A randomized prospective trial of airway pressure release ventilation and low tidal volume ventilation in adult trauma patients with acute respiratory failure

Successful application of airway pressure release ventilation in a child with severe acute respiratory distress syndrome induced by trauma: a case report

BACKGROUND

Trauma has been identified as one of the risk factors for acute respiratory distress syndrome. Respiratory support can be further complicated by comorbidities of trauma such as primary or secondary lung injury. Conventional ventilation strategies may not be suitable for all trauma-related acute respiratory distress syndrome. Airway pressure release ventilation has emerged as a potential rescue method for patients with acute respiratory distress syndrome and hypoxemia refractory to conventional mechanical ventilation. However, there is a lack of research on the use of airway pressure release ventilation in children with trauma-related acute respiratory distress syndrome. We report a case of airway pressure release ventilation applied to a child with falling injury, severe acute respiratory distress syndrome, hemorrhagic shock, and bilateral hemopneumothorax. We hope this case report presents a potential option for trauma-related acute respiratory distress syndrome and serves as a basis for future research.

CASE PRESENTATION

A 15-year-old female with falling injury who developed severe acute respiratory distress syndrome, hemorrhagic shock, and bilateral hemopneumothorax was admitted to the surgical intensive care unit. She presented refractory hypoxemia despite the treatment of conventional ventilation with deep analgesia, sedation, and muscular relaxation. Lung recruitment was ineffective and prone positioning was contraindicated. Her oxygenation significantly improved after the use of airway pressure release ventilation. She was eventually extubated after 12 days of admission and discharged after 42 days of hospitalization.

CONCLUSION

Airway pressure release ventilation may be considered early in the management of trauma patients with severe acute respiratory distress syndrome when prone position ventilation cannot be performed and refractory hypoxemia persists despite conventional ventilation and lung recruitment maneuvers.

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.

ARDS Clinical Practice Guideline 2021

Background

The joint committee of the Japanese Society of Intensive Care Medicine/Japanese Respiratory Society/Japanese Society of Respiratory Care Medicine on ARDS Clinical Practice Guideline has created and released the ARDS Clinical Practice Guideline 2021.

Methods

The 2016 edition of the Clinical Practice Guideline covered clinical questions (CQs) that targeted only adults, but the present guideline includes 15 CQs for children in addition to 46 CQs for adults. As with the previous edition, we used a systematic review method with the Grading of Recommendations Assessment Development and Evaluation (GRADE) system as well as a degree of recommendation determination method. We also conducted systematic reviews that used meta-analyses of diagnostic accuracy and network meta-analyses as a new method.

Results

Recommendations for adult patients with ARDS are described: we suggest against using serum C-reactive protein and procalcitonin levels to identify bacterial pneumonia as the underlying disease (GRADE 2D); we recommend limiting tidal volume to 4–8 mL/kg for mechanical ventilation (GRADE 1D); we recommend against managements targeting an excessively low SpO₂ (PaO₂) (GRADE 2D); we suggest against using transpulmonary pressure as a routine basis in positive end-expiratory pressure settings (GRADE 2B); we suggest implementing extracorporeal membrane oxygenation for those with severe ARDS (GRADE 2B); we suggest against using high-dose steroids (GRADE 2C); and we recommend using low-dose steroids (GRADE 1B). The recommendations for pediatric patients with ARDS are as follows: we suggest against using non-invasive respiratory support (non-invasive positive pressure ventilation/high-flow nasal cannula oxygen therapy) (GRADE 2D), we suggest placing pediatric patients with moderate ARDS in the prone position (GRADE 2D), we suggest against routinely implementing NO inhalation therapy (GRADE 2C), and we suggest against implementing daily sedation interruption for pediatric patients with respiratory failure (GRADE 2D).

Conclusions

This article is a translated summary of the full version of the ARDS Clinical Practice Guideline 2021 published in Japanese (URL: https://www.jsicm.org/publication/guideline.html). The original text, which was written for Japanese healthcare professionals, may include different perspectives from healthcare professionals of other countries.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40560-022-00615-6.

The efficacy of airway pressure release ventilation in acute respiratory distress syndrome adult patients: A meta-analysis of clinical trials

BACKGROUND

To recruit poorly ventilated lung areas by providing active and adequate oxygenation is a core aspect of treating patients with acute respiratory distress syndrome (ARDS). The airway pressure release ventilation (APRV) mode is increasingly accepted as a means of supporting patients with ARDS. This study aimed to determine whether the APRV mode is effective in improving oxygenation, compared to conventional ventilation, in adult ARDS patients.

METHODS

We conducted the study according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. We searched for clinical trials in PubMed, Embase, Web of Science, and the Cochrane Library until April 2019. We included all studies comparing APRV and other conventional mechanical ventilation modes for adult ARDS patients. Our primary outcome was oxygenation status (defined as the day 3 PaO2/FiO2 ratio). The secondary outcomes were the length of stay (LOS) in the intensive care unit (ICU) and mortality. Sensitivity analyses were performed including studies with conventional low-tidal volume ventilation as a comparator ventilation strategy.

RESULTS

We included six clinical trials enrolling a total of 375 patients. The day 3 PaO2/FiO2 was reported in all the studies, and it was significantly higher in patients receiving APRV (mean difference [MD] 51.9 mmHg, 95% confidence intervals (CI) 8.2-95.5, P = 0.02, I 2= 92%). There was no significant difference in mortality between APRV and the other conventional ventilator modes (risk difference 0.07, 95% CI: -0.01-0.15, P = 0.08, I 20%). The point estimate for the effect of APRV on the LOS in ICU indicated a significant reduction in the ICU LOS for the APRV group compared to the counter group (MD 3.1 days, 95% CI 0.4-5.9, P = 0.02, I 2= 53%).

CONCLUSION

In this study, using the APRV mode may improve oxygenation on day 3 and contribute to reducing the LOS in ICU. However, it is difficult to draw a clinical message about APRV, and well-designed clinical trials are required to investigate this issue.

Management of ARDS - What Works and What Does Not

Acute respiratory distress syndrome (ARDS) is a clinically and biologically heterogeneous disorder associated with a variety of disease processes that lead to acute lung injury with increased non-hydrostatic extravascular lung water, reduced compliance, and severe hypoxemia. Despite significant advances, mortality associated with this syndrome remains high. Mechanical ventilation remains the most important aspect of managing patients with ARDS. An in-depth knowledge of lung protective ventilation, optimal PEEP strategies, modes of ventilation and recruitment maneuvers are essential for ventilatory management of ARDS. Although, the management of ARDS is constantly evolving as new studies are published and guidelines being updated; we present a detailed review of the literature including the most up-to-date studies and guidelines in the management of ARDS. We believe this review is particularly helpful in the current times where more than half of the acute care hospitals lack in-house intensivists and the burden of ARDS is at large.

Airway pressure release ventilation versus low tidal volume ventilation for patients with acute respiratory distress syndrome/acute lung injury: a meta-analysis of randomized clinical trials

Background

It is uncertain whether airway pressure release ventilation (APRV) is better than low tidal volume ventilation (LTVV) for patients with acute respiratory distress syndrome (ARDS). The purpose of this meta-analysis was to compare APRV and LTVV on patients with ARDS.

