Myths and Misconceptions of Airway Pressure Release Ventilation: Getting Past the Noise and on to the Signal

Physiologic Comparison of Airway Pressure Release Ventilation and Low Tidal Volume Ventilation in ARDS: A Randomized Controlled Trial

BACKGROUND

The physiologic effects of different ventilation strategies on patients with ARDS need to be better understood.

RESEARCH QUESTION

In patients with ARDS receiving controlled mandatory ventilation, does airway pressure release ventilation (APRV) improve lung ventilation/perfusion (V˙/Q˙) matching and ventilation homogeneity compared with low tidal volume (LTV) ventilation?

STUDY DESIGN AND METHODS

This study was a single-center randomized controlled trial. Patients with moderate to severe ARDS were ventilated randomly with APRV or LTV ventilation. Electrical impedance tomography (EIT) was used to assess lung ventilation and perfusion. EIT-based data and clinical variables related to respiratory and hemodynamic conditions were collected shortly before randomization (0 hours) and at 12 and 24 hours after randomization.

RESULTS

A total of 40 patients were included and randomized to the APRV or LTV ventilation group (20 per group). During the 24-hour trial period, patients receiving APRV exhibited significantly increased dorsal ventilation (difference value [24 hours minus 0 hours]: median, 10.82% [interquartile range (IQR), 2.62%-13.74%] vs 0.12% [IQR, -2.81% to 4.76%]; P = .017), decreased dorsal shunt (median, -4.67% [IQR, -6.83% to 0.59%] vs 1.73% [IQR, -0.95% to 5.53%]; P = .008), and increased dorsal V˙/Q˙ matching (median, 4.13% [IQR, -0.26% to 10.47%] vs -3.29% [IQR, -5.05% to 2.81%]; P = .026) than those receiving LTV ventilation. No difference in ventral dead space was observed between study groups (P = .903). Additionally, two indicators of ventilation distribution heterogeneity, global inhomogeneity index and center of ventilation, significantly decreased and significantly increased, respectively, in the APRV group compared with the LTV ventilation group. Patients receiving APRV showed significantly higher Pao2 to Fio2 ratio, higher respiratory system static compliance and lower Paco2 than those receiving LTV ventilation at 24 hours. The cardiac output was comparable in both groups.

INTERPRETATION

APRV, as compared with LTV ventilation, could recruit dorsal region, reduce dorsal shunt, increase dorsal V˙/Q˙ matching, and improve ventilation homogeneity of the lungs, leading to better gas exchange and respiratory system static compliance in patients with moderate to severe ARDS.

CLINICAL TRIAL REGISTRY

ClinicalTrials.gov; No.: NCT05767125; URL: www.

CLINICALTRIALS

gov.

Comparison of airway pressure release ventilation (APRV) versus biphasic positive airway pressure (BIPAP) ventilation in COVID-19 associated ARDS using transpulmonary pressure monitoring

BACKGROUND

APRV has been used for ARDS in the past. Little is known about the risk of ventilator- induced lung- injury (VILI) in APRV vs. BIPAP in the management of in COVID19-associated ARDS (CARDS). This study aimed to compare transpulmonary pressures (TPP) in APRV vs. BIPAP in CARDS in regard to lung protective ventilator settings.

METHODS

This retrospective, monocentric cohort study (ethical approval: 21-1553) assessed all adult ICU- patients with CARDS who were ventilated with BIPAP vs. APRV and monitored with TPP from 03/2020 to 10/2021. Ventilator-settings / -pressures, TPP, hemodynamic and arterial blood gas parameters were compared in both modes.

RESULTS

20 non- spontaneously breathing patients could be included in the study: Median TPPendexpiratory was lower / negative in APRV (-1.20mbar; IQR - 4.88 / +4.53) vs. positive in BIPAP (+ 3.4mbar; IQR + 1.95 / +8.57; p < .01). Median TPPendinspiratory did not differ. In APRV, mean tidal- volume per body- weight (7.05 ± 1.28 vs. 5.03 ± 0.77 ml; p < .01) and mean airway- pressure (27.08 ± 1.67 vs. 22.68 ± 2.62mbar; p < .01) were higher. There was no difference in PEEP, peak-, plateau- or driving- pressure, compliance, oxygenation and CO2- removal between both modes.

