What are possible mechanisms for the improvement of prone position oxygenation in acute respiratory distress syndrome (ARDS)?

Updated: Mar 27, 2020
  • Author: Eloise M Harman, MD; Chief Editor: Michael R Pinsky, MD, CM, Dr(HC), FCCP, FAPS, MCCM  more...
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Possible mechanisms for the improvement noted are recruitment of dependent lung zones, increased functional residual capacity (FRC), improved diaphragmatic excursion, increased cardiac output, and improved ventilation-perfusion matching.

Despite improved oxygenation with the prone position, early randomized controlled trials of the prone position in ARDS did not demonstrate improved survival. In an Italian study, the survival rate to discharge from the ICU and the survival rate at 6 months were unchanged compared with patients who underwent care in the supine position, despite a significant improvement in oxygenation. [48] This study was criticized because patients were kept in the prone position for an average of only 7 hours per day. In addition, a subsequent French study, in which patients were in the prone position for at least 8 hours per day, did not document a benefit from the prone position in terms of 28- or 90-day mortality, duration of mechanical ventilation, or development of ventilator-associated pneumonia (VAP). [49] However, a subsequent randomized controlled trial in which patients with severe ARDS were placed in the prone position early and for at least 16 hours a day showed a significant mortality benefit. [50] In this study, patients with severe ARDS (PaO2/FiO2 of <150) were randomized to prone position after 12-24 hours of stabilization. The 28-day mortality rate was 16% in the prone group and 32.8% in the supine group. Patients were turned manually. A specialized bed was not required.

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