Recruitment-Potential-Oriented Mechanical Ventilation Protocol and Narrative Review for Patients with Acute Respiratory Distress Syndrome.

Even though much progress has been made to improve clinical outcomes, acute respiratory distress syndrome (ARDS) remains a significant cause of acute respiratory failure. Protective mechanical ventilation is the backbone of supportive care for these patients; however, there are still many unresolved issues in its setting. The primary goal of mechanical ventilation is to improve oxygenation and ventilation. The use of positive pressure, especially positive end-expiratory pressure (PEEP), is mandatory in this approach. However, PEEP is a double-edged sword. How to safely set positive end-inspiratory pressure has long been elusive to clinicians. We hereby propose a pressure-volume curve measurement-based method to assess whether injured lungs are recruitable in order to set an appropriate PEEP. For the most severe form of ARDS, extracorporeal membrane oxygenation (ECMO) is considered as the salvage therapy. However, the high level of medical resources required and associated complications make its use in patients with severe ARDS controversial. Our proposed protocol also attempts to propose how to improve patient outcomes by balancing the possible overuse of resources with minimizing patient harm due to dangerous ventilator settings. A recruitment-potential-oriented evaluation-based protocol can effectively stabilize hypoxemic conditions quickly and screen out truly serious patients.

Inconsistent Methods Used to Set Airway Pressure Release Ventilation in Acute Respiratory Distress Syndrome: A Systematic Review and Meta-Regression Analysis.

Airway pressure release ventilation (APRV) is a protective mechanical ventilation mode for patients with acute respiratory distress syndrome (ARDS) that theoretically may reduce ventilator-induced lung injury (VILI) and ARDS-related mortality. However, there is no standard method to set and adjust the APRV mode shown to be optimal. Therefore, we performed a meta-regression analysis to evaluate how the four individual APRV settings impacted the outcome in these patients. Methods: Studies investigating the use of the APRV mode for ARDS patients were searched from electronic databases. We tested individual settings, including (1) high airway pressure (PHigh); (2) low airway pressure (PLow); (3) time at high airway pressure (THigh); and (4) time at low pressure (TLow) for association with PaO2/FiO2 ratio and ICU length of stay. Results: There was no significant difference in PaO2/FiO2 ratio between the groups in any of the four settings (PHigh difference -12.0 [95% CI -100.4, 86.4]; PLow difference 54.3 [95% CI -52.6, 161.1]; TLow difference -27.19 [95% CI -127.0, 72.6]; THigh difference -51.4 [95% CI -170.3, 67.5]). There was high heterogeneity across all parameters (PhHgh I2 = 99.46%, PLow I2 = 99.16%, TLow I2 = 99.31%, THigh I2 = 99.29%). Conclusions: None of the four individual APRV settings independently were associated with differences in outcome. A holistic approach, analyzing all settings in combination, may improve APRV efficacy since it is known that small differences in ventilator settings can significantly alter mortality. Future clinical trials should set and adjust APRV based on the best current scientific evidence available.

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.

Knowledge and practice of using airway pressure release ventilation mode in ARDS patients: A survey of physicians.

