Association of Postoperative Cumulative Fluid Balance and Outcomes Following Elective Cardiac Surgery.

Abstract

The complexity of patients undergoing cardiac surgery underscores the need to improve understanding of the factors that augment or predict risks of adverse postoperative outcomes. Our study set out to determine the extent to which postoperative fluid imbalance is related to clinically important outcomes following elective cardiac surgery. In this retrospective cohort study, we studied 2557 elective coronary artery bypass graft (CABG) and/or valve surgery patients at an academic medical center from 2015 to 2020. We examined the relationship between cumulative fluid balance during intensive care unit (ICU) stay and subsequent clinical outcomes. We considered cumulative fluid balance as both a continuous and categorical variable based on cohort-based tertiles: negative (<less than ~500 mL negative), neutral (between ~500 mL negative and ~750 mL positive), or positive (more than ~750 mL positive). The primary outcome was a composite of 30-day mortality, ICU readmission, and postoperative hospital length of stay ≥30 days. The primary outcome occurred in 7.0% (n = 60), 2.3% (n = 20), and 9.3% (n = 79) of patients in the negative, neutral, and positive groups, respectively. In multivariable-adjusted analyses, cumulative fluid balance as a continuous variable demonstrated a U-shaped relationship with the primary outcome, with thresholds of significantly elevated risk observed at negative 1380 mL and positive 1700 mL. In multivariable-adjusted analyses of cumulative fluid balance as a categorical variable, patients who left the ICU with either negative (odds ratio 2.76 [95% confidence interval {CI}, 1.62-4.70]; P < .01) or positive cumulative fluid balance (3.53 [2.09-5.96]; P < .01) had higher risk for the primary outcome compared to those with a neutral cumulative fluid balance. A negative or positive cumulative fluid balance on the day of ICU discharge was associated with ~3 to 4 times greater odds of adverse postoperative outcomes, respectively, which was further elevated when fluid imbalance exceeded ~1.5 L. Our findings suggest that postoperative cumulative fluid balance in real-world practice, particularly for elective cardiac surgery patients, warrants greater attention.