Background:
Cardiac surgery with cardiopulmonary bypass (CPB) is associated with impaired renal oxygenation and acute kidney injury. We investigated whether a higher than our standard blood flow during CPB could improve renal blood flow, oxygen demand/supply relationship, function and attenuate tubular injury.
Methods:
After ethical approval and informed consent, 36 adult patients undergoing cardiac surgery received either high-flow (2.9 L/min/m2, n=19) or standard-flow (2.4 L/min/m2, n=17) during CPB in this randomized, non-blinded, 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.
Results:
During CPB, high-flow lead to a larger increase in systemic oxygen delivery (100 ml/min/m2, 95% CI [60;141], vs 31[1.9;65], 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 µg/kg/min [-0.01;0.06] vs 0.10 [0.02;0.19], 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 ml/min/1.73m2 [1.9;10.9]), but not in the standard-flow group (-2.3 [-10.9;6.2], between group p=0.044, Cohen´s dz 0.66). The peak urinary excretion of N-acetyl-β-D-glucosaminidase was 1.42 units/µmol creatinine [0.87,3.6] vs 3.74 [1.5,7.7] in the high-flow and standard-flow groups, respectively (p=0.049). No perfusion-related adverse events were seen in either group.
Conclusions:
A 20% higher than standard CPB flow during cardiac surgery improved renal function while 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.