Association between postoperative nocturnal blood pressure rising and mortality in patients receiving cardiac surgery: a retrospective cohort study

Postoperative blood pressure (BP) patterns may provide prognostic information in cardiac surgery patients, yet their clinical significance remains unclear. We investigated the association between early postoperative nocturnal BP rising and mortality in this population. This retrospective cohort study used the MIMIC-IV database (2008–2019) including adult patients undergoing coronary artery bypass grafting (CABG) or valvular surgery. Patients with an intensive care unit (ICU) stay less than 24 h, insufficient BP records, or indeterminate ICU admission were excluded. Nocturnal BP rising was defined as nocturnal mean arterial pressure (MAP) exceeding diurnal MAP within the first 24 h postoperatively. Outcomes included 30-day, 90-day, and 1-year mortality. Restricted cubic splines, Kaplan–Meier survival curves, and Cox proportional hazards models were used to assess associations between nocturnal BP rising and mortality, adjusting for confounders. Subgroup and sensitivity analyses were also conducted to confirm consistency and robustness. A total of 6139 patients were included in this study. Among them, 1997 (32.5%) exhibited nocturnal BP rising. Patients with nocturnal BP rising experienced higher mortality rates at 90-day (3.3% vs. 2.0%) and at 1-year (5.9% vs. 3.9%). Adjusted Cox models revealed that nocturnal BP rising was statistically associated with 90-day (HR: 1.54, 95% CI: 1.11–2.12) and 1-year mortality (HR: 1.37, 95% CI: 1.08–1.74), but not 30-day mortality. In subgroup analysis, there was no significant interaction effect between nocturnal BP rising and mortality across different subgroups. After a series of sensitivity analyses, the association remained consistent. Early postoperative nocturnal BP rising is common and independently associated with an increased risk of medium- and long-term mortality after cardiac surgery.