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 cmH2O) and a high (16.0 +/- 2 cmH2O) 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 (CPPV(LO)); (2) CPPV at the high PEEP level (CPPV(HI)); (3) CPPV at low PEEP with the superimposition of periodic VRMs (CPPV(VRM)). 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 CPPV(LO), CPPV(VRM) 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 (Q(VA)/Q(T)) (0.42 +/- 0.07 vs 0.48 +/- 0.07, P < 0.01). During CPPV(HI), we observed significantly higher PaO2 (139.3 +/- 32.5 mmHg) and lower Q(VA)/Q(T) (0.37 +/- 0.08) compared to CPPV(LO) (P < 0.01) and to CPPV(VRM) (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.