Zero-Balance Ultrafiltration during Cardiopulmonary Bypass Is Associated with Decreased Urine Output

Zero-balance ultrafiltration (ZBUF) during cardiopulmonary bypass (CPB) has been purported to reduce pro-inflammatory mediators during cardiac surgery. However, its clinical benefit is equivocal and its effect on renal function unknown. The purpose of this study was to examine the effect of ZBUF on urine output in adult patients undergoing CPB. Following institutional review board approval, 98,953 records from a national registry of adult patients at 215 U.S. hospitals between January 2016 and September 2019 were reviewed. Groups were stratified according to ZBUF use. Anuric patients were excluded from the study as they were patients with missing data on urine output, ultrafiltration use, or ZBUF volume. The primary endpoint was intraoperative urine output normalized to body weight and procedure duration (total operative time). Final analysis of this endpoint was carried out using a linear mixed-effects regression model adjusting for patient and procedural characteristics, as well as practice patterns associated with surgeons and perfusionists. There was a significant 16.1% reduction in median urine output for ZBUF patients (.94 [.54, 1.47] mL/kg/h) vs. the non-ZBUF group (1.12 [.70,-1.73] mL/kg/h), p < .001. After statistically adjusting for patient and procedural characteristics, each liter of ZBUF volume was associated with an estimated change in intraoperative urine output of -.03 mL/kg/h (95% CI: [-.04 to -.02], p < .001). The median ZBUF volume was 1,550 [1,000, 2,600] mL, and when ZBUF was used, conventional ultrafiltration (CUF) was more likely to be used as well (88.4% vs. 44.8%, p < .001). ZBUF patients had median asanguineous volume and crystalloid cardioplegia nearly two times more than non-ZBUF patients, and had slightly higher red blood cell transfusions (17.6% vs. 16.3%, p < .05). The application of ZBUF during CPB was associated with patients having lower urine output and significantly higher use of CUF. Further research is required to determine if these results are reproducible in prospective clinical studies.