Association between low Bispectral Index™ values during anesthesia maintenance and one-year mortality in older patients with different comorbidities: a retrospective cohort study.

Abstract

Purpose: We aimed to investigate the correlation between the duration of low Bispectral Index™ (BIS™) values and 1-year mortality in older patients, particularly in those with different comorbidities.

Methods: We conducted a retrospective cohort study of 5,927 older patients (≥ 65 yr of age) who underwent elective noncardiac surgery under general anesthesia with BIS monitoring between February 2015 and February 2022. We used univariable and multivariable Cox proportional hazard models to explore the associations between the cumulative duration of BIS values < 40 and postoperative 1-year mortality. We performed exploratory subgroup and interaction analyses to investigate whether any association with outcome differed in patients with multimorbidity as assessed by the Charlson comorbidity index (CCI).

Results: We included 5,927 patients undergoing elective noncardiac surgery, with a mean (standard deviation [SD]) age of 71 (5) yr. Among them, 2,234 (38%) patients with multimorbidity had a CCI ≥ 3, and 3,693 (62%) had CCI < 3. Postoperatively, 588/5,927 (10%) patients died within 1 year. After adjusting for covariates, multivariable Cox proportional hazard analysis showed that the cumulative duration of BIS < 40 was not significantly associated with 1-year mortality (adjusted hazard ratio, 1.07; 95% confidence interval [CI], 0.99 to 1.15; P = 0.08); this association remained stable among patients with multimorbidity (adjusted hazard ratio, 1.06; 95% CI, 0.96 to 1.16).

Conclusions: In this retrospective cohort study of 5,927 older patients, the cumulative duration of BIS < 40 was not significantly associated with 1-year mortality, especially in patients with multimorbidity.