Chest
Contemporary Reviews in Critical Care MedicineTreatment of ARDS With Prone Positioning
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.
References (78)
- et al.
Acute respiratory distress in adults
Lancet
(1967) - et al.
Influence of positioning on ventilation-perfusion relationships in severe adult respiratory distress syndrome
Chest
(1994) - et al.
Prone position prevents regional alveolar hyperinflation and mechanical stress and strain in mild experimental acute lung injury
Respir Physiol Neurobiol
(2009) - et al.
Effects of prone position on inflammatory markers in patients with ARDS due to community-acquired pneumonia
J Formos Med Assoc
(2007) - et al.
Prone positioning unloads the right ventricle in severe ARDS
Chest
(2007) - et al.
Influence of abdominal obesity on multiorgan dysfunction and mortality in acute respiratory distress syndrome patients treated with prone positioning
J Crit Care
(2014) - et al.
The efficacy and safety of prone positional ventilation in acute respiratory distress syndrome: updated study-level meta-analysis of 11 randomized controlled trials
Crit Care Med
(2014) - et al.
American Lung Association: lung disease data
(2008) - et al.
Evolution of mechanical ventilation in response to clinical research
Am J Respir Crit Care Med
(2008) - et al.
Two-year outcomes, health care use, and costs of survivors of acute respiratory distress syndrome
Am J Respir Crit Care Med
(2006)
Comments of a devil’s advocate
Am Rev Respir Dis
Use of extreme position changes in acute respiratory failure
Crit Care Med
A multicenter trial of prolonged prone ventilation in severe acute respiratory distress syndrome
Am J Respir Crit Care Med
Effects of systematic prone positioning in hypoxemic acute respiratory failure: a randomized controlled trial
JAMA
Prone positioning in severe acute respiratory distress syndrome
N Engl J Med
Effect of prone positioning on the survival of patients with acute respiratory failure
N Engl J Med
Prone positioning in patients with moderate and severe acute respiratory distress syndrome: a randomized controlled trial
JAMA
Improved oxygenation in patients with acute respiratory failure: the prone position
Am Rev Respir Dis
Dramatic effect on oxygenation in patients with severe acute lung insufficiency treated in the prone position
Crit Care Med
Mechanism by which the prone position improves oxygenation in acute lung injury
Am J Respir Crit Care Med
Short-term effects of prone position in critically ill patients with acute respiratory distress syndrome
Intensive Care Med
Pleural pressure distribution and its relationship to lung volume and interstitial pressure
J Appl Physiol
Role of the heart in the loss of aeration characterizing lower lobes in acute resiratory distress syndrome
Am J Respir Crit Care Med
Vertical gradient of regional lung inflation in adult respiratory distress syndrome
Am J Respir Crit Care Med
A computed tomography scan assessment of regional lung volume in acute lung injury
Am J Respir Crit Care Med
Left lower lobe ventilation is reduced in patients with cardiomegaly in the supine but not the prone position
Am Rev Respir Dis
The gravitational distribution of ventilation-perfusion ratio is more uniform in prone than supine posture in the normal human lung
J Appl Physiol
Prone position alters the effect of volume overload on regional pleural pressures and improves hypoxemia in pigs in vivo
Am Rev Respir Dis
Topographical distribution of regional lung volume in anesthetized dogs
J Appl Physiol
Prone position in acute respiratory distress syndrome: rationale, indications, and limits
Am J Respir Crit Care Med
Body position changes redistribute lung computed-tomographic density in patients with acute respiratory failure
Anesthesiology
Supine and prone differences in regional lung density and pleural pressure gradients in the human lung with constant shape
J Appl Physiol
Regional ventilation-perfusion distribution is more uniform in the prone position
J Appl Physiol
Prone position augments recruitment and prevents alveolar overinflation in acute lung injury
Am J Respir Crit Care Med
Pulmonary gas exchange in pigs improves in the prone position with abdominal distension
Am J Respir Crit Care Med
Volume infusion produces abdominal distension, lung compression, and chest wall stiffening in pigs
J Appl Physiol
Effect of prone position on regional shunt, aeration, and perfusion in experimental acute lung injury
Am J Respir Crit Care Med
Pulmonary perfusion in the prone and supine postures in the normal human lung
J Appl Physiol
Gravity is a minor determinant of pulmonary blood flow distribution
J Appl Physiol
Cited by (249)
Evolution of extracorporeal membrane oxygenation trigger criteria in COVID-19 acute respiratory distress syndrome
2024, Journal of Thoracic and Cardiovascular SurgeryProne Positioning of Ventilated Patients During Air Medical Evacuation: A Case Series
2024, Air Medical JournalProne Ventilation in a Case of Tracheal Compression
2023, American Journal of MedicineProne position in the third trimester of pregnancy during the COVID-19 era: A transdisciplinary approach
2023, Clinica e Investigacion en Ginecologia y ObstetriciaLessons Learned in Mechanical Ventilation/Oxygen Support in Coronavirus Disease 2019
2023, Clinics in Chest Medicine