Opioid-Associated vs Undifferentiated Out-of-Hospital Cardiac Arrest: Examining differences in outcomes and the relationship with Utstein variables.

BACKGROUND

The pathophysiology of out-of-hospital cardiac arrest (OHCA) due to opioid toxicity is different from other OHCAs. Our aims were to determine: (1) whether opioid-toxicity is associated with OHCA outcomes; and, (2) whether the relationship between Utstein variables and outcomes differ between those with opioid-associated (OA) and other OHCA.

METHODS

We analysed adult emergency medical services (EMS)-treated OHCAs from the British Columbia Cardiac Arrest Registry. Using post-mortem toxicological investigations, death certificates, and hospital-based diagnoses, we classified as OA-OHCA or "undifferentiated OHCA". We fit a multivariable logistic regression model to assess the association between OA-OHCA (versus undifferentiated OHCA) and favourable neurological outcome at hospital discharge. We then added pre-specified interaction terms to individual models for: sex, initial cardiac rhythm, bystander CPR, witnessed arrest, and location type.

RESULTS

Of 10,786 OHCAs: 1349 (13%) were OA-OHCA, of whom 331 (25%) were female, and the median age was 40 years (IQR 31-50); 9437 (87%) were undifferentiated, of whom 2910 (31%) were female, and the median age was 70 years (IQR 58-81). We did not detect an association between OA-OHCA (OR 1.02, 95% CI 0.77, 1.35) and survival with favourable neurological outcomes. Models adding interaction terms demonstrated statistically significant interactions for: sex (p=0.032), initial cardiac rhythm (p=0.024), and bystander-witnessed status (p=<0.001).

CONCLUSION

Overall, we did not detect an association between opioid toxicity and outcomes. In models with interaction terms, the relationship between Utstein and outcomes differed between opioid-associated and other OHCAs, highlighting the impact opioid-associated cases may have in observational OHCA analyses.