Does the Use of Electroencephalographic Bispectral Index or Auditory Evoked Potential Index Monitoring Facilitate Recovery after Desflurane Anesthesia in the Ambulatory Setting?
Authors: White Paul F. , Ma Hong , Tang Jun , Wender Ronald H. , Sloninsky Alexander , Kariger Robert 
Published: March 2004

Background
Analogous to the Bispectral Index (BIS) monitor, the auditory evoked potential monitor provides an electroencephalographic-derived index (AAI), which is alleged to correlate with the central nervous system depressant effects of anesthetic drugs. This clinical study was designed to test the hypothesis that intraoperative cerebral monitoring guided by either the BIS or the AAI value would facilitate recovery from general anesthesia compared with standard clinical monitoring practices alone in the ambulatory setting.

Methods
Sixty consenting outpatients undergoing gynecologic laparoscopic surgery were randomly assigned to one of three study groups: (1) control (standard practice), (2) BIS guided, or (3) AAI guided. Anesthesia was induced with 1.5-2.5 mg/kg propofol and 1-1.5 microg/kg fentanyl given intravenously. Desflurane, 3%, in combination with 60% nitrous oxide in oxygen was administered for maintenance of general anesthesia. In the control group, the inspired desflurane concentration was varied based on standard clinical signs. In the BIS- and AAI-guided groups, the inspired desflurane concentrations were titrated to maintain BIS and AAI values in targeted ranges of 50-60 and 15-25, respectively. BIS and AAI values, hemodynamic variables, and the end-tidal desflurane concentration were recorded at 5-min intervals during the maintenance period. The emergence times and recovery times to achieve specific clinical endpoints were recorded at 1- to 10-min intervals. The White fast-track and modified Aldrete recovery scores were assessed on arrival in the PACU, and the quality of recovery score was evaluated at the time of discharge home.

Results
A positive correlation was found between the AAI and BIS values during the maintenance period. The average BIS and AAI values (mean +/- SD) during the maintenance period were significantly lower in the control group (BIS, 41 +/- 10; AAI, 11 +/- 6) compared with the BIS-guided (BIS, 57 +/- 14; AAI, +/- 11) and AAI-guided (BIS, 55 +/- 12; AAI, 20 +/- 10) groups. The end-tidal desflurane concentration was significantly reduced in the BIS-guided (2.7 +/- 0.9%) and AAI-guided (2.6 +/- 0.9%) groups compared with the control group (3.6 +/- 1.5%). The awakening (eye-opening) and discharge times were significantly shorter in the BIS-guided (7 +/- 3 and 132 +/- 39 min, respectively) and AAI-guided (6 +/- 2 and 128 +/- 39 min, respectively) groups compared with the control group (9 +/- 4 and 195 +/- 57 min, respectively). More importantly, the median [range] quality of recovery scores was significantly higher in the BIS-guided (18 [17-18]) and AAI-guided (18 [17-18]) groups when compared with the control group (16 [10-18]).

Conclusion
Compared with standard anesthesia monitoring practice, adjunctive use of auditory evoked potential and BIS monitoring can improve titration of desflurane during general anesthesia, leading to an improved recovery profile after ambulatory surgery.