Halothane and Isoflurane Only Slightly Impair Arterial Oxygenation during One-lung Ventilation in Patients Undergoing Thoracotomy

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Abstract
Controversy exists as to whether the halogenated inhalation (IH) anesthetics impair arterial oxygenation during one-lung ventilation (1-LV). Accordingly, the authors have answered this question in 12 consenting patients who required 1-LV to facilitate the performance of thoracic surgery, by comparing arterial oxygenation during a prolonged period of IH anesthesia with arterial oxygenation during a prolonged period of intravenous (IV) anesthesia during stable 1-LV conditions. The patients were equally divided into halothane and isoflurane groups. Each patient in each IH anesthetic group underwent the following experimental sequence: step 1, two-lung ventilation (2-LV), 1 MAC IH anesthesia; step 2, 1-LV, 1 MAC IH anesthesia; step 3, 1-LV, iv anesthesia; step 4, 2-LV, iv anesthesia. Stable 1-LV conditions were proven by serial arterial blood gas measurement. Conversion from 2-LV to 1-LV during IH anesthesia (step 1 to step 2) caused a very large and significant decrease in PaO2 (from 484 .+-. 49 to 116 .+-. 61, and from 442 .+-. 58 to 232 .+-. 97 mmHg in the halothane and isoflurane groups, respectively) and increase in shunt (from 14 .+-. 4 to 44 .+-. 9, and from 19 .+-. 5 to 31 .+-. 8% in the halothane and isoflurane groups, respectively). Conversion from 1 MAC halothane anesthesia to iv anesthesia during 1-LV caused a slight but significant decrease in shunt (7 .+-. 2% of the cardiac output) and increase in PaOo2 (39 .+-. 29 mmHg), whereas conversion from 1 MAC isoflurane anesthesia to iv anesthesia caused a very slight and nonsignificant decrease in shunt (2 .+-. 2% of the cardiac output) and increase in PaO2 (13 .+-. 19 mmHg). Return to 2-LV (step 3 to step 4) caused a large and significant increase in PaO2 (from 155 .+-. 84 to 411 .+-. 101 mmHg, and from 245 .+-. 97 to 431 .+-. 104 mmHg in the halothane and isoflurane groups, respectively) and a large decrease in shunt (from 37 .+-. 9 to 20 .+-. 8, and from 36 .+-. 5 to 20 .+-. 7% in the halothane and isoflurane groups, respectively). The authors calculated that the atelectatic lung had hypoxic pulmonary vasoconstriction (HPV) and that the slight increase in shunt and decrease in PaO2 caused by changing from IH to iv anesthesia was consistent with the finding in animal studies that 1 MAC IH anesthesia causes a 20% inhibition of HPV. In view of the usual efficacy of nondependent lung CPAP, the authors conclude that IH anesthetic drugs are safe to use in patients undergoing 1-LV.