Systemic haemodynamic, renal perfusion and renal oxygenation responses to changes in inspired oxygen fraction during total intravenous or volatile anaesthesia

Background: Anaesthesia-induced changes in renal perfusion are dependent on the choice of anaesthetic agent. However, the effects of varying inspired oxygen fraction (FiO₂) on renal perfusion and oxygenation during TIVA (propofol + fentanyl) or volatile anaesthesia (VA; isoflurane) are unknown. Methods: In 16 Merino ewes, we surgically implanted a renal artery flow probe and laser-Doppler and oxygen-sensing probes in the renal medulla and cortex. We compared the systemic and renal effects of graded alterations in FiO₂ (0.21, 0.40, 0.60, and 1.0) during TIVA or VA and compared the changes with those in the non-anaesthetised state. Results: Compared with the non-anaesthetised state, TIVA and VA decreased renal blood flow (−50% vs −75%), renal oxygen delivery (−50% vs −80%), and renal cortical (−40% vs −60%) and medullary perfusion (−50% vs −75%). At an FiO₂ of 0.21, both anaesthetic regimens induced similar reductions in cortical (−58 vs −65%) and medullary (−37% vs −38%) oxygenation. At higher concentrations of FiO₂, renal blood flow and renal tissue perfusion were not changed, but intrarenal oxygenation improved similarly under TIVA and VA. In particular, at an FiO₂ of ≥0.40 and ≤0.60, cortical and medullary oxygen tension were similar to the non-anaesthetised state. Conclusions: Irrespective of FiO₂, TIVA decreased renal and intrarenal perfusion less than VA, but at low FiO₂ concentrations both led to equivalent reductions in renal cortical and medullary oxygenation. However, with FiO₂ between 0.40 and 0.60 during TIVA or VA, both cortical and medullary oxygenation was maintained at normal physiological levels.