Cold water immersion: the gold standard for exertional heatstroke treatment

Heat Safety in the Workplace: Modified Delphi Consensus to Establish Strategies and Resources to Protect the US Workers

The purpose of this consensus document was to develop feasible, evidence-based occupational heat safety recommendations to protect the US workers that experience heat stress. Heat safety recommendations were created to protect worker health and to avoid productivity losses associated with occupational heat stress. Recommendations were tailored to be utilized by safety managers, industrial hygienists, and the employers who bear responsibility for implementing heat safety plans. An interdisciplinary roundtable comprised of 51 experts was assembled to create a narrative review summarizing current data and gaps in knowledge within eight heat safety topics: (a) heat hygiene, (b) hydration, (c) heat acclimatization, (d) environmental monitoring, (e) physiological monitoring, (f) body cooling, (g) textiles and personal protective gear, and (h) emergency action plan implementation. The consensus-based recommendations for each topic were created using the Delphi method and evaluated based on scientific evidence, feasibility, and clarity. The current document presents 40 occupational heat safety recommendations across all eight topics. Establishing these recommendations will help organizations and employers create effective heat safety plans for their workplaces, address factors that limit the implementation of heat safety best-practices and protect worker health and productivity.

Roundtable on Preseason Heat Safety in Secondary School Athletics: Prehospital Care of Patients With Exertional Heat Stroke

OBJECTIVE

First, we will update recommendations for the prehospital management and care of patients with exertional heat stroke (EHS) in the secondary school setting. Second, we provide action items to aid clinicians in developing best-practice documents and policies for EHS. Third, we supply practical strategies clinicians can use to implement best practice for EHS in the secondary school setting.

DATA SOURCES

An interdisciplinary working group of scientists, physicians, and athletic trainers evaluated the current literature regarding the prehospital care of EHS patients in secondary schools and developed this narrative review. When published research was nonexistent, expert opinion and experience guided the development of recommendations for implementing life-saving strategies. The group evaluated and further refined the action-oriented recommendations using the Delphi method.

CONCLUSIONS

Exertional heat stroke continues to be a leading cause of sudden death in young athletes and the physically active. This may be partly due to the numerous barriers and misconceptions about the best practice for diagnosing and treating patients with EHS. Exertional heat stroke is survivable if it is recognized early and appropriate measures are taken before patients are transported to hospitals for advanced medical care. Specifically, best practice for EHS evaluation and treatment includes early recognition of athletes with potential EHS, a rectal temperature measurement to confirm EHS, and cold-water immersion before transport to a hospital. With planning, communication, and persistence, clinicians can adopt these best-practice recommendations to aid in the recognition and treatment of patients with EHS in the secondary school setting.

Ethical dilemmas and validity issues related to the use of new cooling technologies and early recognition of exertional heat illness in sport

The Tokyo 2020 Olympic Games is expected to be among the hottest Games in modern history, increasing the chances for exertional heat stroke (EHS) incidence, especially in non-acclimatised athletes/workers/spectators. The urgent need to recognise EHS symptoms to protect all attendees' health has considerably accelerated research examining the most effective cooling strategies and the development of wearable cooling technology and real-time temperature monitoring. While these technological advances will aid the early identification of EHS cases, there are several potential ethical considerations for governing bodies and sports organisers. For example, the impact of recently developed cooling wearables on health and performance is unknown. Concerning improving athletic performance in a hot environment, there is uncertainty about this technology's availability to all athletes. Furthermore, the real potential to obtain real-time core temperature data will oblige medical teams to make crucial decisions around their athletes continuing their competitions or withdraw. Therefore, the aim of this review is (1) to summarise the practical applications of the most novel cooling strategies/technologies for both safety (of athletes, spectators and workers) and performance purposes, and (2) to inform of the opportunities offered by recent technological developments for the early recognition and diagnosis of EHS. These opportunities are presented alongside several ethical dilemmas that require sports governing bodies to react by regulating the validity of recent technologies and their availability to all.

Effect of ice slurry ingestion on core temperature and blood pressure response after exercise in a hot environment

Delays in the restoration of thermoregulation after exercise in a hot environment has been associated with post-exercise hypotension. This study tested the hypothesis that simultaneous internal cooling and rehydration by ingesting ice slurry prevents the excessive decrease in mean arterial pressure (MAP) and promotes recovery of core and skin temperatures in male athletes. Seven male athletes participated in this randomized controlled trial with a crossover design. The participants ran on a treadmill at 75% of their maximal oxygen uptake in the heat (35 °C, 60% relative humidity), up to exhaustion. Immediately after exercise, participants ingested either 4 g⋅kg ^-1 body weight of ice slurry (0.5 °C, ICE) or a control beverage (28 °C, CON). The participants then recovered by sitting for 20 min. We measured participants' rectal temperature (T_re), skin temperature (T_sk), mean arterial pressure (MAP), heart rate (HR), cardiac output (CO), total peripheral resistance (TPR), and physiological strain index (PSI) before exercise (Pre), after running to exhaustion (PEx), and at 0 (P0), 10 (P10), and 20 (P20) minutes after ice slurry or control beverage ingestion. MAP, CO, HR, TPR, or PSI did not change significantly during the recovery period. At P10 and P20, T_re and T_sk significantly decreased in the ICE group compared to the CON group (p < 0.05). These results suggested that ingestion of ice slurry, post-exercise, promoted core and skin temperature recovery but did not affect the central and peripheral cardiovascular responses during the acute recovery period.

Proposing the VetCompass clinical grading tool for heat-related illness in dogs

Heat-related illness is a potentially fatal condition in dogs. Rapid and accurate recognition of the severity can improve clinical management in affected dogs and lead to better outcomes. This study explored retrospective VetCompass veterinary clinical records to investigate the clinical signs recorded for dogs presenting with heat-related illness to primary-care veterinary practice from 2016 to 2018. The relative risk of death associated with these clinical signs was reported and used to develop a novel clinical grading tool. From the clinical records of 856 heat-related illness events, the most frequently recorded clinical signs were respiratory changes (68.73%) and lethargy (47.79%). The clinical signs with the highest relative risk of death were neurological dysfunction, gastrointestinal haemorrhage and bleeding disorders. The novel VetCompass Clinical Grading Tool for Heat-Related Illness in dogs defines three grades: mild (altered respiration, lethargy), moderate (gastrointestinal signs, a single seizure, episodic collapse) and severe (neurological dysfunction, gastrointestinal haemorrhage, bleeding disorders). This novel grading tool offers a simple, evidence-based device to improve recognition of heat-related illness in dogs and promote improved decision-making for earlier interventions such as cooling and hospitalisation. This could improve outcomes and protect the welfare of dogs in the face of rising global temperatures.

