Outcomes after out-of-hospital cardiac arrests by anaphylaxis: A nationwide population-based observational study.

Aim: The objective of this study was to focus on outcomes of anaphylaxis-associated out-of hospital cardiac arrest (OHCA) in non-cardiac cases.

Methods: All residents with OHCA due to non-cardiac cause in Japan from 2013 to 2015 were included for analysis. Propensity score matching and logistic regression analyses were used to assess outcome-related factors in anaphylaxis cases and non-anaphylaxis cases. The comparison group was comprised of non-anaphylaxis cases, which consisted of other cases of non-cardiac etiology.

Results: A total of 375,874 OHCA cases were included, of which 148,598 were due to non-cardiac cause. In these non-cardiac OHCA cases, 147 were due to anaphylaxis, with an annual incidence of 0.04 per 100,000. In the patients' characteristics, witnessed ratio, shockable rhythm, defibrillation by emergency medical services (EMS), and treatment with adrenaline by EMS were significantly greater in the anaphylaxis cases compared with the non-anaphylaxis cases. In anaphylaxis cases, the crude 1-month survival rate (32.7% versus 5.3%) and crude favorable neurological outcomes rate (24.5% versus 2.2%) were higher compared with non-anaphylaxis cases ( P  < 0.001). The differences in outcomes between the two types of cases were also marked after we adjusted these variables by propensity score matching. By logistic regression analyses, administration of a drug by EMS was negatively associated with good neurological outcomes (odds ratio, 0.27; 95% confidence interval, 0.09-0.87), but bystander cardiopulmonary resuscitation was positively associated with good neurological outcomes (odds ratio, 2.33; 95% confidence interval, 0.99-5.52).

Conclusion: Neurological outcome was markedly more favorable in cases with anaphylaxis than non-anaphylaxis cases. Further studies are needed to explain this result.