Abstract
SUMMARY The effect of anesthesia with xylazine-guaifenesinketamine and maintained with isoflurane or sevoflurane on the arrhythmogenic dose of epinephrine (ADE) was measured in 8 horses. The hypothesis to be tested was that the ADE for sevoflurane would not be different than the ADE of isoflurane. When horses were at a stable plane (1.25 × minimal alveolar concentration [MAC]) of inhalant anesthesia, graded increasing concentrations (0.25, 0.5, 0.75, 1.0, 1.25, 1.5, 1.75, to a maximum of 2.0 µg/kg/min) of epinephrine were infused for 10 minutes or until 4 ventricular premature contractions (VPCs) or other serious arrhythmia occurred. The ADE was defined as the dose at which the above criteria were met or the highest dose administered. Base-apex electrocardiogram (ECG), heart rate (HR), direct arterial blood pressures, temperature, and arterial blood gases were monitored. The mean ADE for sevoflurane (4 horses = 1.31 ± 0.29, 4 horses >2.0 µg/kg/min) was not significantly different from the mean ADE for isoflurane (4 horses = 1.06 ± 0.52, 4 horses >2.0 µg/kg/min). Numerous arrhythmias were seen, and atrial fibrillation developed in 3 horses, but no horse had fatal ventricular fibrillation. Systolic pressure was significantly higher at ADE with sevoflurane than isoflurane. The dose of epinephrine required to produce significant ventricular arrhythmias (arrhythmogenic dose of epinephrine or ADE) has been used as a measure of the
Published Version
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