[Pharmacotherapy of ventricular fibrillation. A prospective study in an emergency medical service]

Abstract

This prospective study investigated the effects of standard pharmacotherapy in out-of-hospital ventricular fibrillation (VF) after i.v. or endobronchial (e.b.) administration of epinephrine and lidocaine. METHODS. Only patients presenting with out-of-hospital VF were included in this study, whereby VF of noncardiac origin was excluded. Cardiopulmonary resuscitation (CPR) was performed according to the guidelines of the American Heart Association. Basic life support was initiated by Emergency Medical Service (EMS) technicians. The first step of advanced life support was immediate defibrillation by the EMS physician. Epinephrine was given in doses of 2.5 mg e.b. or 1.0 mg i.v. If indicated, patients received 200-500 mg lidocaine e.b. or 100 mg i.v. The course of CPR was tape-recorded and 2-3 blood samples were taken from each patient for drug monitoring. Plasma levels of epinephrine and lidocaine were measured by high-pressure liquid and gas chromatography, respectively, and then correlated to the course of CPR. RESULTS. Forty-seven patients presented VF on arrival of the EMS physician. Restoration of spontaneous circulation was achieved in 64% (Table 3), and 30% of the patients were discharged from hospital without major neurologic deficits. Immediate defibrillation before initiation of pharmacotherapy produced a success rate of 15.8%, whereas defibrillation after drug therapy was successful in 61.5% of cases. Following e.b. instillation of 2.5 mg epinephrine (Fig. 1), median peak concentrations of epinephrine (40.2, range 4.0-79.8 ng/ml) were reached after 3-4 min and plasma levels greater than or equal to 10 ng/ml were seen for 20 min. After i.v. injection of 1.0 mg epinephrine (Fig. 2) maximum concentrations (71.6, range 4.7-104.2 ng/ml) were measured after 1-2 min and plasma levels decreased below 10 ng/ml after 10 min. Following e.b. instillation of 400-500 mg lidocaine mean lidocaine concentrations within the therapeutic range (2-5 micrograms/ml) were reached after 4-5 min and remained within these limits for 20-30 min. Peak concentrations were obtained after 12 min. Doses of 200-320 mg lidocaine e.b. failed to achieve therapeutic plasma levels (Fig. 3). Regarding the pharmacodynamic aspects of drug therapy, 22.5% of the initial survivors were resuscitated from VF without therapeutic epinephrine, presenting with mean endogenous epinephrine concentrations of 7.1 ng/ml, 51.6% of patients were resuscitated after epinephrine therapy with plasma concentrations greater than 20 ng/ml. In only 1 case could a relationship be demonstrated between the administration of lidocaine and resuscitation success. CONCLUSION. In CPR, the e.b. administration of epinephrine and lidocaine is a reliable alternative to the i.v. injection route of these drugs. Recommended doses are 2.5 mg for epinephrine and 400-500 mg for lidocaine. Resuscitation from VF requires immediate epinephrine therapy if initial defibrillation is not successful. Lidocaine has no effect on resuscitation from VF and therefore should be used specifically for antiarrhythmic therapy after restoration of spontaneous circulation.