Background: Limited data is available on awareness and clinical management of the airway pressure release ventilation (APRV) mode of ventilation for acute respiratory distress syndrome (ARDS) patients among physicians who work at in adult critical areas. This study aimed to assess the knowledge and current practice of using APRV mode with ARDS patients and identify barriers to not using this mode of ventilation among physicians who work in adult critical areas in Saudi Arabia. Methods: Between November 2022 and April 2023, a cross-sectional online survey was disseminated to physicians who work in adult critical 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, 498 physicians responded to the online survey. All responders (498, 100 %) reported that APRV is indicated in patients with ARDS, but 260 (52.2 %) did not know if there was an institutionally approved APRV protocol. Prone positioning was the highest recommended intervention by 164 (33.0 %) when a conventional MV failed to improve oxygenation in patients with ARDS. 136 (27.3 %) responders stated that the P-high should be set equal to the plateau pressure on a conventional ventilator while 198 (39.8 %) said that P-low should be 0 cmH2O. Almost half of (229, 46.0 %) responders stated that the T-high should be set between 4 and 6 s, while 286 (57.4 %) said that the T-low should be set at 0.4-0.8 s. The maximum allowed tidal volume during the release phase should be 4-6 ml/kg. Moreover, just over half (257, 51.6 %) believed that the maximum allowed P-high setting should be 35 cmH2O. One third of the responders (171, 34.3 %) stated that when weaning patients with ARDS while in APRV mode, the P-high should be reduced gradually to reach a target of 10 cmH2O. However, 284 (36.9 %) thought that the T-high should be gradually increased to reach a target of 10 s. Most responders (331, 66.5 %) felt that the criteria to switch the patient to CPAP would be to have an FiO2 ≤ 0.4, P-high ≤10 cm H2O, and T-high ≥10 s. Lack of training has been the most common barrier to not using APRV by 388 (77.9 %). Conclusion: There is a lack of consensus on the use of APRV mode, probably due to several barriers. While there were some agreements on the management of ventilation and oxygenation, there were variations in the selection of the initial setting of APRV. Education, training, and the presence of standardized protocols may help to provide better management.

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.

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.

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

In the pursuit of science, competitive ideas and debate are necessary means to attain knowledge and expose our ignorance. To quote Murray Gell-Mann (1969 Nobel Prize laureate in Physics): "Scientific orthodoxy kills truth". In mechanical ventilation, the goal is to provide the best approach to support patients with respiratory failure until the underlying disease resolves, while minimizing iatrogenic damage. This compromise characterizes the philosophy behind the concept of "lung protective" ventilation. Unfortunately, inadequacies of the current conceptual model-that focuses exclusively on a nominal value of low tidal volume and promotes shrinking of the "baby lung" - is reflected in the high mortality rate of patients with moderate and severe acute respiratory distress syndrome. These data call for exploration and investigation of competitive models evaluated thoroughly through a scientific process. Airway Pressure Release Ventilation (APRV) is one of the most studied yet controversial modes of mechanical ventilation that shows promise in experimental and clinical data. Over the last 3 decades APRV has evolved from a rescue strategy to a preemptive lung injury prevention approach with potential to stabilize the lung and restore alveolar homogeneity. However, several obstacles have so far impeded the evaluation of APRV's clinical efficacy in large, randomized trials. For instance, there is no universally accepted standardized method of setting APRV and thus, it is not established whether its effects on clinical outcomes are due to the ventilator mode per se or the method applied. In addition, one distinctive issue that hinders proper scientific evaluation of APRV is the ubiquitous presence of myths and misconceptions repeatedly presented in the literature. In this review we discuss some of these misleading notions and present data to advance scientific discourse around the uses and misuses of APRV in the current literature.

Inclusion of airway pressure release ventilation in the management of respiratory failure and refractory hypercapnia in a dog.

OBJECTIVE: To describe the use of airway pressure release ventilation (APRV) to relieve hypercapnia in a dog undergoing mechanical ventilation. CASE SUMMARY: A 3-month-old male Shar-Pei mix presented to the emergency department with suspected noncardiogenic pulmonary edema. Due to severe hypercapnia, mechanical ventilation was initiated. The hypercapnia failed to improve with conventional pressure control mechanical ventilation, bronchodilator administration, suctioning, or endotracheal tube replacement. The dog was transitioned to APRV and maintained in this mode for 36 hours. A modified APRV protocol in which inverse inspiratory to expiratory ratios ranged from 4.3:1 to 6.0:1 was utilized, resulting in a drastic improvement in the patient's hypercapnia. The patient eventually was transitioned off the ventilator, and no respiratory abnormalities have been noted at subsequent recheck examinations. NEW OR UNIQUE INFORMATION PROVIDED: This case documents the first use of APRV to relieve refractory hypercapnia in a dog undergoing mechanical ventilation and is one of the only recorded cases of using APRV for this purpose in the medical literature at large. APRV may be considered in cases of hypercapnia when traditional therapies fail, although caution is warranted as this mode of ventilation can also worsen hypercapnia.

Airway Pressure Release Ventilation: A Field Guide for the Emergency Physician.