Evidence-Based Heatstroke Management in the Emergency Department

INTRODUCTION

Climate change is causing an increase in the frequency and intensity of extreme heat events, which disproportionately impact the health of vulnerable populations. Heatstroke, the most serious heat-related illness, is a medical emergency that causes multiorgan failure and death without intervention. Rapid recognition and aggressive early treatment are essential to reduce morbidity and mortality. The objective of this study was to evaluate current standards of care for the emergent management of heatstroke and propose an evidence-based algorithm to expedite care.

METHODS

We systematically searched PubMed, Embase, and key journals, and reviewed bibliographies. Original research articles, including case studies, were selected if they specifically addressed the recognition and management of heatstroke in any prehospital, emergency department (ED), or intensive care unit population. Reviewers evaluated study quality and abstracted information regarding demographics, scenario, management, and outcome.

RESULTS

In total, 63 articles met full inclusion criteria after full-text review and were included for analysis. Three key themes identified during the qualitative review process included recognition, rapid cooling, and supportive care. Rapid recognition and expedited external or internal cooling methods coupled with multidisciplinary management were associated with improved outcomes. Delays in care are associated with adverse outcomes. We found no current scalable ED alert process to expedite early goal-directed therapies.

CONCLUSION

Given the increased risk of exposure to heat waves and the time-sensitivity of the condition, EDs and healthcare systems should adopt processes for rapid recognition and management of heatstroke. This study proposes an evidence-based prehospital and ED heat alert pathway to improve early diagnosis and resource mobilization. We also provide an evidence-based treatment pathway to facilitate efficient patient cooling. It is hoped that this protocol will improve care and help healthcare systems adapt to changing environmental conditions.

Cooling Capacity of Transpulmonary Cooling and Cold-Water Immersion After Exercise-Induced Hyperthermia

CONTEXT

Cold-water immersion (CWI) may not be feasible in some remote settings, prompting the identification of alternative cooling methods as adjunct treatment modalities for exertional heat stroke (EHS).

OBJECTIVE

To determine the differences in cooling capacities between CWI and the inspiration of cooled air.

DESIGN

Randomized controlled clinical trial.

SETTING

Laboratory.

PATIENTS OR OTHER PARTICIPANTS

A total of 12 recreationally active participants (7 men, 5 women; age = 26 ± 4 years, height = 170.6 ± 10.1 cm, mass = 76.0 ± 18.0 kg, body fat = 18.5% ± 9.7%, peak oxygen uptake = 42.7 ± 8.9 mL·kg-1·min-1).

INTERVENTION(S)

After exercise in a hot environment (40°C and 40% relative humidity), participants were randomized to 3 cooling conditions: cooling during passive rest (PASS; control), CWI, and the Polar Breeze thermal rehabilitation machine (PB) with which participants inspired cooled air (22.2°C ± 1.0°C).

MAIN OUTCOME MEASURE(S)

Rectal temperature (TREC) and heart rate were continuously measured throughout cooling until TREC reached 38.25°C.

RESULTS

Cooling rates during CWI (0.18°C·min-1 ± 0.06°C·min-1) were greater than those during PASS (mean difference [95% confidence interval] of 0.16°C·min-1 [0.13°C·min-1, 0.19°C·min-1]; P < .001) and PB (0.15°C·min-1 [0.12°C·min-1, 0.16°C·min-1]; P < .001). Elapsed time to reach a TREC of 38.25°C was also faster with CWI (9.71 ± 3.30 minutes) than PASS (-58.1 minutes [-77.1, -39.9 minutes]; P < .001) and PB (-46.8 minutes [-65.5, -28.2 minutes]; P < .001). Differences in cooling rates and time to reach a TREC of 38.25°C between PASS and PB were not different (P > .05).

CONCLUSIONS

Transpulmonary cooling via cooled-air inhalation did not promote an optimal cooling rate (>0.15°C·min-1) for the successful treatment of EHS. In remote settings where EHS is a risk, access and use of treatment methods via CWI or cold-water dousing are imperative to ensuring survival.

TRIAL REGISTRY

ClinicalTrials.gov (NCT0419026).

Athletic training employment in secondary schools by geographic setting and school size within the United States

CONTEXT

The Athletic Training Locations and Services (ATLAS) Annual Report suggests there are differences in athletic trainer (AT) employment status on the basis of geographic locale. However, the influence of geographic locale and the school size on AT employment is undetermined.

OBJECTIVE

To describe if differences exist in the odds of having AT services by locale for public and private schools, and by student enrollment for public schools.

DESIGN

Cross-sectional study.

SETTING

Public and private secondary schools with athletics programs.

PATIENTS OR OTHER PARTICIPANTS

Data from 20,078 US public and private secondary schools were obtained.

MAIN OUTCOME MEASURES(S)

Data were collected by the ATLAS Project. AT employment status, locales (City, Suburban, Town, and Rural) for public and private schools, and school size category (large, moderate, medium, and small) only for public schools were obtained. AT employment status was examined for each category with odds ratios. A prediction model was produced by Logistic Regression Analysis.

RESULTS

Of the 19,918 public and private schools with AT employment status and locale, Suburban schools had the highest access to AT services (80.1%) with an increased odds compared with Rural schools (OR = 3.55 [3.28 to 3.850]). Of 15,850 public schools with AT employment status and student enrollment, large schools had the highest rate of having AT services (92.1%) with nearly 18.5 times greater odds (OR = 18.480 [16.197 to 21.083]) versus small schools. The logistic model determined that an odds of having access to AT increases by 2.883 times as the school size goes up by one category.

CONCLUSIONS

Nationally, Suburban schools and large public schools have the largest access to AT services compared to schools that are in more remote areas and with less student enrollment. These findings elucidate the geographic locales and student enrollment levels where AT services are most prevalent.

