Spontaneous Versus Controlled Mechanical Ventilation in Patients with Acute Respiratory Distress Syndrome

A survey of preferences for respiratory support in the intensive care unit for patients with acute hypoxaemic respiratory failure

BACKGROUND

When caring for mechanically ventilated adults with acute hypoxaemic respiratory failure (AHRF), clinicians are faced with an uncertain choice between ventilator modes allowing for spontaneous breaths or ventilation fully controlled by the ventilator. The preferences of clinicians managing such patients, and what motivates their choice of ventilator mode, are largely unknown. To better understand how clinicians' preferences may impact the choice of ventilatory support for patients with AHRF, we issued a survey to an international network of intensive care unit (ICU) researchers.

METHODS

We distributed an online survey with 32 broadly similar and interlinked questions on how clinicians prioritise spontaneous or controlled ventilation in invasively ventilated patients with AHRF of different severity, and which factors determine their choice.

RESULTS

The survey was distributed to 1337 recipients in 12 countries. Of these, 415 (31%) completed the survey either fully (52%) or partially (48%). Most respondents were identified as medical specialists (87%) or physicians in training (11%). Modes allowing for spontaneous ventilation were considered preferable in mild AHRF, with controlled ventilation considered as progressively more important in moderate and severe AHRF. Among respondents there was strong support (90%) for a randomised clinical trial comparing spontaneous with controlled ventilation in patients with moderate AHRF.

CONCLUSIONS

The responses from this international survey suggest that there is clinical equipoise for the preferred ventilator mode in patients with AHRF of moderate severity. We found strong support for a randomised trial comparing modes of ventilation in patients with moderate AHRF.

Mechanical ventilation in patients with acute respiratory distress syndrome: current status and future perspectives

INTRODUCTION

Although there has been extensive research on mechanical ventilation for acute respiratory distress syndrome (ARDS), treatment remains mainly supportive. Recent studies and new ventilatory modes have been proposed to manage patients with ARDS; however, the clinical impact of these strategies remains uncertain and not clearly supported by guidelines. The aim of this narrative review is to provide an overview and update on ventilatory management for patients with ARDS.

AREAS COVERED

This article reviews the literature regarding mechanical ventilation in ARDS. A comprehensive overview of the principal settings for the ventilator parameters involved is provided as well as a report on the differences between controlled and assisted ventilation. Additionally, new modes of assisted ventilation are presented and discussed. The evidence concerning rescue strategies, including recruitment maneuvers and extracorporeal membrane oxygenation support, is analyzed. PubMed, EBSCO, and the Cochrane Library were searched up until June 2023, for relevant literature.

EXPERT OPINION

Available evidence for mechanical ventilation in cases of ARDS suggests the use of a personalized mechanical ventilation strategy. Although promising, new modes of assisted mechanical ventilation are still under investigation and guidelines do not recommend rescue strategies as the standard of care. Further research on this topic is required.

Techniques for Oxygenation and Ventilation in Coronavirus Disease 2019

This paper discusses mechanisms of hypoxemia and interventions to oxygenate critically ill patients with COVID-19 which range from nasal cannula to noninvasive and mechanical ventilation. Noninvasive ventilation includes continuous positive airway pressure ventilation (CPAP) and high-flow nasal cannula (HFNC) with or without proning. The evidence for each of these modalities is discussed and thereafter, when to transition to mechanical ventilation (MV). Various techniques of MV, again with and without proning, and rescue strategies which would include extra corporeal membrane oxygenation (ECMO) when it is available and permissive hypoxemia where it is not, are discussed.

Early spontaneous breathing for acute respiratory distress syndrome in individuals with COVID-19

BACKGROUND

Acute respiratory distress syndrome (ARDS) represents the most severe course of COVID-19 (caused by the SARS-CoV-2 virus), usually resulting in a prolonged stay in an intensive care unit (ICU) and high mortality rates. Despite the fact that most affected individuals need invasive mechanical ventilation (IMV), evidence on specific ventilation strategies for ARDS caused by COVID-19 is scarce. Spontaneous breathing during IMV is part of a therapeutic concept comprising light levels of sedation and the avoidance of neuromuscular blocking agents (NMBA). This approach is potentially associated with both advantages (e.g. a preserved diaphragmatic motility and an optimised ventilation-perfusion ratio of the ventilated lung), as well as risks (e.g. a higher rate of ventilator-induced lung injury or a worsening of pulmonary oedema due to increases in transpulmonary pressure). As a consequence, spontaneous breathing in people with COVID-19-ARDS who are receiving IMV is subject to an ongoing debate amongst intensivists.

