Abstract 254 Poster Session III, Monday, 5/3 (poster 114)

Introduction: The choice of mechanical ventilation strategy influences the course of lung disease. Strategies that permit alveolar closure and cyclic overdistension can exacerbate preexisting lung injury. We hypothesized that lung recruitment strategies that avoid cyclic overdistension of alveoli while maintaining adequate functional residual capacity would be associated with more favorable physiologic outcomes in a model of acute lung injury.

Methods: Forty-two anesthetized NZW rabbits were instrumented with a tracheostomy and vascular catheters. Lung injury was induced by repeated saline lavage. Following injury (PaO2< 100 torr), all animals were subjected to high frequency oscillatory ventilation (HFOV) for 15 minutes to equalize volume history. The animals were then assigned to one of 4 strategies: (1) Low PEEP: Vt=10 ml/kg, PEEP=2 cmH2O; (2) High PEEP: Vt=10 ml/kg, PEEP=10 cmH2O; (3) Permissive hypercapnia (P-Hyp): Vt=6 ml/kg, PEEP=14 cmH2O (>Pflex); (4) HFOV: Paw=16 cmH2O, f=10 Hz, Ti=33%. Uninjured rabbits ventilated with Vt=10 ml/kg, PEEP=5 cmH2O served as controls. Animals were ventilated with FiO2=1.0 for 4 hours prior to sacrifice. Arterial blood gases and tracheal lavage fluid for measurement of total protein content were analyzed.

Results: Data are means ± SD. (Table)

Table 1 No caption available

Conclusion: Strategies that promote lung recruitment and avoid alveolar overdistension, such as HFOV and P-Hyp with PEEP> Pflex are associated with more favorable oxygenation and acid-base status, as well as decreased protein leak into lung fluid. Animals in the P-Hyp with PEEP> Pflex group experienced more hemodynamic instability in comparison to HFOV. In this small-animal model of acute lung injury, P-Hyp with PEEP> Pflex supports oxygenation, but at the apparent cost of hemodynamic instability.

Supported, in part, by SensorMedics Corporation, Yorba Linda, CA.