Does prone positioning improve oxygenation and reduce mortality in patients with acute respiratory distress syndrome?

Abstract

The emergence of computed tomography imaging more than 25 years ago led to characterization of acute respiratory distress syndrome (ARDS) as areas of relatively normal lung parenchyma juxtaposed with areas of dense consolidation and atelectasis. Given that this heterogeneity is often dorsally distributed, investigators questioned whether care for ARDS patients in the prone position would lead to improved mortality outcomes. This clinical review discusses the physiological rationale and clinical evidence supporting prone positioning in treating ARDS, in addition to its complications and contraindications.

Figure 1)

Schematic representation of changes in the volume of ventilated lung between the supine and prone positions. The vertebral column and associated structures is represented by the white triangle while the heart and associated structures is represented by the white oval. In a chest cavity containing symmetrical lungs, the amount of lung that is well ventilated (where the alveolar pressure exceeds the pleural pressure) roughly equals the amount of lung that is atelectatic and poorly ventilated (where pleural pressure exceeds intra-alveolar pressure) in both supine and prone positions (A and B). However, when the space occupied by the mediastinum and heart are accounted for, and the effects of the compression of lung tissue subjacent to these structures are considered, there is less ventilated tissue in the supine position (C) than in the prone position (D). Effects of the transmitted abdominal pressure on the caudal posterior lung are not reflected in this diagram