The Clinical Effectiveness of the Bispectral Index (BIS) To Reduce the Risk of Awareness for Elective Surgical Patients Undergoing General Anesthesia: A Prospective, Randomized, Double-Blind, Controlled Trial

Background: Unintended intra-operative awareness is a serious complication of general anesthesia. The incidence of such awareness has been reported to be about 0.1-0.6% of patients under general anesthesia. Reminiscence of what occurred during the operation can be felt by patients, which can be stressful and leave lasting mental suffering afterward the operation. Patients that experience unintended intra-operative awareness may have some combination of auditory function, tactual feeling, a sense of weakness, an inability to move, pain, and dread. Bispectral Index (BIS) monitoring has been shown to decrease awareness and boost recovery time from anesthesia. Aims of the study is to evaluate the clinical impact of BIS monitoring to reduce the incidence of awareness and its impact on hemodynamic parameters, drug consumption, the recovery time and the end-tidal concentration of volatile anesthetics in adult patients undergoing various types of surgery under general anesthesia.

Methods: The design adopted for this study is a prospective, randomized, doubleblind trial. The study involved fifty-nine adult patients with American Society of Anesthesiologists (ASA) physical status I-III, aged 18 to 72 years. 41 males and 18 females scheduled for different types of operations under general anesthesia participated in the study. Patients were randomized for inclusion in the BIS-handled anesthesia group (n=30), with the BIS value controlled between 40 and 60, which is considered convenient for surgical anesthesia; or the regular care (RC) group without BIS-control (n=29). A BIS sensor was placed on the forehead of patients. Hemodynamic specifications were recorded before induction of anesthesia and every five minutes during surgery until the removal of the endotracheal tube. The patients were interviewed by a blinded observer at 24-36 hours after operation through the use of a structured questionnaire. Two independent endpoint adjudication committees blinded to group identity assessed the interview results and identified the confirmed awareness cases.

Findings: There were no significant differences between the two groups in all the general characteristics of the patients. Regarding anesthetic time, the mean ± SD in the RC group was 76.6 ± 84.3 minutes, and 124.2 ± 124.4 minutes in the BIS group; the difference was not significant. Surgical time was 73.8 ± 85.8 minutes in the RC group and 116.4 ± 106.2 minutes in the BIS group; the difference was not significant. Of the total 59 patients 29 patients were assigned to the routine control group and 30 patients to the BIS group. No case of awareness was reported in the BIS-guided group but 4 reports (13.8%) in the control group (P=0.035), BISguided anesthesia decreased awareness by 13.8% (95% CI (1.3%-26.4%). The most common forms of awareness was auditory perceptions, tactile perception and the sense of paralysis.

There was a statistically significant difference in the mean dose of inhaled anesthetic agents between the RC group (0.029 ±0.008 %) and the BIS group (0.025 ± 0.009%), P=-0.023, which indicates that BIS monitoring could reduce the needed use of inhalation anesthesia. Regarding the opioid fentanyl there was also a significant difference in the used dose of fentanyl for the BIS group (115.56 ± 94.18 mcg and the RC group (77.76 ± 40.52 mcg), P=0.035.There was found to be a difference in the propofol dosage between the BIS group (474.07 ± 711.3 mg) and the RC group(230 ± 59.938 mg), P=0.235. It is clear that patients in the RC group had a lower dosage of propofol than patients in the BIS group, but the difference was not significant. Low doses of fentanyl and propofol may be one of the causes of awareness in the RC group. We found no significant differences in somatic responses of sweating, tearing, pupil dilation and coughing intra-operatively between BIS-monitored and RC patients. However, a significant reduction in intra-operational jerking was recorded for the favor of BIS group .The percentage of patients who experienced jerking movements intra-operatively was 27.6% in the RC group and 6.9% in the BIS group, P=0.037.

There were no statistically significant differences between the two study groups in any of the time measures under study which are: time from cessation of inhalational agents to eye opening; time to respond to commands; time to eye opening (either spontaneously or in response to command, time to first movement response; and time to extubation. The time to phonation for the RC group was 12.82 ± 6.11 minutes and only 10.21 ± 5.127 minutes for the BIS group, P=0.026, this occurs for the favor of BIS group.

There is a statistically significant difference between the two groups in the time to discharge from the PACU at 12.38 ± 4.989 minutes for the RC group and 9.23 ± 3.819 minutes for the BIS group, P=0.007. In other words, patients in the BIS-monitored group were discharged earlier from the Post Anesthetic Care Unit (PACU) than the RC patients.

Conclusions: BIS-guided anesthesia where the BIS score is kept between 40 and 60, reduced the risk of awareness compared to routine care. The main reason for the occurrence of awareness in the RC group could be due to a light general anesthetic. In addition, BIS monitoring reduces the usage of volatile anesthesia and the time of discharge from the Post Anesthetic Care Unit.


Aidah Alkaissi, Tasneem Tarayra and Abdelbaset Nazzal

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