Epinephrine arrhythmogenicity is enhanced by acute, but not chronic, aminophylline administration during halothane anesthesia in dogs.

The authors determined the effect of acute and chronic aminophylline treatment on the arrhythmogenicity of epinephrine during halothane anesthesia. The dose of epinephrine required to achieve an arrhythmia threshold (ADE) was determined in nine unpremedicated dogs anesthetized with halothane (1.5% v/v) in oxygen (A0). Aminophylline was then infused to achieve and sustain a therapeutic theophylline level (mean +/- SD) of 17 +/- 2 micrograms X ml-1 (A1), at which time the ADE was reassessed. The aminophylline infusion regimen was then adjusted to provide a supratherapeutic level of theophylline of 34 micrograms X ml-1 (A2) and the ADE was reassessed. In an additional seven dogs the ADE was assessed before and after 6 weeks of oral aminophylline treatment that yielded a plasma theophylline level of 18 +/- 3 micrograms X ml-1. The ADE was significantly (P less than 0.01) reduced from a basal value (mean +/- SD) of 2.63 +/- 0.97 micrograms X kg X -1 X min-1 to 1.39 +/- 0.47 in the A1 state. There was no further decrement in the ADE at the A2 state (1.17 +/- 0.36). The plasma epinephrine level at the arrhythmia threshold decreased commensurately from 50.7 +/- 40.2 ng X ml-1 (A0) to 20.0 +/- 7.9 and 19.2 +/- 7.6 in the A1 and A2 states, respectively (P less than 0.01). In contrast to these acute treatment experiments, neither the ADE (2.65 +/- 0.95 vs. 2.97 +/- 1.49 micrograms X kg-1 X min-1) nor the plasma epinephrine levels at the arrhythmia threshold (47.2 +/- 13.7 vs. 51.1 +/- 22.0 ng X ml-1) were different after chronic aminophylline treatment.(ABSTRACT TRUNCATED AT 250 WORDS)