Myocardial oxygen requirements during experimental cardiopulmonary resuscitation

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.

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.

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.

These findings suggest that endogenous sympathetic stimulation of the fibrillating heart results in high myocardial oxygen requirements during CPR.