A comparison of BIS recordings during propofol-based total intravenous anaesthesia and sevoflurane-based inhalational anaesthesia in obese patients

BACKGROUND: Intraoperative awareness is a rarely occurring phenomenon. Obesity is considered as one of the factors increasing the probability of intraoperative awareness due to problems with the dosing of anaesthetics. In a randomized prospective study we compared bispectral index (BIS) recordings during propofol-based total intravenous anaesthesia (TIVA) and sevoflurane-based inhalation anaesthesia in morbidly obese patients as a sign of possible intraoperative awareness. METHODS: 120 morbidly obese patients were randomly allocated into two subgroups: TIVA or SEVO. Propofol TIVA was performed following the Servin formula, while sevoflurane was administered based on the age of the patients. The physician administering anaesthesia was blinded to the BIS recordings while the evaluation of the depth of anaesthesia was conducted based on the clinical symptoms of adequate anaesthesia. BIS recordings were evaluated for periods of BIS > 60. Blinded structured interviews were conducted 2 hours after anaesthesia was administrated. RESULTS: The incidence of BIS > 60 occurred in 90% vs. 91.67% of patients while the mean duration of periods of BIS > 60 was 13.74 ± 21.74% vs. 14.21 ± 18.78% of the duration of anaesthesia in TIVA and SEVO groups, respectively ( P > 0.05). There was no correlation between the BMI value and the duration of elevated BIS values observed during anaesthesia in both studied methods of anaesthesia, nor between the total time of anaesthesia and the duration of elevated BIS values above 60 in this study. No patient complained of intraoperative awareness when asked in the post-operative period, probably due to the administration of midasolam. CONCLUSIONS: Although the incidence of BIS > 60 are very common in obese patients, true awareness during anaesthesia infrequent in this group of patients despite the type of anaesthesia, whether intravenous or inhalation.