Influence of isoflurane on renal and intestinal vascular responses to stress

Renal and intestinal vasoconstrictor responses elicited by either hypothalamic defence alarm area activation or stimulation of somatic and visceral afferents were studied in 17 cats. In part I, the circulatory adjustments during 2% (end-tidal) isoflurane plus 70% nitrous oxide in oxygen were compared with a medium-dose fentanyl in 70% nitrous oxide-oxygen sequence which was supplemented by diazepam. In part II, three end-tidal concentrations of isoflurane (1.4%, 2% and 3%) plus nitrous oxide in oxygen were evaluated before and after pre-treatment with droperidol 200 micrograms kg-1. During fentanyl-diazepam anaesthesia, intense vasoconstrictor responses with associated decreases in renal and intestinal blood flows were observed. Isoflurane 2% counteracted this reflex vasoconstriction, particularly in the renal vascular bed. The pressor and vasoconstrictor responses were suppressed by isoflurane in a dose-dependent fashion. After the administration of droperidol, the vascular beds were unaffected by noxious stimulation. It is concluded that isoflurane blunts stress-related vasoconstriction in a dose-dependent fashion, especially in the renal, but also in the intestinal, circulation. Droperidol adds to the vasodilatory effect of isoflurane.