Risk Assessment And Lethal Analysis Of Exertional Heat Illness/stroke In The Military

Background:Exertional heat illness/stroke（EHI/EHS）is one of the major training injuries resulting in non-combat attrition or even death during summer military training.In particular,EHS is an urgent disease with rapid progress and high fatality.In addition to early cooling,there is currently a lack of clinically specific treatment.The key to reducing EHI/EHS morbidity and mortality lies in risk factor control,early identification and early cooling treatment.However,there are few reliable data on risk factors for morbidity,mortality and evaluation of preventive measures.Therefore,four studies were designed to preliminarily explore these issues.Objectives:（1）To preliminarily explore the feasibility of classifying military training subjects according to the exercise load by evaluating it in military volunteers participating in training,and meanwhile to provide reference data for the follow-up studies.（2）To explore the influence of environmental factors and training factors on the incidence of EHI and then establish a risk assessment scale by investigating the incidence of EHI in four military physical training subjects of long-distance running.（3）To explore a new scheme of active EHI prevention on the basis of conventional medical support and evaluate its effect through following training support for the light 10km.（4）To discuss the relationship between certain indicators（demographic characteristics,environmental factors,clinical features and cooling intervention effect）in the early stage of EHS and death through retrospective analysis of hospitalized EHS cases.Methods:（1）18 healthy volunteers were recruited from a company of Chinese army,all of whom participated in the training of mixed martial arts,light 3km,light 5km and light10km respectively according to the usual intensity standards.The change of heart rate was monitored in real time during the training.After the training,the objective Edwards’training impulse（TRIMP）formula and the subjective rating of perceived exertion（CR-10 scale）were used to evaluate the exercise loads of the four subjects.（2）Cluster sampling was used to conduct a cross-sectional survey on the incidence of EHI in long-distance running military physical training of 5 military units from May to October 2019.The training subjects investigated were armed 5km,light 5km,armed 3km and light 3km.The meteorological factors,training subjects,training types（routine training or performance assessment）,personnel composition,training attendance and EHI incidence were investigated.The relationship between risk factors and EHI incidence was analyzed by establishing multiple linear regression models.EHI risk assessment scale was constructed based on partial regression coefficient.（3）Based on cluster sampling,42 healthy military volunteers were recruited from 2 whole training companies and randomly divided into control group（n=22）and intervention group（n=20）,and all of them should complete light 10km training according to the usual standard.The control group received conventional medical support in the training,while the intervention group received additional active hydration and cooling measures on the basis of conventional support.Changes in body temperature and heart rate,weight loss,water supplementation,urine sodium concentration before and after training,sweat specific gravity and sodium concentration,training performance,exercise load（TRIMP）and subjective CR-10 score were compared between the two groups.（4）A retrospective case-control design was used to analyze the data of 335 inpatients with EHS admitted to 12 large hospitals in China from January 1,2012 to December 31,2018.Demographic information,underlying diseases,ambient temperature at onset,clinical manifestations,initial body temperature,time from onset to diagnosis of EHI/EHS（including suspected）(T_o-d),cooling treatment or not,and the duration of body temperature>38℃of all enrolled patients were recorded.The number of damaged organs and in-hospital deaths were recorded and the patients were divided into death group and survival group.Results:（1）All 18 volunteers completed the training of 4 subjects,which were graded according to the calculated value of TRIMP and the score of CR-10 respectively,and the ranking was basically the same.The largest exercise load was light 10km,followed by light5km,light 3km and mixed martial arts training.There was a good correlation between TRIMP and CR-10 score（R=0.863,P<0.05）.