Propofol, but not thiopentone or etomidate, enhances isoflurane-induced coronary vasodilatation in dogs

Abstract

Purpose: To test the hypothesis that thiopentone, propofol, and etomidate alter the coronary vascular effects of abruptly administered isoflurane. Methods: Dogs (n = 6) received inspired isoflurane 5% in the presence of thiopentone (20 mg·kg-1 induction dose and 20 mg·kg-1·hr-1 infusion), propofol (5 mg·kg-1 induction dose and 40 mg·kg-1·hr-1 infusion), etomidate (2 mg·kg-1 induction dose and 5 mg·kg-1·hr-1 infusion), or isoflurane (1.0 MAC) anaesthesia in a random fashion. Haemodynamics were assessed in the conscious state, during baseline anaesthesia, and at 30 sec intervals for five minutes after beginning isoflurane 5%. Results: Rapidly administered isoflurane caused greater (P < 0.05) reductions in coronary vascular resistance in thiopentone- or propofol- than in isoflurane-anaesthetized dogs. Isoflurane produced greater (P < 0.05) increases in the ratio of coronary blood flow velocity to pressure- work index (an index of myocardial oxygen consumption; + 109 ± 19% during isoflurane alone vs + 182 ± 27% change from baseline during propofol and isoflurane) consistent with relatively greater direct coronary vasodilatation during baseline propofol than during baseline isoflurane anaesthesia. Isoflurane caused larger increases in coronary blood flow velocity in dogs anaesthetized with etomidate concomitant with higher coronary perfusion pressure and pressure-work index than in those anaesthetized with isoflurane alone. Conclusions: The results suggest that thiopentone, propofol, and etomidate each uniquely modify the coronary vascular responses to abrupt administration of high inspired concentrations of isoflurane in chronically instrumented dogs.