Methods

Randomized controlled trials (RCTs) comparing outcomes in ARDS ventilator therapy with APRV or LTVV were identified using Medical Literature Analysis and Retrieval System Online (MEDLINE), Excerpta Medica Database (EMBASE), Cumulative Index to Nursing and Allied Health Literature (CINAHL), Web of Science, the Cochrane Library, and The Chinese Biomedicine Literature Database (SinoMed) from inception to March 2019.

Results

A total of 7 RCTs with a 405 patients were eligible for our meta-analysis. The results revealed that APRV was associated with lower hospital mortality [405 patients; odds ratio (OR), 0.57; 95% confidence interval (CI), 0.37-0.88; P=0.01], a shorter time of ventilator therapy [373 patients; mean difference (MD), 5.36; 95% CI, 1.99-8.73; P=0.002], and intensive care unit (ICU) stay (315 patients; MD, -4.50; 95% CI, -6.56 to -2.44; P<0.0001), better respiratory system compliance on day 3 (202 patients; MD, 8.19; 95% CI, 0.84-15.54; P=0.03), arterial partial pressure of oxygen/fraction of inspired oxygen (PaO2/FiO2) on day 3 (294 patients; MD, 44.40; 95% CI, 16.05-72.76; P=0.002), and higher mean arterial pressure (MAP) on day 3 (285 patients; MD, 4.18; 95% CI, 3.10-5.25; P<0.00001). There was no statistical difference in the incidence of pneumothorax (170 patients; OR, 0.40; 95% CI, 0.12-1.34; P=0.14).

Conclusions

The meta-analysis showed that APRV could reduce hospital mortality, duration of ventilation and ICU stay, improve lung compliance, oxygenation index, and MAP compared with LTVV for patients with ARDS. We found APRV to be a safe and effective ventilation mode for patients with ARDS.

Evidence-Based Management of the Critically Ill Adult With SARS-CoV-2 Infection

Human infection by the novel viral pathogen SARS-CoV-2 results in a clinical syndrome termed Coronavirus Disease 2019 (COVID-19). Although the majority of COVID-19 cases are self-limiting, a substantial minority of patients develop disease severe enough to require intensive care. Features of critical illness associated with COVID-19 include hypoxemic respiratory failure, acute respiratory distress syndrome (ARDS), shock, and multiple organ dysfunction syndrome (MODS). In most (but not all) respects critically ill patients with COVID-19 resemble critically ill patients with ARDS due to other causes and are optimally managed with standard, evidence-based critical care protocols. However, there is naturally an intense interest in developing specific therapies for severe COVID-19. Here we synthesize the rapidly expanding literature around the pathophysiology, clinical presentation, and management of COVID-19 with a focus on those points most relevant for intensivists tasked with caring for these patients. We specifically highlight evidence-based approaches that we believe should guide the identification, triage, respiratory support, and general ICU care of critically ill patients infected with SARS-CoV-2. In addition, in light of the pressing need and growing enthusiasm for targeted COVID-19 therapies, we review the biological basis, plausibility, and clinical evidence underlying these novel treatment approaches.

Management of primary blast lung injury: a comparison of airway pressure release versus low tidal volume ventilation

BACKGROUND

Primary blast lung injury (PBLI) presents as a syndrome of respiratory distress and haemoptysis resulting from explosive shock wave exposure and is a frequent cause of mortality and morbidity in both military conflicts and terrorist attacks. The optimal mode of mechanical ventilation for managing PBLI is not currently known, and clinical trials in humans are impossible due to the sporadic and violent nature of the disease.

METHODS

A high-fidelity multi-organ computational simulator of PBLI pathophysiology was configured to replicate data from 14 PBLI casualties from the conflict in Afghanistan. Adaptive and responsive ventilatory protocols implementing low tidal volume (LTV) ventilation and airway pressure release ventilation (APRV) were applied to each simulated patient for 24 h, allowing direct quantitative comparison of their effects on gas exchange, ventilatory parameters, haemodynamics, extravascular lung water and indices of ventilator-induced lung injury.

RESULTS

The simulated patients responded well to both ventilation strategies. Post 24-h investigation period, the APRV arm had similar PF ratios (137 mmHg vs 157 mmHg), lower sub-injury threshold levels of mechanical power (11.9 J/min vs 20.7 J/min) and lower levels of extravascular lung water (501 ml vs 600 ml) compared to conventional LTV. Driving pressure was higher in the APRV group (11.9 cmH₂O vs 8.6 cmH₂O), but still significantly less than levels associated with increased mortality.

CONCLUSIONS

Appropriate use of APRV may offer casualties with PBLI important mortality-related benefits and should be considered for management of this challenging patient group.

Airway Pressure Release Ventilation: A Review of the Evidence, Theoretical Benefits, and Alternative Titration Strategies

Objective:

To review the theoretical benefits of airway pressure release ventilation (APRV), summarize the evidence for its use in clinical practice, and discuss different titration strategies.

Data Source:

Published randomized controlled trials in humans, observational human studies, animal studies, review articles, ventilator textbooks, and editorials.

Data Summary:

Airway pressure release ventilation optimizes alveolar recruitment, reduces airway pressures, allows for spontaneous breathing, and offers many hemodynamic benefits. Despite these physiologic advantages, there are inconsistent data to support the use of APRV over other modes of ventilation. There is considerable heterogeneity in the application of APRV among providers and a shortage of information describing initiation and titration strategies. To date, no direct comparison studies of APRV strategies have been performed. This review describes 2 common management approaches that bedside providers can use to optimally tailor APRV to their patients.

Conclusion:

Airway pressure release ventilation remains a form of mechanical ventilation primarily used for refractory hypoxemia. It offers unique physiological advantages over other ventilatory modes, and providers must be familiar with different titration methods. Given its inconsistent outcome data and heterogeneous use in practice, future trials should directly compare APRV strategies to determine the optimal management approach.

Airway pressure release ventilation in children

PURPOSE OF REVIEW

In patients with acute respiratory distress syndrome (ARDS), airway pressure release ventilation (APRV) has been purported to have several physiological benefits. This review synthesizes recent research evaluating APRV mode and provides perspectives on the utility of this mode in children with ARDS.

RECENT FINDINGS

Two single-center clinical trials on APRV, one adult and one pediatric, have been published this year. These two trials have not only elicited editorials and letters that highlight some of their strengths and weaknesses but also rekindled debate on several aspects of APRV. Despite their contradicting results, both trials provide significant insights into APRV strategies that work and those that may not. This review places the newer evidence in the context of existing literature and provides a comprehensive analysis of APRV use in children.

SUMMARY

There have been significant recent advancements in our understanding of the clinical utility of APRV in children with ARDS. The recent trial highlights the urgent need to evolve a consensus on definition of APRV and identify strategies that work. Pending further research, clinicians should avoid the use of a zero-PLOW Personalized-APRV strategy as a primary ventilation modality in children with moderate-severe ARDS.

