Lung Recruitment in Obese Patients with Acute Respiratory Distress Syndrome

Background: Obese patients are characterized by normal chest-wall elastance and high pleural pressure and have been excluded from trials assessing best strategies to set positive end-expiratory pressure (PEEP) in acute respiratory distress syndrome (ARDS). The authors hypothesized that severely obese patients with ARDS present with a high degree of lung collapse, reversible by titrated PEEP preceded by a lung recruitment maneuver. Methods: Severely obese ARDS patients were enrolled in a physiologic crossover study evaluating the effects of three PEEP titration strategies applied in the following order: (1) PEEP ARDSNET : the low PEEP/Fio(2) ARDSnet table; (2) PEEP INCREMENTAL : PEEP levels set to determine a positive end-expiratory transpulmonary pressure; and (3) PEEP DECREMENTAL : PEEP levels set to determine the lowest respiratory system elastance during a decremental PEEP trial following a recruitment maneuver on respiratory mechanics, regional lung collapse, and overdistension according to electrical impedance tomography and gas exchange. Results: Fourteen patients underwent the study procedures. At PEEP ARDSNET (13 +/- 1 cm H2O) end-expiratory transpulmonary pressure was negative (-5 +/- 5 cm H2O), lung elastance was 27 +/- 12 cm H2O/L, and PaO2/Fio(2) was 194 +/- 111 mmHg. Compared to PEEP ARDSNET, at PEEP INCREMENTAL level (22 +/- 3 cm H2O) lung volume increased (977 +/- 708 ml), lung elastance decreased (23 +/- 7 cm H2O/l), lung collapse decreased (18 +/- 10%), and ventilation homogeneity increased thus rising oxygenation (251 +/- 105 mmHg), despite higher overdistension levels (16 +/- 12%), all values P < 0.05 versus PEEP ARDSnet. Setting PEEP according to a PEEP DECREMENTAL trial after a recruitment maneuver (21 +/- 4 cm H2O, P = 0.99 vs. PEEP INCREMENTAL) further lowered lung elastance (19 +/- 6 cm H2O/l) and increased oxygenation (329 +/- 82 mmHg) while reducing lung collapse (9 +/- 2%) and overdistension (11 +/- 2%), all values P < 0.05 versus PEEP ARDSnet and PEEP INCREMENTAL. All patients were maintained on titrated PEEP levels up to 24 h without hemodynamic or ventilation related complications. Conclusions: Among the PEEP titration strategies tested, setting PEEP according to a PEEP DECREMENTAL trial preceded by a recruitment maneuver obtained the best lung function by decreasing lung overdistension and collapse, restoring lung elastance, and oxygenation suggesting lung tissue recruitment.