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Prone ventilation, sometimes called prone positioning or proning, refers to mechanical ventilation with the patient lying face-down (prone). It improves oxygenation in most patients with acute respiratory distress syndrome (ARDS) and reduces mortality

The earliest trial investigating the benefits of prone ventilation occured in 1976.

Since that time, many meta-analyses and one randomized control trial, the PROSEVA trial, have shown an increase in patients' survival with the more severe versions of ARDS. .

The mechanism behind this effect is uncertain. There are many proposed mechanisms for this effect, but they are not fully known. Some research has shown that this improved oxygenation is not accompanied by a change in survival.

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Of note, multiple RCTs were performed before a benefit from low tidal volume ventilation (a staple of open lung ventilation utilized in ARDS) was established. Therefore an investigation into the benefits of prone ventilation will likely be ongoing in the future

Physiologic effects
The purpose of prone ventilation is to facilitate lung mechanics to improve ventilation/perfusion ratio mismatches in ARDS

By redistributing pulmonary blood flow, oxygen levels can increase systemically from areas of low ventilation to higher ventilation.

The physiologic mechanism can be explained by a gravity-dependent increase in pleural pressure when supine compared to prone. In the prone position, the lungs' dorsal aspects have less pleural pressure, which alleviates forces trying to collapse the alveoli. When there is less pleural pressure, the alveoli can stay open and thus increase the amount of surface area for ventilation. Because there are more alveoli dorsally than ventrally, a prone position allows for more dorsal alveoli to stay open and thus increase the amount of ventilation available to be perfused.

Another benefit of prone ventilation may come from reduced VALI (Ventilator-associated lung injury). Proning and the redistribution of dependent fluid lead to more homogenous compliance of the lung and thus minimizes the barotrauma that usually occurs from more heterogeneous lungs and the repeated opening and closing of alveoli associated with it produces

Clinical applications
The studies that have found survival benefit of prone ventilation derived benefit only from patients with severe ARDS defined as a Horowitz index of less than 200-150 mmHg

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A meta-analysis published in 2017 suggested that patients only benefit from prone ventilation when they are in a prone position for longer than 12 hours a day.

COVID-19 pandemic
During the 2020 COVID-19 pandemic, awake high flow nasal cannula in the prone position, awake proning, was utilized to keep patients from being intubated.

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A retrospective analysis showed that the number needed to treat and keep people off the ventilator was 6

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This significantly reduced amount of required ventilators allowing for the use of ventilators in those in critical condition. The Society of Critical Care Medicine gave prone ventilation a weak recommendation in The Surviving Sepsis Campaign COVID-19 panel

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The panel cited the few studies that showed morality benefit from prone ventilation in ARDS and that this was a low-cost intervention; however, they cautioned the use due to the necessity of needing competent staff and complications that can occur if done incorrectly.

Considerations in the pediatric population
Special precautions must be in place for prone ventilation in children because of their risk of sudden infant death syndrome (SIDS)

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One meta-analysis looking at 53 studies showed benefit in oxygen saturation when prone ventilation preterm infants with ARDS. Importantly, the analysis found no adverse events; however, the authors emphasized the difference between healthy children and those in the hospital with continuous monitoring systems.

Contraindications

 * 1) hemodynamic instability.
 * 2) unstable fractures or polytrauma patients with unstable fracture spine
 * 3) tracheostomy
 * 4) chest tubes
 * 5) obesity
 * 6) pregnancy
 * 7) intracranial pressure raised
 * 8) cardiac surgery
 * 9) massive hemoptysis
 * 10) aspiration pneumonia

Complications
Increase in endotracheal tube obstruction Pressure sores, Corneal abrasions, brachial plexopathies, vascular and endotracheal tube displacement, heomodynamic instability, facial injuyr