform analysis, improve synchrony without abrupt ICP shifts. Sedation using agents with minimal ICP impact (propofol, dexmedetomidine) helps dampen excessive respiratory drive. Neuromuscular blocking agents should remain a rescue strategy given deleterious effects on neurological assessment.

Empirical antibiotics are justified when aspiration is likely and temperature rises; however, fever alone (37.7 °C) warrants cultures before escalation. Early bronchoscopy clears obstructive debris, reducing ventilator demands.

This manuscript has been proof-read and formatted for clarity. Figures and tables are included to aid comprehension.

Guardian consent obtained for IRB-approved clinical research aimed at disseminating better clinical practices in hemodynamics.

Written on May 1, 2025

Clinical Senario

#1. Management of Elevated CO₂ Levels in a Ventilated Patient

A patient initially managed on Pressure Support Ventilation (PSV) with a Positive End-Expiratory Pressure (PEEP) of 5 cm H₂O and Pressure Support (PS) of 10 cm H₂O was transitioned to Synchronized Intermittent Mandatory Ventilation (SIMV) mode due to an episode of apnea. The new ventilator settings included PEEP 5 cm H₂O, Respiratory Rate (RR) 12 breaths per minute, and Inspiratory Pressure (IP) 5 cm H₂O. Subsequent arterial blood gas analysis (ABGA) revealed mild acidosis with a partial pressure of carbon dioxide (PaCO₂) at 55 mmHg, oxygen saturation (SpO₂) at 100%, and a reduction in FiO₂ from 0.6 to 0.4.

Primary Concern: Elevated PaCO₂ levels necessitate adjustments to the ventilatory strategy to enhance alveolar ventilation and mitigate respiratory acidosis.

Strategies to Lower Elevated CO₂

(A) Increase Respiratory Rate (RR)

Rationale: Augmenting RR directly increases minute ventilation (MV = RR × Tidal Volume [TV]), facilitating greater elimination of CO₂.

Considerations:

• Advantages: Simple to implement and can effectively reduce PaCO₂ if TV is adequate.
• Risks: Excessively high RR may lead to patient discomfort, increased work of breathing, or inadequate time for exhalation, potentially causing auto-PEEP.

(B) Adjust Tidal Volume (TV) via Pressure Support (PS) or Inspiratory Pressure (IP)

Rationale: Enhancing TV increases MV, thereby promoting CO₂ clearance.

Implementation:

• Calculate TV Appropriately: Utilize 6-8 mL/kg of Ideal Body Weight (IBW) to prevent volutrauma and barotrauma.
• Modify PS/IP Settings: Carefully increase PS or IP to achieve the target TV without exceeding safe pressure limits.

Considerations:

• Advantages: Ensures adequate ventilation without over-reliance on RR adjustments.
• Risks: Over-inflation of the lungs can lead to lung injury; requires meticulous monitoring of airway pressures and lung mechanics.

Recommended Approach

(A) Assess Current Ventilator Settings and Patient Parameters

• Confirm that the current TV aligns with the recommended range (6-8 mL/kg IBW).
• Evaluate the patient’s comfort, synchrony with the ventilator, and potential signs of respiratory distress.

(B) Optimize Minute Ventilation

If TV is Adequate:

• Increase RR: Gradually elevate the RR within a safe range (e.g., up to 20 breaths per minute) to boost MV and reduce PaCO₂.

If TV is Inadequate:

• Adjust PS/IP: Incrementally raise PS or IP to achieve the target TV, ensuring that airway pressures remain within safe limits to avoid barotrauma.

(C) Mode of Ventilation Considerations

Switch to Assist-Control (AC) Mode if Apnea Persists:

• Rationale: AC mode provides mandatory breaths with each patient effort, ensuring consistent ventilation and CO₂ removal, which is particularly beneficial if apnea is related to inadequate respiratory drive.

Evaluate Necessity of Sedation:

• Rationale: Excessive sedation can suppress respiratory drive, contributing to apnea. Assess and adjust sedation protocols as needed to restore spontaneous breathing efforts.

Investigate Underlying Causes of Apnea:

• Potential Factors: Electrolyte imbalances, neurological events, metabolic disturbances, or medication effects.
• Action: Address reversible causes to improve respiratory drive and overall ventilatory status.

Transition to Pressure Control (PC) Mode for Respiratory Muscle Rest:

• Rationale: PC mode allows for precise control of inspiratory pressures and can be tailored to optimize TV and MV, providing respiratory muscle rest and facilitating recovery.
• Implementation:
• Calculate and set appropriate TV based on IBW.
• Monitor patient’s respiratory mechanics and adjust settings to maintain target ABGA values.