CONCLUSION

Despite higher tidal- volumes / airway-pressures in APRV vs. BIPAP, TPPendinspiratory was not increased. However, in APRV median TPPendexpiratory was negative indicating an elevated risk of occult atelectasis in APRV- mode in CARDS. Therefore, TPP- monitoring could be a useful tool for monitoring a safe application of APRV- mode in CARDS.

Current practice of using the airway pressure release ventilation mode in acute respiratory distress syndrome patients among respiratory therapists in Saudi Arabia

Background

There is a limited data examining the practice of using the airway pressure release ventilation mode for patients with acute respiratory distress syndrome among respiratory therapists.

Objectives

To evaluate the current practice and barriers when using airway pressure release ventilation mode in the management of patients with acute respiratory distress syndrome.

Methods

A cross-sectional online survey was disseminated between November 2022 and April 2023 to respiratory therapists in Saudi Arabia. Descriptive statistics were used to analyze the respondents' characteristics.

Results

Overall, 802 respiratory therapists (male: 59.60%) completed the survey. Five hundred nineteen (64.71%) did not receive training on airway pressure release ventilation mode. Moreover, 325 (40.52%) and 391 (48.75%) did not know if airway pressure release ventilation was used at their hospitals and if the mode was managed via protocol with acute respiratory distress syndrome patients. Of the participants, 276 (34.41%) reported that plateau pressure should be used as a target when setting P-high initially, while 427 (53.24%) believed that the initial P-low should be equal to 0 cmH2O. Moreover, 468 (58.36%) believed that the initial T-high should be between 4 and 6 s, while 548 (68.33%) believed the initial T-low should be a set time (between 0.4 and 0.8) seconds. The most appropriate intervention to improve ventilation and oxygenation was to increase the P-high, which was reported by 370 (46.14%) and 326 (40.65%) respiratory therapists, respectively. Inadequate training was the most common barrier (678, 84.54%) to airway pressure release ventilation implementation.

Conclusion

Airway pressure release ventilation management varies between respiratory therapists which may be due to inadequate training and the absence of protocols.

The use of protective mechanical ventilation during extracorporeal membrane oxygenation for the treatment of acute respiratory failure

Acute respiratory failure (ARF) strikes an estimated two million people in the United States each year, with care exceeding US$50 billion. The hallmark of ARF is a heterogeneous injury, with normal tissue intermingled with a large volume of low compliance and collapsed tissue. Mechanical ventilation is necessary to oxygenate and ventilate patients with ARF, but if set inappropriately, it can cause an unintended ventilator-induced lung injury (VILI). The mechanism of VILI is believed to be overdistension of the remaining normal tissue known as the 'baby' lung, causing volutrauma, repetitive collapse and reopening of lung tissue with each breath, causing atelectrauma, and inflammation secondary to this mechanical damage, causing biotrauma. To avoid VILI, extracorporeal membrane oxygenation (ECMO) can temporally replace the pulmonary function of gas exchange without requiring high tidal volumes (VT) or airway pressures. In theory, the lower VT and airway pressure will minimize all three VILI mechanisms, allowing the lung to 'rest' and heal in the collapsed state. The optimal method of mechanical ventilation for the patient on ECMO is unknown. The ARDSNetwork Acute Respiratory Management Approach (ARMA) is a Rest Lung Approach (RLA) that attempts to reduce the excessive stress and strain on the remaining normal lung tissue and buys time for the lung to heal in the collapsed state. Theoretically, excessive tissue stress and strain can also be avoided if the lung is fully open, as long as the alveolar re-collapse is prevented during expiration, an approach known as the Open Lung Approach (OLA). A third lung-protective strategy is the Stabilize Lung Approach (SLA), in which the lung is initially stabilized and gradually reopened over time. This review will analyze the physiologic efficacy and pathophysiologic potential of the above lung-protective approaches.

Awareness and practice of airway pressure release ventilation mode in acute respiratory distress syndrome patients among nurses in Saudi Arabia

BACKGROUND

This study aimed to assess the knowledge and current practice of using the airway pressure release ventilation (APRV) mode with acute respiratory distress syndrome (ARDS) patients and identify barriers to not using this mode of ventilation among nurses who work in critical areas in Saudi Arabia.

