Objective: Changing the position from supine to prone is an emerging strategy to improve gas exchange in patients with the acute respiratory distress syndrome (ARDS). The aim of this study was to evaluate the acute effects on gas exchange, hemodynamics, and respiratory system mechanics of turning critically ill patients with ARDS from supine to prone.
Design: Open, prospective study.
Setting: General intensive care units.
Patients: 23 patients [mean age 56 +/- 17 (SD) years] who met ARDS criteria and had a Lung Injury Score > 2.5 (mean 3.25 +/- 0.3).
Interventions: The decision to turn a patient was made using a protocol based on impaired oxygenation despite the use of positive end-expiratory pressure and a fractional inspired oxygen (FIO2) of 1.
Measurements and results: We measured gas exchange and hemodynamic variables in all patients and in 16 patients calculated respiratory system compliance when they were supine and 60 to 90 min after turning them to a prone position. This latter position was remarkably well tolerated and no clinically relevant complications or events were detected either during turning or while prone. The partial pressure of oxygen in arterial blood (PaO2)/FIO2 ratio improved from 78 +/- 37 mm Hg supine to 115 +/- 31 mm Hg prone (p < 0.001), and intrapulmonary shunt decreased from 43 +/- 11 to 34 +/- 8% (p < 0.001). Cardiac output and other hemodynamic parameters were not affected. Respiratory system compliance slightly improved from 24.7 +/- 10.2 ml/cmH20 supine to 27.8 +/- 13.2 ml/cmH20 prone (p < 0.05). An improvement in PaO2/FIO2 of more than 15% from changing from supine to prone was found in 16 patients (responders). Responders had more hypoxemia (PaO2/FIO2 70 +/- 23 vs 99 +/- 53 mm Hg in non-responders, p < 0.01), more hypercapnia (partial pressure of carbon dioxide in arterial blood (70 +/- 27 vs 64 +/- 9 mm Hg, p < 0.01) and a shorter elapsed time to the onset of ARDS and turning to the prone position (11.8 +/- 16 vs 32.8 +/- 42 days, p < 0.01).
Conclusions: Turning critically ill, severely hypoxemic patients from the supine to the prone position is a safe and useful therapeutic intervention. Our data suggest that prone positioning should be carried out early in the course of ARDS.