Gas exchange and lung mechanics in patients with acute respiratory distress syndrome: comparison of three different strategies of positive end expiratory pressure selection.

PURPOSE: The purpose of the study was to compare gas exchange and lung mechanics between different strategies to select positive end-expiratory pressure (PEEP) in acute respiratory distress syndrome (ARDS).

METHODS: In 20 consecutive ARDS patients, 3 PEEP selection strategies were evaluated. One strategy was based on oxygenation using the ARDS network PEEP/fraction of inspired oxygen (Fio2) table; and two were based on lung mechanics, either PEEP titrated to reach a plateau pressure of 28 to 30 cm H2O as in the ExPress trial or best respiratory compliance method during a derecruitment maneuver. Gas exchange, airway pressures, stress index (SI), and end-expiratory transpulmonary pressure (P(tpe)) and end-inspiratory transpulmonary pressure (P(tpi)) values were assessed. Data are expressed as median (interquartile range [IQR]).

RESULTS: Lower total PEEP levels were observed with the use of the PEEP/Fio2 table (8.7 [6-10] cm H2O); intermediate PEEP levels, with the Best Compliance approach (13.0 [10.2-13.8] cm H2O); and higher PEEP levels, with the ExPress strategy (16.5 [15.0-18.5] cm H2O) (P < .01). Pao2/Fio2 ratio was lower with the PEEP/Fio2 table. Oxygenation with Best Compliance approach and ExPress strategy was not different with lower plateau pressure in the former (23 [20-25] vs 30 [29-30] cm H2O; P < .01). Paco2 was slightly higher with the ExPress method than the others 2 strategies. Negative P(tpe) was observed in 35% of the patients with the PEEP/Fio2 table, in 15% applying the Best Compliance, and in only 1 case with the ExPress method. Higher SI and P(tpi), with lower lung compliance, were obtained with ExPress strategy.

CONCLUSIONS: Using a best respiratory compliance approach resulted in better oxygenation levels without risk of overdistension according to SI and P(tpi), achieving a mild risk of lung collapse according to P(tpe).