Evaluating the Accuracy of Surrogate Markers for Identifying Opioid-Associated Out-of-Hospital Cardiac Arrests.

Abstract

Background: Previous studies have used emergency medical services (EMS) naloxone administration and EMS overdose impression as surrogate markers to identify opioid-associated (OA) out-of-hospital cardiac arrests (OA-OHCA). We evaluated the accuracy of these two surrogate markers using medical examiner post-mortem toxicology data in OHCA patients who died.

Methods: We conducted a retrospective cohort study of all adult (≥ 18) non-traumatic OHCA patients treated by Milwaukee County EMS between January 1^st,2015 to December 31^st, 2016. EMS naloxone administration and EMS impression of cardiac arrest etiology were used to classify expired patients into 2 groups: 1a) Received ≥ 1 Naloxone 1b) No Naloxone, and 2a) EMS-impression overdose, 2b) Not EMS-impression overdose. Milwaukee County Medical Examiner (MCME) opioid toxicology data was used as the reference standard and matched to EMS-treated OHCA patients that expired to determine the sensitivity (SN), specificity (SP), positive predictive value (PPV), and the negative predictive value (NPV) of both surrogate markers.

Results: 1,654 OHCA cases were included; 112 (6.8%) received ≥ 1 Naloxone and 1,542 (93.2%) received No Naloxone; 60 (3.6%) were EMS-impression overdose and 1,594 (96.4%) were not EMS-impression overdose. Of the 525 opioid-associated deaths in the MCME Drug-related Death Database, 150 (28.6%) were OA-OHCA cases treated by EMS. The SN, SP, PPV, and NPV for EMS naloxone administration was 39%,96%, 52%, and 94% respectively. The SN, SP, PPV, and NPV for EMS- impression overdose was 27%, 99%, 68%, and 93% respectively.

Conclusion: EMS naloxone administration and EMS- impression overdose had limited sensitivity for identifying OA- OHCA in expired patients in this large urban EMS system. Prehospital and public health researchers should identify improved methods for accurately classifying this OHCA subpopulation.