Prone Positioning (PP) is a non-pharmacological treatment used during invasive mechanical ventilation for severe Acute Respiratory Distress Syndrome (ARDS) where patients lay on their stomach rather than their back (1) improving the redistribution of lung density from dorsal to ventral areas and increasing lung aeration from ventral to atelectatic dorsal regions and therefore, improving gas exchange and reducing mortality (2).
Prone positioning in non-intubated patients outside the Intensive Care Unit (ICU) has recently gained attention as a potential treatment through anecdotal reports, case series and social media. Notably, it has received significant attention during the current COVID-19 pandemic in spontaneously breathing patients with acute respiratory failure (3); however, there is no evidence that regular PP in awake patients impacts relevant clinical outcomes.
One of the first evidence on proning spontaneously breathing awake patients before COVID-19 has been published by Ding et al. In their small prospective cohort study conducted in two teaching hospitals, authors studied 20 consecutive non-intubated patients with moderate to severe ARDS (accordingly to the Berlin criteria - 10 moderate and 10 severe ARDS) mostly having viral pneumonia.
Patients admitted to the ICU with a PaO₂/FiO₂ < 200 while on Noninvasive Ventilation (NIV) with CPAP 5 cmH₂O and FiO₂ of 0.5 were enrolled. Patients with altered mental status, agitation or respiratory distress were excluded.
All the patients started with High Flow Nasal Cannula (HFNT) alone (flow rate up to 60 L/min and FiO₂ max 0.9) and were escalated to HFNT combined with PP or to NIV (CPAP or BIPAP and oro-nasal mask) or to NIV combined with PP to maintain SpO2 > 90%. Prone positioning was applied at least twice per day for a minimum of 30 minutes per session, with an average of 2 hours per session, for 3 days without sedation.
The primary outcome was the rate of avoidance for endotracheal intubation (ETI); secondary outcomes included improvement in P/F with the combination of PP+HFNT/NIV. Safety outcomes were the tolerance of each PP session in terms of time duration.

Research findings showed:
55% (11) of patients avoided ETI (success group), 45% (9) of patients were intubated (failure group).
The 9 intubated patients had a median initial PaO₂/FiO₂ of 83 vs. 151 in non-intubated patients, and 3/9 intubated patients underwent ECMO, suggesting that severe ARDS patients are not appropriate candidates for PP.
PaO₂/FiO₂ in HFNT or NIV+PP was significantly higher in the success group than in the failure group 125 ± 41 mmHg vs. 119 ± 19 mmHg, p = 0.043, with a decrease in the need for intubation (study outcome) in patients with moderate ARDS.
Only one safety outcome was formally assessed – the ability to tolerate prone positioning.

Key points

• The addition of PP to noninvasive respiratory supports (NIV or HFNT) may assist in avoiding intubation.
• PaO₂/FiO₂ ratio increased by 25–35 mmHg following awake prone positioning, but 78% (7 patients) of participants with severe ARDS eventually required IMV. Therefore, awake prone positioning in severe ARDS may delay the use of IMV when indicated.
• The main limitations of this study are the small sample size and the lack of a control group.
• Additional limitations are the multiple sources of confounding due to the heterogeneous cohort and different approaches for respiratory support.

References

1. Scholten EL, Beitler JR, Prisk GK, Malhotra A. Treatment of ARDS with prone positioning. Chest 2017;151:215-24.
2. Pelosi P, Tubiolo D, Mascheroni D, et al. Effects of the prone position on respiratory mechanics and gas exchange during acute lung injury. Am J Respir Crit Care Med 1998;157:387-93.
3. Elharrar X, Trigui Y, Dols A, et al. Use of prone positioning in nonintubated patients with COVID-19 and hypoxemic acute respiratory failure. JAMA 2020;323:2336-8.