Effects of Increased Cardiopulmonary Bypass Pump Flow on Renal Filtration, Perfusion, Oxygenation, and Tubular Injury in Cardiac Surgical Patients: A Randomized Controlled Trial.

backgroundCardiac surgery with cardiopulmonary bypass (CPB) is associated with impaired renal oxygenation and acute kidney injury. The authors investigated whether an amount higher than their standard blood flow during CPB could improve renal blood flow, the oxygen demand-supply relationship, and function and attenuate tubular injury.

methodsAfter ethical approval and informed consent, 36 adult patients undergoing cardiac surgery received either high flow (2.9 l · min -1 · m -2 , n = 19) or standard flow (2.4 l · min -1 · m -2 , n = 17) during CPB in this randomized, nonblinded, parallell-arm study. Systemic hemodynamics and renal variables were measured before and during CPB. Glomerular filtration rate was measured by infusion clearance of iohexol and renal blood flow by infusion clearance of para-aminohippuric acid, corrected for renal extraction of para-aminohippuric acid, using a renal vein catheter. Renal oxygen demand-supply relationship was estimated from renal oxygen extraction and tubular injury assessed by urinary N -acetyl-β- d -glucosaminidase.

resultsDuring CPB, high flow led to a larger increase in systemic oxygen delivery (100 [95% CI, 60 to 141] vs. 31 [1.9 to 65] ml · min -1 · m -2 ]; between-group P < 0.001; effect size Cohen's dz , 0.59) and target mean arterial pressure was maintained at a lower norepinephrine dose (0.03 [-0.01 to 0.06] µg · kg -1 · min -1 ] vs. 0.10 [0.02 to 0.19] µg · kg -1 · min -1 ; P = 0.048; Cohen's dz , 0.62) compared with standard flow. There were no differences in renal blood flow or oxygen extraction between groups. Glomerular filtration rate increased during high-flow CPB (6.4 [1.9 to 10.9] ml · min -1 · 1.73 m -2 ), but not in the standard-flow group (-2.3 [-10.9 to 6.2] ml · min -1 · 1.73 m -2 ; between-group P = 0.044; Cohen's dz , 0.66). The peak urinary excretion of N -acetyl-β- d -glucosaminidase was 1.42 (0.87 to 3.6) versus 3.74 (1.5 to 7.7) units/µmol creatinine in the high-flow and standard-flow groups, respectively ( P = 0.049). No perfusion-related adverse events were seen in either group.

conclusionsA 20% higher-than-standard CPB flow during cardiac surgery improved renal function, whereas no change in renal blood flow or oxygen demand-supply relationship could be detected. Higher CPB flow was associated with a less pronounced tubular injury marker release compared with standard flow.