（2）A total of 134 batches of training were investigated in 5 military training units.The total person-times participating in training was14,316.The subject with the highest incidence of EHI was armed 5km,followed by light 5km,armed 3km and light 3km,respectively.Ambient temperature,relative humidity,distance category（3km or 5km）and training type had significant influences on the incidence of EHI after screening by multiple linear regression models（P<0.05）.The fitted regression equation was P=-7.299+ambient temperature×0.189+relative humidity%×0.022+distance category×0.720+training type×0.902.The multiple correlation coefficient R was0.718,and the goodness of fit R² was 0.516（P<0.05）.With the mean incidence of EHI as threshold of low risk or high risk,the area under the ROC curve of the EHI risk assessment scale constructed based on partial regression coefficient was 0.954（95%CI 0.921～0.986）,with a sensitivity of 100%and specificity of 83.3%.The cutoff value was defined as:≤26points predicted low risk,and>26 points predicted high risk.（3）In the following training support study,both the control group and the intervention group had significant weight loss during the training.Weight loss in control group was significantly higher than that in intervention group（P<0.05）,and the water supplement during training in control group was significantly lower than that in intervention group（P<0.05）.The concentration of urinary sodium was similar in the two groups before training（P>0.05）,and was significantly lower in control group than in intervention group after training（P<0.05）.The body temperature of92.86%volunteers increased significantly during training,the highest body temperature of45.24%volunteers reached 38.0～39.0℃,and of 23.81%exceeded 39℃.The average maximum body temperature of control group was significantly higher than that of intervention group（P<0.05）.Three volunteers dropped out of the trial due to EHI,all from the control group.There was no significant difference in the average heart rate,the ratio of average heart rate to maximum heart rate（HRmax）,TRIMP,CR-10 score and training performance between the two groups（P>0.05）.（4）Among 335 hospitalized patients with EHS,285 survived and 50 died,with an overall fatality of 14.93%（50/335）.There was no significant difference in baseline demographic characteristics between the death group and the survival group（P>0.05）,and the median of ambient temperature at onset was 29（5.25）℃and 29（3）℃respectively（P>0.05）,the median of initial body temperature was 39.6（1.75）℃and 39.2（1.5）℃respectively（P<0.05）,the median of T_o-d was 0.3（2.63）h and 1.1（6.5）h respectively（P<0.05）,the median duration of body temperature>38℃was 13（17）h and2.00（2.00）h respectively（P<0.05）,and the median number of damaged organs/systems within 72h was 8.00（1.25）and 5.00（2.00）respectively（P<0.05）.The most vulnerable organs/systems were,in order,the central nervous system,the coagulation system,the striated muscles,the liver,the myocardium,the kidney,the gastrointestinal tract,the circulatory system and the respiratory system.The Logistic regression model showed that only the duration of body temperature>38℃,the number of damaged organs within 72h and the ambient temperature were statistically significant,with the OR values of 2.002,9.410and 0.772,respectively.The areas under the ROC were 0.987（95%CI 0.978～0.997,P<0.05）,0.946（95%CI 0.917～0.975,P<0.05）,and 0.543（95%CI 0.448～0.637,P>0.05）,respectively.Conclusions:（1）It might be feasible to classify military training subjects according to exercise load degree by subjective or objective exercise load assessment tool.The subjective index of CR-10 score has a good correlation with the objective index of TRIMP,but CR-10scale was simpler and more feasible.（2）Among the four military training subjects of conventional long-distance running,ambient temperature,relative humidity and subject type had a significant influence on the incidence of EHI.The cutoff value of EHI risk assessment scale established based on them was defined as:≤26 points predicted low risk and>26 points predicted high risk,with good sensitivity and specificity,but it still needs further verification.（3）The active hydration and cooling medical support scheme might promote drinking during training,reduce water and sodium loss,help the body to dissipate heat and slows down the body temperature rise;The new scheme did not increase the discomfort of the volunteers,and was easy to implement,and the overall effect was evaluated as satisfactory.（4）The retrospective case-control study showed that EHS still had a high fatality,and among the factors in the early stage,duration of high body temperature and the number of damaged organs within 72h were the most significant risk factors and predictors of death.For EHS,emphasis should be placed not only on the timing（as early as possible）but also on the effectiveness of cooling therapy.