Airway pressure release ventilation (APRV) is a mode of ventilation that uses high airway pressures to recruit and maintain patients' lung volumes. The goal of this mode of ventilation is 2-fold: first, to maintain patients as close to their functional residual capacity as possible and second, to promote safe spontaneous breathing. APRV should essentially be viewed as continuous positive airway pressure (CPAP), with intermittent releases of that pressure to metabolically support patients who are incapable of managing their ventilatory load. As patients recruit and lungs approach the patients' natural lung volumes, their ability to breathe spontaneously and manage their own ventilatory needs improves. Eventually, patients are able to fully support their ventilatory needs and no longer require any release breaths to maintain normal CO2 levels. Now, patients can be "stretched" to CPAP.

Time-Controlled Adaptive Ventilation Does Not Induce Hemodynamic Impairment in a Swine ARDS Model.

Background: The current standard of care during severe acute respiratory distress syndrome (ARDS) is based on low tidal volume (VT) ventilation, at 6 mL/kg of predicted body weight. The time-controlled adaptive ventilation (TCAV) is an alternative strategy, based on specific settings of the airway pressure release ventilation (APRV) mode. Briefly, TCAV reduces lung injury, including: (1) an improvement in alveolar recruitment and homogeneity; (2) reduction in alveolar and alveolar duct micro-strain and stress-risers. TCAV can result in higher intra-thoracic pressures and thus impair hemodynamics resulting from heart-lung interactions. The objective of our study was to compare hemodynamics between TCAV and conventional protective ventilation in a porcine ARDS model. Methods: In 10 pigs (63-73 kg), lung injury was induced by repeated bronchial saline lavages followed by 2 h of injurious ventilation. The animals were then randomized into two groups: (1) Conventional protective ventilation with a VT of 6 mL/kg and PEEP adjusted to a plateau pressure set between 28 and 30 cmH2O; (2) TCAV group with P-high set between 27 and 29 cmH2O, P-low at 0 cmH2O, T-low adjusted to terminate at 75% of the expiratory flow peak, and T-high at 3-4 s, with I:E > 6:1. Results: Both lung elastance and PaO2:FiO2 were consistent with severe ARDS after 2 h of injurious mechanical ventilation. There was no significant difference in systemic arterial blood pressure, pulmonary blood pressure or cardiac output between Conventional protective ventilation and TCAV. Levels of total PEEP were significantly higher in the TCAV group (p < 0.05). Driving pressure and lung elastance were significantly lower in the TCAV group (p < 0.05). Conclusion: No hemodynamic adverse events were observed in the TCAV group compared as to the standard protective ventilation group in this swine ARDS model, and TCAV appeared to be beneficial to the respiratory system.

Study on the Pressure Regulation Method of New Automatic Pressure Regulating Valve in the Electronically Controlled Pneumatic Brake Systems in Commercial Vehicles.

In order to adapt the development of vehicle driving automation technology for driving conditions under different levels of automation and based on the independently invented LF automatic pressure regulating valve (LF-APRV) for electronically controlled pneumatic brake systems (ECPBS), the dynamic PWM coupling pressure regulation method is proposed. This method realizes pressure regulation by adjusting the duty cycle of the control signal of the LF-APRV at different stages in the pressure regulation cycle. A co-simulation model was established to verify the feasibility of the method, and a test system was built to verify the correctness of the co-simulation model. Through the test, the pressure regulation performance of dynamic PWM coupling pressure regulation method and conventional on/off pressure regulation method was compared. The results show that the new method can improve the stability of pressure regulation, although the response time increases; under the new method, the overshoot of the pressure rising from 0 to 0.5 MPa was reduced by 69%, and the overshoot of the pressure decreasing from 0.5 MPa to 0.2 MPa was basically 0. Finally, tests and simulations showed that the dynamic PWM coupling pressure regulation method can meet the continuous graded braking requirements of vehicles, and the pressure response has good tracking performance on the target pressure.

Airway Pressure Release Ventilation With Time-Controlled Adaptive Ventilation (TCAV™) in COVID-19: A Community Hospital's Experience.

