Renal Hemodynamics and Oxygenation during Experimental Cardiopulmonary Bypass in Sheep Under Total Intravenous Anesthesia

Renal medullary hypoxia may contribute to the pathophysiology of acute kidney injury, including that associated with cardiac surgery requiring cardiopulmonary bypass (CPB). When performed under volatile (isoflurane) anesthesia in sheep, CPB causes renal medullary hypoxia. There is evidence that total intravenous anesthesia (TIVA) may preserve renal perfusion and renal oxygen delivery better than volatile anesthesia. Therefore, we assessed the effects of CPB on renal perfusion and oxygenation in sheep under propofol/fentanyl-based TIVA. Sheep (n = 5) were chronically instrumented for measurement of whole renal blood flow and cortical and medullary perfusion and oxygenation. Five days later, these variables were monitored under TIVA using propofol and fentanyl and then on CPB at a pump flow of 80 mL kg^-1min^-1 and target mean arterial pressure of 70 mmHg. Under anesthesia, prior to CPB, renal blood flow was preserved under TIVA (mean difference ± standard deviation from conscious state: -16 ± 14%). However, during CPB renal blood flow was reduced (-55 ± 13%), and renal medullary tissue became hypoxic (-20 ± 13 mmHg versus conscious sheep). We conclude that renal perfusion and medullary oxygenation are well preserved during TIVA before CPB. However, CPB under TIVA leads to renal medullary hypoxia, of a similar magnitude to that we observed previously under volatile (isoflurane) anesthesia. Thus, use of propofol/fentanyl-based TIVA may not be a useful strategy to avoid renal medullary hypoxia during CPB.