Cognitive impairment is a common neurologic complication after cardiac surgery with cardiopulmonary bypass (CPB). This study evaluated postoperative cognitive function to determine predictors of cognitive dysfunction, including intraoperative cerebral regional tissue oxygen saturation (rSO₂).

A prospective observational cohort study.

At a single academic tertiary-care center.

A total of 60 adults undergoing cardiac surgery with CPB from January to August 2021.

None.

All patients underwent Mini-Mental State Examination (MMSE) and quantified electroencephalography (qEEG) 1 day before cardiac surgery, 7 days postoperatively (POD7), and POD60. Intraoperative cerebral rSO₂ was monitored continuously. For MMSE, no significant decrease in MMSE score was found on POD7 versus preoperatively (p = 0.09), but POD60 scores showed significant improvement compared with both preoperative (p = 0.02) and POD7 scores (p < 0.001). On qEEG, relative theta power on POD7 was increased versus preoperatively (p < 0.001), but it was decreased on POD60 (POD7 versus POD60, p < 0.001), and was close to preoperative data (p > 0.99). Baseline rSO₂ was an independent factor for postoperative MMSE. Both baseline and mean rSO₂ showed a significant influence in postoperative relative theta activity, whereas mean rSO₂ was the only predictor for the theta-gamma ratio (p = 0.04).

The MMSE in patients undergoing CPB declined at POD7 and recovered by POD60. Lower baseline rSO₂ indicated a higher potential for MMSE decline at POD60. Inferior intraoperative mean rSO₂ was related to higher postoperative relative theta activity and theta-gamma ratio, implying subclinical or further cognitive impairment.