LAUSR

Abstract Background Circadian rhythm involved with physiology has been reported to affect pharmacokinetics or pharmacodynamics. We hypothesized that circadian variations in physiology disturb anesthesia and eventually affect recovery after anesthesia. Methods A retrospective cohort study initially included 107,406 patients (1 June 2016–6 June 2021). Patients were classified into morning or afternoon surgery groups. The primary outcome was daytime variation in PACU (post-anesthesia care unit) recovery time and Steward score. Inverse probability weighting (IPW) approach based on propensity score and univariable/multivariable linear regression were used to estimate this outcome. Results Of 28,074 patients, 13,418 (48%) patients underwent morning surgeries, and 14,656 (52%) patients underwent afternoon surgeries. LOWESS curves and IPW illustrated daytime variation in PACU recovery time and Steward score. Before adjustment, compared to morning surgery group, afternoon surgery group had less PACU recovery time (median [interquartile range], 57 [46, 70] vs. 54 [43, 66], p < 0.001) and a higher Steward score (5.62 [5.61, 5.63] vs. 5.66 [5.65, 5.67], p < 0.001). After adjustment, compared to morning surgery group, afternoon surgery group had less PACU recovery time (58 [46, 70] vs. 54 [43, 66], p < 0.001). In multivariable linear regression, morning surgery is statistically associated with an increased PACU recovery time (coefficient, −3.20; 95% confidence interval, −3.55 to −2.86). Conclusion Among non-cardiac surgeries, daytime variation might affect recovery after general anesthesia. These findings indicate that the timing of surgery improves recovery after general anesthesia, with afternoon surgery providing protection. KEY MESSAGES In this retrospective cohort study of 28,074 participants, the afternoon surgery group has a higher Steward score than the morning surgery group. In multivariable linear regression, morning surgery is statistically associated with an increased PACU recovery time. Among non-cardiac surgeries, daytime variation affects the recovery after general anesthesia, with afternoon surgery providing protection.