Prone Positioning in Acute Respiratory Distress Syndrome

Abstract

Prone positioning is nowadays considered as one of the most effective strategies for patients with severe acute respiratory distress syndrome (ARDS). The evolution of the pathophysiological understanding surrounding the prone position closely follows the history of ARDS. At the beginning, the focus of the prone position was the improvement in oxygenation attributed to a perfusion redistribution. However, the mechanisms behind the prone position are more complex. Indeed, the positive effects on oxygenation and CO2 clearance of the prone position are to be ascribed to a more homogeneous inflation–ventilation, to the lung/thoracic shape mismatch, and to the change of chest wall elastance. In the past 20 years, five major trials have tried, starting from different theories, hypotheses, and designs, to demonstrate the effectiveness of the prone position, which finally found its definitive place among the different ARDS supportive therapies.

Clinical strategies for implementing lung and diaphragm-protective ventilation: avoiding insufficient and excessive effort

“…The prone position has been used for decades in early ARDS to improve oxygenation and over time an appreciation for the lung-protective benefit of prone positioning has emerged [ 67 ]. As the amount of lung tissue is larger in dorsal lung regions, gravitational forces generate more dependent atelectasis in the supine position compared to prone position.…”

A physiological approach to understand the role of respiratory effort in the progression of lung injury in SARS-CoV-2 infection

“…Prone position has been extensively studied in patients with ARDS and invasive MV, showing an improvement of oxygenation due to many mechanisms, like improving FRC, ventilation/perfusion heterogeneity, diaphragm motion in dorsal regions, increasing regional ventilation in dependent lung regions, among others [72,73]. Some principles of prone position can be applied to awake extubated patients, but physiology is still not known in depth.…”

Prone positioning in conscious patients on medical wards: A review of the evidence and its relevance to patients with COVID-19 infection

“…This is due to both gravity and the 'shape mismatch' of the triangular lung expanding within a spherical chest cavity on inspiration. 22 This results in heterogenous distribution of transpulmonary pressures (thus ventilation) across a ventral-dorsal axis. 23 The graduated non-cardiogenic pulmonary oedema in dependent regions seen in typical ARDS may exacerbate this.…”