Effects of epidural and intravenous buprenorphine on halothane minimum alveolar anesthetic concentration and hemodynamic responses.

There is limited information regarding the effects of epidural or intravenous (i.v.) buprenorphine on minimum alveolar anesthetic concentration (MAC) of volatile anesthetic and hemodynamic responses to tracheal intubation and surgical incision. This study was conducted to find the effects of i.v. and epidural buprenorphine required for postoperative pain relief on halothane MAC and hemodynamic responses to tracheal intubation and surgical incision in 126 female patients. Patients were randomly assigned to the four groups: Group I received i.v. and epidural saline as a control; Group II was given buprenorphine 4 micrograms/kg i.v.; and Groups III and IV received buprenorphine 2 and 4 micrograms/kg epidurally, respectively. Groups II-IV were divided into the two subgroups according to the timing of administration, either at induction of anesthesia in the operating room (OR) (OR group) or 90 min before anesthetic induction in the ward (Ward group). Anesthesia was induced with only halothane in oxygen, and the trachea was intubated without other drugs. Halothane MAC was determined by logistic regression analysis and the Dixon up-and-down method. Halothane MAC in the seven study groups was as follows: 0.75% +/- 0.05% (mean +/- SE) in Group I; 0.49% +/- 0.03% and 0.59% +/- 0.04%, respectively, in Groups II OR and Ward; 0.65% +/- 0.003% and 0.49% +/- 0.07%, respectively, in Groups III OR and Ward; and 0.51% +/- 0.07% and 0.37% +/- 0.02%, respectively, in Groups IV OR and Ward. Halothane MAC decreased significantly (P < 0.05) in groups that received buprenorphine except Group III-OR compared with Group I. Systolic blood pressure did not change significantly in Groups II-OR and IV-OR after tracheal intubation and in Group III-Ward and IV-Ward after surgical incision but increased significantly (P < 0.05) in the remaining groups in response to noxious stimuli. Heart rate responses to tracheal intubation and surgical incision were similar to those in systolic blood pressure. These results indicate that preanesthetic administration of epidural or IV buprenorphine required for postoperative analgesia reduces halothane MAC and attenuates hemodynamic responses to tracheal intubation and surgical incision according to the dose, route, and timing of administration.