Troubleshooting

Considerations When Using a Jet Nebulizer in Respiratory Therapy

When using a pneumatic jet nebulizer in respiratory therapy, it's crucial to consider its impact on mechanical ventilation parameters. (1) First, introducing a jet nebulizer can significantly increase the flow within the ventilatory circuit, which in turn may inadvertently raise the tidal volume (TV) delivered to the patient. This increase can lead to unexpectedly high lung volumes, risking volutrauma if not closely monitored and adjusted. (2) Additionally, this extra flow can cause a slight increase in airway pressure. While generally mild, this increase requires careful monitoring to prevent potential adverse effects on patients with compromised lung function or those at risk of barotrauma.

(3) Another consideration is the effect on the fraction of inspired oxygen (FiO2). The use of a jet nebulizer can dilute the oxygen concentration within the ventilatory circuit as air is utilized to nebulize the medication, resulting in a reduced FiO2. Adjusting the oxygen settings to compensate for this dilution is essential to ensure that the desired level of oxygenation is maintained. (4) Furthermore, the additional flow and pressure fluctuations introduced by the nebulizer can interfere with the ventilator's sensitivity settings, complicating the initiation of spontaneous breathing by the patient. This may increase the work of breathing and lead to discomfort or fatigue. To mitigate these effects, it may be necessary to adjust the trigger sensitivity settings on the ventilator to lower the threshold required for triggering, thereby reducing the respiratory effort needed from the patient.

Ventilator Troubleshooting Guide

High Airway Pressure (Paw) Alarm: This alarm can be triggered by increased airway resistance or decreased lung compliance. To reduce airway resistance, perform suctioning and administer nebulized treatments. If the issue is related to lung compliance, consider interventions such as inhaled nitric oxide or extracorporeal membrane oxygenation (ECMO) to enhance lung flexibility and functionality.

Decreased Oxygen Saturation: When decreased oxygen saturation is detected, indicated by alarms or monitoring systems, several critical steps must be taken to ensure optimal patient care. Oxygen levels are primarily monitored using SpO2 and arterial oxygen partial pressure (PaO2). Immediate actions include resolving any High Paw Alarm by suctioning and nebulization to decrease airway resistance. It is also vital to thoroughly check the ventilatory circuit for any disconnections or leaks, as these can significantly compromise the oxygen delivery system.

To assess the patient's oxygenation status more comprehensively, performing an arterial blood gas analysis (ABGA) is recommended to check PaO2 levels. Based on these results, adjustments to the fraction of inspired oxygen (FiO2) and positive end-expiratory pressure (PEEP) should be considered. Initially, FiO2 may be increased to deliver more oxygen, especially in acute settings. Concurrently, adjusting PEEP can help improve oxygenation and ensure the patient receives adequate oxygen while preventing potential lung damage.

A practical approach involves starting with higher FiO2 and PEEP settings and then gradually reducing them as the patient's condition stabilizes or improves. For example, beginning with an FiO2 of 100% paired with a PEEP of 12 cm H2O, and methodically lowering both to potentially an FiO2 of 30% and a PEEP of 5 cm H2O as the patient's oxygenation status allows. This systematic and intuitive adjustment process is aligned with the ARDSnet protocol guidelines, which provide extensive tables and further recommendations for managing FiO2 and PEEP in different clinical scenarios.

High Carbon Dioxide Levels (PaCO2): If this alarm activates, first assess whether increased airway resistance is contributing to inadequate CO2 removal. To enhance CO2 clearance, adjust the tidal volume (TV) upwards. Increasing the respiratory rate (RR) can also help by augmenting the overall ventilation. Another strategy is to modify the inspiratory to expiratory ratio (I:E Ratio), which can improve ventilation efficiency. However, care must be taken to ensure that these adjustments do not lead to air trapping, especially in patients with conditions like Chronic Obstructive Pulmonary Disease (COPD).

PEEP High Alarm Due to Filter Obstruction: A 'PEEP High Alarm' in mechanical ventilation typically signals a blockage in the expiratory phase, often due to a clogged filter that impedes the flow of expired air, leading to increased end-expiratory pressure. The crucial step in troubleshooting is to promptly remove the filter to check if it is the source of the obstruction. If removing the filter resolves the alarm and normal ventilation function is restored, this confirms the filter as the culprit. The immediate replacement of the obstructed filter is critical to maintain unimpeded airflow, ensuring the ventilation system operates efficiently and safely.

