Postoperative blood pressure variability as a risk factor for postoperative delirium in the patients receiving cardiac surgery

Background: Delirium is one of the most common neurological complications after cardiac surgery. The purpose of our study was to assess the relationship between perioperative blood pressure variability (BPV) and postoperative delirium (POD) in the patients after cardiac surgery. Methods : Adult patients received cardiac surgery and stayed in Cardiovascular Intensive Care Unit (ICU) for more than 24h after surgery during the study period between June 2019 and December 2022 were included in this study. Baseline characteristics, perioperative hemodynamic variables and postoperative laboratory results of the cardiac patients were collected and analyzed. Perioperative BPV was quantified by calculating the standard deviation (SD) and average real variability (ARV) of blood pressure. Assessment of delirium was based on the mental status of the patients and CAM-positive. The relationship between perioperative BPV and POD was analyzed by LASSO and logistic regression using R (R package, 4.3.2). Results: The incidence of POD was 15.0% (324/2164) in the patients receiving cardiac surgery, and the average day for POD occurred at day 3 after surgery. Patients with delirium had markedly lower levels of intraoperative mean blood pressure (BP_mean, P=0.015) and BP variability (BP_arv, P<0.001) as well as postoperative mean blood pressure within 24h (PM_IBPm_24h_mean, P=0.003) when compared to those patients without delirium. Whereas, postoperative ARV for systolic blood pressure (PM_IBPs_24h_arv, 8.64 [7.32, 10.2] vs. 7.91 [6.57, 9.43] mmHg, P<0.001), diastolic blood pressure (PM_IBPd_24h_arv, 4.00 [3.17, 4.83] vs. 3.77 [3.11, 4.60] mmHg, P=0.014) and mean blood pressure (PM_IBPm_24h_arv, 5.23 [4.46, 6.19] vs. 4.94 [4.11, 5.94] mmHg, P=0.001) at 24h was significantly higher in the patients with POD than those without. LASSO regression and further logistic regression revealed that intraoperative BP_arv (OR:0.92, 95%CI: 0.89-0.96, P<0.001), PM_CVPm_24h_mean (mean central venous pressure at 24h postoperatively, OR:1.05, 95%CI: 1.00-1.10, P=0.048) and PM_IBPs_24h_arv (OR:1.17, 95%CI: 1.06-1.30, P=0.002) were independent risk factors for POD. Conclusions : Postoperatively high BPV exposure rather than hypotension contributed to the occurrence of POD in the patients after cardiac surgery. Maintaining a relatively stable blood pressure after surgery might be beneficial in reducing the incidence of POD in the patients receiving cardiac surgery.