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 definitive.
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