A comprehensive review of the use and understanding of airway pressure release ventilation

Introduction: Airway pressure release ventilation (APRV) is a mode of ventilation typically utilized as a rescue or alternative mode for patients with acute respiratory distress syndrome (ARDS) and hypoxemia that is refractory to conventional mechanical ventilation. APRV's indication and efficacy continue to remain unclear given lack of consensus amongst practitioners, inconsistent methodology for its use, and scarcity of convincing evidence.Areas covered: This review discusses the history of APRV, how APRV works, rationales for its use, and its theoretical advantages and disadvantages. This is followed by a review of current available literature examining APRV's use in the intensive care unit, with further focus on its use in the pediatric intensive care unit.Expert opinion: APRV is a ventilation mode with theoretical risks and benefits. Appropriate study of APRV's clinical efficacy is difficult given a heterogeneous patient population and widely variable use of APRV between centers. Despite a paucity of definitive evidence in support of either mode, it is possible that the use of APRV will begin to outpace the use of high-frequency oscillatory ventilation (HFOV) for the management of refractory hypoxemia as more attention is paid to benefits of spontaneous breathing and minimizing sedation. Furthermore, APRV's role during ECMO deserves further investigation.

ICU Management of Trauma Patients

OBJECTIVES

To describe the current state of the art regarding management of the critically ill trauma patient with an emphasis on initial management in the ICU.

DATA SOURCES AND STUDY SELECTION

A PubMed literature review was performed for relevant articles in English related to the management of adult humans with severe trauma. Specific topics included airway management, hemorrhagic shock, resuscitation, and specific injuries to the chest, abdomen, brain, and spinal cord.

DATA EXTRACTION AND DATA SYNTHESIS

The basic principles of initial management of the critically ill trauma patients include rapid identification and management of life-threatening injuries with the goal of restoring tissue oxygenation and controlling hemorrhage as rapidly as possible. The initial assessment of the patient is often truncated for procedures to manage life-threatening injuries. Major, open surgical procedures have often been replaced by nonoperative or less-invasive approaches, even for critically ill patients. Consequently, much of the early management has been shifted to the ICU, where the goal is to continue resuscitation to restore homeostasis while completing the initial assessment of the patient and watching closely for failure of nonoperative management, complications of procedures, and missed injuries.

CONCLUSIONS

The initial management of critically ill trauma patients is complex. Multiple, sometimes competing, priorities need to be considered. Close collaboration between the intensivist and the surgical teams is critical for optimizing patient outcomes.

Randomized Feasibility Trial of a Low Tidal Volume-Airway Pressure Release Ventilation Protocol Compared With Traditional Airway Pressure Release Ventilation and Volume Control Ventilation Protocols

Supplemental Digital Content is available in the text.

Objectives:

Low tidal volume (= tidal volume ≤ 6 mL/kg, predicted body weight) ventilation using volume control benefits patients with acute respiratory distress syndrome. Airway pressure release ventilation is an alternative to low tidal volume-volume control ventilation, but the release breaths generated are variable and can exceed tidal volume breaths of low tidal volume-volume control. We evaluate the application of a low tidal volume-compatible airway pressure release ventilation protocol that manages release volumes on both clinical and feasibility endpoints.

Design:

We designed a prospective randomized trial in patients with acute hypoxemic respiratory failure. We randomized patients to low tidal volume-volume control, low tidal volume-airway pressure release ventilation, and traditional airway pressure release ventilation with a planned enrollment of 246 patients. The study was stopped early because of low enrollment and inability to consistently achieve tidal volumes less than 6.5 mL/kg in the low tidal volume-airway pressure release ventilation arm. Although the primary clinical study endpoint was Pao₂/Fio₂ on study day 3, we highlight the feasibility outcomes related to tidal volumes in both arms.

Setting:

Four Intermountain Healthcare tertiary ICUs.

Patients:

Adult ICU patients with hypoxemic respiratory failure anticipated to require prolonged mechanical ventilation.

Interventions:

Low tidal volume-volume control, airway pressure release ventilation, and low tidal volume-airway pressure release ventilation.

Measurements and Main Results:

We observed wide variability and higher tidal (release for airway pressure release ventilation) volumes in both airway pressure release ventilation (8.6 mL/kg; 95% CI, 7.8–9.6) and low tidal volume-airway pressure release ventilation (8.0; 95% CI, 7.3–8.9) than volume control (6.8; 95% CI, 6.2–7.5; p = 0.005) with no difference between airway pressure release ventilation and low tidal volume-airway pressure release ventilation (p = 0.58). Recognizing the limitations of small sample size, we observed no difference in 52 patients in day 3 Pao₂/ Fio₂ (p = 0.92). We also observed no significant difference between arms in sedation, vasoactive medications, or occurrence of pneumothorax.

Conclusions:

Airway pressure release ventilation resulted in release volumes often exceeding 12 mL/kg despite a protocol designed to target low tidal volume ventilation. Current airway pressure release ventilation protocols are unable to achieve consistent and reproducible delivery of low tidal volume ventilation goals. A large-scale efficacy trial of low tidal volume-airway pressure release ventilation is not feasible at this time in the absence of an explicit, generalizable, and reproducible low tidal volume-airway pressure release ventilation protocol.

Clinical Guideline for Treating Acute Respiratory Insufficiency with Invasive Ventilation and Extracorporeal Membrane Oxygenation: Evidence-Based Recommendations for Choosing Modes and Setting Parameters of Mechanical Ventilation

For patients with acute respiratory insufficiency, mechanical ("invasive") ventilation is a fundamental therapeutic measure to ensure sufficient gas exchange. Despite decades of strong research efforts, central questions on mechanical ventilation therapy are still answered incompletely. Therefore, many different ventilation modes and settings have been used in daily clinical practice without scientifically sound bases. At the same time, implementation of the few evidence-based therapeutic concepts (e.g., "lung protective ventilation") into clinical practice is still insufficient. The aim of our guideline project "Mechanical ventilation and extracorporeal gas exchange in acute respiratory insufficiency" was to develop an evidence-based decision aid for treating patients with and on mechanical ventilation. It covers the whole pathway of invasively ventilated patients (including indications of mechanical ventilation, ventilator settings, additional and rescue therapies, and liberation from mechanical ventilation). To assess the quality of scientific evidence and subsequently derive recommendations, we applied the Grading of Recommendations, Assessment, Development and Evaluation method. For the first time, using this globally accepted methodological standard, our guideline contains recommendations on mechanical ventilation therapy not only for acute respiratory distress syndrome patients but also for all types of acute respiratory insufficiency. This review presents the two main chapters of the guideline on choosing the mode of mechanical ventilation and setting its parameters. The guideline group aimed that - by thorough implementation of the recommendations - critical care teams may further improve the quality of care for patients suffering from acute respiratory insufficiency. By identifying relevant gaps of scientific evidence, the guideline group intended to support the development of important research projects.

Acute Respiratory Distress Syndrome: Etiology, Pathogenesis, and Summary on Management

The acute respiratory distress syndrome (ARDS) has multiple causes and is characterized by acute lung inflammation and increased pulmonary vascular permeability, leading to hypoxemic respiratory failure and bilateral pulmonary radiographic opacities. The acute respiratory distress syndrome is associated with substantial morbidity and mortality, and effective treatment strategies are limited. This review presents the current state of the literature regarding the etiology, pathogenesis, and management strategies for ARDS.

