Prognostic value of postoperative proteinuria in cardiac surgery: A pilot study

Background: Proteinuria is a non-specific marker of inflammation that may reflect the glomerular component of systemic capillary leak. The objective of this pilot study was to determine if postoperative proteinuria is associated with adverse outcomes following cardiac surgery with cardiopulmonary bypass. Methods: Eligible patients were in dividuals undergoing cardiac surgery with cardiopulmonary bypass who did not have severe pre-existing renal dysfunction. Urine was collected after induction of anesthesia (baseline) and two to four hours after arrival to the intensive care unit (ICU). Proteinuria was measured as random protein creatinine ratio in g·mol^-1. Adverse events were defined a priori as prolonged ICU stay (≥ 90th percentile) and organ dysfunction. The relationship between proteinuria and adverse events was assessed by bivariate (Chi-square or Fisher's exact tests) and multivariable (multiple logistic regression) analyses. Results: The study included 197 (of 243 eligible) patients. Postoperative proteinuria (protein creatinine ratio ≥ 30 g·mol^-1) was associated with prolonged (≥ four days) ICU stay [odds ratio (OR) 7.0; 95% confidence interval (CI) 2.8-17.1] and organ dysfunction (OR 3.9; CI 1.9-8.1). After adjustment for confounders, proteinuria was associated with a 3.2-fold increase in the odds of both prolonged ICU stay (CI 1.1-9.7) and organ dysfunction (CI 1.4-7.0). Conclusions: Proteinuria two to four hours after cardiac surgery with cardiopulmonary bypass may be a useful marker for systemic capillary leak and adverse postoperative events. Large prospective studies are needed to confirm these findings.