Do the kidneys contribute to propofol elimination?

BACKGROUND Propofol is mainly metabolized in the liver, but extrahepatic clearance may also be important since systemic propofol clearance exceeds hepatic clearance. Recent reports suggest that the kidneys contribute to propofol elimination in humans and here we investigated renal elimination of propofol in a controlled animal study. METHODS Seventeen swine were anaesthetized with 5% isoflurane induction and 2% isoflurane maintenance. After a left subcostal incision, the left kidney and renal pedicle were exposed by an approach via the retroperitoneum and the renal vein was identified for blood sampling. Propofol was then administered via the right jugular vein at a rate of 2 mg kg(-1) h(-1). After 120 min of pseudo-steady-state infusion of propofol (Baseline 1), cardiac output (CO) was increased by continuous infusion of dobutamine for 30 min (high-CO state). Thirty minutes after stopping dobutamine (Baseline 2), CO was decreased by bolus administration of propranolol (low-CO state). Blood samples were collected simultaneously from the renal vein (direct puncture) and the femoral artery at Baseline 1, in the high-CO state, at Baseline 2, and in the low-CO state. RESULTS There was no significant difference in propofol concentration between femoral arterial and renal venous blood in all states. The propofol concentration significantly decreased with increased CO, but renal extraction was not observed in any state. CONCLUSIONS The kidneys are a minor site of propofol elimination in a swine model.