Management of Expiratory Filters: Expiratory filters are critical in managing airway resistance within mechanical ventilation systems. These filters usually last one to two days, though high-quality, genuine filters can remain effective for up to five days under ideal conditions. Obstructions in these filters are common and can be caused by various factors, including the administration of specific medications such as colistin and coagulants, or due to excessive nebulization. When filter issues are suspected, such as after administering colistin, it is advisable to perform routine checks and ensure timely maintenance or replacement of the filters to maintain optimal ventilation management.

Strategic Use of PEEP in Patients with V/Q Mismatch and Shunting: For patients exhibiting V/Q mismatch or shunting, often caused by lung infiltration as indicated by a chest X-ray, increasing the positive end-expiratory pressure (PEEP) can enhance their condition by improving oxygenation and reducing shunt effects. However, if the PEEP exceeds 10 cm H2O, it may lead to decreased venous return, potentially resulting in hemodynamic instability. In such scenarios, administering an inotrope may be necessary to help maintain or increase blood pressure.

Auto-PEEP Detection and Management (Version I): Auto-PEEP is a significant concern, particularly in patients receiving medications such as colistin or anticoagulants, which can increase the risk of this complication. Monitoring the end-expiratory flow, known as V̇ee on a Servo ventilator, is critical because an increase in V̇ee may indicate the presence of Auto-PEEP, necessitating prompt assessment and intervention to ensure optimal ventilator function and patient safety.

Effective management of Auto-PEEP includes adjusting the inspiratory to expiratory (I:E) ratio, for example, from 1:2 to 1:3. This adjustment extends the expiratory time relative to the inspiratory time, aiming to provide sufficient expiratory time — ideally more than three times the time constant (Tc). This strategy promotes complete exhalation, prevents lung overdistension, optimizes respiratory mechanics, and aids in preventing complications such as air trapping while ensuring efficient CO2 removal. Maintaining the inspiratory time (Ti) within 0.6 to 1.2 seconds, even when altering the I:E ratio, is essential to avoid negative impacts on the patient's breathing pattern.

In scenarios where there is a rapid increase in respiratory rate (RR), continuous monitoring of V̇ee through the "Trends" function on the ventilator is essential. This allows clinicians to observe changes over time and make informed decisions about ventilatory adjustments. Additionally, performing an arterial blood gas analysis (ABGA) is routine to check for CO2 retention and decreased O2 levels, further informing the adjustment process.

Further strategies to manage Auto-PEEP include ensuring clear airways and, if necessary, adjusting the respiratory rate (RR) and tidal volume (TV). Encouraging patients to take deep breaths can help decrease the buildup of intrinsic PEEP and facilitate better lung decompression. Additionally, adjunctive therapies such as nebulization, the administration of steroids, or bronchoscopy may be necessary to address underlying respiratory issues contributing to Auto-PEEP.

Air Trapping Indicators and Management (Version II): Air trapping, commonly seen in conditions like COPD, asthma, or airway edema, manifests through several indicators:

• Visual Inspection: The flow graph does not return to zero during expiration, indicating incomplete exhalation.
• V̇ee (End-expiratory Flow): A V̇ee greater than or equal to 1 suggests persistent air in the lungs post-expiration.
• Arterial Blood Gas Analysis (ABGA): This analysis is essential for checking CO2 levels, with a PaCO2 above 45 mmHg indicating CO2 retention.
• Lower Inflection Point (LIP) Changes in PC Mode: A rightward shift in LIP points to increased airway resistance, while a swollen or wider LIP indicates decreased lung compliance. Reassessing the LIP through sputum suction can confirm these conditions.
• Monitored PEEP Variations: If the monitored PEEP significantly exceeds the set value, it can lead to decreased cardiac output and unstable blood pressure, indicating severe air trapping. Sometimes, with air trapping, monitored PEEP might significantly exceed the set value (e.g., set at 5 but reads 19 or 20), leading to decreased cardiac output and unstable blood pressure.
• Total PEEP: When total PEEP readings exceed set PEEP, it suggests the presence of auto-PEEP, confirming air trapping (e.g., set PEEP at 5 but total reads 6).
• Re (Expiratory Resistance): Expiratory resistance, when measured during holds, that falls within the 30-40 range indicates severe CO2 retention and requires urgent intervention. This resistance ranges from normal (5-15) to critical levels (30-40), indicating severe CO2 retention and necessitating immediate attention. While Total PEEP primarily helps in assessing the degree of air trapping and managing auto-PEEP, Re (expiratory resistance) is crucial for diagnosing the extent and cause of airway obstruction and evaluating overall lung mechanics.