Physiological interactions with personal-protective clothing, physically demanding work and global warming: An Asia-Pacific perspective

The Asia-Pacific contains over half of the world's population, 21 countries have a Gross Domestic Product <25% of the world's largest economy, many countries have tropical climates and all suffer the impact of global warming. That 'perfect storm' exacerbates the risk of occupational heat illness, yet first responders must perform physically demanding work wearing personal-protective clothing and equipment. Unfortunately, the Eurocentric emphasis of past research has sometimes reduced its applicability to other ethnic groups. To redress that imbalance, relevant contemporary research has been reviewed, to which has been added information applicable to people of Asian, Melanesian and Polynesian ancestry. An epidemiological triad is used to identify the causal agents and host factors of work intolerance within hot-humid climates, commencing with the size dependency of resting metabolism and heat production accompanying load carriage, followed by a progression from the impact of single-layered clothing through to encapsulating ensembles. A morphological hypothesis is presented to account for inter-individual differences in heat production and heat loss, which seems to explain apparent ethnic- and gender-related differences in thermoregulation, at least within thermally compensable states. The mechanisms underlying work intolerance, cardiovascular insufficiency and heat illness are reviewed, along with epidemiological data from the Asia-Pacific. Finally, evidence-based preventative and treatment strategies are presented and updated concerning moisture-management fabrics and barriers, dehydration, pre- and post-exercise cooling, and heat adaptation. An extensive reference list is provided, with >25 recommendations enabling physiologists, occupational health specialists, policy makers, purchasing officers and manufacturers to rapidly extract interpretative outcomes pertinent to the Asia-Pacific.

Assessing the Validity of Aural Thermometry for Measuring Internal Temperature in Patients With Exertional Heat Stroke

CONTEXT

The use of aural thermometry as a method for accurately measuring internal temperature has been questioned. No researchers have examined whether aural thermometry can accurately measure internal body temperature in patients with exertional heat stroke (EHS).

OBJECTIVE

To examine the efffectiveness of aural thermometry as an alternative to the criterion standard of rectal thermometry in patients with and those without EHS.

DESIGN

Cross-sectional study.

SETTING

An 11.3-km road race.

PATIENTS OR OTHER PARTICIPANTS

A total of 49 patients with EHS (15 men [age = 38 ± 17 years], 11 women [age = 28 ± 10 years]) and 23 individuals without EHS (10 men [age = 62 ± 17 years], 13 women [age = 45 ± 14 years]) who were triaged to the finish-line medical tent for suspected EHS.

MAIN OUTCOME MEASURE(S)

Rectal and aural temperatures were obtained on arrival at the medical tent for patients with and those without EHS and at 8.3 ± 5.2 minutes into EHS treatment (cold-water immersion) for patients with EHS.

RESULTS

The mean difference between temperatures measured using rectal and aural thermometers in patients with EHS at medical tent admission was 2.4°C ± 0.96°C (4.3°F ± 1.7°F; mean rectal temperature = 41.1°C ± 0.8°C [106.1°F ± 1.4°F]; mean aural temperature = 38.8°C ± 1.1°C [101.8°F ± 2.0°F]). Rectal and aural temperatures during cold-water immersion in patients with EHS were 40.4°C ± 1.0°C (104.6°F ± 1.8°F) and 38.0°C ± 1.2°C (100.3°F ± 2.2°F), respectively. Rectal and aural temperatures for patients without EHS at medical tent admission were 38.8°C ± 0.87°C (101.9°F ± 1.6°F) and 37.2°C ± 1.0°C (99.1°F ± 1.8°F), respectively.

CONCLUSIONS

Aural thermometry is not an accurate method of diagnosing EHS and should not be used as an alternative to rectal thermometry. Using aural thermometry to diagnosis EHS can result in catastrophic outcomes, such as long-term sequelae or fatality.

A novel cooling method using carbon dioxide-rich water after passive heating

In the event of a marked rise in body temperature, it is often necessary to reduce the temperature quickly. One method to rapidly drop body temperature is cold water immersion. Because carbon dioxide (CO₂)-rich water causes cutaneous vasodilation, it may be that CO₂-rich water reduces body temperature faster than fresh water. To test that idea, I compared the effects of CO₂-rich and tap water immersion on auditory canal temperature (T_ac) after passive heating. Nine healthy male subjects participated in the study. Subjects were first immersed for 15 min in a tap water bath at 40 °C to raise body temperature. They then moved to a tap water or CO₂-rich water bath at 30 °C to reduce body temperature. Immersion in 40 °C tap water caused T_ac to rise 0.64 ± 0.11 °C in the tap water session and 0.71 ± 0.25 °C in the CO₂-rich water session (P > 0.05). During the 30 °C water immersion, T_ac declined and was significantly lower in CO₂-rich water than in tap water. Cooling rates were 0.06 ± 0.04 °C/min in tap water and 0.11 ± 0.05 °C/min in CO₂-rich water (P < 0.05). In addition, both thermal sensation (3.2 ± 1.0 vs. 2.1 ± 0.9; P < 0.01) and thermal comfort (1.2 ± 0.4 vs. 2.1 ± 0.8; P < 0.01) were significantly better in CO₂-rich water than tap water. These results suggest that CO₂-rich water immersion reduces T_ac 1.7 times faster than tap water immersion, and that CO₂-rich water immersion cools the body more comfortably than tap water immersion.

The Use of Percutaneous Thermal Sensing Microchips for Body Temperature Measurements in Horses Prior to, during and after Treadmill Exercise

Accurately measuring body temperature in horses will improve the management of horses suffering from or being at risk of developing postrace exertional heat illness. PTSM has the potential for measuring body temperature accurately, safely, rapidly, and noninvasively. This study was undertaken to investigate the relation between the core body temperature and PTSM temperatures prior to, during, and immediately after exercise. The microchips were implanted into the nuchal ligament, the right splenius, gluteal, and pectoral muscles, and these locations were then compared with the central venous temperature, which is considered to be the "gold standard" for assessing core body temperature. The changes in temperature of each implant in the horses were evaluated in each phase (prior to, during, and immediately postexercise) and combining all phases. There were strong positive correlations ranging from 0.82 to 0.94 (p < 0.001) of all the muscle sites with the central venous temperature when combining all the phases. Additionally, during the whole period, PTSM had narrow limits of agreement (LOA) with central venous temperature, which inferred that PTSM is essentially equivalent in measuring horse body temperature. Overall, the pectoral PTSM provided a valid estimation of the core body temperature.

Methods for improving thermal tolerance in military personnel prior to deployment

Acute exposure to heat, such as that experienced by people arriving into a hotter or more humid environment, can compromise physical and cognitive performance as well as health. In military contexts heat stress is exacerbated by the combination of protective clothing, carried loads, and unique activity profiles, making them susceptible to heat illnesses. As the operational environment is dynamic and unpredictable, strategies to minimize the effects of heat should be planned and conducted prior to deployment. This review explores how heat acclimation (HA) prior to deployment may attenuate the effects of heat by initiating physiological and behavioural adaptations to more efficiently and effectively protect thermal homeostasis, thereby improving performance and reducing heat illness risk. HA usually requires access to heat chamber facilities and takes weeks to conduct, which can often make it impractical and infeasible, especially if there are other training requirements and expectations. Recent research in athletic populations has produced protocols that are more feasible and accessible by reducing the time taken to induce adaptations, as well as exploring new methods such as passive HA. These protocols use shorter HA periods or minimise additional training requirements respectively, while still invoking key physiological adaptations, such as lowered core temperature, reduced heart rate and increased sweat rate at a given intensity. For deployments of special units at short notice (< 1 day) it might be optimal to use heat re-acclimation to maintain an elevated baseline of heat tolerance for long periods in anticipation of such an event. Methods practical for military groups are yet to be fully understood, therefore further investigation into the effectiveness of HA methods is required to establish the most effective and feasible approach to implement them within military groups.

