Out-of-hospital cardiac arrest : a study on factors associated with cardiopulmonary resuscitation, early defibrillation and survival

Abstract

Cardiac disease is the most common cause of mortality in the Western World and the majority of these cardiac deaths is due to out-of-hospital cardiac arrest (OHCA). In Sweden, an estimated 5,000-10,000 people suffer an OHCA annually. The objective of this thesis is to study patient characteristics and survival in patients with OHCA, to explore the importance of pre-hospital factors and in-hospital factors and to investigate the benefits of an early defibrillation program.

Methods and results: Most data in this thesis are based on patient material collected by the Swedish Cardiac Arrest Register. Other data come from case records from patients admitted alive and time measurements from the emergency dispatch centre and defibrillators.

In Study I, 969 cases of OHCA in Stockholm and 398 cases of OHCA in Göteborg between January 2000 and June 2001 were compared. The two groups were similar in terms of age, gender and various factors at resuscitation. All pre-hospital time intervals were longer in Stockholm and the proportion of patients found in ventricular fibrillation (VF) was 18% compared to 31% in Göteborg (p<0.0001). 1-month survival was significantly lower in Stockholm (2.5% vs. 6.8%; p<0.001).

To evaluate the relative roles of pre-hospital and in-hospital factors, 1,542 OHCA in Stockholm and 546 in Göteborg between January 2000 and June 2002 were investigated in Study II. Survival after OHCA was again lower in Stockholm (3.3% vs. 6.1%; p=0.01). Significantly longer time intervals and a lower proportion of VF OHCA were found in Stockholm compared to Göteborg. Patient demography, medical history, in-hospital investigations and interventions as well as in-hospital mortality (78% in Göteborg, 80% in Stockholm) did not differ between the two groups.

To describe temporal trends in 1-month survival after OHCA in Sweden, 38,646 patients between 1992-2005 were investigated in Study III. The proportion of patients surviving to hospital admission increased from 15.3% in 1992 to 21.7% in 2005 (p for trend<0.0001). The corresponding figures for patients being alive after 1 month were 4.8% and 7.3% (p for trend<0.0001). Factors related to the improved survival were an increase in crew-witnessed cases from 9% in 1992 to 15% in 2005 (p for trend <0.0001) and, to a lesser degree, more frequent bystander CPR which rose from 31% in 1992 to 50% in 2005 (p for trend <0.0001).

In Study IV, specially trained fire-fighters equipped with automated external defibrillators were dispatched in addition to traditional medical responders to suspected cases of OHCA in Stockholm from December 2005 to December 2006. 863 OHCA patients were enrolled during the intervention and 657 OHCA from 2004 served as historical controls. Among dual dispatches, fire-fighters assisted with CPR in 94% of cases and arrived first on scene in 36% of cases. The median time from call to arrival of first responder decreased from 7.5 to 7.1 minutes (p=0.004). 1-month survival rose from 4.4% to 6.8% (p=0.047; adjusted OR: 1.6; 95% C.I: 0.9-2.9). 1-month survival among witnessed cases of OHCA rose from 5.7% to 9.7% (p=0.029; adjusted OR: 2.0; 95% C.I: 1.1-3.7).

Conclusions: Survival after OHCA was significantly lower in Stockholm than in Göteborg during 2000-2002 and this difference was associated with pre-hospital factors only rather than with in-hospital factors or patient characteristics. Survival after OHCA in Sweden increased significantly from 1992 to 2005. The increase was particularly marked among patients found with a shockable rhythm and is associated with an increase in the proportion of crew-witnessed cases and, to a lesser degree, an increase in bystander CPR. A dual dispatch early defibrillation program in Stockholm has decreased response times and is likely to have improved survival in patients with OHCA. This increase in survival is believed to be associated with improved CPR and shortened time intervals.