Clinical characteristics, prognostic factors, and outcomes of heat-related illness (Heatstroke Study 2017-2018).

Aim: Heat-related illness is common, but its epidemiology and pathological mechanism remain unclear. The aim of this study was to report current clinical characteristics, prognostic factors, and outcomes of heat-related illness in Japan.

Methods: We undertook a prospective multicenter observational study in Japan. Only hospitalized patients with heat-related illness were enrolled from 1 July to 30 September 2017 and 1 July to 30 September 2018.

Results: A total of 763 patients were enrolled in the study. Median age was 68 years (interquartile range, 49-82 years) and median body temperature on admission was 38.2°C (interquartile range, 36.8-39.8°C). Non-exertional cause was 56.9% and exertional cause was 40.0%. The hospital mortality was 4.6%. The median Japanese Association for Acute Medicine disseminated intravascular coagulation (JAAM DIC), Sequential Organ Failure Assessment (SOFA), and Acute Physiology and Chronic Health Evaluation II (APACHE II) scores on admission were 1 (0-2), 4 (2-6), and 13 (8-22), respectively. To predict hospital mortality, areas under the receiver operating characteristic curves were 0.776 (JAAM DIC score), 0.825 (SOFA), and 0.878 (APACHE II). There were 632 cases defined as heatstroke by JAAM heat-related illness criteria, 73 cases diagnosed as having DIC. A total of 16.6% patients had poor neurological outcome (modified Rankin Scale ≥ 4) at hospital discharge. In the multivariate analysis, Glasgow Coma Scale and platelets were independent predictors of mortality. Type of heatstroke, Glasgow Coma Scale, and platelets were independent predictors of poor neurological outcome. Body temperature was not associated with mortality or poor neurological outcome.

Conclusions: In this study, hospital mortality of heat-related illness was <5%, one-sixth of the patients had poor neurological outcome. The APACHE II, SOFA, and JAAM DIC scores predicted hospital mortality. Body temperature was not associated with mortality or poor neurological outcome.