Adjusting cardiopulmonary bypass flow or arterial pressure to maintain renal medullary oxygen

Cardiopulmonary bypass leads to renal hypoperfusion, resulting in medullary hypoxia and acute kidney injury. In instrumented sheep subjected to cardiopulmonary bypass, Lankadeva et al. found that medullary perfusion and tissue oxygen tension (PO₂) was maintained at low-dose metaraminol, an α₁-adrenoceptor agonist, because low-dose metaraminol increased perfusion pressure without affecting renal vascular resistance. Lankadeva et al. developed a fiber-optic catheter to measure bladder urine PO₂. Urine PO₂ tracks medullary PO₂, and low urine PO₂ predicts acute kidney injury. Adjusting cardiopulmonary bypass to maintain urine PO₂ may help avoid acute kidney injury.