Total-body oxygen consumption after isoflurane anesthesia: Effects of mild hypothermia and combined epidural-general anesthesia

Study Objectives: To determine the effects of epidural anesthesia and avoidance of intraoperative heat loss on the increase in total-body oxygen consumption in the immediate postoperative period after major intraabdominal surgery. Design: Prospective, randomized (with regard to temperature management) study. Setting: University medical center. Patients: 24 ASA physical status I, II, and III adults. Interventions: All patients received either isoflurane-nitrous oxide (N 2O)-opioid general anesthesia or combined epidural-general anesthesia; patients were randomly assigned to active intraoperative warming or routine thermal care. Measurements and Main Results: VO 2 was measured by indirect calorimetry preoperatively (T 0), immediately postoperatively (T 1), and 60 to 90 minutes later (T 2). For all patients, VO 2 was 57 ± 45% (mean ± SD) greater at T 1 than at T 0 ( p < 0.05). After isoflurane-N 2O-opioid general anesthesia, VO 2 increased 15 ± 20% in normothermic patients (core temperature, 36.4 ± 0.2 °C) compared with 69 ± 52% in hypothermic patients (35.0 ± 0.5 °C). After combined epidural-general anesthesia, VO 2 increased 86 ± 39% on emergence in normothermic (36.4 ± 0.2 °C) and 58 ± 11% in hypothermic (35.1 ± 0.4 °C) patients. Conclusions: Total-body VO 2 was increased in the immediate postoperative period. After general anesthesia, the magnitude of the increase in VO 2 was significantly less in normothermic patients than in hypothermic patients. After combined epidural-general anesthesia, VO 2 was increased in normothermic and in hypothermic patients.