Optimal Ventilator Strategies in Acute Respiratory Distress Syndrome

Mechanical ventilation practices in patients with acute respiratory distress syndrome (ARDS) have progressed with a growing understanding of the disease pathophysiology. Paramount to the care of affected patients is the delivery of lung-protective mechanical ventilation which prioritizes tidal volume and plateau pressure limitation. Lung protection can probably be further enhanced by scaling target tidal volumes to the specific respiratory mechanics of individual patients. The best procedure for selecting optimal positive end-expiratory pressure (PEEP) in ARDS remains uncertain; several relevant issues must be considered when selecting PEEP, particularly lung recruitability. Noninvasive ventilation must be used with caution in ARDS as excessively high respiratory drive can further exacerbate lung injury; newer modes of delivery offer promising approaches in hypoxemic respiratory failure. Airway pressure release ventilation offers an alternative approach to maximize lung recruitment and oxygenation, but clinical trials have not demonstrated a survival benefit of this mode over conventional ventilation strategies. Rescue therapy with high-frequency oscillatory ventilation is an important option in refractory hypoxemia. Despite a disappointing lack of benefit (and possible harm) in patients with moderate or severe ARDS, possibly due to lung hyperdistention and right ventricular dysfunction, high-frequency oscillation may improve outcome in patients with very severe hypoxemia.

Successful Ventilation of Acute Respiratory Distress Syndrome Complicated by Pneumothorax Using Airway Pressure Release Ventilation: A Case Report

Pneumothorax can develop in children being mechanically ventilated for 'severe acute respiratory distress syndrome' making the situation worse and challenging for the treating intensivist. There is no evidence on use of 'airway pressure release ventilation' mode in children with acute respiratory distress syndrome complicated by pneumothorax. We present a case of a girl who had severe acute respiratory distress syndrome and developed pneumothorax on pressure control ventilation mode. We had to use 'airway pressure release ventilation' mode in view of severe refractory hypoxemia. Fortunately, the child responded well and weaned off the ventilator over few days. We suggest that 'airway pressure release ventilation' mode may be used successfully in patients with 'acute respiratory distress syndrome' complicated by pneumothorax if intensive and close monitoring is done.

Key messages

APRV may be a useful mode of ventilation in severe ARDS with pneumothorax.

How to cite this article

Chandelia S, Kishore S, Nandan D. Successful Ventilation of Acute Respiratory Distress Syndrome Complicated by Pneumothorax Using Airway Pressure Release Ventilation: A Case Report. Indian J Crit Care Med 2019;23(9):437-438.

Salvage therapies for refractory hypoxemia in ARDS

Acute Respiratory Distress Syndrome (ARDS) is a condition of varied etiology characterized by the acute onset (within 1 week of the inciting event) of hypoxemia, reduced lung compliance, diffuse lung inflammation and bilateral opacities on chest imaging attributable to noncardiogenic (increased permeability) pulmonary edema. Although multi-organ failure is the most common cause of death in ARDS, an estimated 10-15% of the deaths in ARDS are caused due to refractory hypoxemia, i.e.- hypoxemia despite lung protective conventional ventilator modes. In these cases, clinicians may resort to other measures with less robust evidence -referred to as "salvage therapies". These include proning, 48 h of paralysis early in the course of ARDS, various recruitment maneuvers, unconventional ventilator modes, inhaled pulmonary vasodilators, and Extracorporeal membrane oxygenation (ECMO). All the salvage therapies described have been associated with improved oxygenation, but with the exception of proning and 48 h of paralysis early in the course of ARDS, none of them have a proven mortality benefit. Based on the current evidence, no salvage therapy has been shown to be superior to the others and each of them is associated with its own risks and benefits. Hence, the order of application of these therapies varies in different institutions and should be applied following a risk-benefit analysis specific to the patient and local experience. This review explores the rationale, evidence, advantages and risks behind each of these strategies.

Optimal ventilator strategies for trauma-related ARDS

BACKGROUND

Acute respiratory distress syndrome (ARDS) was first described in the 1960s and has become a major area of research due to the mortality and morbidity associated with it. ARDS is currently defined using the Berlin Consensus; however, this is not wholly applicable for trauma-related ARDS.

METHODS

A systematic review of the literature was undertaken using the Preferred Reporting for Systematic Reviews and Meta Analyses methodology. The Ovid Medline, Web of Science and PubMed online databases were interrogated for papers published between 1 January 1995 and 31 December 2017.

RESULTS

The literature search yielded a total of 64 papers that fulfilled the search criteria.

CONCLUSIONS

Despite decades of dedicated research into different treatment modalities, ARDS continues to carry a high burden of mortality. The ARDS definitions laid out in the Berlin consensus are not entirely suited to trauma. While trauma-related ARDS represents a small portion of the available research, the evidence continues to favour low tidal volume ventilation as the benchmark for current practice. Positive end expiratory ventilation and airway pressure release ventilation in trauma cohorts may be beneficial; however, the evidence to date does not show this.

Inhalation Injury in the Burned Patient

Inhalation injury causes a heterogeneous cascade of insults that increase morbidity and mortality among the burn population. Despite major advancements in burn care for the past several decades, there remains a significant burden of disease attributable to inhalation injury. For this reason, effort has been devoted to finding new therapeutic approaches to improve outcomes for patients who sustain inhalation injuries.The three major injury classes are the following: supraglottic, subglottic, and systemic. Treatment options for these three subtypes differ based on the pathophysiologic changes that each one elicits.Currently, no consensus exists for diagnosis or grading of the injury, and there are large variations in treatment worldwide, ranging from observation and conservative management to advanced therapies with nebulization of different pharmacologic agents.The main pathophysiologic change after a subglottic inhalation injury is an increase in the bronchial blood flow. An induced mucosal hyperemia leads to edema, increases mucus secretion and plasma transudation into the airways, disables the mucociliary escalator, and inactivates hypoxic vasocontriction. Collectively, these insults potentiate airway obstruction with casts formed from epithelial debris, fibrin clots, and inspissated mucus, resulting in impaired ventilation. Prompt bronchoscopic diagnosis and multimodal treatment improve outcomes. Despite the lack of globally accepted standard treatments, data exist to support the use of bronchoscopy and suctioning to remove debris, nebulized heparin for fibrin casts, nebulized N-acetylcysteine for mucus casts, and bronchodilators.Systemic effects of inhalation injury occur both indirectly from hypoxia or hypercapnia resulting from loss of pulmonary function and systemic effects of proinflammatory cytokines, as well as directly from metabolic poisons such as carbon monoxide and cyanide. Both present with nonspecific clinical symptoms including cardiovascular collapse. Carbon monoxide intoxication should be treated with oxygen and cyanide with hydroxocobalamin.Inhalation injury remains a great challenge for clinicians and an area of opportunity for scientists. Management of this concomitant injury lags behind other aspects of burn care. More clinical research is required to improve the outcome of inhalation injury.The goal of this review is to comprehensively summarize the diagnoses, treatment options, and current research.

Early application of airway pressure release ventilation may reduce the duration of mechanical ventilation in acute respiratory distress syndrome

PURPOSE

Experimental animal models of acute respiratory distress syndrome (ARDS) have shown that the updated airway pressure release ventilation (APRV) methodologies may significantly improve oxygenation, maximize lung recruitment, and attenuate lung injury, without circulatory depression. This led us to hypothesize that early application of APRV in patients with ARDS would allow pulmonary function to recover faster and would reduce the duration of mechanical ventilation as compared with low tidal volume lung protective ventilation (LTV).

