Association of ambient temperature with the outcomes in witnessed out-of-hospital cardiac arrest patients: a population-based observational study

This study aimed to identify the association between ambient temperature (AT) and patient outcome of witnessed out-of-hospital cardiac arrest (OHCA) occurring outdoors. This retrospective nationwide, population-based cohort study recruited witnessed adult OHCA patients in South Korea from January 2012 to December 2016. Meteorological data of 17 metropolitan cities and provinces were retrieved from the Korea Meteorological Administration database. Primary outcome was sustained return of spontaneous circulation (ROSC) in hospital. Secondary outcome was survival to hospital discharge. By the standard of quartile categories of AT (Q1 = 7.1 °C; Q2 = 17.7 °C; Q3 = 23.5 °C), three comparative analyses for ROSC and survival were performed between low and high AT groups. Propensity score matching (1:1) was performed for both AT groups. Among the 142,906 OHCA patients, 1,295 were included. In the multivariate analysis for matched groups by the standard of 7.1 °C (Q1), proportion of ROSC was significantly higher in the high AT-Q1 group than in the low AT-Q1 group (adjusted odds ratio [aOR] 2.02, 95% confidence interval [CI] 1.19–3.44). No significant difference in survival was shown between both AT-Q1 groups (aOR 1.24, 95% CI 0.61–2.52). In the standard of 17.7 °C (Q2) and 23.5 °C (Q3), no significant differences in ROSC and survival were found between the low and high AT groups. In conclusion, no obvious correlation existed between AT and patient outcomes such as sustained ROSC or survival to discharge in this study.