Bedside selection of positive end-expiratory pressure in mild, moderate, and severe acute respiratory distress syndrome

Abstract

Objective: Positive end-expiratory pressure exerts its effects keeping open at end-expiration previously collapsed areas of the lung; consequently, higher positive end-expiratory pressure should be limited to patients with high recruitability. We aimed to determine which bedside method would provide positive end-expiratory pressure better related to lung recruitability.

Design: Prospective study performed between 2008 and 2011.

Setting: Two university hospitals (Italy and Germany).

Patients: Fifty-one patients with acute respiratory distress syndrome.

Interventions: Whole lung CT scans were taken in static conditions at 5 and 45 cm H2O during an end-expiratory/end-inspiratory pause to measure lung recruitability. To select individual positive end-expiratory pressure, we applied bedside methods based on lung mechanics (ExPress, stress index), esophageal pressure, and oxygenation (higher positive end-expiratory pressure table of lung open ventilation study).

Measurements and main results: Patients were classified in mild, moderate and severe acute respiratory distress syndrome. Positive end-expiratory pressure levels selected by the ExPress, stress index, and absolute esophageal pressures methods were unrelated with lung recruitability, whereas positive end-expiratory pressure levels selected by the lung open ventilation method showed a weak relationship with lung recruitability (r = 0.29; p < 0.0001). When patients were classified according to the acute respiratory distress syndrome Berlin definition, the lung open ventilation method was the only one which gave lower positive end-expiratory pressure levels in mild and moderate acute respiratory distress syndrome compared with severe acute respiratory distress syndrome (8 ± 2 and 11 ± 3 cm H2O vs 15 ± 3 cm H2O; p < 0.05), whereas ExPress, stress index, and esophageal pressure methods gave similar positive end-expiratory pressure values in mild, moderate, and severe acute respiratory distress syndrome. The positive end-expiratory pressure selected by the different methods were unrelated to each other with the exception of the two methods based on lung mechanics (ExPress and stress index).

Conclusions: Bedside positive end-expiratory pressure selection methods based on lung mechanics or absolute esophageal pressures provide positive end-expiratory pressure levels unrelated to lung recruitability and similar in mild, moderate, and severe acute respiratory distress syndrome, whereas the oxygenation-based method provided positive end-expiratory pressure levels related with lung recruitability progressively increasing from mild to moderate and severe acute respiratory distress syndrome.