Hormonal and Osmoregulatory Responses in Intraoperative High-Volume Diuresis During Off-Pump Coronary Artery Bypass Grafting: An Exploratory Cohort Study

<b>Background</b>: Intraoperative high-volume diuresis is a frequent but underrecognized complication in cardiac surgery, potentially leading to hypovolemia, electrolyte imbalances, and hemodynamic instability. Its mechanisms remain poorly defined. This study investigated the hormonal and biochemical regulation of urine output during off-pump coronary artery bypass grafting (OPCABG). <b>Methods</b>: For this single-center observational cohort study, 70 patients undergoing OPCABG were enrolled (diuresis: urine output > 5 mL/kg/h, n = 38; normal, n = 32). Hormonal markers and osmolality parameters were measured perioperatively. Logistic regression was used to identify independent predictors, and receiver operating characteristic (ROC) curves was used to assess model performance. <b>Results</b>: Intraoperative high-volume diuresis occurred in 54.2% of patients. Logistic regression identified a low Body Mass Index (BMI) (OR 0.72, <i>p</i> = 0.002), reduced albumin (OR 0.75, <i>p</i> = 0.014), and lower copeptin (OR 0.43, <i>p</i> = 0.037) as independent predictors (AUC 0.855). Perioperatively, NT-proBNPT0 rose in both groups, aldosterone increased only in the diuresis group, and copeptin showed a slight nonsignificant rise. Plasma sodium was higher in cases of diuresis at the end of surgery (148.4 vs. 144.9 mmol/L, <i>p</i> < 0.001). Despite greater urine output and fluid infusion, the rates of intensive care unit (ICU) admission and hospital stays were similar. <b>Conclusions</b>: Intraoperative high-volume diuresis in OPCABG is strongly associated with reduced antidiuretic hormone activity, suggesting a partial central diabetes insipidus-like mechanism. Although not affecting short-term outcomes, it posed challenges for intraoperative fluid and electrolyte management. Larger multicenter studies are needed for validation.