Effect Of Sustained Inflation On Pulmonary Mechanics, Oxygen Metabolism And Hemodynamics In Patients With Acute Lung Injury

Objective: To observe the influence of sustained inflation(SI) combined with small tidal volume ventilation on pulmonary mechanics, oxygen metabolism and hemodynamics in patients with acute lung injury, and investigate the effects of SI and the best pressure of SI.Method: 31 patients with severe trauma followed by acute lung injury admitted to Clinical College of Third Military Medical University from April 2001 to March 2002 were selected for this study. All patients were admitted to the intensive care unit(ICU) within 24 hours after ALI diagnosed and were mechanical ventilated. First they underwent Ih of small tidal volume ventilation (baseline), then Ih of SI with 20cmH2oX 30s(SIi), 30cmH2Ox30s(SI2), 40cmH2Ox30s(SI3), 50cmH2Ox30s(Si4) respectively, and then Ih of baseline again. Tidal volume, respiratory rate, inspiratory oxygen fraction and positive end-expiratory pressure were kept constant. Parameter of pulmonary mechanics, oxygen metabolism and hemodynamics were measured at Ih of baseline , Ih of SI and Ih of returning baseline. The changes of all parameters have been analyzed by statistical methods.Results: All parameters indicated no significant difference after SI1 and SI2 compared with baseline, but PaO2 increased significantly after Si3 and Si4(from 92.0 14.2mmHg to 121.3 16.9mmHg and 120.4 17.0mmHgrespectively, P<0.01). After Si3 and SL4 oxygen delivery index(DO2I), static compliance(Cst) both increased significantly, puhnonary venous mixture(Qs/Qt) decreased significantly. After SI interruption, all the physiological variables returned to baseline. We found that there were no variables in heart rate(HR), arterial pressure(AP) and cardiac index(CI) after SI, but pulmonary artery pressure(PAP) and pulmonary vascular resistance index(PVRI) decreased significantly after Si3 and Si4. And we found that there were no significant difference on Cst and oxygenation between SI3 and SI4.Conclusions: Treatment with SI combined with small tidal volume ventilation in patients with acute lung injury can improve oxygenation and pulmonary compliance, and there were no significant side effect on hemodynamics. 40cmH2O was the best pressure of SI.