Evidence of a heterogeneous tissue oxygenation: renal ischemia/reperfusion injury in a large animal model.

Renal ischemia that occurs intraoperatively during procedures requiring clamping of the renal artery (such as renal procurement for transplantation and partial nephrectomy for renal cancer) is known to have a significant impact on the viability of that kidney.1–5 Two major modifiable intraoperative variables known to affect renal function during ischemia are the length of ischemic time and the temperature of the kidney at which ischemia occurred. Greater length of renal ischemia is associated with subsequent worse recovery of renal function, whereas cooling of the kidney allows for longer exposure to ischemia.6–12 There remains much controversy as to the specific duration of ischemia that results in renal injury and at what point cold ischemia should be employed. Measurement of direct renal oxygenation intraoperatively during renal artery clamping has been explored to a small extent, with promising results in determining subsequent renal function.13,14 By exploiting the different spectral properties of oxygenated and de-oxygenated hemoglobin, it is possible to quantify the level of oxygenation in the blood by measuring the wavelengths reflected off the kidney. To better understand the dynamics of intraoperative renal ischemia and recovery of renal oxygenation during reperfusion, a visible reflectance imaging system (VRIS) was developed to measure renal oxygenation during renal artery clamping in both cooled and warm kidneys.