Exertional Heat Stroke, Modality Cooling Rate, and Survival Outcomes: A Systematic Review

Background and Objectives: The purpose of this systematic review is to synthesize the influence cooling modality has on survival with and without medical complications from exertional heat stroke (EHS) in sport and military populations. Methods and Materials: All peer-reviewed case reports or series involving EHS patients were searched in the following online databases: PubMed, Scopus, SPORTDiscus, Medline, CINAHL, Academic Search Premier, and the Cochrane Library: Central Registry of Clinical Trials. Cooling methods were subdivided into "adequate" (>0.15 °C/min) versus "insufficient" (<0.15 °C/min) based on previously published literature on EHS cooling rates. Results: 613 articles were assessed for quality and inclusion in the review. Thirty-two case reports representing 521 EHS patients met the inclusion criteria. Four hundred ninety-eight (498) patients survived EHS (95.58%) and 23 (4.41%) patients succumbed to complications. Fischer's Exact test on 2 × 2 contingency tables and relative risk ratios were calculated to determine if modality cooling rate was associated with patient outcomes. EHS patients that survived who were cooled with an insufficient cooling rate had a 4.57 times risk of medical complications compared to patients who were treated by adequate cooling methods, regardless of setting (RR = 4.57 (95%CI: 3.42, 6.28)). Conclusions: This is the largest EHS dataset yet compiled that analyzes the influence of cooling rate on patient outcomes. Zero patients died (0/521, 0.00%) when treatment included a modality with an adequate cooling rate. Conversely, 23 patients died (23/521, 4.41%) with insufficient cooling. One hundred seventeen patients (117/521, 22.46%) survived with medical complications when treatment involved an insufficient cooling rate, whereas, only four patients had complications (4/521, 0.77%) despite adequate cooling. Cooling rates >0.15 °C/min for EHS patients were significantly associated with surviving EHS without medical complications. In order to provide the best standard of care for EHS patients, an aggressive cooling rate >0.15 °C/min can maximize survival without medical complications after exercise-induced hyperthermia.

Emergency Medical Service Directors' Protocols for Exertional Heat Stroke

Background and Objectives: Emergency Medical Service (EMS) protocols vary widely and may not implement best practices for exertional heat stroke (EHS). EHS is 100% survivable if best practices are implemented within 30 min. The purpose of this study is to compare EMS protocols to best practices for recognizing and treating EHS. Materials and Methods: Individuals (n = 1350) serving as EMS Medical or Physician Director were invited to complete a survey. The questions related to the EHS protocols for their EMS service. 145 individuals completed the survey (response rate = 10.74%). Chi-Squared Tests of Associations (χ²) with 95% confidence intervals (CI) were calculated. Prevalence ratios (PR) with 95% CI were calculated to determine the prevalence of implementing best practices based on location, working with an athletic trainer, number of EHS cases, and years of directing. All PRs whose 95% CIs excluded 1.00 were considered statistically significant; Chi-Squared values with p values < 0.05 were considered statistically significant. Results: A majority of the respondents reported not using rectal thermometry for the diagnosis of EHS (n = 102, 77.93%) and not using cold water immersion for the treatment of EHS (n = 102, 70.34%). If working with an athletic trainer, EMS is more likely to implement best-practice treatment (i.e., cold-water immersion and cool-first transport-second) (69.6% vs. 36.9%, χ² = 8.480, p < 0.004, PR = 3.15, 95% CI = 1.38, 7.18). Conclusions: These findings demonstrate a lack of implementation of best-practice standards for EHS by EMS. Working with an athletic trainer appears to increase the likelihood of following best practices. Efforts should be made to improve EMS providers’ implementation of best-practice standards for the diagnosis and management of EHS to optimize patient outcomes.

Effects of Pre-Cooling on Thermophysiological Responses in Elite Eventing Horses

Simple Summary

Horses have a high metabolic capacity for exercise, producing a great deal of heat, and have a small surface area for heat loss. Under limited circumstances, the regulation of heat loss (i.e., across the respiratory tract and by the evaporation of sweat) means heat build-up in the body is reduced. Thermoregulation can be assisted by cooling the horses down to safely perform exercise in thermally challenging environments. The present study showed that pre-cooling (i.e., cooling between the warm-up and exercise performance) slightly reduced the rise in rectal, shoulder and rump skin temperatures of ten international eventing horses during moderately intense canter training in moderate environmental conditions. During the canter training, heart rate, sweat rate and sweat composition were unaffected by pre-cooling. The pre-cooling strategy chosen here was cold-water rinsing for a short period of time (~8 min). Considering the limited time and space at equestrian events, such a pre-cooling strategy could easily be implemented. Reducing heat strain by pre-cooling may potentially improve equine welfare during events.

Abstract

In this study, we examined the effects of pre-cooling on thermophysiological responses in horses exercising in moderate environmental conditions (average wet bulb globe temperature: 18.5 ± 3.8 °C). Ten international eventing horses performed moderate intensity canter training on two separate days, and were either pre-cooled with cold-water rinsing (5–9 °C for 8 ± 3 min; cooling) or were not pre-cooled (control). We determined velocity (V), heart rate (HR), rectal temperature (T_re,), shoulder and rump skin temperature (T_shoulder and T_rump), plasma lactate concentration (LA), gross sweat loss (GSL), and local sweat rate (LSR), as well as sweat sodium, chloride and potassium concentrations. The effect of pre-cooling on T_re was dependent on time; after 20 min of exercise the effect was the largest (estimate: 0.990, 95% likelihood confidence intervals (95% CI): 0.987, 0.993) compared to the control condition, resulting in a lower median T_re of 0.3 °C. Skin temperature was also affected by pre-cooling compared to the control condition (T_shoulder: −3.30 °C, 95% CI: −3.739, −2.867; T_rump: −2.31 °C, 95% CI: −2.661, −1.967). V, HR, LA, GSL, LSR and sweat composition were not affected by pre-cooling. In conclusion, pre-cooling by cold-water rinsing could increase the margin for heat storage, allowing a longer exercise time before a critical T_re is reached and, therefore, could potentially improve equine welfare during competition.