METHODS

Between December 2022 and April 2023, a cross-sectional online survey was disseminated to nurses working in critical care areas in Saudi Arabia. The characteristics of the respondents were analyzed using descriptive statistics. Percentages and frequencies were used to report categorical variables.

RESULTS

Overall, 1,002 nurses responded to the online survey, of whom 592 (59.1%) were female. Only 248 (24.7%) nurses had ever used APRV mode, whereas only 229 (22.8%) received training on APRV mode. Moreover, 602 (60.0%) nurses did not know whether APRV was utilized in their hospital. Additionally, 658 (65.6%) nurses did not know whether APRV mode was managed using a standard protocol. Prone positioning was the highest recommended intervention by 444 (43.8%) when a conventional MV failed to improve oxygenation in patients with ARDS. 323 (32.2%) respondents stated that the P-high should be set equal to the plateau pressure on a conventional ventilator, while 400 (39.9%) said that the P-low should match PEEP from a conventional ventilator. Almost half of the respondents (446, 44.5%) stated that the T-high should be set between 4 and 6 s, while 415 (41.4%) said that the T-low should be set at 0.4 to 0.8 s. Over half of the nurses (540, 53.9%) thought that the maximum allowed tidal volume during the release phase should be 4-6 ml/kg. Moreover, 475 (47.4%) believed that the maximum allowed P-high setting should be 35 cm H2O. One-third of the responders (329, 32.8%) stated that when weaning patients with ARDS while in APRV mode, the P-high should be reduced gradually to reach a target of 10 cm H2O. However, 444 (44.3%) thought that the T-high should be gradually increased to reach a target of 10 s. Half of the responders (556, 55.5%) felt that the criteria to switch the patient to continuous positive airway pressure (CPAP) were for the patient to have an FiO2 ≤ 0.4, P-high ≤ 10 cm H2O, and T-high ≥ 10 s. Lack of training was the most common barrier to not using APRV by 615 (61.4%).

CONCLUSION

The majority of nurses who work in critical care units have not received sufficient training in APRV mode. A significant discrepancy was observed regarding the clinical application and management of APRV parameters. Inadequate training was the most frequently reported barrier to the use of APRV in patients with ARDS.

Time-Controlled Adaptive Ventilation (TCAV): a personalized strategy for lung protection

Acute respiratory distress syndrome (ARDS) alters the dynamics of lung inflation during mechanical ventilation. Repetitive alveolar collapse and expansion (RACE) predisposes the lung to ventilator-induced lung injury (VILI). Two broad approaches are currently used to minimize VILI: (1) low tidal volume (LVT) with low-moderate positive end-expiratory pressure (PEEP); and (2) open lung approach (OLA). The LVT approach attempts to protect already open lung tissue from overdistension, while simultaneously resting collapsed tissue by excluding it from the cycle of mechanical ventilation. By contrast, the OLA attempts to reinflate potentially recruitable lung, usually over a period of seconds to minutes using higher PEEP used to prevent progressive loss of end-expiratory lung volume (EELV) and RACE. However, even with these protective strategies, clinical studies have shown that ARDS-related mortality remains unacceptably high with a scarcity of effective interventions over the last two decades. One of the main limitations these varied interventions demonstrate to benefit is the observed clinical and pathologic heterogeneity in ARDS. We have developed an alternative ventilation strategy known as the Time Controlled Adaptive Ventilation (TCAV) method of applying the Airway Pressure Release Ventilation (APRV) mode, which takes advantage of the heterogeneous time- and pressure-dependent collapse and reopening of lung units. The TCAV method is a closed-loop system where the expiratory duration personalizes VT and EELV. Personalization of TCAV is informed and tuned with changes in respiratory system compliance (CRS) measured by the slope of the expiratory flow curve during passive exhalation. Two potentially beneficial features of TCAV are: (i) the expiratory duration is personalized to a given patient's lung physiology, which promotes alveolar stabilization by halting the progressive collapse of alveoli, thereby minimizing the time for the reopened lung to collapse again in the next expiration, and (ii) an extended inspiratory phase at a fixed inflation pressure after alveolar stabilization gradually reopens a small amount of tissue with each breath. Subsequently, densely collapsed regions are slowly ratcheted open over a period of hours, or even days. Thus, TCAV has the potential to minimize VILI, reducing ARDS-related morbidity and mortality.

