Association between preoperative hydration and cardiac surgery-associated acute kidney injury: a prospective observational study

BACKGROUND: Cardiac surgery associated acute kidney injury (CSA-AKI) is a common and serious complication following cardiac surgery with cardiopulmonary bypass (CPB), associated with prolonged hospitalization, increased costs, and higher mortality rates. Pathophysiological reasons and preventive strategies remain limited. Preoperative hydration and restriction of fluid fasting represent potentially modifiable factors, yet their association with postoperative CSA-AKI remains poorly understood. OBJECTIVE: To explore the association between preoperative oral hydration and CSA-AKI in patients undergoing elective cardiac surgery with CPB. DESIGN, SETTING, AND PARTICIPANTS: Prospective, single centre, observational hypothesis-generating study. Preoperative hydration surrogate was estimated based on patient self-reporting of fluid intake between admission and surgery. ROC analysis yielded a Youden Index-derived cut-off of 51.5 ml/h to stratify patients into low and high intake groups. The cut-off was derived within the study sample for exploratory stratification. MAIN OUTCOMES AND MEASURES: Primary endpoint was incidence of CSA-AKI within seven postoperative days, defined according to KIDIGO creatinine criteria. Secondary endpoints included incidence of renal replacement therapy (RRT), postoperative renal function parameters, intensive care unit (ICU) and hospital length of stay (LOS), 30-day mortality, and postoperative complications. Secondary endpoints were considered exploratory. RESULTS: Of the 92 patients analysed, 16,3% (15/92) of patients developed postoperative CSA-AKI. Using a data-derived expoloratory threshold of 51.5 ml/h, patients with lower preoperative fluid intake had a higher incidence of CSA-AKI thank patients with higher intake (33.3% [13/39]) vs. (3.8% [2/53]) (p < 0.001) respectively. RRT requirement was higher in the low-intake group (17.9% [7/39] vs. 0% [0/53]). The interval from last oral intake to induction of anaesthesia was significantly longer in the low-intake group (14.6 ± 5.1 vs. 11.5 ± 4.9, p = 0.004). CONCLUSIONS: Lower preoperative fluid intake was associated with higher observed rates of postoperative rates of CSA-AKI after applying a data-derived threshold. These exploratory data-driven findings and thresholds require prospective validation studies.