METHODS

A total of 138 patients with ARDS who received mechanical ventilation for <48 h between May 2015 to October 2016 while in the critical care medicine unit (ICU) of the West China Hospital of Sichuan University were enrolled in the study. Patients were randomly assigned to receive APRV (n = 71) or LTV (n = 67). The settings for APRV were: high airway pressure (P_high) set at the last plateau airway pressure (P_plat), not to exceed 30 cmH₂O) and low airway pressure ( P_low) set at 5 cmH₂O; the release phase (T_low) setting adjusted to terminate the peak expiratory flow rate to ≥ 50%; release frequency of 10-14 cycles/min. The settings for LTV were: target tidal volume of 6 mL/kg of predicted body weight; P_plat not exceeding 30 cmH₂O; positive end-expiratory pressure (PEEP) guided by the PEEP-FiO₂ table according to the ARDSnet protocol. The primary outcome was the number of days without mechanical ventilation from enrollment to day 28. The secondary endpoints included oxygenation, P_plat, respiratory system compliance, and patient outcomes.

RESULTS

Compared with the LTV group, patients in the APRV group had a higher median number of ventilator-free days {19 [interquartile range (IQR) 8-22] vs. 2 (IQR 0-15); P < 0.001}. This finding was independent of the coexisting differences in chronic disease. The APRV group had a shorter stay in the ICU (P = 0.003). The ICU mortality rate was 19.7% in the APRV group versus 34.3% in the LTV group (P = 0.053) and was associated with better oxygenation and respiratory system compliance, lower P_plat, and less sedation requirement during the first week following enrollment (P < 0.05, repeated-measures analysis of variance).

CONCLUSIONS

Compared with LTV, early application of APRV in patients with ARDS improved oxygenation and respiratory system compliance, decreased P_plat and reduced the duration of both mechanical ventilation and ICU stay.

Experimental study of airway pressure release ventilation in the treatment of acute respiratory distress syndrome

Airway pressure release ventilation (APRV) is a ventilator mode which has demonstrated potential benefits in acute respiratory distress syndrome (ARDS) patients. We therefore sought to compare relevant pulmonary data and safety outcomes of this mode to the conventional ventilation and sustained inflation. Canines admitted after intravenous injection of oleic acid requiring mechanical ventilation were randomly divided into 3 groups (n=6), namely conventional ventilation group, low tidal volume ventilation with recruitment group (LTV+SI) and APRV group. The changes of oxygenation, ventilation, airway pressure, inflammatory reaction and hemodynamics at the basic state were observed at 0, 1, 2 and 4 h during the experiment. The levels of PaO₂/FiO₂ in APRV group were higher than LTV+SI group at 2 and 4 h (P<0.05). In APRV group, the PCO₂ levels at 1, 2 and 4 h is much lower than LTV+SI group (P<0.05). Outcome variables showed no differences between APRV, LVT+SI and conventional mechanical ventilation for plateau airway pressure (24±1 vs. 29±3 vs. 25±4), mean arterial pressure (92.9±16.5 vs. 85.8±21.4 vs. 88.7±24.4), cardiac index (4.3±1.7 vs. 3.5±1.9 vs. 3.4±2.1), ERO₂ (13.4±10.3 vs. 16.1±6.8 vs. 17.6±9.1), lac (2.5±1.7 vs. 3.1±1.6 vs. 3.9±1.9), tumor necrosis factor (TNF)-α (132±11 vs. 140±6 vs. 195±13) and matrix metalloproteinase (MMP)-9. For canines sustaining acute respiratory distress syndrome requiring mechanical ventilation, APRV can significantly improve oxygenation and keep hemodynamic stability compared with LTV+SI. The results of TNF-α and MMP-9 suggest that APRV could be as protective for ARDS as LTV with recruitment group.

High-Frequency Ventilation Modalities as Salvage Therapy for Smoke Inhalation-Associated Acute Lung Injury: A Systematic Review

BACKGROUND

Smoke inhalation-associated acute lung injury (SI-ALI) is a major cause of morbidity and mortality in victims of fire tragedies. To date, there are no evidence-based guidelines on ventilation strategies in acute respiratory distress syndrome (ARDS) after smoke inhalation. We reviewed the existing literature for clinical studies of salvage mechanical ventilation (MV) strategies in patients with SI-ALI, focusing on mortality and pneumonia as outcomes.

METHODS

A systematic search was designed in accordance with preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines. Risk of bias assessment was performed using the Newcastle-Ottawa Quality Assessment Scale (NOS; 0 to 9 stars), with a score ≥7 being the threshold for inclusion in the meta-analysis. A systematic search strategy was used to search 10 databases. Clinical studies were included in which patients: (1) experienced smoke inhalation, (2) treated with MV, and (3) described a concurrent or historical control group.

RESULTS

A total of 226 potentially relevant studies were identified, of which 7 studies on high-frequency percussive ventilation (HFPV) met inclusion criteria. No studies met inclusion for meta-analysis (NOS ≥ 7). In studies comparing HFPV to conventional mechanical ventilation (CMV), mortality and pneumonia incidence improved in 3 studies and remained unchanged in 3 others. No change in ventilator days or ICU length of stay was observed; however, oxygenation and work of breathing improved with HFPV.

CONCLUSIONS

Mechanical ventilation in patients with SI-ALI has not been well studied. High-frequency percussive ventilation may decrease in-hospital mortality and pneumonia incidence when compared to CMV. The absence of "good" quality evidence precluded meta-analysis. Based upon low-quality evidence, there was a very weak recommendation that HFPV use may be associated with lower mortality and pneumonia rates in patients with SI-ALI. Given SI-ALI's unique underlying pathophysiology, and its potential implications on therapy, randomized controlled studies are required to ensure that patients receive the safest and most effective care.

TRIAL REGISTRATION

The study was registered with PROSPERO International prospective register of systematic reviews (#47015).

Changes in Therapeutic Intensity Level Following Airway Pressure Release Ventilation in Severe Traumatic Brain Injury

PURPOSE

Airway pressure release ventilation (APRV) utilizes high levels of airway pressure coupled with brief expiratory release to facilitate open lung ventilation. The aim of our study was to evaluate the effects of APRV-induced elevated airway pressure mean in patients with severe traumatic brain injury.

MATERIALS AND METHODS

This was a retrospective cohort study at a 424-bed Level I trauma center. Linear mixed effects models were developed to assess the difference in therapeutic intensity level (TIL), intracranial pressure (ICP), and cerebral perfusion pressure (CPP) over time following the application of APRV.

RESULTS

The study included 21 epochs of APRV in 21 patients. In the 6-hour epoch following the application of APRV, the TIL was significantly increased ( P = .002) and the ICP significantly decreased ( P = .041) compared to that before 6 hours. There was no significant change in CPP ( P = .42) over time. The baseline static compliance and time interaction was not significant for TIL (χ² = 0.2 [ df 1], P = .655), CPP (χ² = 0 [ df 1], P = 1), or ICP (χ² = 0.1 [ df 1], P = .752).

CONCLUSIONS

Application of APRV in patients with severe traumatic brain injury was associated with significantly, but not clinically meaningful, increased TIL and decreased ICP. No significant change in CPP was observed. No difference was observed based on the baseline pulmonary static compliance.

