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Arterial Oxygenation during One-lung Ventilation: A Comparison of Enflurane and Isoflurane

Background Because maintaining arterial oxygenation (PAO2) during one-lung ventilation (OLV) can be a clinical problem, it is useful to be aware of factors that influence PaO2 in this situation and are under the control of the anesthesiologist. It is unknown whether, among the commonly used volatile anesthetic agents, one is associated with higher PaO2 levels. Clinical studies suggest that isoflurane provides superior PaO2 during OLV than does halothane. These have not been compared to enflurane. The authors studied PaO2 and hemodynamics during OLV with 1 MAC enflurane versus 1 MAC isoflurane. Methods Twenty-eight adults who had prolonged periods of OLV anesthesia with minimal trauma to the nonventilated lung (thoracoscopic or esophageal surgery) were studied in a crossover design. Patients were randomized to two groups: Group 1 received 1 MAC enflurane in oxygen from induction until after the first 30 min of OLV, then were switched to 1 MAC isoflurane. In group 2, the order of the anesthetics was reversed. Results Isoflurane was associated with higher PaO2 values during OLV (P < 0.0001). Mean PaO2 (plus/minus SD) after 30 min OLV isoflurane was 231 (plus/minus 125) mmHg versus 184 (plus/minus 106) mmHg after 30 min OLV enflurane. The difference in Pa sub O2 between the two anesthetics was most marked in the patients with the highest PaO2 during OLV: PaO2 isoflurane - PaO2 enflurane alpha PaO2 isoflurane (r = 0.65, P < 0.001). There were no other significant differences between anesthetic gases in the measured hemodynamic or respiratory variables. In the subgroup of patients with pulmonary artery catheters (n = 7), PaO sub 2 correlated with cardiac output during OLV for both anesthetics (r = 0.81, P < 0.001). Conclusions During OLV, the PaO2 values with 1 MAC isoflurane were greater than those with enflurane. The dependence of Pa sub O2 on cardiac output does not support the hypothesis that an increase in cardiac output will cause a decrease in hypoxic pulmonary vasoconstriction and a decrease in PaO2 during OLV.