The relationship between rewarming rate during cardiopulmonary bypass (CPB) and postoperative delirium (POD) in cardiac surgery remains unclear. This retrospective study aimed to evaluate whether rapid rewarming is associated with an increased risk of POD.

A total of 548 adult cardiac surgery patients (January 2021–December 2023) were enrolled. POD was identified through medical record review based on Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5)criteria or documented delirium symptoms combined with olanzapine use (serving as a surrogate marker). Rewarming rate was defined as the average temperature increase per minute from the lowest nasopharyngeal temperature during CPB to 36.5°C, calculated as (36.5°C − lowest temperature)/rewarming time (min). Multivariable logistic regression and ROC analysis were performed.

Rewarming rate was significantly higher in the POD group (n = 300) than the non-POD group (n = 248) (0.095 ± 0.044 vs 0.072 ± 0.034°C/min, p < 0.001). Olanzapine dosage (18.5 ± 8.2 mg vs 0 mg) and duration (4.2 ± 2.1 days vs 0 days) in the POD group showed significant positive correlations with rewarming rate (r = 0.887 and r = 0.814, respectively, both p < 0.01). Rewarming rate (OR = 1.782), red blood cell transfusion (OR = 1.456), CPB duration (OR = 1.023), and mean CVP (OR = 1.156) were identified as independent risk factors for POD (all p < 0.05). The predictive model achieved an AUC of 0.775 (95% CI: 0.736–0.814).

Rapid rewarming during CPB is associated with increased POD risk and may be a modifiable perioperative factor. Prospective studies with standardized POD screening are warranted to validate these findings.