Increasing CPR duration prior to first defibrillation does not improve return of spontaneous circulation or survival in a swine model of prolonged ventricular fibrillation.

INTRODUCTION: The optimum duration of cardiopulmonary resuscitation (CPR) prior to first rescue shock is unknown. Clinical trials have used 90 and 180 s. Neither of these durations may be optimal. We sought to determine the optimum duration of CPR prior to first defibrillation attempt and whether this varied depending on the duration of ventricular fibrillation (VF). In this porcine model of basic life support, our outcomes were rates of return of spontaneous circulation (ROSC), survival, and coronary perfusion pressure (CPP).
METHODS: We anesthetized and instrumented 45 swine and then induced VF. After 5 or 8 min of untreated VF, we randomized the swine to mechanical CPR for 90, 180, or 300 s. A single rescue shock (150 J biphasic) was then administered. If this shock failed, 2 min of mechanical CPR were completed prior to the next rescue shock. CPP was calculated for each 30s epoch. ROSC was defined as a blood pressure >80 mmHg sustained for 60s. Survival was defined as sustained ROSC for 20 min. Data were analyzed with descriptive statistics, Fisher's exact test, and ANOVA.
RESULTS: In the 5 min VF cohort, the rate of ROSC did not differ between the three groups (90 s: 25%; 180 s: 38%; 300 s: 38%, p>.05). Survival rates did not differ (90 s: 25%; 180 s: 25%; 300 s: 25%, p>0.05). In the 8 min VF cohort, no animals experienced ROSC or survival. CPP were calculated by 30s epoch and did not differ between the three groups (p>0.05). CPPs decline after 180 s of CPR.
CONCLUSIONS: ROSC and survival were equivalent regardless of VF duration and CPR duration. When CPR begins late, CPPs are low, stressing the importance of early CPR. We do not recommend 300 s of CPR unless a defibrillator is unavailable.