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 (N2O)-opioid general anesthesia or combined epidural-general anesthesia; patients were randomly assigned to active intraoperative warming or routine thermal care. Measurements and Main Results: VO2 was measured by indirect calorimetry preoperatively (T-0), immediately postoperatively (T-1), and 60 to 90 minutes later (T-2). For all patients, VO2 was 57 +/- 45% (mean +/- SD) greater at T-1 than at T-0 (p < 0.05). After isoflurane-N2O-opioid general anesthesia, VO2 increased 15 +/- 20% in normothermic patients (core temperature, 36.4 +/- 0.2 degrees C) compared with 69 +/- 52% in hypothermic patients (35.0 +/- 0.5 degrees C). After combined epidural-general anesthesia, VO2 increased 86 +/- 39% on emergence in normothermic (36.4 +/- 0.2 degrees C) and 58 +/- 11% in hypothermic (35.1 +/- 0.4 degrees C) patients. Conclusions: Total-body VO2 was increased in the immediate postoperative period. After general anesthesia, the magnitude of the increase in VO2 was significantly less in normothermic patients than in hypothermic patients. After combined epidural-general anesthesia, VO2 was increased in normothermic and in hypothermic patients.