Effect of Prone Positioning on Mortality in Patients With Mild to Moderate Acute Respiratory Distress Syndrome.

Acute Respiratory Distress Syndrome, ARDS, Intensive Care Unit, Mechanical Ventilation

ARDS, Acute Respiratory Distress Syndrome, Intensive Care Unit, ICU, Prone position

Acute respiratory distress syndrome (ARDS) accounts for almost 10% of intensive care units (ICU) admissions. Three ARDS stages have been defined, based on the PaO2/FIO2 ratio measured with positive end-expiratory pressure (PEEP) ≥5 cmH2O: mild (201-300 mmHg), moderate (200-101 mmHg), and severe (≤100mmHg). They represent 30.0%, 46.6%, and 23.4% of ARDS, respectively. Mechanical invasive ventilation (MV), the cornerstone of ARDS patient care, has a primary goal to protect the lung from ventilator-induced lung injury (VILI). Delivering MV in a prone position (PP) has been shown to improve oxygenation, protect the lung through a better homogenization of lung stress/strain, and stabilize hemodynamics. A meta-analysis of four randomized controlled trials showed beneficial effect of PP vs. supine position (SP) in the most hypoxemic patients. A fifth randomized controlled trial further showed a significant reduction in mortality with PP in ARDS patients with PaO2/FIO2 \<150 mmHg, when neuromuscular blockade and long prone positioning sessions were used. Therefore, PP has since been strongly recommended for ARDS patients with PaO2/FIO2 \<150 mmHg. Yet, there is limited evidence in patients with mild to moderate ARDS. There are, however, strong arguments supporting the need for a new trial in ARDS patients with PaO2/FIO2 in the range 150-300 mmHg: 1. There is no trial that has specifically tested PP in this ARDS subset; 2. PP is safe and has become a standard of care in ICU; 3. Should VILI prevention be a mechanism through which PP improves survival, this should be involved in all ARDS patients; 4. The mortality at hospital discharge in this subset of ARDS remains significant, amounting to 34.9% (95% confidence intervals 31.4-38.5%) in mild and 40.3% (37.4-43.3) in moderate stages; 5. Among 580 patients with mild ARDS at admission to the ICU, in-hospital mortality was 10%, 30%, and 37% for those who improved, persisted, and worsened ARDS, respectively. 6. Finally, PP has been shown to be cost-effective under commonly accepted thresholds. The hypothesis is that in patients within the 150-300mmHg PaO2/FIO2 range at the time of ARDS diagnosis, PP can reduce mortality as compared to a similar group left in the SP.

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