Urinary and renal oxygenation during dexmedetomidine infusion in critically ill adults with mechanistic insights from an ovine model.

PURPOSE:Examine effects of dexmedetomidine on bladder urinary oxygen tension (PuO2) in critically ill patients and delineate mechanisms in an ovine model. MATERIALS AND METHODS:In 12 critically ill patients: oxygen-sensing probe inserted in the bladder catheter and dexmedetomidine infusion at a mean (SD) rate of 0.9 ± 0.3 μg/kg/h for 24-h. In 9 sheep: implantation of flow probes around the renal and pulmonary arteries, and oxygen-sensing probes in the renal cortex, renal medulla and bladder catheter; dexmedetomidine infusion at 0.5 μg/kg/h for 4-h and 1.0 μg/kg/h for 4-h then 16 h observation. RESULTS:In patients, dexmedetomidine decreased bladder PuO2at 2 (-Δ11 (95% CI 7-16)mmHg), 8 (-Δ 7 (0.1-13)mmHg) and 24 h (-Δ 11 (0.4-21)mmHg). In sheep, dexmedetomidine at 1 μg/kg/h reduced renal medullary oxygenation (-Δ 19 (14-24)mmHg) and bladder PuO2 (-Δ 12 (7-17)mmHg). There was moderate correlation between renal medullary oxygenation and bladder PuO2; intraclass correlation co-efficient 0.59 (0.34-0.80). Reductions in renal medullary oxygenation were associated with reductions in blood pressure, cardiac output and renal blood flow (P < 0.01). CONCLUSIONS:Dexmedetomidine decreases PuO2in critically ill patients and in sheep. In sheep this reflects a decrease in renal medullary oxygenation, associated with reductions in cardiac output, blood pressure and renal blood flow.