Association between intraoperative BIS variability and postoperative recovery quality in adults undergoing laparoscopic cholecystectomy: a prospective observational study

The bispectral index (BIS) is widely used for intraoperative monitoring of anesthetic depth; however, the clinical relevance of its dynamic behavior — particularly intraoperative variability — remains poorly understood. This study aimed to investigate the association between intraoperative BIS variability during the maintenance phase and postoperative recovery quality in adult patients undergoing elective laparoscopic cholecystectomy. In this single-center, prospective observational study, 126 adult patients (ASA I–III, aged 18–65 years) were enrolled. BIS data were recorded continuously at one-minute intervals, and variability was quantified using standard deviation (SD) and coefficient of variation (CV) during the maintenance phase. The primary outcome was the change in Quality of Recovery-15 score from baseline to postoperative day 1 (ΔQoR-15). Secondary outcomes included postoperative cognitive status assessed by the Nursing Delirium Screening Scale (Nu-DESC) and pain intensity by the numerical rating scale (NRS). Associations were evaluated using Spearman correlation analysis with 95% bootstrap confidence intervals, and multivariable linear regression models were additionally constructed to assess the independence of observed associations. Greater intraoperative BIS variability was weakly-to-moderately associated with poorer postoperative recovery quality (a greater decline in QoR-15): both BIS SD and BIS CV showed significant inverse correlations with ΔQoR-15 (SD: rho = − 0.253 [95% CI − 0.414, − 0.093], p = 0.004; CV: rho = − 0.240 [95% CI − 0.404, − 0.069], p = 0.007), and these associations remained significant after multivariable adjustment (SD: B = − 1.131 [95% CI − 1.906, − 0.355], p = 0.005; CV: B = − 0.478 [95% CI − 0.808, − 0.148], p = 0.005). In contrast, mean BIS was not consistently associated with ΔQoR-15 across the two models. No significant associations were observed between BIS variability and secondary outcomes (Nu-DESC, NRS). Intraoperative BIS variability during the maintenance phase was independently associated with postoperative recovery quality, whereas mean BIS was not consistently associated with ΔQoR-15 across regression models. These associations were weak-to-moderate in magnitude, and the underlying mechanisms remain speculative and were not directly evaluated in this study; whether the observed differences correspond to clinically meaningful improvements in recovery remains unclear. These findings suggest that the dynamic characteristics of BIS may carry independent prognostic information beyond mean anesthetic depth, a hypothesis warranting confirmation in larger, interventional study designs. ClinicalTrials.gov, NCT07454629. Registered retrospectively on 18 February 2026; patient recruitment had begun on 1 January 2026.