Santa Cabrini Ospedale, a community hospital in Montreal, Canada, used the airway pressure release ventilation following a time-controlled adaptive ventilation (APRV-TCAV™) approach for several patients in the first wave of the coronavirus disease 2019 (COVID-19) outbreak in the spring of 2021. Based on favorable patient responses, it became the primary mode of invasive mechanical ventilation-from initiation through extubation-during the second and third waves of COVID-19. In this article, we describe our success with APRV-TCAV™ over more conventional modes and protocols and look at three cases that aptly demonstrate our experience. We then outline several risks with our approach and the lessons learned from our experience. While we generally saw improvement in patients' clinical course with APRV-TCAV™, there are inherent risks with this approach that others must prepare for if they attempt to implement it in their practice.

The effect of preemptive airway pressure release ventilation on patients with high risk for acute respiratory distress syndrome: a randomized controlled trial.

BACKGROUND AND OBJECTIVES: The objective of this study was to investigate the use of early APRV mode as a lung protective strategy compared to conventional methods with regard to ARDS development. METHODS: The study was designed as a randomized, non-blinded, single-center, superiority trial with two parallel groups and a primary endpoint of ARDS development. Patients under invasive mechanical ventilation who were not diagnosed with ARDS and had Lung Injury Prediction Score greater than 7 were included in the study. The patients were assigned to APRV and P-SIMV + PS mode groups. RESULTS: Patients were treated with P-SIMV+PS or APRV mode; 33 (50.8%) and 32 (49.2%), respectively. The P/F ratio values were higher in the APRV group on day 3 (p = 0.032). The fraction of inspired oxygen value was lower in the APRV group at day 7 (p = 0.011).While 5 of the 33 patients (15.2%) in the P-SIMV+PS group developed ARDS, one out of the 32 patients (3.1%) in the APRV group developed ARDS during follow-up (p = 0.197). The groups didn't differ in terms of vasopressor/inotrope requirement, successful extubation rates, and/or mortality rates (p = 1.000, p = 0.911, p = 0.705, respectively). Duration of intensive care unit stay was 8 (2-11) days in the APRV group and 13 (8-81) days in the P-SIMV+PS group (p = 0.019). CONCLUSIONS: The APRV mode can be used safely in selected groups of surgical and medical patients while preserving spontaneous respiration to a make benefit of its lung-protective effects. In comparison to the conventional mode, it is associated with improved oxygenation, higher mean airway pressures, and shorter intensive care unit stay. However, it does not reduce the sedation requirement, ARDS development, or mortality.

Efficacy of airway pressure release ventilation for acute respiratory distress syndrome: a systematic review with meta-analysis.

BACKGROUND: For many years, airway pressure release ventilation (APRV) has been used to manage patients with lung conditions such as acute respiratory distress syndrome (ARDS). However, it is still unclear whether APRV improves outcomes in critically ill ARDS patients who have been admitted to an intensive care unit (ICU). METHODS: In this study, randomized controlled trials (RCTs) were used to compare the efficacy of APRV to traditional modes of mechanical ventilation. RCTs were sourced from PubMed, Cochrane, and Embase databases (the last dates from August 8, 2019). The Cochrane Handbook for Systematic Reviews of Interventions was used to assess the risk of bias. The relative risk (RR), mean difference (MD), and 95% confidence intervals (CI) were then determined. Article types such as observational studies, case reports, animal studies, etc., were excluded from our meta-analysis. In total, the data of 6 RCTs and 360 ARDS patients were examined. RESULTS: Six studies with 360 patients were included, our meta-analysis showed that the mean arterial pressure (MAP) in the APRV group was higher than that in the traditional mechanical ventilation group (MD =2.35, 95% CI: 1.05-3.64, P=0.0004). The peak pressure (Ppeak) was also lower in the APRV group with a statistical difference noted (MD =-2.04, 95% CI: -3.33 to -0.75, P=0.002). Despite this, no significant beneficial effect on the oxygen index (PaO2/FiO2) was shown between the two groups (MD =26.24, 95% CI: -26.50 to 78.97, P=0.33). Compared with conventional mechanical ventilation, APRV significantly improved 28-day mortality (RR =0.66, 95% CI: 0.47-0.94, P=0.02). DISCUSSION: All the included studies were considered to have an unclear risk of bias. We determined that for critically ill patients with ARDS, the application of APRV is associated with an increase in MAP. Inversely, a reduction of the airway Ppeak and 28-day mortality was recorded. There was no sufficient evidence to support the idea that APRV is superior to conventional mechanical ventilation in improving PaO2/FiO2.

