Purpose: The bispectral (BIS) index has been used to interpret electroencephalogram (EEG) recordings to predict the level of sedation and loss of consciousness in patients undergoing general anesthesia. It was the purpose of this project to assess the usefulness of BIS technology in determining the level of sedation in patients undergoing third molar extraction under conscious sedation.
Patients and methods: Twenty-five subjects undergoing third molar extraction in an outpatient setting were analyzed. The EEG activity was recorded continually during surgery using a microcomputer (Aspect-1050 Monitor; Aspect Co, Natick, MA) with real-time bispectral data obtained by EEG skin electrodes through a frontotemporal montage. The Observer's Assessment of Alertness and Sedation (OAA/S) scale was used to subjectively assess the level of sedation observed by the anesthetist before initiating the sedation procedure and then at 5-minute intervals until the end of the procedure. The BIS level was simultaneously recorded. The initial sedation was accomplished using a standard dose of midazolam (0.05 mg/kg) and fentanyl (1.5 microg/kg) followed by a 10- to 30-mg bolus of propofol until a level of sedation at which the patient's eyes were closed and he or she was responsive only to vigorous stimulation or repeated loud calling of their name (OAA/S level of 1 to 2). Local anesthesia was then administered. Additional doses of sedative medication (midazolam or propofol) were given during the procedure to maintain the desired level of sedation (an OAA/S level of 2 to 3). The time and dose of the drug given were recorded. The level of sedation based on a single anesthetist's interpretation (OAA/S) and the BIS readings were then compared.
Results: A strong positive relationship between the BIS index and OAA/S readings was found (P < .0001). Pairwise comparisons of mean BIS index and its corresponding OAA/S level were significantly different from each other (P < .003) except for OAA/S levels 2 and 3 (P = .367).
Conclusion: BIS technology offers an objective, ordinal means of assessing the depth of sedation. There was a strong relationship between the objective BIS values and subjective assessment (OAA/S scale) of the depth of anesthesia. This can be invaluable in providing an objective assessment of sedation in oral and maxillofacial surgery where it may be difficult to determine the level of sedation clinically.