Exertional Heatstroke in a Marathon Runner Complicated by Concurrent Use of an Antipsychotic Medication Affecting Thermoregulation

We report the case of a half-marathon runner who presented with exertional heatstroke (EHS), whose management was confounded by concurrent treatment of his bipolar disorder with olanzapine. Antipsychotics can have a profound effect on thermoregulation and can cause athletes to present with features of neuroleptic malignant syndrome in the setting of EHS. It is vital for medical providers to consider the thermoregulatory effects of all medications, including antipsychotics, when providing care during sporting events.

COVID-19 and thermoregulation-related problems: Practical recommendations

The COVID-19 pandemic started in the cold months of the year 2020 in the Northern hemisphere. Concerns were raised that the hot season may lead to additional problems as some typical interventions to prevent heat-related illness could potentially conflict with precautions to reduce coronavirus transmission. Therefore, an international research team organized by the Global Health Heat Information Network generated an inventory of the specific concerns about this nexus and began to address the issues. Three key thermal and covid-19 related topics were highlighted: 1) For the general public, going to public cool areas in the hot season interferes with the recommendation to stay at home to reduce the spread of the virus. Conflicting advice makes it necessary to revise national heat plans and alert policymakers of this forecasted issue. 2) For medical personnel working in hot conditions, heat strain is exacerbated due to a reduction in heat loss from wearing personal protective equipment to prevent contamination. To avoid heat-related injuries, medical personnel are recommended to precool and to minimize the increase in body core temperature using adopted work/rest schedules, specific clothing systems, and by drinking cold fluids. 3) Fever, one of the main symptoms of COVID-19, may be difficult to distinguish from heat-induced hyperthermia and a resting period may be necessary prior to measurement to avoid misinterpretation. In summary, heat in combination with the COVID-19 pandemic leads to additional problems; the impact of which can be reduced by revising heat plans and implementing special measures attentive to these compound risks.

Effects of feed removal on thermoregulation and intestinal morphology in pigs recovering from acute hyperthermia

Feed consumption increases body temperature and may delay a return to euthermia and exacerbate intestinal injury following acute hyperthermia recovery in pigs. Therefore, the study objective was to evaluate the effects of feed removal on body temperature and intestinal morphology in pigs exposed to acute hyperthermia and then rapidly cooled. Twenty-four gilts (78.53 ± 5.46 kg) were exposed to thermoneutral (TN; n = 12 pigs; 21.21 ± 0.31 °C; 61.88 ± 6.93% RH) conditions for 6 h, or heat stress (HS; 38.51 ± 0.60 °C; 36.38 ± 3.40% RH) conditions for 3 h followed by a 3-h recovery period of rapid cooling (HSC;n = 12 pigs; TN conditions and cold water dousing). Within each recovery treatment, one-half of the pigs were provided feed ad libitum (AF; n = 6 pigs per recovery treatment) and one-half of the pigs were not provided feed (NF; n = 6 pigs per recovery treatment). Gastrointestinal (TGI), vaginal (TV), and skin (TSK) temperatures and respiration rate (RR) were recorded every 15 min. Pigs were video-recorded to assess feeding and drinking attempts. Immediately following the 6-h thermal stress period, pigs were euthanized, and intestinal samples were collected to assess morphology. During the HS period, Tv, TGI, TSK, and RR were increased (P < 0.01; 1.63, 2.05, 8.32 °C, and 88 breaths per min, respectively) in HSC vs. TN pigs, regardless of feeding treatment. Gastrointestinal temperature was greater (P = 0.03; 0.97 °C) in HSC + AF vs. HSC + NF pigs from 45 to 180 min of the recovery period. During the recovery period, feeding attempts were greater (P = 0.02; 195.38%) in AF vs. NF pigs. No drinking attempt differences were detected with any comparison (P > 0.05). A decrease (P < 0.01) in jejunum and ileum villus height (24.72% and 26.11%, respectively) and villus height-to-crypt depth ratio (24.03% and 25.29%, respectively) was observed in HSC vs. TN pigs, regardless of feeding treatment. Ileum goblet cells were reduced (P = 0.01; 37.87%) in HSC vs. TN pigs, regardless of feeding treatment. In summary, TGI decreased more rapidly following acute hyperthermia when the feed was removed, and this may have implications toward using feed removal as a strategy to promote acute hyperthermia recovery in pigs.

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.

Effects of heat: UK exercise Saif Sareea 3 and interpreting military climatic guidance

Introduction

Over recent years much research, both civilian and military, has occurred in the field of heat illness. This has helped force health protection and medical management of service personnel operating in hot climates. Exercise Saif Sareea 3 in Oman saw a collection of presentations to the deployed UK medical treatment facilities due to the effects of heat.

Method

This paper aims to describe the case series of 24 casualties that presented to the deployed primary care facilities and 17 that were admitted to the deployed secondary care facility due to the effects of heat.

Results

Only 10 casualties fulfilled the in-theatre diagnostic criteria for heat illness, of which two were of moderate severity and required aeromedical evacuation to the UK.

Conclusions

Commanders appeared extremely well read on Joint Service Publication 539 (JSP539; May 2017) Heat Illness and Cold Injury: Prevention and Management, following the Brecon enquiry, and were proactive in managing their force in preventative measures. This likely contributed towards the low numbers of patients with heat illness seen on the exercise. JSP539 did, however, appear to have some limitations when trying to apply it to all patients seen within the operational patient care pathway, and some areas for development are discussed.

Do Alternative Cooling Methods Have Effective Cooling Rates for Hyperthermia Compared With Previously Established CWI Cooling Rates?

Clinical Scenario: In the last few years, there have been several studies examining alternative cooling strategies in the treatment of exertional heat stroke (EHS). Morbidity and mortality with EHS are associated with how long the patient's core body temperature remains above the critical threshold of 40.5°C. Although cold-water immersion (CWI) is the gold standard of treatment when cooling a patient with EHS, more recent alternative cooling techniques have been examined for use in settings where CWI may not be feasible (ie, remote locations). Clinical Question: Do alternative cooling methods have effective core body temperature cooling rates for hyperthermia compared with previously established CWI cooling rates? Summary of Key Findings: The authors searched for studies using alternative cooling methods to cool hyperthermic individuals. To be included, the studies needed a PEDro score ≥6 and a level of evidence ≥2. They found 9 studies related to our focused clinical question; of these, 5 studies met the inclusion criteria. The cooling rates for hand cooling, cold-water shower, and ice-sheet cooling were 0.03°C/min, 0.08°C/min, and 0.06°C/min, respectively, whereas the tarp-assisted cooling with oscillation (TACO) method was the only method that had an acceptable cooling rate (range 0.14-0.17°C/min). Clinical Bottom Line: When treating EHS, if CWI is not available, the tarp-assisted cooling method may be a reasonable alternative. Clinicians should not use cold shower, hand cooling, or ice-sheet cooling if better cooling methods are available. Clinicians should always use CWI when available. Strength of Recommendation: Five level 2 studies with PEDro scores ≥6 suggest the TACO method is the only alternative cooling method that decreases core body temperature at a similar, though slower, rate of CWI. Hand cooling, cold showering, and ice-sheet cooling do not decrease core body temperature at an appropriate rate and should not be used in EHS situations if a modality with a better cooling rate is available.

