Elevated Cardiopulmonary Bypass Flow for Renal Protection in Cardiac Surgery: A Randomized Trial.

BACKGROUND: Acute kidney injury (AKI) is a common and severe complication after cardiac surgery with cardiopulmonary bypass (CPB). Experimental data suggest that increasing CPB flow beyond standard targets may improve renal oxygenation, but clinical evidence is limited. We hypothesized that increasing CPB flow would attenuate renal injury and improve organ perfusion. METHODS: In this single-center, randomized controlled trial, 89 adults undergoing elective cardiac surgery were allocated to either high-flow (2.9 L·min·m-2) or standard-flow (2.4 L·min·m-2) during CPB. Mean arterial pressure (MAP) was maintained at 60 to 80 mm Hg by use of norepinephrine. Primary outcomes were urine biomarkers of renal injury; N-acetyl-β-d-glucoseaminidase (NAG) and tissue inhibitor of metalloproteinase-2 × insulin-like growth factor binding protein-7 [TIMP-2 × IGFBP-7] levels at 60 minutes post-CPB. Additional outcomes included serum creatinine changes, AKI incidence, perioperative norepinephrine dose, and fluid balance. RESULTS: High-flow significantly reduced renal injury biomarkers compared to standard-flow, geometric mean ratio for NAG: 0.43; 95% confidence interval (CI), 0.26 to 0.70, P < .001, and [TIMP-2 × IGFBP-7]: 0.46; 95% CI, 0.30 to 0.73; P < .001. Median S-creatinine remained below baseline for the first three postoperative days in the high-flow group, and above baseline in the standard-flow group. AKI incidence was 16% (7/45) in the high-flow group vs 25% (11/44) in the standard-flow group, odds ratio 1.90; 95% CI, 0.64 to 5.60, P = .248. Norepinephrine doses were significantly reduced in the high-flow-group, both intraoperatively and up until 4 hours after CPB. There were no significant differences in fluid balance, bleeding, or adverse events. CONCLUSIONS: Increasing CPB flow by 20% reduced renal injury biomarkers and postoperative creatinine and improved early hemodynamic stability. Further large-scale, multicenter trials are required to validate these findings and determine patient subgroups most likely to benefit.