The 30-year evolution of airway pressure release ventilation (APRV)

Airway pressure release ventilation (APRV) was first described in 1987 and defined as continuous positive airway pressure (CPAP) with a brief release while allowing the patient to spontaneously breathe throughout the respiratory cycle. The current understanding of the optimal strategy to minimize ventilator-induced lung injury is to "open the lung and keep it open". APRV should be ideal for this strategy with the prolonged CPAP duration recruiting the lung and the minimal release duration preventing lung collapse. However, APRV is inconsistently defined with significant variation in the settings used in experimental studies and in clinical practice. The goal of this review was to analyze the published literature and determine APRV efficacy as a lung-protective strategy. We reviewed all original articles in which the authors stated that APRV was used. The primary analysis was to correlate APRV settings with physiologic and clinical outcomes. Results showed that there was tremendous variation in settings that were all defined as APRV, particularly CPAP and release phase duration and the parameters used to guide these settings. Thus, it was impossible to assess efficacy of a single strategy since almost none of the APRV settings were identical. Therefore, we divided all APRV studies divided into two basic categories: (1) fixed-setting APRV (F-APRV) in which the release phase is set and left constant; and (2) personalized-APRV (P-APRV) in which the release phase is set based on changes in lung mechanics using the slope of the expiratory flow curve. Results showed that in no study was there a statistically significant worse outcome with APRV, regardless of the settings (F-ARPV or P-APRV). Multiple studies demonstrated that P-APRV stabilizes alveoli and reduces the incidence of acute respiratory distress syndrome (ARDS) in clinically relevant animal models and in trauma patients. In conclusion, over the 30 years since the mode's inception there have been no strict criteria in defining a mechanical breath as being APRV. P-APRV has shown great promise as a highly lung-protective ventilation strategy.

Characteristics and outcomes of patients treated with airway pressure release ventilation for acute respiratory distress syndrome: A retrospective observational study

BACKGROUND

The optimal mode of ventilation in acute respiratory distress syndrome (ARDS) remains uncertain. Airway pressure release ventilation (APRV) is a recognized treatment for mechanically-ventilated patients with severe hypoxaemia. However, contemporary data on its role as a rescue modality in ARDS is lacking. The goal of this study was to describe the clinical and physiological effects of APRV in patients with established ARDS.

METHODS

This retrospective observational study was performed in a 23-bed adult intensive care unit in a tertiary extracorporeal membrane oxygenation (ECMO) referral centre. Patients with ARDS based on Berlin criteria were included through a prospectively-collected APRV database. Patients receiving APRV for less than six hours were excluded.

RESULTS

Fifty patients fulfilled the eligibility criteria. Prior to APRV initiation, median Murray Lung Injury Score was 3.5 (interquartile range (IQR) 2.5-3.9) and PaO2/FiO2 was 99mmHg (IQR 73-137). PaO2/FiO2 significantly improved within twenty-four hours post-APRV initiation (ANOVA F(1, 27)=24.34, P<.005). Two patients (4%) required intercostal catheter insertion for barotrauma. Only one patient (2%) required ECMO after APRV initiation, despite a majority (68%) fulfilling previously established criteria for ECMO at baseline. Hospital mortality rate was 38%.

CONCLUSIONS

In patients with ARDS-related refractory hypoxaemia treated with APRV, an early and sustained improvement in oxygenation, low incidence of clinically significant barotrauma and progression to ECMO was observed. The safety and efficacy of APRV requires further consideration.

Experimental blunt chest trauma--cardiorespiratory effects of different mechanical ventilation strategies with high positive end-expiratory pressure: a randomized controlled study

Background

Uncertainty persists regarding the optimal ventilatory strategy in trauma patients developing acute respiratory distress syndrome (ARDS). This work aims to assess the effects of two mechanical ventilation strategies with high positive end-expiratory pressure (PEEP) in experimental ARDS following blunt chest trauma.

Methods

Twenty-six juvenile pigs were anesthetized, tracheotomized and mechanically ventilated. A contusion was applied to the right chest using a bolt-shot device. Ninety minutes after contusion, animals were randomized to two different ventilation modes, applied for 24 h: Twelve pigs received conventional pressure-controlled ventilation with moderately low tidal volumes (V_T, 8 ml/kg) and empirically chosen high external PEEP (16cmH₂O) and are referred to as the HP-CMV-group. The other group (n = 14) underwent high-frequency inverse-ratio pressure-controlled ventilation (HFPPV) involving respiratory rate of 65breaths · min⁻¹, inspiratory-to-expiratory-ratio 2:1, development of intrinsic PEEP and recruitment maneuvers, compatible with the rationale of the Open Lung Concept. Hemodynamics, gas exchange and respiratory mechanics were monitored during 24 h. Computed tomography and histology were analyzed in subgroups.

Results

Comparing changes which occurred from randomization (90 min after chest trauma) over the 24-h treatment period, groups differed statistically significantly (all P values for group effect <0.001, General Linear Model analysis) for the following parameters (values are mean ± SD for randomization vs. 24-h): PaO₂ (100 % O₂) (HFPPV 186 ± 82 vs. 450 ± 59 mmHg; HP-CMV 249 ± 73 vs. 243 ± 81 mmHg), venous admixture (HFPPV 34 ± 9.8 vs. 11.2 ± 3.7 %; HP-CMV 33.9 ± 10.5 vs. 21.8 ± 7.2 %), PaCO₂ (HFPPV 46.9 ± 6.8 vs. 33.1 ± 2.4 mmHg; HP-CMV 46.3 ± 11.9 vs. 59.7 ± 18.3 mmHg) and normally aerated lung mass (HFPPV 42.8 ± 11.8 vs. 74.6 ± 10.0 %; HP-CMV 40.7 ± 8.6 vs. 53.4 ± 11.6 %). Improvements occurring after recruitment in the HFPPV-group persisted throughout the study. Peak airway pressure and V_T did not differ significantly. HFPPV animals had lower atelectasis and inflammation scores in gravity-dependent lung areas.

Conclusions

In this model of ARDS following unilateral blunt chest trauma, HFPPV ventilation improved respiratory function and fulfilled relevant ventilation endpoints for trauma patients, i.e. restoration of oxygenation and lung aeration while avoiding hypercapnia and respiratory acidosis.

Pressure-controlled versus volume-controlled ventilation for acute respiratory failure due to acute lung injury (ALI) or acute respiratory distress syndrome (ARDS)

BACKGROUND

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) account for one-quarter of cases of acute respiratory failure in intensive care units (ICUs). A third to half of patients will die in the ICU, in hospital or during follow-up. Mechanical ventilation of people with ALI/ARDS allows time for the lungs to heal, but ventilation is invasive and can result in lung injury. It is uncertain whether ventilator-related injury would be reduced if pressure delivered by the ventilator with each breath is controlled, or whether the volume of air delivered by each breath is limited.

OBJECTIVES

To compare pressure-controlled ventilation (PCV) versus volume-controlled ventilation (VCV) in adults with ALI/ARDS to determine whether PCV reduces in-hospital mortality and morbidity in intubated and ventilated adults.

SEARCH METHODS

In October 2014, we searched the Cochrane Central Register of Controlled Trials (CENTRAL) (2014, Isssue 9), MEDLINE (1950 to 1 October 2014), EMBASE (1980 to 1 October 2014), the Latin American Caribbean Health Sciences Literature (LILACS) (1994 to 1 October 2014) and Science Citation Index-Expanded (SCI-EXPANDED) at the Institute for Scientific Information (ISI) Web of Science (1990 to 1 October 2014), as well as regional databases, clinical trials registries, conference proceedings and reference lists.

