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

Abstract

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. 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. 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. 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.