The American Heart Association highlights the stepwise nature of successful out-of-hospital resuscitation, framing it as a “chain of sur- vival” with 4 links: early access (alerting emergency medical services), early CPR, early defibrillation, and early ACLS (Figure 7).63 A study from the Ontario Prehospital Advanced Life Support (OPALS) Study Group determined that the odds
ratios for increased survival attributable to the presence of the first 3 links were 4.4, 3.7, and 3.4, respectively.64 Data supporting the fourth link, early ACLS, has been less defin- itive. Although a meta-analysis suggested that the odds ratio of survival from outpatient arrest by resuscitation with ACLS versus without ACLS was 2.3,65 the OPALS study found no improvement in outpatient survival with the addition of ACLS.64