Optimizing Health, Wellness, and Performance of the Tactical Athlete

Tactical athletes are individuals in service occupations with significant physical fitness and performance requirements such as law enforcement, firefighters, emergency responders, and military service members. Tactical athletes also may have specific administrative requirements related to documenting physical injuries. Musculoskeletal injuries are a large burden on the tactical athlete population, with incident rates varying based on the specific profession. Chronic exertional compartment syndrome (CECS) is difficult to manage in the tactical athlete population due to their limited ability to reduce impact activities and poor surgical outcomes. Botulinum neurotoxin-A and gait retraining show promise as alternative treatments for CECS. Heat injuries are frequent in the tactical athlete populations, and a graduated return to play process helps to prevent morbidity. Management of musculoskeletal injuries in tactical athletes requires consideration of operational schedules and adequate reconditioning, in addition to traditional injury evaluation.

Body cooling effects of immersion of the forearms in high-concentration artificial carbonic acid water at 25°C

BACKGROUND

This study examined the effects of immersion in stirred, high-concentration, artificial carbonic acid water on body cooling.

METHODS

Seven healthy male students (23 ± 2 years old) participated in the experiment. Signed informed consent was obtained from all subjects before the experiment. The subjects changed into shorts and T-shirts and entered an experimental room (with room temperature controlled at 30 °C and relative humidity maintained at 70%) at least 30 min before starting the experiment. After starting the experiment, the subjects were asked to rest on an exercise bike for 5 min and then pedal for 20 min. The exercise load was set to reach 50% of each subject's presumed maximum oxygen intake at 5 min after starting exercise. Subjects then continued pedaling for 1 min to cool down. After this exercise, subjects sat on a chair and immersed forearms in tap water or artificial carbonic acid water (CO2 water) at 25 °C for 20 min. During immersion, tap water or CO2 water was stirred slowly with a pump. After immersion, subjects rested for 10 min. Skin temperature and skin blood flow (left forearm), as well as heart rate and ear canal temperature, were measured continuously. Thermal sensation and thermal comfort were measured intermittently.

RESULTS

Skin blood flow of the immersed forearms was higher in CO2 water than in tap water during immersion. The blood flow in the last 5 min (average at rest was 100%) was significantly higher in CO2 water (290.85 ± 84.81%) than in tap water (104.80 ± 21.99%). Thermal sensation and thermal comfort were not different between conditions. Ear canal temperature significantly declined more in CO2 water (- 0.56 ± 0.31 °C) than in tap water (- 0.48 ± 0.30 °C) during immersion.

CONCLUSIONS

Our study suggests that immersion of the forearms in slowly stirred CO2 water at 25 °C reduces core temperature elevated by heat stress or exercise more effectively than does tap water at the same temperature. Immersion of the forearms in stirred CO2 water at 25 °C could be useful as a preventive measure against heat stroke from summer work or exercise.

A body bag can save your life: a novel method of cold water immersion for heat stroke treatment

Non-exertional heat stroke is a life-threatening condition characterized by passive exposure to high ambient heat, a core body temperature of 40°C (104°F) or greater, and central nervous system dysfunction. Rapid cooling is imperative to minimize mortality and morbidity. Although evaporative and convective measures are often used for cooling heat stroke patients, cold water immersion produces the fastest cooling. However, logistical difficulties make cold water immersion challenging to implement in the emergency department. To our knowledge, there is no documented case utilizing a body bag (ie, human remains pouch) as a cold water immersion tank for rapid resuscitation of heat stroke. During a regional heat wave an elderly woman was found unconscious in a parking lot with an oral temperature of 40°C (104°F) and altered mental status. She was cooled to 38.4°C (101.1°F) in 10 minutes by immersion in an ice- and water-filled body bag. The patient rapidly regained normal mentation and was discharged home from the ED. This case highlights a novel method for efficient and convenient cold water immersion for heat stroke treatment in the emergency department.

First aid cooling techniques for heat stroke and exertional hyperthermia: A systematic review and meta-analysis

BACKGROUND

Heat stroke is an emergent condition characterized by hyperthermia (>40 °C/>104 °F) and nervous system dysregulation. There are two primary etiologies: exertional which occurs during physical activity and non-exertional which occurs during extreme heat events without physical exertion. Left untreated, both may lead to significant morbidity, are considered a special circumstance for cardiac arrest, and cause of mortality.

METHODS

We searched Medline, Embase, CINAHL and SPORTDiscus. We used Grading of Recommendations Assessment, Development and Evaluation (GRADE) methods and risk of bias assessments to determine the certainty and quality of evidence. We included randomized controlled trials, non-randomized trials, cohort studies and case series of five or more patients that evaluated adults and children with non-exertional or exertional heat stroke or exertional hyperthermia, and any cooling technique applicable to first aid and prehospital settings. Outcomes included: cooling rate, mortality, neurological dysfunction, adverse effects and hospital length of stay.

RESULTS

We included 63 studies, of which 37 were controlled studies, two were cohort studies and 24 were case series of heat stroke patients. Water immersion of adults with exertional hyperthermia [cold water (14-17 °C/57.2-62.6 °F), colder water (8-12 °C/48.2-53.6 °F) and ice water (1-5 °C/33.8-41 °F)] resulted in faster cooling rates when compared to passive cooling. No single water temperature range was found to be associated with a quicker core temperature reduction than another (cold, colder or ice).

CONCLUSION

Water immersion techniques (using 1-17 °C water) more effectively lowered core body temperatures when compared with passive cooling, in hyperthermic adults. The available evidence suggests water immersion can rapidly reduce core body temperature in settings where it is feasible.