Airway Pressure Release Ventilation in COVID-19-Associated Acute Respiratory Distress Syndrome-A Multicenter Propensity Score-Matched Analysis

Background: There are limited and partially contradictory data on the effects of airway pressure release ventilation (APRV) in COVID-19-associated acute respiratory distress syndrome (CARDS). Therefore, we analyzed the clinical outcome, complications, and longitudinal course of ventilation parameters and laboratory values in patients with CARDS, who were mechanically ventilated using APRV. Methods: Respective data from 4 intensive care units (ICUs) were collected and compared to a matched cohort of patients receiving conventional low tidal volume ventilation (LTV). Propensity score matching was performed based on age, sex, blood gas analysis, and APACHE II score at admission, as well as the implementation of prone positioning. Findings: Forty patients with CARDS, who were mechanically ventilated using APRV, and 40 patients receiving LTV were matched. No significant differences were detected for tidal volumes per predicted body weight, peak pressure values, and blood gas analyses on admission, 6 h post admission as well as on day 3 and day 7. Regarding ICU survival, no significant difference was identified between APRV patients (40%) and LTV patients (42%). Median duration of mechanical ventilation and duration of ICU treatment were comparable in both groups. Similar complication rates with respect to ventilator-associated pneumonia, septic shock, thromboembolic events, barotrauma, as well as the necessity for hemodialysis were detected for both groups. Clinical characteristics that were associated with increased mortality in a Cox proportional hazards regression analysis included age (hazard ratio [HR] 1.08, 95% confidence interval [CI] 1.04-1.1; P < .001), severe acute respiratory distress syndrome (HR 2.62, 95% CI 1.02-6.7; P = .046) and the occurrence of septic shock (HR 17.18, 95% CI 2.06-143.2; P = .009), but not the ventilation mode. Interpretation: Intensive care unit survival, duration of mechanical ventilation, and ICU treatment as well as ventilation-associated complication rates were equivalent using APRV compared to conventional LTV in patients with CARDS.

First Stabilize and then Gradually Recruit: A Paradigm Shift in Protective Mechanical Ventilation for Acute Lung Injury

Acute respiratory distress syndrome (ARDS) is associated with a heterogeneous pattern of injury throughout the lung parenchyma that alters regional alveolar opening and collapse time constants. Such heterogeneity leads to atelectasis and repetitive alveolar collapse and expansion (RACE). The net effect is a progressive loss of lung volume with secondary ventilator-induced lung injury (VILI). Previous concepts of ARDS pathophysiology envisioned a two-compartment system: a small amount of normally aerated lung tissue in the non-dependent regions (termed "baby lung"); and a collapsed and edematous tissue in dependent regions. Based on such compartmentalization, two protective ventilation strategies have been developed: (1) a "protective lung approach" (PLA), designed to reduce overdistension in the remaining aerated compartment using a low tidal volume; and (2) an "open lung approach" (OLA), which first attempts to open the collapsed lung tissue over a short time frame (seconds or minutes) with an initial recruitment maneuver, and then stabilize newly recruited tissue using titrated positive end-expiratory pressure (PEEP). A more recent understanding of ARDS pathophysiology identifies regional alveolar instability and collapse (i.e., hidden micro-atelectasis) in both lung compartments as a primary VILI mechanism. Based on this understanding, we propose an alternative strategy to ventilating the injured lung, which we term a "stabilize lung approach" (SLA). The SLA is designed to immediately stabilize the lung and reduce RACE while gradually reopening collapsed tissue over hours or days. At the core of SLA is time-controlled adaptive ventilation (TCAV), a method to adjust the parameters of the airway pressure release ventilation (APRV) modality. Since the acutely injured lung at any given airway pressure requires more time for alveolar recruitment and less time for alveolar collapse, SLA adjusts inspiratory and expiratory durations and inflation pressure levels. The TCAV method SLA reverses the open first and stabilize second OLA method by: (i) immediately stabilizing lung tissue using a very brief exhalation time (≤0.5 s), so that alveoli simply do not have sufficient time to collapse. The exhalation duration is personalized and adaptive to individual respiratory mechanical properties (i.e., elastic recoil); and (ii) gradually recruiting collapsed lung tissue using an inflate and brake ratchet combined with an extended inspiratory duration (4-6 s) method. Translational animal studies, clinical statistical analysis, and case reports support the use of TCAV as an efficacious lung protective strategy.