Is airway pressure release ventilation, a better primary mode of post-operative ventilation for adult patients undergoing open heart surgery? A prospective randomised study.

Context: Cardiopulmonary bypass (CPB) induced acute lung injury is accounted for most of the post-operative pulmonary dysfunction which leads to decreased compliance and hypoxemia. Airway Pressure Release Ventilation (APRV) as compared to other modes of ventilation has shown to improve gas exchange in Acute lung injury (ALI)/Acute respiratory distress syndrome (ARDS) lungs. Aims: We hypothesized APRV as a better primary mode of postoperative ventilation in adult post-cardiac surgery patients. Methodology: The study included 90 postoperative surgical patients, which were randomized into three groups: SIMV-PC(P), APRV(A), and SIMV-VC(V) with 30 patients in each group. Subjects and Methods: Lung compliance and serial arterial blood gas were assessed at regular intervals. PaO2/FiO2 ratio (a measure of oxygenation) and lung compliance were used as an indirect indicator for improvement in lung function. Hemodynamic parameters were closely observed for all the patients. Statistical Analysis Used: Statistical analysis was done using 'R' software. Results: There was a statistically significant improvement in PaO2/FiO2 ratio in the APRV group as compared to other groups. There was also an improvement in lung compliance after 6 h of ventilation and lesser duration of ventilation in the APRV group. However, it was not statistically significant. Conclusions: Our study suggests that APRV can be a useful alternative primary mode of ventilation to improve lung compliance and oxygenation in adult post-cardiac surgical patients.

Airway pressure release ventilation in mechanically ventilated patients with COVID-19: a multicenter observational study.

BACKGROUND: Evidence prior to the coronavirus disease 2019 (COVID-19) pandemic suggested that, compared with conventional ventilation strategies, airway pressure release ventilation (APRV) can improve oxygenation and reduce mortality in patients with acute respiratory distress syndrome. We aimed to assess the association between APRV use and clinical outcomes among adult patients receiving mechanical ventilation for COVID-19 and hypothesized that APRV use would be associated with improved survival compared with conventional ventilation. METHODS: A total of 25 patients with COVID-19 pneumonitis was admitted to intensive care units (ICUs) for invasive ventilation in Perth, Western Australia, between February and May 2020. Eleven of these patients received APRV. The primary outcome was survival to day 90. Secondary outcomes were ventilation-free survival days to day 90, mechanical complications from ventilation, and number of days ventilated. RESULTS: Patients who received APRV had a lower probability of survival than did those on other forms of ventilation (hazard ratio, 0.17; 95% confidence interval, 0.03-0.89; P=0.036). This finding was independent of indices of severity of illness to predict the use of APRV. Patients who received APRV also had fewer ventilator-free survival days up to 90 days after initiation of ventilation compared to patients who did not receive APRV, and survivors who received APRV had fewer ventilator-free days than survivors who received other forms of ventilation. There were no differences in mechanical complications according to mode of ventilation. CONCLUSIONS: Based on the findings of this study, we urge caution with the use of APRV in COVID-19.

The severity of footrot lesions induced by aprV2-positive strains of Dichelobacter nodosus varies between strains.

