Effects of periodic lung recruitment maneuvers on gas exchange and respiratory mechanics in mechanically ventilated acute respiratory distress syndrome (ARDS) patients

Objective: We wished to investigate whether volume recruitment maneuvers (VRMs) could improve alveolar recruitment and oxygenation in acute respiratory distress syndrome (ARDS) patients, ventilated at relatively low positive end-expiratory pressure (PEEP). Setting: General intensive care unit (ICU) located in a teaching hospital. Patients: 15 PEEP responder ARDS patients undergoing continuous positive pressure ventilation (CPPV) with sedation and muscle paralysis. Interventions: We identified a low (9.4 +/- 3 cmH(2)O) and a high (16.0 +/- 2 cmH(2)O) level of PEEP associated with target oxygenation values. Using a custom modified mechanical ventilator, we applied in random order three steps lasting 30 min: (1) CPPV at the low PEEP level (CPPVLo); (2) CPPV at the high PEEP level (CPPVHI); (3) CPPV at low PEEP with the superimposition of periodic VRMs (CPPVVRM). VRMs were performed twice a minute by increasing PEEP to the high level for two breaths. Each brace of two breaths was spaced 30 seconds from the preceding one. Measurements and results: We measured gas exchange, hemodynamics, respiratory mechanics, and the end expiratory lung volume (EELV). Compared to CPPVLo, CPPVVRM resulted in higher PaO2 (117.9 +/- 40.6 vs 79.4 +/- 13.6 mmHg, P < 0.01) and EELV (1.50 +/- 0.62 vs 1.26 +/- 0.50 l, P < 0.05), and in lower venous admixture (QVA/QT) (0.42 +/- 0.07 vs 0.48 +/- 0.07, P < 0.01). During CPPVHI, we observed significantly higher PaO2 (139.3 +/- 32.5 mmHg) and lower QVA/QT (0.37 +/- 0.08) compared to CPPVLo (P < 0.01) and to CPPVVRM (P < 0.05). Conclusions: VRMs can improve oxygenation and alveolar recruitment during CPPV at relatively low PEEP, but are relatively less effective than a continuous high PEEP level.