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Electrical Therapy for Adult Advanced Life Support. ARC and NZRC Guideline 2010

The likelihood of defibrillation success decreases with time until definitive treatment (ie defibrillation) is initiated. Interruptions to external cardiac compression (eg. for rhythm assessment or pulse checks) should be minimised. However, good CPR may even increase the likelihood of defibrillation success. The results of clinical studies assessing the usefulness of a strategy providing a period of CPR before defibrillation rather than a strategy providing immediate defibrillation are not consistent. In two randomized controlled trials, a period of 1.5 to 3 minutes of CPR by EMS personnel before defibrillation did not improve return of spontaneous circulation (ROSC) or survival to hospital discharge in patients with out-of-hospital VF or pulseless ventricular tachycardia (VT), regardless of EMS response interval. One before and after study and another case series failed to demonstrate significant improvements in ROSC or survival to hospital discharge when a strategy of CPR before defibrillation (CPR first) was compared to a shock first strategy. In the Hayakawa study, the CPR first group showed a higher rate of favourable neurologic outcome 30 days and one year after cardiac arrest. One randomized controlled trial and one clinical trial with historic controls comparing CPR first versus shock first also found no overall difference in outcomes. However, in both studies, improvements in ROSC, survival to hospital discharge, neurologic outcome and one-year survival were observed in a subgroup of patients who received CPR first where the EMS response interval was greater than 4 to 5 minutes.