OBJECTIVES: The primary objective of this study was to evaluate the clinical virulence of aprV2-positive lesser virulent field isolates of footrot bacteria Dichelobacter nodosus in comparison with an aprV2-positive clinically virulent reference strain. Correlations between the clinical expression of the disease and the presence of aprV2 (detected using PCR tests) have been inconsistent. A second objective was to evaluate the elimination of D. nodosus following treatment of sheep as some strains of D. nodosus have been reported to be difficult to eliminate. METHODS: The virulence of three aprV2-positive field isolates of D. nodosus which had lesser virulent phenotypes, and an aprV2-positive virulent reference strain was evaluated in a sheep trial using a pasture-based experimental infection model. In the second phase of the study, treatments including footbathing and a long-acting antibiotic were administered and their efficacy in elimination of these strains was evaluated. RESULTS: Severe underrun (score 4) lesions developed in sheep infected with the aprV2-positive virulent reference strain but not in sheep infected with the field isolates; they had mild lesions (score 2 or 3). The three field isolates and the virulent reference strain of D. nodosus were eliminated by intensive foot bathing and antibiotic therapy in combination with housing the animals in dry conditions post-treatment. CONCLUSION: The results suggest that the presence of aprV2 gene in isolates of D. nodosus may not be a reliable indicator of virulence and that further investigation of the factors that determine clinical virulence is required. While the treatment regime was successful, based on a range of considerations, the use of such an intensive treatment involving antibiotics should be limited to small groups of high-value animals, such as rams.

Assessment of spontaneous breathing during pressure controlled ventilation with superimposed spontaneous breathing using respiratory flow signal analysis.

Integrating spontaneous breathing into mechanical ventilation (MV) can speed up liberation from it and reduce its invasiveness. On the other hand, inadequate and asynchronous spontaneous breathing has the potential to aggravate lung injury. During use of airway-pressure-release-ventilation (APRV), the assisted breaths are difficult to measure. We developed an algorithm to differentiate the breaths in a setting of lung injury in spontaneously breathing ewes. We hypothesized that differentiation of breaths into spontaneous, mechanical and assisted is feasible using a specially developed for this purpose algorithm. Ventilation parameters were recorded by software that integrated ventilator output variables. The flow signal, measured by the EVITA® XL (Lübeck, Germany), was measured every 2 ms by a custom Java-based computerized algorithm (Breath-Sep). By integrating the flow signal, tidal volume (VT) of each breath was calculated. By using the flow curve the algorithm separated the different breaths and numbered them for each time point. Breaths were separated into mechanical, assisted and spontaneous. Bland Altman analysis was used to compare parameters. Comparing the values calculated by Breath-Sep with the data from the EVITA® using Bland-Altman analyses showed a mean bias of - 2.85% and 95% limits of agreement from - 25.76 to 20.06% for MVtotal. For respiratory rate (RR) RRset a bias of 0.84% with a SD of 1.21% and 95% limits of agreement from - 1.53 to 3.21% were found. In the cluster analysis of the 25th highest breaths of each group RRtotal was higher using the EVITA®. In the mechanical subgroup the values for RRspont and MVspont the EVITA® showed higher values compared to Breath-Sep. We developed a computerized method for respiratory flow-curve based differentiation of breathing cycle components during mechanical ventilation with superimposed spontaneous breathing. Further studies in humans and optimizing of this technique is necessary to allow for real-time use at the bedside.

Mechanical ventilation in aneurysmal subarachnoid hemorrhage: systematic review and recommendations.

OBJECTIVE: Mechanical ventilation (MV) has a complex interplay with the pathophysiology of aneurysmal subarachnoid hemorrhage (aSAH). We aim to provide a review of the physiology of MV in patients with aSAH, give recommendations based on a systematic review of the literature, and highlight areas that still need investigation. DATA SOURCES: PubMed was queried for publications with the Medical Subject Headings (MeSH) terms "mechanical ventilation" and "aneurysmal subarachnoid hemorrhage" published between January 1, 1990, and March 1, 2020. Bibliographies of returned articles were reviewed for additional publications of interest. STUDY SELECTION: Study inclusion criteria included English language manuscripts with the study population being aSAH patients and the exposure being MV. Eligible studies included randomized controlled trials, observational trials, retrospective trials, case-control studies, case reports, or physiologic studies. Topics and articles excluded included review articles, pediatric populations, non-aneurysmal etiologies of subarachnoid hemorrhage, mycotic and traumatic subarachnoid hemorrhage, and articles regarding tracheostomies. DATA EXTRACTION: Articles were reviewed by one team member, and interpretation was verified by a second team member. DATA SYNTHESIS: Thirty-one articles met the inclusion criteria for this review. CONCLUSIONS: We make recommendations on oxygenation, hypercapnia, PEEP, APRV, ARDS, and intracranial pressure monitoring.