Comparison of recovery times by using bispectral index monitoring versus end-tidal agent concentration monitoring in patients undergoing inhalational general anaesthesia

Background and Aims: End-tidal anaesthetic gas concentration (ETAG) and bispectral index (BIS) are both used to monitor depth of anaesthesia. Maintaining an accurate depth of anaesthesia helps in early post-operative recovery. This study compared the recovery times from sevoflurane-nitrous oxide anaesthesia using ETAG monitoring with BIS monitoring. Methods: Four hundred and two patients undergoing elective surgeries under sevoflurane- nitrous oxide anaesthesia were enroled in this double blinded parallel group prospective randomised trial and allocated into two groups. The depth of anaesthesia was monitored using BIS in BIS group (n = 202) and end-tidal sevoflurane concentration (EtSevo) in ETAG group (n = 200). The time to extubation and recovery were compared between the groups. Parametric, non-parametric and categorical variables were compared using Student's 't' test, Wilcoxon's rank sum test and Chi-square test, respectively. Results: Time to extubation (min) [BIS group - 10, 5; ETAG group - 10, 5 (median, inter-quartile range, IQR), P = 0.32] and time to recovery (min) [BIS group - 14, 6; ETAG group - 13.5, 7 (median, IQR), P = 0.34] did not differ significantly between the two groups. The EtSevo concentration (vol%) was significantly higher in the BIS group at 5 min [BIS group - 1.2, 0.4; ETAG group - 1.0, 0.4 (median, IQR), P < 0.001], 30 min [BIS group - 1.1, 0.4; ETAG group - 1.0, 0.3 (median, IQR), P = 0.002] and 120 min [BIS group - 1.11 +/- 0.28; ETAG group - 0.96 +/- 0.27 (mean +/- standard deviation), P = 0.014] after induction of anaesthesia. Conclusions: BIS and ETAG monitoring are associated with comparable recovery profiles. ETAG monitoring is associated with significantly less sevoflurane consumption.