Comparative accuracy of continuous electronic urine output monitoring in the post-cardiac surgery intensive care unit

Acute kidney injury (AKI) is a serious complication following coronary artery bypass grafting (CABG) and is clinically identified by changes in serum creatinine and urine output (UO). Currently, UO is typically monitored via visual inspection (VI), a method with limited precision. This prospective observational study evaluated the measurement accuracy of a continuous electronic UO monitoring system (Device) compared to VI, using graduated cylinder (GC) measurements as the gold standard. Hourly UO was measured in 52 post-CABG patients in a cardiac ICU (Guilan University of Medical Sciences, Rasht, Iran). For each patient, UO was recorded hourly across all three methods over a 6-hour period, resulting in 936 total measurements (312 per method). Statistical agreement was assessed using Lin’s concordance correlation coefficient (CCC), intraclass correlation coefficients (ICC), and Bland–Altman plots, with analyses adjusted for repeated-measures clustering. The Device demonstrated excellent agreement with the GC (CCC = 0.997; ICC = 0.997), significantly outperforming the VI method (CCC = 0.858; ICC = 0.859). Bland–Altman analysis revealed minimal systematic bias for the Device (mean bias = 4.4 ml; 95% LoA: 0.1 to 8.7 ml) compared to the GC, whereas VI showed notable overestimation (mean bias = 31.2 ml; 95% LoA: -18.2 to 80.7 ml). These results indicate that the electronic monitoring system offers significantly higher accuracy than visual inspection for real-time UO recording in post-CABG patients.