Epinephrine-induced arrhythmias: effects of thoracic epidural anesthesia and vagotomy during enflurane anesthesia in rabbits

For evaluating the effects of thoracic epidural anesthesia, with or without bilateral vagotomy, epinephrine-induced arrhythmias were studied in 31 rabbits anesthetized with 1 minimum alveolar concentration of enflurane. We divided the rabbits into 5 groups: Group I (epidural saline as control group; n=6), Group II (epidural lidocaine without vagotomy; n=6), Group III (intravenous lidocaine; n=7), Group IV (epidural saline with vagotomy; n=6), and Group V (epidural lidocaine with vagotomy; n=6). Using logdose protocol, epinephrine was infused at an initial rate of 0.67microg/kg/min and increased by Exp[0.4] until arrhythmias occurred; if arrhythmias occurred at any of these doses, a smaller dose, divided by Exp[0.2], was tested. Arrhythmic dose of epinephrine was defined as the smallest infusion rate needed to produce four or more arrhythmias within 15 sec during epinephrine infusion. Arrhythmic dose of epinephrine and its plasma concentration in epidural lidocaine group were significantly higher than control (p<0.05). Similarity of results was also noted amongst the intravenous lidocaine group, vagotomy only group, and vagotomized epidural lidocaine group with respect to the control. These results suggest that thoracic epidural anesthesia raises the threshold for enflurane-epinephrine induced arrhythmias in rabbits and that this effect is eliminated by bilateral vagotomy.