Air Flow Reductions: In scenarios where there is inspiratory pressure but the airflow drops to zero, urgent assessment and management are crucial to identify and rectify underlying causes. This issue often points to problems with lung compliance or mechanical impediments in the ventilation system. Evaluating lung elasticity is essential, and it's important to ensure that inspiratory pressures are not excessively high, as this could exacerbate lung stiffness and compromise function.

In terms of mechanical causes, obstructions in the endotracheal tube (ET tube) should be checked. Such obstructions can be due to kinking, blockage within the tube, or from the patient biting the tube. Inspecting and, if necessary, replacing the ET tube is crucial. If the patient is biting the tube, using a bite block can prevent occlusion and ensure continuous airflow. Addressing these issues promptly is vital not only to restoring proper airflow but also to preventing potential lung damage from inadequate ventilation.

Additionally, understanding lung compliance through static and dynamic indices can provide insights into lung health and guide appropriate ventilatory support. Static Compliance (Cstat) is calculated from the formula VTe / Pplat - PEEP, where VTe is the exhaled tidal volume, Pplat is the plateau pressure after an inhalation pause, and PEEP is the positive end-expiratory pressure, with normal values ranging from 60 to 100 ml/cm H₂O. A value below this range indicates increased lung stiffness. Dynamic Compliance (Cdyn), calculated as VTe / EIP - PEEP, where EIP is the end-inspiratory pressure, typically ranges from 50 to 80 ml/cm H₂O. Values below 30 ml/cm H₂O suggest severe lung conditions such as Acute Respiratory Distress Syndrome (ARDS). Monitoring these indices helps in fine-tuning ventilatory settings to optimize patient care and outcomes.

Static and dynamic compliance insights into lung health

Static Compliance (C_stat)

Measures lung compliance without the influence of airway resistance.

Cstat = VT / (Pplat − PEEP)

Where P_plat is Plateau Pressure and P_EEP is Positive End-Expiratory Pressure.

Dynamic Compliance (C_dyn)

Dynamic compliance is measured during airflow and includes resistance.

Cdyn = VT / (Ppeak − PEEP)

Where P_peak is Peak Inspiratory Pressure and P_EEP is Positive End-Expiratory Pressure.

Others

Ventilator Parameter Settings for Patient Transfer

SIMV-PCV-PS is a ventilator mode that integrates Synchronized Intermittent Mandatory Ventilation (SIMV), Pressure Control Ventilation (PCV), and Pressure Support (PS). This configuration ensures that the ventilator delivers a set number of mandatory breaths at a predetermined pressure as defined by PCV. These breaths are synchronized with any spontaneous efforts by the patient, maintaining necessary ventilation support even in the absence of patient-initiated breathing.

In this mode, if the patient initiates a spontaneous breath, the ventilator shifts to Pressure Support (PS) mode. PS applies a consistent pressure during these spontaneous breaths, facilitating easier breathing by reducing the effort needed to inhale. If no spontaneous efforts occur, the ventilator continues with mandatory PCV breaths, providing uninterrupted support. Therefore, PS is only active during patient-initiated breathing; otherwise, ventilation defaults to the controlled settings of PCV.

• Vsens (Volume Sensitivity): Activates support when a spontaneous breath exceeds a preset volume threshold.
• Esens (Expiratory Sensitivity): Ends inspiratory support to allow natural exhalation based on the patient's breath.
• Ti (Inspiratory Time): Specifies the duration of pressure application during each ventilator-assisted breath.
• Pi (Inspiratory Pressure): Sets the pressure during the inspiratory phase to achieve the target breath volume in PCV mode.
• Psupp (Pressure Support): Provides additional pressure during spontaneous breaths to ease inhalation.
• Rate (Breathing Rate): Ensures a minimum set number of breaths per minute to meet ventilatory needs.
• PEEP (Positive End-Expiratory Pressure): Keeps the lungs slightly inflated at the end of exhalation to prevent collapse and enhance oxygenation.

• Rise Time: Adjusts the speed at which the set inspiratory pressure is reached during a breath in PS mode, enhancing patient comfort and synchrony with the ventilator.