Time course determination of the effects of rapid and gradual cooling after acute hyperthermia on body temperature and intestinal integrity in pigs

Rapid cooling after acute hyperthermia may cause a sustained increase in body temperature and exacerbate intestinal damage in pigs. Therefore, the study objective was to evaluate the temporal effects of rapid and gradual cooling on body temperature response and intestinal integrity after acute hyperthermia in pigs. In three repetitions, 54 pigs [83.3 ± 6.7 kg initial body weight (BW)], balanced by sex were exposed to thermoneutral conditions for 6 h (TN; n = 6 pigs/repetition; 21.1 ± 2.0°C), or heat stress conditions (HS; 39.3 ± 1.6°C) for 3 h, followed by a 3 h recovery period of gradual cooling [HSGC; n = 6 pigs/repetition; gradual decrease from HS to TN conditions] or rapid cooling [HSRC; n = 6 pigs/repetition; rapid TN exposure and cold water (4.0°C) dousing every 30 min for 1.5 h]. Feed was withheld throughout the entire 6 h period, but water was provided ad libitum. Gastrointestinal (T_GI) and rectal (T_R) temperatures were recorded every 15 min during the HS and recovery periods. Six pigs per repetition (n = 2/treatment) were euthanized and jejunal and ileal samples were collected for histology immediately after (d 0), 2 d after, and 4 d after the recovery period. Data were analyzed using PROC MIXED in SAS 9.4. Overall, rapid cooling reduced T_R and T_GI (P < 0.01; 0.95°C and 0.74°C, respectively) compared to gradual cooling. Jejunal villus height was reduced overall (P = 0.02; 14.01%) in HSGC compared to HSRC and TN pigs. Jejunal villus height-to-crypt depth ratio was reduced overall (P = 0.05; 16.76%) in HSGC compared to TN pigs. Ileal villus height was reduced overall (P < 0.01; 16.95%) in HSGC compared to HSRC and TN pigs. No other intestinal morphology differences were detected. In summary, HSRC did not cause a sustained increase in body temperature and did not negatively impact biomarkers of intestinal integrity in pigs.

Renal and segmental artery hemodynamics during whole body passive heating and cooling recovery

High environmental temperatures are associated with increased risk of acute kidney injury, which may be related to reductions in renal blood flow. The susceptibility of the kidneys may be increased because of heat stress-induced changes in renal vascular resistance (RVR) to sympathetic activation. We tested the hypotheses that, compared with normothermia, increases in RVR during the cold pressor test (CPT, a sympathoexcitatory maneuver) are attenuated during passive heating and exacerbated after cooling recovery. Twenty-four healthy adults (22 ± 2 yr; 12 women, 12 men) completed CPTs at normothermic baseline, after passive heating to a rise in core temperature of ~1.2°C, and after cooling recovery when core temperature returned to ~0.2°C above normothermic baseline. Blood velocity was measured by Doppler ultrasound in the distal segment of the right renal artery (Renal, n = 24 during thermal stress, n = 12 during CPTs) or the middle portion of a segmental artery (Segmental, n = 12). RVR was calculated as mean arterial pressure divided by renal or segmental blood velocity. RVR increased at the end of CPT during normothermic baseline in both arteries (Renal: by 1.0 ± 1.0 mmHg·cm−1·s, Segmental: by 2.2 ± 1.2 mmHg·cm−1·s, P ≤ 0.03), and these increases were abolished with passive heating ( P ≥ 0.76). At the end of cooling recovery, RVR in both arteries to the CPT was restored to that of normothermic baseline ( P ≤ 0.17). These data show that increases in RVR to sympathetic activation during passive heating are attenuated and return to that of normothermic baseline after cooling recovery.

NEW & NOTEWORTHY Our data indicate that increases in renal vascular resistance to the cold pressor test (i.e., sympathetic activation) are attenuated during passive heating, but at the end of cooling recovery this response returns to that of normothermic baseline. Importantly, hemodynamic responses were assessed in arteries going to (renal artery) and within (segmental artery) the kidney, which has not been previously examined in the same study during thermal and/or sympathetic stressors.

Health Risks and Interventions in Exertional Heat Stress

BACKGROUND

With climate change, heat waves are expected to become more frequent in the near future. Already, on average more than 25 000 "heat deaths" are estimated to occur in Europe every year. However, heat stress and heat illnesses arise not just when ambient temperatures are high. Physical exertion increases heat production within the organism many times over; if not enough heat is lost, there is a risk of exertional heat stress. This review article discusses contributing factors, at-risk groups, and the diagnosis and treatment of heat illnesses.

METHODS

A selective literature search was carried out on PubMed. Current guidelines and expert recommendations were also included.

RESULTS

Apart from muscular heat production (>70% of converted energy), there are other factors that singly or in combination can give rise to heat stress: clothing, climate/acclimatization, and individual factors. Through its insulating properties, clothing reduces the evaporation of sweat (the most effective physiological cooling mechanism). A sudden heat wave, or changing the climate zone (as with air travel), increases the risk of a heat-related health event. Overweight, low fitness level, acute infections, illness, dehydration, and other factors also reduce heat tolerance. In addition to children, older people are particularly at risk because of their reduced physiological adaptability, (multi-)morbidity, and intake of prescription drugs. A heat illness can progress suddenly to life-threatening heat stroke. Successful treatment depends on rapid diagnosis and cooling the body down as quickly as possible. The aim is to reduce core body temperature to <40 °C within 30 minutes.

CONCLUSION

Immediately effective cooling interventions are the only causal treatment for heat stroke. Time once lost cannot be made up. Prevention (acclimatization, reduced exposure, etc.) and terminating the heat stress in good time (e.g., stopping work) are better than any cure.

Elevated Core Temperature in Florida Fernery Workers: Results of a Pilot Study

With expected increases in extreme weather, there may be a greater risk of injury from extreme heat in outdoor worker populations. To plan for future adaptation measures, studies are needed that can characterize workers’ physiologic responses to heat in outdoor settings such as agriculture. The objective of this study was to characterize occupational heat exposure, key vulnerability factors (e.g., gender, energy expenditure), and physiologic heat stress response in a sample of fernery workers. Forty-three fernery workers over 86 workdays were examined regarding heat-related illness (HRI) during the summer months of 2012 and 2013. The key outcome measure was whether a participant’s body core temperature (Tc) reached or exceeded 38.0°C (100.4ºF; Tc38). Participants’ Tc exceeded 38.0°C on 49 (57%) of the workdays, with 30 of 40 participants reaching or exceeding Tc38 on at least one workday. Adjusting for sex, there was a 12% increase in the odds of Tc38 for every 100 kilocalories of energy expended (OR: 1.12; 95% Confidence Interval [CI]: [1.03, 1.21]). Adjusting for energy expenditure, females had 5 times greater odds of Tc38 compared with males (OR: 5.38; 95% CI: [1.03, 18.30]). These findings provide evidence of elevated Tc in Florida fernery workers, indicating an increased risk of occupational HRI, and the need for policy and interventions to address this health risk.