Effects of airway pressure release ventilation on lung physiology assessed by electrical impedance tomography in patients with early moderate-to-severe ARDS

OBJECTIVE

The aim of this study was to investigate the physiological impact of airway pressure release ventilation (APRV) on patients with early moderate-to-severe acute respiratory distress syndrome (ARDS) by electrical impedance tomography (EIT).

METHODS

In this single-center prospective physiological study, adult patients with early moderate-to-severe ARDS mechanically ventilated with APRV were assessed by EIT shortly after APRV (T0), and 6 h (T1), 12 h (T2), and 24 h (T3) after APRV initiation. Regional ventilation and perfusion distribution, dead space (%), shunt (%), and ventilation/perfusion matching (%) based on EIT measurement at different time points were compared. Additionally, clinical variables related to respiratory and hemodynamic condition were analyzed.

RESULTS

Twelve patients were included in the study. After APRV, lung ventilation and perfusion were significantly redistributed to dorsal region. One indicator of ventilation distribution heterogeneity is the global inhomogeneity index, which decreased gradually [0.61 (0.55-0.62) to 0.50 (0.42-0.53), p < 0.001]. The other is the center of ventilation, which gradually shifted towards the dorsal region (43.31 ± 5.07 to 46.84 ± 4.96%, p = 0.048). The dorsal ventilation/perfusion matching increased significantly from T0 to T3 (25.72 ± 9.01 to 29.80 ± 7.19%, p = 0.007). Better dorsal ventilation (%) was significantly correlated with higher PaO₂/FiO₂ (r = 0.624, p = 0.001) and lower PaCO₂ (r = -0.408, p = 0.048).

CONCLUSIONS

APRV optimizes the distribution of ventilation and perfusion, reducing lung heterogeneity, which potentially reduces the risk of ventilator-induced lung injury.

Management of refractory hypoxemia using recruitment maneuvers and rescue therapies: A comprehensive review

Refractory hypoxemia in patients with acute respiratory distress syndrome treated with mechanical ventilation is one of the most challenging conditions in human and veterinary intensive care units. When a conventional lung protective approach fails to restore adequate oxygenation to the patient, the use of recruitment maneuvers and positive end-expiratory pressure to maximize alveolar recruitment, improve gas exchange and respiratory mechanics, while reducing the risk of ventilator-induced lung injury has been suggested in people as the open lung approach. Although the proposed physiological rationale of opening and keeping open previously collapsed or obstructed airways is sound, the technique for doing so, as well as the potential benefits regarding patient outcome are highly controversial in light of recent randomized controlled trials. Moreover, a variety of alternative therapies that provide even less robust evidence have been investigated, including prone positioning, neuromuscular blockade, inhaled pulmonary vasodilators, extracorporeal membrane oxygenation, and unconventional ventilatory modes such as airway pressure release ventilation. With the exception of prone positioning, these modalities are limited by their own balance of risks and benefits, which can be significantly influenced by the practitioner's experience. This review explores the rationale, evidence, advantages and disadvantages of each of these therapies as well as available methods to identify suitable candidates for recruitment maneuvers, with a summary on their application in veterinary medicine. Undoubtedly, the heterogeneous and evolving nature of acute respiratory distress syndrome and individual lung phenotypes call for a personalized approach using new non-invasive bedside assessment tools, such as electrical impedance tomography, lung ultrasound, and the recruitment-to-inflation ratio to assess lung recruitability. Data available in human medicine provide valuable insights that could, and should, be used to improve the management of veterinary patients with severe respiratory failure with respect to their intrinsic anatomy and physiology.