Effects of positive end-expiratory pressure on anesthesia-induced atelectasis and gas exchange in anesthetized and mechanically ventilated sheep

摘要

Objective-To evaluate the effects of 10 cm H2O of positive end-expiratory pressure (PEEP) on lung aeration and gas exchange in mechanically ventilated sheep during general anesthesia induced and maintained with propofol.Animals-10 healthy adult Bergamasca sheep.Procedures-Sheep were sedated with diazepam (0.4 mg/kg, IV). Anesthesia was induced with propofol (5 mg/kg, IV) and maintained with propofol via constant rate infusion (0.4 mg/kg/min). Muscular paralysis was induced by administration of vecuronium (25 mu g/kg, bolus IV) to facilitate mechanical ventilation. After intubation, sheep were positioned in right lateral recumbency and mechanically ventilated with pure oxygen and zero end-expiratory pressure (ZEEP). After 60 minutes, 10 cm H2O of PEEP was applied for 20 minutes. Spiral computed tomography of the thorax was performed, and data were recorded for hemodynamic and gas exchange variables and indicators of respiratory mechanics after 15 (T-15), 30 (T-30), and 60 (T-60) minutes of ZEEP and after 20 minutes of PEEP (T-PEEP). Computed tomography images were analyzed to determine the extent of atelectasis before and after PEEP application.Results-At T-PEEP the volume of poorly aerated and atelectatic compartments was significantly smaller than at T-15, T-30, and T-60, which indicated that there was PEEP-induced alveolar recruitment and clearance of anesthesia-induced atelectasis. Arterial oxygenation and static respiratory system compliance were significantly improved by use of PEEPConclusions and Clinical Relevance-Pulmonary atelectasis can develop in anesthetized and mechanically ventilated sheep breathing pure oxygen; application of 10 cm H2O of PEEP significantly improved lung aeration and gas exchange. (Am J Vet Res 2010;71:567-874)