Accidental hypothermia: characteristics, outcomes, and prognostic factors-A nationwide observational study in Japan (Hypothermia study 2018 and 2019).

Aim: This study describes the clinical characteristics and outcomes as well as the prognostic factors of patients with accidental hypothermia (AH) using Japan's nationwide registry data.

Methods: The Hypothermia study 2018 and 2019, which included patients aged 18 years or older with a body temperature of 35°C or less, was a multicenter registry conducted at 87 and 89 institutions throughout Japan, with data collected from December 2018 to February 2019 and December 2019 to February 2020, respectively.

Results: In total, 1363 patients were enrolled in the registry, of which 1194 were analyzed in this study. The median (interquartile range) age was 79 (68-87) years, and the median (interquartile range) body temperature at the emergency department was 30.8°C (28.4-33.6°C). Forty-three percent of patients with AH had a mild condition, 35.2% moderate, and 21.9% severe. AH occurred in an indoor setting in 73.4% and was caused by acute medical illness in 49.3% of patients. A total of 101 (8.5%) patients suffered from cardiopulmonary arrest on arrival at the hospital. The overall 30-day mortality rate was 24.5%, the median (interquartile range) intensive care unit stay was 4 (2-7) days, and the median (interquartile range) hospital stay was 13 (4-27) days. In the multivariable logistic analysis, the prognostic factors were age (≥75 years old), male, activities of daily living (needing total assistance), cause of AH (trauma, alcohol), Glasgow Coma Scale score, and potassium level (>5.5 mEq/L).

Conclusion: The mortality rate of AH was 24.5% in Japan. The prognostic factors developed in this study may be useful for the early prediction, prevention, and awareness of severe AH.