SELECTION CRITERIA

Randomized controlled trials (RCTs) and quasi-RCTs (irrespective of language or publication status) of adults with a diagnosis of acute respiratory failure or acute on chronic respiratory failure and fulfilling the criteria for ALI/ARDS as defined by the American-European Consensus Conference who were admitted to an ICU for invasive mechanical ventilation, comparing pressure-controlled or pressure-controlled inverse-ratio ventilation, or an equivalent pressure-controlled mode (PCV), versus volume-controlled ventilation, or an equivalent volume-controlled mode (VCV).

DATA COLLECTION AND ANALYSIS

Two review authors independently screened and selected trials, assessed risk of bias and extracted data. We sought clarification from trial authors when needed. We pooled risk ratios (RRs) for dichotomous data and mean differences (MDs) for continuous data with their 95% confidence intervals (CIs) using a random-effects model. We assessed overall evidence quality using the GRADE (Grades of Recommendation, Assessment, Development and Evaluation) approach.

MAIN RESULTS

We included three RCTs that randomly assigned a total of 1089 participants recruited from 43 ICUs in Australia, Canada, Saudi Arabia, Spain and the USA. Risk of bias of the included studies was low. Only data for mortality and barotrauma could be combined in the meta-analysis. We downgraded the quality of evidence for the three mortality outcomes on the basis of serious imprecision around the effect estimates. For mortality in hospital, the RR with PCV compared with VCV was 0.83 (95% CI 0.67 to 1.02; three trials, 1089 participants; moderate-quality evidence), and for mortality in the ICU, the RR with PCV compared with VCV was 0.84 (95% CI 0.71 to 0.99; two trials, 1062 participants; moderate-quality evidence). One study provided no evidence of clear benefit with the ventilatory mode for mortality at 28 days (RR 0.88, 95% CI 0.73 to 1.06; 983 participants; moderate-quality evidence). The difference in effect on barotrauma between PCV and VCV was uncertain as the result of imprecision and different co-interventions used in the studies (RR 1.24, 95% CI 0.87 to 1.77; two trials, 1062 participants; low-quality evidence). Data from one trial with 983 participants for the mean duration of ventilation, and from another trial with 78 participants for the mean number of extrapulmonary organ failures that developed with PCV or VCV, were skewed. None of the trials reported on infection during ventilation or quality of life after discharge.

AUTHORS' CONCLUSIONS

Currently available data from RCTs are insufficient to confirm or refute whether pressure-controlled or volume-controlled ventilation offers any advantage for people with acute respiratory failure due to acute lung injury or acute respiratory distress syndrome. More studies including a larger number of people given PCV and VCV may provide reliable evidence on which more firm conclusions can be based.

Airway pressure release ventilation reduces conducting airway micro-strain in lung injury

BACKGROUND

Improper mechanical ventilation can exacerbate acute lung damage, causing a secondary ventilator-induced lung injury (VILI). We hypothesized that VILI can be reduced by modifying specific components of the ventilation waveform (mechanical breath), and we studied the impact of airway pressure release ventilation (APRV) and controlled mandatory ventilation (CMV) on the lung micro-anatomy (alveoli and conducting airways). The distribution of gas during inspiration and expiration and the strain generated during mechanical ventilation in the micro-anatomy (micro-strain) were calculated.

STUDY DESIGN

Rats were anesthetized, surgically prepared, and randomized into 1 uninjured control group (n = 2) and 4 groups with lung injury: APRV 75% (n = 2), time at expiration (TLow) set to terminate appropriately at 75% of peak expiratory flow rate (PEFR); APRV 10% (n = 2), TLow set to terminate inappropriately at 10% of PEFR; CMV with PEEP 5 cm H2O (PEEP 5; n = 2); or PEEP 16 cm H2O (PEEP 16; n = 2). Lung injury was induced in the experimental groups by Tween lavage and ventilated with their respective settings. Lungs were fixed at peak inspiration and end expiration for standard histology. Conducting airway and alveolar air space areas were quantified and conducting airway micro-strain was calculated.

RESULTS

All lung injury groups redistributed inspired gas away from alveoli into the conducting airways. The APRV 75% minimized gas redistribution and micro-strain in the conducting airways and provided the alveolar air space occupancy most similar to control at both inspiration and expiration.

CONCLUSIONS

In an injured lung, APRV 75% maintained micro-anatomic gas distribution similar to that of the normal lung. The lung protection demonstrated in previous studies using APRV 75% may be due to a more homogeneous distribution of gas at the micro-anatomic level as well as a reduction in conducting airway micro-strain.

Mechanical ventilation in acute hypoxemic respiratory failure: a review of new strategies for the practicing hospitalist

BACKGROUND

The goal of mechanical ventilation in acute hypoxemic respiratory failure is to support adequate gas exchange without harming the lungs. How patients are mechanically ventilated can significantly impact their ultimate outcomes.

METHODS

This review focuses on emerging evidence regarding strategies for mechanical ventilation in patients with acute hypoxemic respiratory failure including: low tidal volume ventilation in the acute respiratory distress syndrome (ARDS), novel ventilator modes as alternatives to low tidal volume ventilation, adjunctive strategies that may enhance recovery in ARDS, the use of lung-protective strategies in patients without ARDS, rescue therapies in refractory hypoxemia, and an evidence-based approach to weaning from mechanical ventilation.

RESULTS

Once a patient is intubated and mechanically ventilated, low tidal volume ventilation remains the best strategy in ARDS. Adjunctive therapies in ARDS include a conservative fluid management strategy, as well as neuromuscular blockade and prone positioning in moderate-to-severe disease. There is also emerging evidence that a lung-protective strategy may benefit non-ARDS patients. For patients with refractory hypoxemia, extracorporeal membrane oxygenation should be considered. Once the patient demonstrates signs of recovery, the best approach to liberation from mechanical ventilation involves daily spontaneous breathing trials and protocolized assessment of readiness for extubation.

CONCLUSIONS

Prompt recognition of ARDS and use of lung-protective ventilation, as well as evidence-based adjunctive therapies, remain the cornerstones of caring for patients with acute hypoxemic respiratory failure. In the absence of contraindications, it is reasonable to consider lung-protective ventilation in non-ARDS patients as well, though the evidence supporting this practice is less conclusive.

Potentially harmful effects of inspiratory synchronization during pressure preset ventilation

PURPOSE

Pressure preset ventilation (PPV) modes with set inspiratory time can be classified according to their ability to synchronize pressure delivery with patient's inspiratory efforts (i-synchronization). Non-i-synchronized (like airway pressure release ventilation, APRV), partially i-synchronized (like biphasic airway pressure), and fully i-synchronized modes (like assist-pressure control) can be distinguished. Under identical ventilatory settings across PPV modes, the degree of i-synchronization may affect tidal volume (VT), transpulmonary pressure (PTP), and their variability. We performed bench and clinical studies.

METHODS

In the bench study, all the PPV modes of five ventilators were tested with an active lung simulator. Spontaneous efforts of -10 cmH2O at rates of 20 and 30 breaths/min were simulated. Ventilator settings were high pressure 30 cmH2O, positive end-expiratory pressure (PEEP) 15 cmH2O, frequency 15 breaths/min, and inspiratory to expiratory ratios (I:E) 1:3 and 3:1. In the clinical studies, data from eight intubated patients suffering from acute respiratory distress syndrome (ARDS) and ventilated with APRV were compared to the bench tests. In four additional ARDS patients, each of the PPV modes was compared.