High Flow Nasal Cannula (HFNC): Addressing the Limitations of Conventional Oxygen Delivery Systems and the Transition to Mechanical Ventilation

High Flow Nasal Cannula (HFNC) therapy is increasingly recognized in modern respiratory care for its ability to deliver heated and humidified medical gas at high flows through a nasal cannula. This advanced respiratory support technique offers significant improvements over traditional low-flow systems (LFNC), which typically provide only up to 6 liters per minute, achieving maximum FiO2 levels of around 0.37 to 0.45. Although systems such as the 8-10L oxygen reservoir mask can deliver FiO2 levels of up to 80% or more, HFNC is preferred for its capability to provide up to 100% humidified and heated oxygen at flow rates reaching 60 liters per minute. This feature ensures a stable fraction of inspired oxygen (FiO2), even amid changing patient demands or respiratory patterns, effectively addressing a key limitation of traditional oxygen therapy methods like wall oxygen with a reservoir mask, which cannot guarantee stable FiO2 during flow changes.

HFNC significantly enhances oxygenation and ventilation by delivering air at rates that exceed a patient's physiological capacity, effectively addressing the limitations posed by physiological dead space. Typically, dead space accounts for about one-third of the tidal volume, leading to CO2 accumulation and decreased availability of oxygen for diffusion. HFNC uses high flow rates to displace stagnant CO2 with fresh O2, increasing the partial pressure of oxygen (PAO2) and creating a more favorable oxygen diffusion gradient. This mechanism is particularly beneficial for enhancing CO2 clearance and alleviating symptoms of dyspnea, thereby increasing minute ventilation and effectively reducing dead space. These benefits are especially advantageous for patients with chronic obstructive pulmonary disease (COPD), as HFNC therapy eases their work of breathing and improves overall respiratory efficiency.

Additionally, HFNC reduces nasopharyngeal airway resistance by applying positive pressure that dilates the airways. According to the Hagen-Poiseuille law, airway resistance is inversely proportional to the fourth power of the airway radius (R = 8 n l / π r⁴), meaning that increasing the radius decreases resistance and enhances airflow. This physiological advantage is pivotal in managing respiratory conditions that involve compromised airway dynamics or ineffective air exchange, making HFNC an essential tool in respiratory care. The clinical benefits of HFNC are particularly evident in conditions like acute hypoxemic respiratory failure and COPD exacerbations, where the reduction in airway resistance can improve gas exchange and reduce the work of breathing. In acute settings, the positive airway pressure provided by HFNC helps maintain alveolar stability, enhancing oxygenation and comfort, which is crucial for patient outcomes. Studies such as the FLORALI trial highlight HFNC's role in reducing mortality and increasing ventilator-free days compared to conventional oxygen therapies. Additionally, HFNC's consistent oxygen delivery makes it highly effective for patients during critical pre and post-extubation periods, ensuring optimal respiratory support.

Moreover, the humidification and heating provided by HFNC reduce dryness in the nasal passages and mouth, minimizing gastrointestinal disturbances and the risk of atelectasis by maintaining mucociliary function and airway patency. HFNC's effectiveness extends to neonatal care, providing gentle and appropriate respiratory support for the delicate nature of neonatal airways. This is facilitated by adjustable flow rates from systems like the widely used Airvo, OmniOx and MC FLO HFNC devices, which offer settings ranging from 10 to 60 L/min for adults and 15 to 30 L/min for pediatrics, managed by controlling the flow meter connected to wall oxygen.

However, HFNC is not without potential drawbacks. It can lead to excessive CO2 reduction, potentially suppressing the respiratory drive if not carefully monitored. The therapy may also increase expiratory resistance, leading to an inadvertent continuous positive airway pressure (CPAP) effect that could elevate airway pressures and result in complications such as barotrauma, volutrauma, and pneumothorax. Additionally, the possibility of patients adjusting or removing the nasal cannula can create stability issues and compromise the delivery of precise FiO2. In scenarios of severe respiratory failure where higher levels of support are necessary, traditional mechanical ventilation may be required. This includes situations necessitating intubation and invasive ventilation to manage higher pressures safely and effectively, highlighting HFNC's limitations in more critical care scenarios.

• Sharma, S., et al. (2023). High-flow nasal cannula. In StatPearls [Internet]. Treasure Island, FL: StatPearls Publishing.
• Frat, J.-P., et al. (2015). High-flow oxygen through nasal cannula in acute hypoxemic respiratory failure. The New England Journal of Medicine, 372(23), 2185-2196.

Reference

Amato, M. B. P. et al. (2015). Driving pressure and survival in the acute respiratory distress syndrome. The New England Journal of Medicine, 372(8), 747-755. https://doi.org/10.1056/NEJMsa1410639

ARDSnet. (2008, July). Mechanical Ventilation Protocol Summary. NIH NHLBI ARDS Clinical Network. View Protocol.

