Impact of Extreme Temperature and Particulate Matter 2.5 on Outcomes of Out-of-Hospital Cardiac Arrest

Background: Extreme temperature and particulate matter-2.5 (PM_2.5) are known to affect the outcomes of out-of-hospital cardiac arrest (OHCA). However, studies that examine their effects at the exact time of OHCA occurrence are limited. Objective: This study aimed to investigate the impact of extreme cold, extreme heat, and PM_2.5 on OHCA outcomes at the time of occurrence. Methods: We analyzed data from 82,497 OHCAs (aged > 18 years) in South Korea between January 2016 and December 2021. Extreme temperatures were defined as extreme cold (≤5th percentile) and extreme heat (≥95th percentile). PM_2.5 refers to particulate matter ≤ 2.5 micrometers, with extreme PM_2.5 defined as ≥95th percentile. The outcomes were survival to discharge and good neurological outcome, defined as a cerebral performance category of 1 or 2 at hospital discharge. We performed a multivariable logistic regression analysis to assess the impact of extreme temperature and PM_2.5 on OHCA outcomes. Results: Extreme cold (-4.2°C to -20.2°C) showed no association with OHCA outcomes when compared to normal conditions (-0.9°C to 26.6°C). However, OHCAs during extreme heat (28.7°C to 39.3°C) showed a 15% significantly lower probability of survival to discharge (adjusted odds ratio [aOR]: 0.85, 95% confidence interval (CI): 0.74–0.98) compared to normal conditions. OHCAs during extreme PM_2.5 (56 to 218 µg/m³) were associated with 14% lower probability of survival to discharge (aOR: 0.86, 95% CI: 0.75–0.99) compared to normal PM_2.5 (0 to 43 µg/m³). Conclusion: Extreme heat and PM_2.5 were significantly associated with a decreased probability of survival to discharge in OHCA patients.