Epidemiology, treatment and outcome of out-of-hospital cardiac arrest
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Introduction: Every year in the Western world, emergency medical system (EMS) personnel attempt to resuscitate approximately 500,000 patients who experience out of the hospital cardiac arrest (OHCA). Reported incidences and outcomes numbers of OHCA show substantial variations. System and quality differences in the chain of survival and post resuscitation care may contribute to these variations. This thesis aims to update our knowledge about incidence and outcomes of OHCA in an area, which previously have reported high survival rates after OHCA.
Aims: The specific aims of this thesis are to present current epidemiology, outcomes and factors linked to survival in adult patients after OHCA, to examine the relationship between the angiotensin-converting enzyme (ACE) genotype and the return of spontaneous circulation (ROSC), study the use of therapeutic hypothermia (TH) after OHCA, estimate the life years saved by resuscitation efforts and present a calculation of the overall mortality risk after hospital discharge in OHCA survivors.
Methods: In paper I, we accessed a prospectively collected Utstein template database to identify all resuscitation attempts in patients with OHCA of cardiac origin and compared the outcomes during two periods (2001–2005 vs. 2006- 2008). In paper II, we performed a prospective observational study of all OHCAs of cardiac origin between 2007 and 2010. The ACE genotype was identified and used together with the Utstein template parameters to examine the relationship between ROSC and the ACE genotype. In paper III, we conducted a retrospective observational study of OHCA patients admitted to the ICU from 2004 to 2008 and examined the factors predicting the use of TH and survival. Paper IV was a retrospective observational study of long term survival of OHCA patients between 2002 and 2011 discharged from hospital. We calculated the potential life years saved, the standardised mortality rates (SMR) and reported the causes of death after hospital discharge.
Results: In paper I, we found that the overall survival to discharge increased from 18% to 25% and in witnessed OHCA with shockable rhythm from 37% to 52%. There were no significant differences between the two time periods regarding age, sex distribution, OHCA location, proportion of shockable rhythms and ROSC rate. In paper II, we measured the ACE gene polymorphism distribution in OHCA patients to be similar to the general population, but no correlation to ROSC was found. In paper III, we found that TH was used in 70% of all unconsciousness OHCA patients. Witnessed arrest, bystander CPR, shockable rhythm and cardiac origin, were all positive predictors of TH use and survival. Increasing age, and within a subgroup female gender, predicted a lower utilisation of TH and lower survival. In paper IV, we found the mean number of potential life years saved per patient to be 23 years. The overall SMR in the study cohort was 2.3, and cardiac disease was the prominent cause of late deaths.
Conclusions: Overall, we found good outcome to be achievable in every fourth resuscitation attempt and in every second resuscitation attempt when patients have a shockable rhythm. No significant association between the ACE gene polymorphism and ROSC was demonstrated. TH was used in the majority of OHCA patients who were admitted to the ICU, with an observed underutilisation in some subgroups. The resuscitation of OHCA victims lead to a significant long-term benefit with respect to the number of life years saved. Cardiac disease was the main cause of death after hospital discharge. The reasons for overall improved outcomes are probably multi-factorial and related to improvements in all links of the chain of survival.