Cairo, J.M. (2023). Pilbeam's Mechanical Ventilation: Physiological and Clinical Applications (8th ed.). Elsevier.

Tobin, M. J. (Ed.). (2013). Principles and Practice of Mechanical Ventilation (3rd ed.). McGraw-Hill Education.

The Acute Respiratory Distress Syndrome Network. (2000). Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and the acute respiratory distress syndrome. The New England Journal of Medicine, 342(18), 1301-1308. https://doi.org/10.1056/NEJM200005043421801

Check out the YouTube channel LOVmediteck for more information.

Home and Hospital Ventilator Trends and Settings

Home Ventilators

Philips Respironics:

• Trilogy Series (Trilogy 100, Trilogy 200): Commonly used for home mechanical ventilation.

ResMed:

• Astral Series (Astral 100, Astral 150): Portable and suitable for home use.
• P(A)CV (Pressure (Assisted) Control Ventilation): This mode operates similarly to P(A)C but with a focus on maintaining a consistent pressure throughout the ventilation process. P(A)CV delivers breaths at a set pressure above Positive End-Expiratory Pressure (PEEP) during inhalation, which is meticulously maintained along with the PEEP during exhalation. The term "Ventilation" emphasizes comprehensive control over the entire respiratory process, including precise volume delivery and consistent pressure maintenance across all breaths — whether machine-initiated or patient-triggered. This mode is particularly useful in clinical scenarios where stable and precise pressure levels are necessary for patient care, ensuring consistent respiratory support regardless of patient effort.

  

---

• P(A)C (Pressure (Assisted) Control): Also known as Pressure Control or Pressure Assist Control, this mode supports both patient-initiated and ventilator-controlled breaths. The ventilator delivers breaths at a preset Inspiratory Positive Airway Pressure (IPAP) when it detects a patient's effort to inhale, and switches to a lower Expiratory Positive Airway Pressure (EPAP) during exhalation. The clinician can set the rate at which these breaths are delivered, and the inspiratory time is preset to ensure each breath achieves sufficient ventilation. This mode adapts dynamically to the patient's spontaneous efforts, providing more or less support based on the patient's own breathing pattern, making it ideal for patients who are capable of initiating breaths but need help to maintain effective ventilation.

  

      P(A)C (Pressure (Assisted) Control) ventilation, despite incorporating elements like EPAP and IPAP settings, is essentially a controlled mode of ventilation but with the capability to adapt to patient-initiated efforts. This dual-functionality places P(A)C as a hybrid mode, offering both controlled and assisted ventilation aspects. In P(A)C mode, the ventilator delivers breaths at a preset Inspiratory Positive Airway Pressure (IPAP) and switches to a lower Expiratory Positive Airway Pressure (EPAP) during exhalation. These settings allow the ventilator to dynamically adjust the support provided based on the patient's respiratory efforts. This is particularly beneficial for patients who can initiate breaths but still require consistent support to maintain effective ventilation and oxygenation. P(A)C ensures that, even if the patient's spontaneous efforts are insufficient, ventilation requirements are met by automatically providing controlled breaths at set intervals.
  
      P(A)C vs. SIMV: Differing significantly from P(A)C, SIMV (Synchronized Intermittent Mandatory Ventilation) allows for more spontaneous breathing with less intervention, only delivering mandatory breaths at set intervals which synchronize with patient efforts to prevent breath stacking and facilitate a more natural breathing pattern. This mode is particularly useful for weaning patients from mechanical ventilation as it supports both patient-initiated and ventilator-controlled breaths in a way that encourages independence.
  
