Bispectral index monitoring during isoflurane and sevoflurane anesthesia

The bispectral [BIS] index has previously been shown to be a quantifiable measure of the sedative and hypnotic effects of anesthetic drugs. This study was designed to test the hypothesis that the BIS monitoring would facilitate recovery from volatile anesthetics compared with standard clinical monitoring practices after ambulatory surgery. Eighty consenting patients undergoing laparoscopic cholecystectomies were randomly assigned to one of four treatment groups. After a standardized induction, anesthesia was maintained with isoflurane in combination with nitrous oxide, 65% and fentanyl 1.5 micro g/kg [Groups I and II]. Patients in Group III and IV, received sevoflurane in combination with nitrous oxide, 65% and fentanyl 1.5 micro g/kg. In the control groups [Group I and III], the anesthesiologists were blinded to the BIS value, and the volatile anesthetics were administered according to standard clinical practice to maintain vital signs within 20% of preoperative values. In Groups II and IV, the volatile anesthetics were titrated to maintain the BIS value of 50-60. Hemodynamic variables, the end-tidal isoflurane and sevoflurane concentrations and BIS values were recorded at 5-min intervals during the maintenance period. The volatile anesthetic usage and the times from discontinuation of anesthesia to verbal response, extubation, spontaneous eye opening, and orientation, PACU stay and time to tolerate fluid intake and home-readiness were recorded. During the operation, the BIS index values [mean +/- SD] were significantly lower in the control groups compared with the BIS-titrated groups [42 +/- 8 and 44 +/- 6 in Groups I and III vs. 55 +/- 4 and 57 +/- 5 in Groups II and IV, respectively]. During the maintenance period, the end-tidal concentrations of isoflurane and sevoflurane were significantly lower [P < 0.001] in the two BIS-titrated groups compared with the control groups [1 +/- 0.2% vs. 0.6 +/- 0.1% in Groups I and II and 1.5 +/- 0.3% vs. 1 +/- 0.2% in Groups III and IV, respectively. Compared with the control groups, the volatile anesthetic requirements [MAC-h] and the usage [ml] of isoflurane and sevoflurane were significantly lower in their respective BIS-titrated groups. The volatile anesthetic usage in the BIS-titrated groups was 38 and 33% lower [P < 0.05] compared with the control groups in patients receiving isoflurane and sevoflurane respectively. Times to verbal responsiveness, extubation, spontaneous eye opening, orientation, PACU stay and time to tolerate fluid intake were significantly shorter in the BIS-titrated groups compared with the control groups [P < 0.05]. However, there was no significant difference in times to achieve home readiness between BIS monitored groups and control groups. Titrating isoflurane or sevoflurane using the BIS monitor decreased their consumption and contributed to a faster emergence and recovery from anesthesia in outpatients undergoing laparoscopic cholecystectomies