Hemodynamic effects of repeated doses of epinephrine after prolonged cardiac arrest and CPR: preliminary observations in an animal model.

STUDY PURPOSE: To assess the hemodynamic response to repeated doses of epinephrine (EPI) in an animal model of prolonged cardiac arrest and CPR.

DESIGN: Basic laboratory investigation. Fourteen canines were subjected to electrically induced ventricular fibrillation (VF) followed by 7.5 min of VF without CPR.

INTERVENTIONS: After 7.5 min of VF, manual closed-chest CPR (80-100 compressions per minute, compression to ventilation ratio 8:1) was initiated. Countershocks were performed, recommended advanced cardiac life support drugs were given, and CPR was continued until restoration of spontaneous circulation (ROSC) or for 20 min. Epinephrine, 1 mg (approximately 0.04 mg kg(-1)), was administered when indicated and at recommended time intervals.

METHODS: Aortic and right atrial pressures were measured with micromanometer catheters before and after EPI, and CPR coronary perfusion pressure (CPP) was calculated (CPR diastolic aortic to right atrial pressure difference). Survival was defined as maintenance of ROSC for 30 min.

RESULTS: Countershocks after 7.5 min resulted in asystole in ten animals and persistant VF in four. In those animals successfully resuscitated (n = 3), the change in CPP was 21 +/- 11 mm Hg after the first dose of EPI. Only one animal required a second dose of EPI. The majority of the study group (n = 11) could not be resuscitated. The increase in CPP after EPI averaged only 3 +/- 2 mm Hg and subsequent doses produced no significant effect on CPP (2 +/- 4 mm Hg).

CONCLUSIONS: The hemodynamic response to the first dose of EPI determines if the critical CPP needed for ROSC and survival will occur. Repeat doses of EPI do not appear to improve CPP to a degree to affect clinically meaningful measures of outcome, i.e., successful countershock and survival.