      P(A)C vs. ST: On the other hand, the ST, SV Mode (Spontaneous/Timed, Synchronized Volume) focuses on delivering a minimum number of mechanical breaths if spontaneous efforts are inadequate while adjusting each breath's volume to ensure consistent ventilation support. Unlike P(A)C, which centers around maintaining specific pressure levels throughout the respiratory cycle, ST, SV mode integrates volume and timing adjustments to tailor support directly to the patient's respiratory requirements.
      Key differences between these modes include i) control versus spontaneity, adaptation to breathing patterns, and application context. P(A)C Mode is primarily a controlled mode with patient-assist features, offering a consistent pressure environment ideal for patients needing stable pressure levels throughout the respiratory cycle. This mode ensures that each breath — whether initiated by the machine or the patient — is delivered at a set pressure, maintaining a controlled environment. Conversely, ST Mode emphasizes spontaneous breathing with a timed backup. It is more flexible in adjusting to the patient's natural breathing patterns while ensuring minimum ventilation. ST mode allows the patient to breathe naturally as much as possible, stepping in only when the patient's spontaneous breathing efforts fall below a certain threshold, ensuring they receive a predetermined number of breaths.
      In terms of ii) adaptation to breathing patterns, P(A)C Mode adjusts support based on spontaneous efforts but maintains control over the respiratory cycle. The mode delivers breaths at preset pressures (IPAP for inhalation and EPAP for exhalation) regardless of whether the breath is patient-initiated or machine-initiated. In contrast, ST Mode prioritizes spontaneous breaths and steps in only when spontaneous efforts are insufficient, providing timed breaths to meet minimum requirements. This approach ensures that the patient's natural breathing is supported while still guaranteeing necessary ventilation if spontaneous efforts decline.
      Regarding iii) application context, P(A)C Mode is suitable for patients who need precise control over pressure levels and consistent support for both machine-initiated and patient-triggered breaths. It is ideal for those requiring a stable and controlled pressure environment. On the other hand, ST Mode is ideal for patients who can breathe spontaneously but require assurance that they will receive adequate ventilation if their spontaneous efforts decrease. This mode is designed to encourage natural breathing patterns while providing a safety net of timed mechanical breaths.

---

• (A)CV (Volume (Assisted) Control Ventilation): This mode is also referred to as Volume Control or Volume Assist/Control. In (A)CV, the ventilator guarantees each breath will receive a preset tidal volume (V_T), whether the breath is initiated by the patient (assisted) or by the machine (controlled). Unlike pressure-oriented modes such as P(A)C or P(A)CV, where pressure is fixed and volume can vary, (A)CV delivers a consistent volume but may allow pressure to fluctuate to achieve that volume.
  • Key Settings: Clinicians can specify the tidal volume (V_T), respiratory rate (RR), PEEP, inspiratory time (T_I), flow shape (e.g., square or decelerating), inspiratory flow (PIF), and sensitivity (trigger). These parameters ensure the patient receives a precise volume of air on each breath while maintaining adequate end-expiratory pressure.
  • How it Works: During inspiration, the ventilator delivers flow until the set tidal volume is reached (or until the set inspiratory time elapses, depending on the ventilator’s design). If the patient triggers an additional breath, the ventilator provides the same set tidal volume. In this way, the clinician has control over minute ventilation by specifying both volume and rate, ensuring consistent alveolar ventilation.
  • Clinical Utility: (A)CV is particularly beneficial when precise control of ventilation is desired, such as controlling CO₂ levels in critical cases. It guarantees that each breath will meet a minimum ventilation requirement regardless of variations in patient effort, making it useful in patients who require strictly regulated tidal volumes due to lung-protective strategies or other clinical considerations.

  

     In contrast to P(A)C or P(A)CV, which focus on maintaining a set pressure throughout the respiratory cycle, (A)CV ensures a set volume is delivered for each breath. Thus, peak pressure may vary depending on lung compliance and airway resistance. This characteristic makes (A)CV more volume-centric, providing consistent ventilation but requiring careful monitoring of peak pressures to prevent barotrauma in patients with changing lung mechanics.

  ---

  (A)C Mode UNCONFIRMED
• (A)C (Volume (Assisted) Control): Also known as Volume Control or Volume Assist/Control, this mode generally ensures a set tidal volume (V_T) is delivered with each breath, whether the patient triggers it (assist) or the ventilator initiates it (control). Similar to how P(A)C uses IPAP/EPAP and a mandatory rate, (A)C mode often provides a parallel set of parameters:
  • Tidal Volume (V_T): Instead of pressure targets (IPAP/EPAP), you specify the exact volume delivered on each breath.
  • Respiratory Rate (RR): A minimum back-up rate ensures the patient receives mandatory breaths if spontaneous efforts are inadequate.
  • PEEP: Similar to EPAP in P(A)C, PEEP maintains a baseline positive pressure at end-expiration.
  • Inspiratory Time (T_I) or I:E Ratio: Defines how long each inspiration lasts and balances inspiratory versus expiratory phases.
  • Flow Pattern/Shape: Determines how airflow is delivered during inspiration (e.g., square or decelerating ramp).
  • Peak Inspiratory Flow (PIF): Sets the maximum flow the ventilator can achieve while delivering the prescribed tidal volume.
  • Trigger Sensitivity: Adjusts how easily the ventilator detects and assists a patient-initiated breath.
     Where P(A)C controls pressure and allows volume to vary, (A)C fixes volume and permits pressure to fluctuate as needed to reach the set tidal volume. This can provide more predictable minute ventilation but requires careful monitoring of peak pressures, particularly if the patient’s lung mechanics change.

