MYOCARDIAL OXYGEN REQUIREMENTS DURING EXPERIMENTAL CARDIOPULMONARY-RESUSCITATION

Objective: The aims were to determine myocardial oxygen requirements during cardiopulmonary resuscitation (CPR), and to test the hypothesis that endogenous catecholamines have a major effect on myocardial oxygen requirements in this setting. Methods: Myocardial oxygen consumption (MVO2) was measured during 20 minutes of CPR in eight anaesthetised dogs. Coronary blood flow was maintained at prearrest levels using an external pump to provide a permissive level of oxygen delivery during ventricular fibrillation. Oxygen content was measured in arterial and coronary sinus blood samples under prearrest conditions and at 5 min intervals during CPR. Four dogs were given propranolol (1 mg.kg-1) following the 5 min measurements. Results: MVO2 averaged 108.7(SEM 12.8)% of the initial prearrest values after 5 min CPR (n=8). After 10 min CPR, MVO2 fell to 53.8(13.3)% of the initial prearrest values in the subset of animals given propranolol after the 5 min measurements (n=4), but remained at prearrest levels in untreated animals (p<0.05 for an interactive effect between treatment and time). MVO2 subsequently tended to decrease with time in untreated animals, but remained a high percentage of prearrest values throughout the 20 min period Of CPR. Conclusions: These findings suggest that endogenous sympathetic stimulation of the fibrillating heart results in high myocardial oxygen requirements during CPR.