Concerns have been raised about ventricular arrhythmias and myocardial dysfunction following epinephrine treatment in patients with cardiac arrest, and laboratory studies of vasopressin have demonstrated some beneficial effects in cardiopulmonary resuscitation (CPR). Wenzel and colleagues report on a study for the European Resuscitation Council comparing vasopressin and epinephrine in patients with cardiac arrest.

This multinational trial initially screened 5,967 adult patients with out-of-hospital cardiac arrest. After excluding patients who were successfully defibrillated without need for a vasopressor and patients with terminal illness, lack of intravenous access, or several other clinical variables, 1,186 patients remained in whom vasopressin and epinephrine could be compared. Patients needing vasopressor drugs during CPR were randomly assigned to receive 1 mg of epinephrine or 40 IU of vasopressin; the dose was repeated in three minutes if spontaneous circulation had not been restored. After two doses of the assigned study drug, an injection of epinephrine could be given at the discretion of the resuscitating physician (the median dose given was 5 mg).

There were no significant differences between the medications in overall rates of spontaneous circulation recovery (24.6 percent versus 28.0 percent), survival to hospital discharge (9.9 percent versus 9.9 percent), or good neurologic outcome in survivors (32.6 percent versus 34.8 percent). Patients with a witnessed cardiac arrest and those in whom CPR was begun within 10 minutes of arrest had improved chances of survival to hospital admission, as did patients who received amiodarone or fibrinolysis in the resuscitation regimen. The only subgroup with a significant difference in outcome between vasopressin and epinephrine represented patients with asystole as the presenting rhythm (44.5 percent of arrest patients overall). More patients with asystole who were treated with vasopressin survived to hospital discharge than those assigned to receive epinephrine. The discretionary dose of epinephrine helped improve outcomes in patients who were randomized to vasopressin but not in patients who had already received epinephrine.

The authors conclude that vasopressin and epinephrine have similar efficacy in patients with out-of-hospital cardiac arrest, and that vasopressin is advantageous in the subgroup of patients with asystole as a presenting rhythm.

editor’s note: The authors mention in their discussion of the study that the outcome data did not confirm earlier studies that showed an advantage to use of vasopressin in cardiac arrest patients with ventricular fibrillation and pulseless electrical activity. An accompanying editorial¹ by McIntyre speculates on the reasons that the survival advantage of vasopressin may be limited to patients with asystole. Epinephrine and other catecholamines appear to be less effective vasopressors in the hypoxic, acidotic cardiac environment of asystole. He notes that the increased myocardial oxygen consumption occurring with epinephrine may have harmful effects in patients with asystolic cardiac arrest.—B.Z.