Objective: To determine the optimal pressure of sustained inflation (SI) in treatment of acute respiratory distress syndrome (ARDS).
Methods: SI was applied at pressures of 1 approximately 6 times of mean airway pressure (P(m)) for 20 s on saline alveoli-lavaged anesthetized rabbits. Hemodynamics, pulmonary mechanics and gas exchange were observed before, during, and 2 min, 5 min after applying SI. Lung histology was observed after the experiment.
Results: When the pressure of SI was higher than 3P(m), partial pressure of arterial oxygen (PaO(2)) and arterial oxygen saturation were improved. The difference of PaO(2) before and during SI were (65 +/- 40) mm Hg and (52 +/- 25) mm Hg respectively in the 5P(m) and 6P(m) group, being significantly higher than that in the 1P(m) group [(-5 +/- 4) mm Hg, P < 0.05]. After SI, dynamic pulmonary compliance (C(dyn)) in the 5P(m) group [(3.06 +/- 0.24) ml/cm H(2)O] was increased markedly, as compared with C(dyn) before SI [(1.09 +/- 0.18) ml/cm H(2)O, P < 0.05]. SI with 5P(m) resulted in immediate significant increase in lung volume [(44.0 +/- 3.1) ml/kg in the 5P(m) group, (8.3 +/- 0.7) ml/kg in the 1P(m) group]. Histologically, Smith lung injury score was 4.40 +/- 1.66 in the 5P(m) group, which was less than that in the group of ARDS model 6.10 +/- 0.77. SI with 6P(m) led to alveolar overdistention. With the increasing of SI pressure, mean arterial pressure decreased markedly.
Conclusion: 5P(m) (25 approximately 35 cm H(2)O) may be the optimal pressure of SI in rabbits with severe ARDS.