The latest evidence I have seen is that proning more than 16 to 18 hours/day showed benefits. Was the 12-hour mark a new change?
The current evidence suggests that patients should remain in the prone position for most of the day (>16 h), if tolerated. Derecruitment of the lungs can occur when the patient is turned supine because of an increase in ventral-dorsal pleural pressure on the lungs. The greater than 12-hour mark is the recommendation from the American Thoracic Society/Society of Critical Care Medicine guidelines for patients with moderate to severe adult respiratory distress syndrome (ARDS) who are receiving mechanical ventilation. If no improvement is seen on initial prone positioning, consider a consecutive 48-hour trial, then stop if no improvement. Evidence of improvement includes fraction of inspired oxygen (Fio2) reduced by 0.10 or a 30-point increase in Pao2/Fio2 ratio. Discontinue proning if instability occurs...