Heightened mortality risk after a non‐fatal opioid overdose: Risk factors for mortality in the week following emergency treatment

Abstract Aims To measure all‐cause mortality risk after an ambulance‐attended non‐fatal opioid overdose and associations with number of days following attendance, and individual and clinical characteristics. Design A prospective observational study. Setting Oslo, Norway. Participants Patients treated with naloxone for opioid overdose by Oslo Emergency Services between 1 June 2014 and 31 December 2018. Measurements Medical records were linked to the national Cause of Death Registry (1 June 2014–31 December 2019). Crude mortality rates (CMR) and incidence risk ratios (IRR) with 95% confidence intervals (CI) were estimated for the time periods (0–7 days, 8–31 days, 32–91 days, 92–183 days, >183 days) using multivariate Poisson regression analysis. IRR were estimated for sex, age, Glasgow Coma Scale (GCS), respiration rate, place of attendance and non‐transportation following treatment. Robust variance estimates applied due to multiple risk periods. Standardized Mortality Rates (SMR) were estimated. Findings Overall, 890 patients treated for 1764 overdoses contributed to a total time at risk of 3142 person‐years (PY). Median number of attendances was 1 (range 1–27). The majority were male (75.5%) and the mean age was 37.7 years. In total, 112 (12.6%) died; 5.2% within 183 days and 2.2% between 184 and 365 days. Acute poisoning was the most common single cause of death (52.7%). The CMR was 3.6 (95% CI = 3.0–4.2) per 100‐PY. The women had a SMR of 32 (95% CI = 15.8–57.9) and the men 24.9 (95% CI = 17.7–34.2). The CMR (22.2, 95% CI = 10.6–46.8) was particularly high in the first 7 days, and significantly higher than in the following periods. However, this finding was only valid for those with severe overdose symptoms (GCS score = 3/15 and/or respiratory rate ≤6/min). Except for increasing age, no other indicators were associated with the mortality risk. Conclusion Patients treated by Oslo Emergency Services between June 2014 and December 2018 for a non‐fatal opioid overdose with severe overdose symptoms at attendance had an overall high mortality risk compared with the general population, but particularly during the first 7 days after attendance.