Evaluation of a Novel Classification of Heat-Related Illnesses: A Multicentre Observational Study (Heat Stroke STUDY 2012)

Abstract

The Japanese Association for Acute Medicine Committee recently proposed a novel classification system for the severity of heat-related illnesses. The illnesses are simply classified into three stages based on symptoms and management or treatment. Stages I, II, and III broadly correspond to heat cramp and syncope, heat exhaustion, and heat stroke, respectively. Our objective was to examine whether this novel severity classification is useful in the diagnosis by healthcare professionals of patients with severe heat-related illness and organ failure. A nationwide surveillance study of heat-related illnesses was conducted between 1 June and 30 September 2012, at emergency departments in Japan. Among the 2130 patients who attended 102 emergency departments, the severity of their heat-related illness was recorded for 1799 patients, who were included in this study. In the patients with heat cramp and syncope or heat exhaustion (but not heat stroke), the blood test data (alanine aminotransferase, creatinine, blood urea nitrogen, and platelet counts) for those classified as Stage III were significantly higher than those of patients classified as Stage I or II. There were no deaths among the patients classified as Stage I. This novel classification may avoid underestimating the severity of heat-related illness.

Keywords: heat cramp; heat exhaustion; heat stroke; heat-related illness; international classification; novel classification; syncope.

Figure 1

Flow chart of this study.

Figure 2

Numbers of patients with heat-related illness in 10-year age bins. Patient ages ranged from 1 to 102 years, and teenagers presented most frequently.

Figure 3

Acute Physiology and Chronic Health Evaluation (APACHE) II scores. Box-and-whisker plots comparing the APACHE II scores for patients classified with the international classification method or with our novel classification method. The box plots show the medians and interquartile ranges (difference between the first and third quartiles). The whiskers on the box plots indicate the maximum and minimum levels. Comparisons of the APACHE II scores among three degrees of severity in the novel classification and in the international classification were made with the Kruskal–Wallis H test. There was no significant difference between the two classification systems.

Figure 4

Distributions of the severity of heat-related illness according to the novel and international classifications. The distribution of severity determined with the novel classification correlated significantly with that determined with the international classification (Spearman’s rank correlation coefficient ρ = 0.448, p < 0.001, n = 1799).

Figure 5

Mortality rate. There were no deaths among the patients classified in Stage I with the novel classification. The mortality rates for the three levels of severity according to the novel classification and the international classification were compared with a χ² test. There was no significant difference between the two classifications.

Figure 6

Management of patients with heat-related illness after leaving the emergency room. Home, general ward, and the ICU were assigned to 90%, 8% and 2% of Stage I patients, 81%, 11% and 8% of heat cramp and syncope patients, 72%, 20% and 8% of Stage II patients, 77%, 16% and 7% of heat exhaustion patients, 10%, 28% and 62% of Stage III patients, and 16%, 21% and 63% of heat stroke patients, respectively.