Bystander CPR Technique and Outcomes for Cardiac Arrest With and Without Opioid Toxicity.

Importance: Previous studies support bystander provision of chest compression-only cardiopulmonary resuscitation (CC-CPR) for out-of-hospital cardiac arrest (OHCA). However, it is unknown whether OHCA secondary to opioid toxicity may benefit from chest compression plus ventilation CPR (CCV-CPR). Objective: To examine the association between bystander CPR technique and outcomes among both opioid-associated OHCA (OA-OHCA) and otherwise undifferentiated OHCA. Design, Setting, and Participants: This cohort study (performed from August 1, 2023, to December 31, 2024) analyzed cases of adult emergency medical services-treated OHCA that occurred from December 1, 2014, to March 31, 2020, as identified through the British Columbia Cardiac Arrest Registry. Exposures: Cases were classified as OA-OHCA based on positive postmortem toxicologic investigations, death certificates, or opioid-specific hospital-based diagnoses. All other cases were classified as undifferentiated OHCA. Main Outcomes and Measures: Favorable neurologic outcome at hospital discharge (cerebral performance category ≤2). A multivariable Utstein-adjusted logistic regression model of complete cases was used to assess the association between bystander CPR technique (CC-CPR [reference] vs both CCV-CPR and no CPR individually) with outcomes. An interaction term between the OA-OHCA and bystander CPR technique was used to estimate associations among OA-OHCA and undifferentiated OHCA cases separately. Results: The study included 10 923 OHCAs. After removing 24 cases only treated with ventilatory support, there were 1343 OA-OHCAs (median [IQR] patient age, 40 [31-50] years; 1015 [76%] male) and 9556 undifferentiated OHCAs (median [IQR] patient age, 70 [58-81] years; 6636 (69%) male). In the OA-OHCA group, bystander CCV-CPR was associated with an increased odds of a favorable neurologic outcome (adjusted odds ratio [AOR], 2.85; 95% CI, 1.21-6.75) when compared with CC-CPR. No association was detected with favorable neurologic outcome (AOR, 1.52; 95% CI, 0.82-2.82) when no CPR was compared with CC-CPR. Among undifferentiated OHCAs, no association was detected with a favorable neurologic outcome (AOR, 1.16; 95% CI, 0.80-1.67) when CCV-CPR was compared with CC-CPR. No CPR was associated with a decreased odds of a favorable neurologic outcome (AOR, 0.69; 95% CI, 0.55-0.87) when compared with CC-CPR. The interaction term was statistically significant (P for interaction = .04). Conclusions and Relevance: In this cohort study of OHCA, bystander CCV-CPR (compared with CC-CPR) was associated with improved outcomes in opioid-associated OHCA; however, this association was not observed among undifferentiated cardiac arrests. These results suggest that the optimal bystander CPR technique for OA-OHCA and undifferentiated OHCA may differ and that ventilations may improve outcomes in OA-OHCA resuscitation.