Epinephrine versus methoxamine in survival postventricular fibrillation and cardiopulmonary resuscitation in dogs

Previous studies have indicated that methoxamine (an α adrenergic receptor agonist) may provide an advantage compared to epinephrine (a mixed α and β adrenergic agonist) during cardiac arrest and CPR. To test this theory, we compared the effects of bolus injections of epinephrine vs. methoxamine on survival, hemo-dynamic variables, blood gases, and blood lactate concentrations during ventricular fibrillation and CPR in 12 dogs. Each dog underwent a 3-min fibrillatory arrest followed by 10 min of fibrillation and CPR, at which time the animals were defibrillated. Epinephrine (0.05 mg/kg, n = 6) or methoxamine (2 mg/kg, n = 6) was administered at the start of CPR. Both epinephrine and methoxamine produced identical survival rates (5/6) with no differences in coronary perfusion pressure gradients or blood gases (aortic, venous, or great cardiac venous pH, Pao2, or Paco2) during CPR. Also, there were no differences between the two study groups in myocardial lactate or oxygen extraction ratios during CPR. We conclude that in the dosages tested in our experimental model, epinephrine and methoxamine produce similar results in the variables which we measured.