Naloxone and Patient Outcomes in Out-of-Hospital Cardiac Arrests in California.

Importance: The incidence of opioid-associated out-of-hospital cardiac arrest (OA-OHCA) has grown from less than 1% of OHCA in 2000 to between 7% and 14% of OHCA in recent years; American Heart Association (AHA) protocols suggest that emergency medical service (EMS) clinicians consider naloxone in OA-OHCA. However, it is unknown whether naloxone improves survival in these patients or in patients with undifferentiated OHCA. Objective: To evaluate the association of naloxone with clinical outcomes in patients with undifferentiated OHCA. Design, Setting, and Participants: Retrospective cohort study of EMS-treated patients aged 18 or older who received EMS treatment for nontraumatic OHCA in 3 Northern California counties between 2015 and 2023. Data were analyzed using propensity score-based models from February to April 2024. Exposure: EMS administration of naloxone. Main Outcomes and Measures: The primary outcome was survival to hospital discharge; the secondary outcome was sustained return of spontaneous circulation (ROSC). Covariates included patient and cardiac arrest characteristics (eg, age, sex, nonshockable rhythm, any comorbidity, unwitnessed arrest, and EMS agency) and EMS clinician determination of OHCA cause as presumed drug-related. Results: Among 8195 patients (median [IQR] age, 65 [51-78] years; 5540 male [67.6%]; 1304 Asian, Native Hawaiian, or Pacific Islander [15.9%]; 1119 Black [13.7%]; 2538 White [31.0%]) with OHCA treated by 5 EMS agencies from 2015 to 2023, 715 (8.7%) were believed by treating clinicians to have drug-related OHCA. Naloxone was administered to 1165 patients (14.2%) and was associated with increased ROSC using both nearest neighbor propensity matching (absolute risk difference [ARD], 15.2%; 95% CI, 9.9%-20.6%) and inverse propensity-weighted regression adjustment (ARD, 11.8%; 95% CI, 7.3%-16.4%). Naloxone was also associated with increased survival to hospital discharge using both nearest neighbor propensity matching (ARD, 6.2%; 95% CI, 2.3%-10.0%) and inverse propensity-weighted regression adjustment (ARD, 3.9%; 95% CI, 1.1%-6.7%). The number needed to treat with naloxone was 9 for ROSC and 26 for survival to hospital discharge. In a regression model that assessed effect modification between naloxone and presumed drug-related OHCA, naloxone was associated with improved survival to hospital discharge in both the presumed drug-related OHCA (odds ratio [OR], 2.48; 95% CI, 1.34-4.58) and non-drug-related OHCA groups (OR, 1.35; 95% CI, 1.04-1.77). Conclusions and Relevance: In this retrospective cohort study, naloxone administration as part of EMS management of OHCA was associated with increased rates of ROSC and increased survival to hospital discharge when evaluated using propensity score-based models. Given the lack of clinical practice data on the efficacy of naloxone in OA-OHCA and OHCA in general, these findings support further evaluation of naloxone as part of cardiac arrest care.