Myocardial Epinephrine Sensitization with Subanesthetic Concentrations of Halothane in Dogs

The authors investigated myocardial epinephrine sensitization by subanesthetic concentrations of halothane. The dose-response relationship for the action of halothane was examined with etomidate plus varying subanesthetic concentrations of halothane in dogs. The arrhythmogenic threshold of epinephrine was decreased in a dose-dependent manner at end-tidal concentrations of halothane between 0.1 and 0.3%. At end-tidal halothane is greater than 0.3%, and no further reduction of arrhythmogenic threshold of epinephrine occurred. The plasma concentrations of epinephrine producing four or more premature ventricular contractions in 15 s were 201.3 +/- 34.3, 98.1 +/- 13.9, 60.3 +/- 8.63, 57.9 +/- 12.8, 54.5 +/- 8.61, and 53.9 +/- 4.86 ng/ml (mean +/- SEM), at 0, 0.1, 0.3, 0.5, 1.0, and 1.5% of halothane at end-tidal concentrations, respectively. The results suggest that in the presence of etomidate, halothane produces myocardial sensitization to epinephrine at subanesthetic concentrations as low as 0.1%. Increasing halothane to 0.3% produces a further reduction in the arrhythmogenic dose of epinephrine.