LAUSR

OBJECTIVES Poor medullary oxygenation is implicated in the evolution of acute kidney injury. The authors sought to determine if increasing systemic flow and mean arterial pressure could improve urine oxygen tension (PuO2) measured in the bladder, a surrogate of kidney medullary oxygenation, in patients undergoing on-pump cardiac surgery. DESIGN Randomized crossover study. SETTING University-affiliated hospital. PARTICIPANTS Twenty adult patients undergoing cardiopulmonary bypass (CPB) with expected cross-clamp time of >60 minutes and estimated glomerular filtration rate of >30 mL/min/1.73m2. INTERVENTIONS Sequential 20-minute periods of 2 interventions: Intervention H ("High") or Intervention N ("Normal"). The order of interventions was determined by randomization. Intervention H: targeted CPB flow 3.0 L/min/m2 and mean arterial pressure (MAP) 80 mmHg. Intervention N: targeted CPB flow 2.4 L/min/m2 and MAP 65 mmHg. MEASUREMENTS AND MAIN RESULTS PuO2 was measured by an oxygen sensor introduced into the bladder via a urinary catheter. Clear separation was achieved in CPB flow and MAP between intervention periods (p < 0.001 for group-time interaction). PuO2 during Intervention H was higher than during Intervention N (p < 0.001 for group-time interaction). After 17 minutes, PuO2 was statistically higher in Intervention H at each time point. There were no differences in markers of hemolysis between interventions. CONCLUSIONS PuO2 was higher when systemic flow and MAP were increased during CPB. These findings suggest that PuO2 is responsive to changes in hemodynamics and that higher flow and pressure may improve medullary oxygenation.