OBJECTIVES

To assess the benefits and harms of early spontaneous breathing activity in invasively ventilated people with COVID-19 with ARDS compared to ventilation strategies that avoid spontaneous breathing.

SEARCH METHODS

We searched the Cochrane COVID-19 Study Register (which includes CENTRAL, PubMed, Embase, Clinical Trials.gov WHO ICTRP, and medRxiv) and the WHO COVID-19 Global literature on coronavirus disease to identify completed and ongoing studies from their inception to 2 March 2022.

SELECTION CRITERIA

Eligible study designs comprised randomised controlled trials (RCTs) that evaluated spontaneous breathing in participants with COVID-19-related ARDS compared to ventilation strategies that avoided spontaneous breathing (e.g. using NMBA or deep sedation levels). Additionally, we considered controlled before-after studies, interrupted time series with comparison group, prospective cohort studies and retrospective cohort studies. For these non-RCT studies, we considered a minimum total number of 50 participants to be compared as necessary for inclusion. Prioritised outcomes were all-cause mortality, clinical improvement or worsening, quality of life, rate of (serious) adverse events and rate of pneumothorax. Additional outcomes were need for tracheostomy, duration of ICU length of stay and duration of hospitalisation.

DATA COLLECTION AND ANALYSIS

We followed the methods outlined in the Cochrane Handbook for Systematic Reviews of Interventions. Two review authors independently screened all studies at the title/abstract and full-text screening stage. We also planned to conduct data extraction and risk of bias assessment in duplicate. We planned to conduct meta-analysis for each prioritised outcome, as well as subgroup analyses of mortality regarding severity of oxygenation impairment and duration of ARDS. In addition, we planned to perform sensitivity analyses for studies at high risk of bias, studies using NMBA in addition to deep sedation level to avoid spontaneous breathing and a comparison of preprints versus peer-reviewed articles. We planned to assess the certainty of evidence using the GRADE approach.

MAIN RESULTS

We identified no eligible studies for this review.

AUTHORS' CONCLUSIONS

We found no direct evidence on whether early spontaneous breathing in SARS-CoV-2-induced ARDS is beneficial or detrimental to this particular group of patients.  RCTs comparing early spontaneous breathing with ventilatory strategies not allowing for spontaneous breathing in SARS-CoV-2-induced ARDS are necessary to determine its value within the treatment of severely ill people with COVID-19. Additionally, studies should aim to clarify whether treatment effects differ between people with SARS-CoV-2-induced ARDS and people with non-SARS-CoV-2-induced ARDS.

Brain-lung interactions and mechanical ventilation in patients with isolated brain injury

During the last decade, experimental and clinical studies have demonstrated that isolated acute brain injury (ABI) may cause severe dysfunction of peripheral extracranial organs and systems. Of all potential target organs and systems, the lung appears to be the most vulnerable to damage after brain injury (BI). The pathophysiology of these brain–lung interactions are complex and involve neurogenic pulmonary oedema, inflammation, neurodegeneration, neurotransmitters, immune suppression and dysfunction of the autonomic system. The systemic effects of inflammatory mediators in patients with BI create a systemic inflammatory environment that makes extracranial organs vulnerable to secondary procedures that enhance inflammation, such as mechanical ventilation (MV), surgery and infections. Indeed, previous studies have shown that in the presence of a systemic inflammatory environment, specific neurointensive care interventions—such as MV—may significantly contribute to the development of lung injury, regardless of the underlying mechanisms. Although current knowledge supports protective ventilation in patients with BI, it must be born in mind that ABI-related lung injury has distinct mechanisms that involve complex interactions between the brain and lungs. In this context, the role of extracerebral pathophysiology, especially in the lungs, has often been overlooked, as most physicians focus on intracranial injury and cerebral dysfunction. The present review aims to fill this gap by describing the pathophysiology of complications due to lung injuries in patients with a single ABI, and discusses the possible impact of MV in neurocritical care patients with normal lungs.