Prone positioning for ARDS: Defining the target

Abstract

Although variation of position is innate to healthy subjects, practitioners usually orient critically ill patients in a supine, semirecumbent posture for days to weeks, with only periodic, side-to-side repositioning through a relatively shallow 30-60° arc. Experimental data [1] and clinical observations [2-4] demonstrate physiologic benefit from prone positioning during acute lung injury (ALI), but recent large clinical trials have been unable to confirm survival benefit in diverse populations of patients labeled as having ALI/acute respiratory distress syndrome (ARDS) [5-7]. However, posttrial subgroup analyses hint that certain patient subgroups may indeed benefit from prone orientation. Severely ill patients, those experiencing improved CO2 exchange, and those ventilated with large tidal volumes appear more likely to benefit than other members of the general cohort [5]. A superb meta-analysis of pooled data appears in this issue, focusing on those relative few with the worst oxygen exchange [8]. This analysis shows convincingly that, while proning cannot be recommended for all patients with acute lung injury, it does hold therapeutic value for some.