Indoor Versus Outdoor Occurrence in Mortality of Accidental Hypothermia in Japan: The J-Point Registry.

The impact of the location where accidental hypothermia (AH) occurs has not been fully investigated thus far. This was a multicenter retrospective study of patients with a body temperature ≤35°C obtained at the emergency department of 12 hospitals in Japan between April 2011 and March 2016. We divided the patients into two groups according to the location where AH occurred (indoor group versus outdoor group). The association between each location of the occurrence of AH and in-hospital mortality was evaluated via a multivariable logistic regression analysis. The primary outcome of this study was in-hospital death. The secondary outcomes were the lengths of ICU and hospital stay. A total of 572 patients were enrolled in the hypothermia database, and 537 patients were included in the analyses. A total of 119 and 418 patients experienced hypothermia with outdoor and indoor occurrence, respectively. The indoor group was older and had worse activities of daily living compared with the outdoor group. With regard to the outcome, the proportion of in-hospital death was higher in the indoor group than in the outdoor group (28.2% [118/418] vs. 10.9% [13/119], p < 0.001). The multivariable logistic regression analysis showed that the adjusted odds ratio of the indoor group was 2.48 (95% confidence interval, 1.18-5.17). In terms of secondary outcomes, both the lengths of ICU and hospital stay of the survivors were longer in the indoor group than in the outdoor group. Hypothermia with indoor occurrence accounts for ∼78% of the total AH cases in this study, and the proportion of in-hospital deaths was higher in the indoor group than in the outdoor group. Warnings about the indoor onset of AH must be provided, and countermeasures for the prevention and early recognition of AH with indoor occurrence must be taken.