Chest
Volume 151, Issue 1, January 2017, Pages 215-224
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Contemporary Reviews in Critical Care Medicine
Treatment of ARDS With Prone Positioning

https://doi.org/10.1016/j.chest.2016.06.032Get rights and content

Prone positioning was first proposed in the 1970s as a method to improve gas exchange in ARDS. Subsequent observations of dramatic improvement in oxygenation with simple patient rotation motivated the next several decades of research. This work elucidated the physiological mechanisms underlying changes in gas exchange and respiratory mechanics with prone ventilation. However, translating physiological improvements into a clinical benefit has proved challenging; several contemporary trials showed no major clinical benefits with prone positioning. By optimizing patient selection and treatment protocols, the recent Proning Severe ARDS Patients (PROSEVA) trial demonstrated a significant mortality benefit with prone ventilation. This trial, and subsequent meta-analyses, support the role of prone positioning as an effective therapy to reduce mortality in severe ARDS, particularly when applied early with other lung-protective strategies. This review discusses the physiological principles, clinical evidence, and practical application of prone ventilation in ARDS.

Section snippets

Prone Positioning and Gas Exchange

When a person is supine, the weight of the ventral lungs, heart, and abdominal viscera increase dorsal pleural pressure. This compression reduces transpulmonary pressure (airway opening pressure – pleural pressure) in the dorsal lung regions.17, 18 The increased mass of the edematous ARDS lung further increases the ventral-dorsal pleural pressure gradient and reduces regional ventilation of dependent dorsal regions.19, 20 The ventral heart is estimated to contribute approximately an additional

Lung Protection

Adequate oxygenation is necessary for organ function, but many interventions in acute lung injury that raise arterial oxygen tension do not confer a survival advantage (eg, high tidal volume ventilation, oxygen toxicity).36, 37 The prone position generally improves oxygenation, but its ability to attenuate mechanical lung injury may be the more important mechanism of clinical benefit. Indeed, although all major clinical trials of prone positioning in ARDS significantly improved oxygenation, the

Extrapulmonary Organ Systems

In addition to its lung-protective effects, a prone position impacts cardiac and abdominal pressures. In general, total cardiac output is unchanged when patients with ARDS are placed in a prone position. However, while prone, the right atrium moves ventrally so that venous return is now aided by gravity. Thus, preload responsive patients may augment their cardiac output by being placed in a prone position.54 Additionally, right ventricular afterload typically falls, likely due to relief of

Clinical Trials

Although the physiological effects of prone positioning are well described, clinical trials have yielded mixed results regarding the clinical benefit. Table 1 reviews five major randomized trials of prone ventilation in adults.7, 8, 9, 10, 11, 64 Note the significant mortality benefit of the prone position in the PROSEVA trial, with no mortality benefit in the previous trials. What accounts for these discrepant findings?

The 2013 PROSEVA trial design benefited from recognition of the limitations

Practical Considerations

With this evidence base, prone positioning moves from a salvage therapy for refractory hypoxemia to an upfront lung-protective strategy intended to improve survival in severe ARDS. Indeed, prone positioning has never been proved to afford a survival benefit when used as a late rescue therapy for refractory hypoxemia. However, a contemporary prospective observational study (the 2016 Large Observational Study to Understand the Global Impact of Severe Acute Respiratory Failure [LUNG-SAFE] study)

Next Steps

Future studies of prone positioning will need to emulate the extended-duration and low tidal volume approach of PROSEVA. Several clinical questions remain regarding the optimal approach to prone positioning and concomitant lung-protective therapies: (1) What is the optimal approach to PEEP management in prone positioning, and is prone positioning effective in patients undergoing a high-PEEP strategy or might these therapies even be synergistic? (2) Does effective prone positioning necessitate

Acknowledgments

Financial/nonfinancial disclosures: None declared.

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