RESULTS

As the degree of i-synchronization among the different PPV modes increased, mean VT and PTP swings markedly increased while breathing variability decreased. This was consistent with clinical comparison in four ARDS patients. Observational results in eight ARDS patients show low VT and a high variability with APRV.

CONCLUSION

Despite identical ventilator settings, the different PPV modes lead to substantial differences in VT, PTP, and breathing variability in the presence spontaneous efforts. Clinicians should be aware of the possible harmful effects of i-synchronization especially when high VT is undesirable.

Airway Pressure Release Ventilation in Morbidly Obese Surgical Patients with Acute Lung Injury and Acute Respiratory Distress Syndrome

Morbidly obese patients with body mass index greater than 40 kg/m2 and respiratory failure requiring critical care services are increasingly seen in trauma and acute care surgical centers. Baseline respiratory pathophysiology including decreased pulmonary compliance with dependent atelectasis and abnormal ventilation–perfusion relationships predisposes these patients to acute lung injury (ALI) and adult respiratory distress syndrome (ARDS) as well as prolonged stays in the intensive care unit. Airway pressure release ventilation (APRV) is an increasingly used alternative mode for salvage therapy in patients with hypoxemic respiratory failure that also provides lung protection from ventilator-induced lung injury. APRV provides the conceptual advantage of an “open lung” approach to ventilation that may be extended to the morbidly obese patient population with ALI and ARDS. We discuss the theoretical benefits and a recent clinical experience of APRV ventilation in the morbidly obese patient with respiratory failure at a Level I trauma, surgical critical care, and acute care surgery center.

The effect of APRV ventilation on ICP and cerebral hemodynamics

BACKGROUND

Airway pressure release ventilation (APRV) is an alternative approach to the low-tidal volume "open-lung" ventilation strategy. APRV is associated with a higher mean airway pressure than conventional ventilation and has therefore not been evaluated in patients with acute neurological injuries.

METHODS

Case report.

RESULTS

We report a patient with severe progressive hypoxemia following a subarachnoid hemorrhage who was converted from pressure-controlled mechanical ventilation to APRV. This change in ventilatory mode was associated with a significant improvement in oxygenation and alveolar ventilation with an associated increase in cerebral blood flow and a negligible increase in intracranial pressure.

CONCLUSION

APRV may safely be applied to neurocritically ill patients, and that this mode of ventilation may increase cerebral blood flow without increasing intracranial pressure.

Current knowledge of acute lung injury and acute respiratory distress syndrome

Acute lung injury/acute respiratory distress syndrome (ALI/ARDS) continues to be a major cause of mortality in adult and pediatric critical care medicine. This article discusses the pulmonary sequelae associated with ALI and ARDS, the support of ARDS with mechanical ventilation, available adjunctive therapies, and experimental therapies currently being tested. It is hoped that further understanding of the fundamental biology, improved identification of the patient's inflammatory state, and application of therapies directed at multiple sites of action may ultimately prove beneficial for patients suffering from ALI/ARDS.

High-frequency oscillatory ventilation in pediatric acute hypoxemic respiratory failure: disease-specific morbidity survival analysis

Background

Multiple ventilatory strategies for acute hypoxemic respiratory failure (AHRF) in children have been advocated, including high-frequency oscillatory ventilation (HFOV). Despite the frequent deployment of HFOV, randomized controlled trials remain elusive and currently there are no pediatric trials looking at its use. Our longitudinal study analyzed the predictive clinical outcome of HFOV in pediatric AHRF given disease-specific morbidity.

Methods

A retrospective 8-year review on pediatric intensive care unit admissions with AHRF ventilated by HFOV was performed. Primary outcomes included survival, morbidity, length of stay (LOS), and factors associated with survival or mortality.

Results

A total of 102 patients underwent HFOV with a 66 % overall survival rate. Survivors had a greater LOS than nonsurvivors (p = 0.001). Mortality odds ratio (OR) for patients without bronchiolitis was 8.19 (CI = 1.02, 65.43), and without pneumonia it was 3.07 (CI = 1.12, 8.39). A lower oxygenation index (OI) after HFOV commencement and at subsequent time points analyzed predicted survival. After 24 h, mortality was associated with an OI > 35 [OR = 31.11 (CI = 3.25, 297.98)]. Sepsis-related mortality was associated with a higher baseline FiO₂ (0.88 vs. 0.65), higher OI (42 vs. 22), and augmented metabolic acidosis (pH of 7.25 vs. 7.32) evaluated 4 h on HFOV (p < 0.05).

Conclusion

High-frequency oscillatory ventilation may be safely utilized. It has a 66 % overall survival rate in pediatric AHRF of various etiologies. Patients with morbidity limited to the respiratory system and optimized oxygenation indices are most likely to survive on HFOV.

Mechanical ventilation after injury

Injury is a major cause of critical illness worldwide. Severely injured patients often require mechanical ventilation not only to manage primary respiratory failure but also as adjunct to manage other conditions. Injury induces fundamental changes in multiple organ systems which directly impact ventilator management; these changes are not shared by patients without concomitant tissue injury. In this article, we review the physiologic changes after injury and discuss the impact of injury on ventilator strategies and management. We also explore the special considerations in patients with traumatic brain injury, thermal injury, blast injury or bronchopleural fistula.

Management of a patient with severe sepsis

Severe sepsis and septic shock affect more than 700,000 people annually and represent approximately $17 billion annually in health care costs. Mortality in patients with 3 or more failed organs is up to 70%. Early identification and prevention of severe sepsis and septic shock are key factors in impacting mortality rates. Health care providers must be knowledgeable in early identification and aggressive management. This case presentation outlines the components of care identified in the literature in the early and ongoing management of patients with severe sepsis and septic shock.

Emerging modes of ventilation in the intensive care unit

Potentially harmful effects of positive pressure mechanical ventilation have been recognized since its inception in the 1950s. Since then, the risk factors for and mechanisms of ventilator-induced lung injury (VILI) have been further characterized. Publication of the ARDSnet tidal volume trial in 2000 demonstrated that a ventilator strategy limiting tidal volumes and plateau pressure in patients with acute respiratory distress syndrome was associated with a 22% reduction in mortality. Since then, a variety of ventilator modes have emerged seeking to improve gas exchange, reduce injurious effects of ventilation, and improve weaning from the ventilator. We review here emerging ventilator modes in the intensive care unit (ICU). Airway pressure release ventilation seeks to optimize alveolar recruitment and maintain spontaneous ventilatory effort. It is associated with improved indices of respiratory and cardiovascular physiology, but data to support outcome benefit are lacking. High-frequency oscillatory ventilation is associated with improvements in gas exchange, but outcome data are conflicting. Extracorporeal modes of ventilation continue to evolve, and extra-corporeal CO₂ removal is a technique that could be used in non-specialist ICUs. Proportional-assist ventilation and neutrally adjusted ventilator assist are modes that vary level of assistance with patient ventilatory effort. They result in greater patient-ventilator synchrony, but at present there is no evidence of a reduction in the duration of mechanical ventilation or outcome benefit. Although the use of many of these modes is likely to increase in intensive care units, further evidence of a beneficial effect is desirable before they are recommended.