  Note: The exact naming conventions and parameter options may vary by device or manufacturer. While these settings typically apply to ResMed devices that offer an (A)C or Volume Control mode, be sure to verify with the official device manual or manufacturer guidelines to confirm the specific parameters available on a particular model.

---

• V-SIMV (Volume Synchronized Intermittent Mandatory Ventilation): Combines set volume mandatory breaths with patient's spontaneous breathing, allowing pressure support for spontaneous breaths.

  

• P-SIMV (Pressure Synchronized Intermittent Mandatory Ventilation):

  

---

• ST, SV Mode: This stands for "Spontaneous/Timed, Synchronized Volume," is a sophisticated ventilation setting engineered to manage a patient's respiratory needs precisely and effectively. This mode ensures the provision of a minimum number of mechanical breaths when the patient does not initiate enough breaths independently, while also adapting to support any spontaneous breathing efforts. As a patient initiates a breath, the ventilator synchronizes this action and delivers air based on predetermined parameters to meet the healthcare provider's set respiratory requirements.
      This mode encompasses both Spontaneous/Timed (ST) functions and Synchronized Volume (SV) controls. In practice, ST supports the patient's natural breathing, providing mechanical breaths when needed, whereas SV manages the volume or pressure of air delivered per breath, ensuring consistent support whether the breaths are patient-initiated or mechanically delivered. The integrated nature of ST and SV functionalities means that volume synchronization does not require a separate operational mode, allowing for tailored ventilation support without additional complexity.
  • ST (Spontaneous/Timed): This feature supports the patient's natural breathing efforts. When the patient initiates a breath, the ventilator detects this effort and provides appropriate support. If the patient does not initiate sufficient breaths on their own, the ventilator automatically delivers timed mechanical breaths to ensure the patient meets the minimum respiratory requirement set by healthcare providers.
  • SV (Synchronized Volume): This aspect of the mode involves the ventilator delivering a specific volume of air per breath, matching the set parameters that align with the patient's breathing efforts. This synchronization occurs regardless of whether the breaths are initiated by the patient or delivered mechanically by the ventilator, ensuring consistent support.
      In the context of ResMed ventilators and similar devices, this mode is labeled as "(S)T" for Spontaneous/Timed. This can create some confusion, as it might seem to suggest separate modes, but in practice, it refers to a unified mode that supports both spontaneous and timed breaths:
  • Spontaneous (S): The ventilator aids breaths that the patient starts, sensing the effort and providing necessary support.
  • Timed (T): If the patient fails to initiate a breath within a preset interval, the ventilator ensures the patient still receives adequate ventilation by automatically providing a breath.

  

---

• PS (Pressure Support): This mode is more supportive of spontaneous breathing. The ventilator augments the patient's own breaths with additional pressure, thus reducing the work of breathing. The ventilator does not initiate breaths; it only helps to make the breaths the patient initiates easier by adding pressure. This mode relies more on the patient's ability to breathe independently and provides assistance only when the patient initiates a breath. Compared to "ST, SV mode," PS (Pressure Support) is generally considered more of a voluntary breathing type and requires less help from the ventilator. Pressure Support is more about assisting the natural breathing efforts of the patient rather than controlling or ensuring a certain number of breaths.

  

• Stellar Series: Also designed for home and non-invasive ventilation.

Hospital Ventilators

Hamilton Medical

• Adaptive Support Ventilation (ASV) mode: automates adjustments to ventilation parameters, improving patient comfort and reducing the need for manual settings adjustments by clinicians.

Maquet Servo (Getinge Group)

• Neurally Adjusted Ventilatory Assist (NAVA): improves patient-ventilator synchrony by using the electrical activity of the diaphragm to control the ventilator, which leads to more natural breathing patterns and potentially reduces the time patients need to spend on mechanical ventilation.
• Maquet is a subsidiary of the Getinge Group.

Medtronic (Puritan Bennett)

• As of April 19th, 2024, there are rumors suggesting that Medtronic intends to discontinue the production of Puritan Bennett ventilators.
• Puritan Bennett is a brand of Medtronic, incorporated into its Minimally Invasive Therapies Group. Medtronic, a major medical device company, acquired Puritan Bennett to enhance its portfolio in respiratory and monitoring solutions.