The Epidemiology and Management of Exertional Heat Illnesses in High School Sports During the 2012/2013–2016/2017 Academic Years

Context: Recent data on exertional heat illness (EHI) in high school sports are limited yet warranted to identify specific settings with the highest risk of EHI. Objective: To describe the epidemiology of EHI in high school sports during the 2012/2013-2016/2017 academic years. Design: Descriptive epidemiology study. Setting: Aggregate injury and exposure data collected from athletic trainers working in high school sports in the United States. Patients or Other Participants: High school athletes during the 2012/2013-2016/2017 academic years. Intervention: High School Reporting Information Online surveillance system data from the 2012/2013-2016/2017 academic years were analyzed. Main Outcome Measures: EHI counts, rates per 10,000 athlete exposures (AEs), and distributions were examined by sport, event type, and US census region. EHI management strategies provided by athletic trainers were analyzed. Injury rate ratios with 95% confidence intervals (CIs) compared EHI rates. Results: Overall, 300 EHIs were reported for an overall rate of 0.13/10,000 AE (95% CI, 0.11 to 0.14). Of these, 44.3% occurred in American football preseason practices; 20.7% occurred in American football preseason practices with a registered air temperature ≥90°F and ≥1 hour into practice. The EHI rate was higher in American football than all other sports (0.52 vs 0.04/10,000 AE; injury rate ratio = 11.87; 95% CI, 9.22 to 15.27). However, girls' cross-country had the highest competition EHI rate (1.18/10,000 AE). The EHI rate was higher in the South US census region than all other US census regions (0.23 vs 0.08/10,000 AE; injury rate ratio = 2.96; 95% CI, 2.35 to 3.74). Common EHI management strategies included having medical staff on-site at the onset of EHI (92.7%), removing athlete from play (85.0%), and giving athlete fluids via the mouth (77.7%). Conclusions: American football continues to have the highest overall EHI rate although the high competition EHI rate in girls' cross-country merits additional examination. Regional differences in EHI incidence, coupled with sport-specific variations in management, may highlight the need for region- and sport-specific EHI prevention guidelines.

Heart rate variability dynamics during treatment for exertional heat strain when immediate response is not possible

NEW FINDINGS

What is the central question of this study? Does a delay in cold water immersion treatment affect the cardiac autonomic control of exertionally heat-strained individuals? What is the main finding and its importance? Cold water immersion is effective for treating exertionally heat-strained individuals even when treatment is commenced with a significant delay. However, that treatment delay leads to only partial/transient restoration of cardiac autonomic control. Therefore, we recommend that exertional heatstroke patients are continuously monitored for several hours even after core temperature has returned to normal values.

ABSTRACT

Immediate cold water immersion (CWI) is the gold-standard treatment for exertional heatstroke. In the field, however, treatment is often delayed, primarily owing to a delayed paramedic response and/or inaccurate diagnosis. We examined the effect of treatment (reduction of rectal temperature to 37.5°C) delays of 5 (short), 20 (moderate) and 40 (prolonged) min on cardiac autonomic control [as assessed via heart rate variability (HRV)] in eight exertionally heat-strained (40.0°C rectal temperature) individuals. Eleven HRV indices were computed that have been described commonly in the literature and characterize almost all known domains of the variability and complexity of the cardiopulmonary system. We found that the cardiac autonomic control (as assessed via HRV) of exertionally heat-strained individuals was significantly affected by the amount of time it took for the CWI treatment to be applied. Six out of 11 HRV indices studied, from all variability domains, displayed strong (P ≤ 0.005) time × delay interaction effects. Moreover, the number of significantly (P ≤ 0.005) abnormal (i.e. different from the short delay) HRV indices more than doubled (seven versus 15) from the moderate delay to the prolonged delay. Finally, our results demonstrated that a CWI treatment applied with delays of 20 and, primarily, 40 min did not lead to a full restoration of cardiac autonomic control of exertionally heat-strained individuals. In conclusion, this study supports CWI for treating exertionally heat-strained individuals even when applied with prolonged delay, but it highlights the importance of continued cardiac monitoring of patients who have suffered exertional heatstroke for several hours after restoration of core temperature to normal.

Successful Management of Severe Exertional Heat Stroke with Endovascular Cooling After Failure of Standard Cooling Measures

BACKGROUND

Exertional heat stroke (EHS) is a potentially life-threatening emergency requiring rapid reduction in core body temperature. Methods of cooling include cold water immersion, ice packs, cold water lavage, and chilled saline, among others. We report a case of EHS successfully cooled using an endovascular cooling device after traditional cooling methods failed to reduce core body temperature.

CASE REPORT

A 24-year old soldier collapsed during a 12-mile foot march while training in southern Georgia. His initial rectal temperature was 43.1°C (109.6°F). External cooling measures (ice sheet application) were initiated on site and Emergency Medical Services were called to transport to the hospital. Paramedics obtained a repeat rectal temperature of 42.4°C (108.4°F). Ice sheet application and chilled saline infusion were continued throughout transport to the Emergency Department (ED). Total prehospital treatment time was 50 min. Upon ED arrival, the patient's rectal temperature was 41.2°C (106.2°F). He was intubated due to a Glasgow Coma Scale score of 4, and endovascular cooling was initiated. Less than 45 minutes later his core body temperature was 37.55°C (99.6°F). He was admitted to the intensive care unit, where his mental status rapidly improved. He was found to have rising liver enzymes, and there was concern for his developing disseminated intravascular coagulation, prompting transfer to a tertiary care center. He was subsequently discharged from the hospital 14 days after his initial injury without any persistent sequelae. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: The primary treatment for EHS is rapid reduction of core body temperature. When external cooling methods fail, endovascular cooling can be used to rapidly decrease core body temperature.

Exertional Heat Stroke within Secondary School Athletics

Exertional heat stroke (EHS) remains one of the leading causes of sudden death in sport despite clear evidence showing 100% survivability with the proper standards of care in place and utilized. Of particular concern are student athletes competing at the secondary school level, where the extent of appropriate health care services remains suboptimal compared with organized athletics at the collegiate level and higher. While rapid recognition and rapid treatment of EHS ensures survival, the adoption and implementation of these lifesaving steps within secondary school athletics warrant further discussion within the sports medicine community. Establishing proper policies regarding the prevention and care of EHS coupled with utilizing an interdisciplinary care approach is essential for 1) minimizing risk and 2) guaranteeing optimal outcomes for the patient.

Inconsistency in the Standard of Care-Toward Evidence-Based Management of Exertional Heat Stroke

Tokyo 2020 Summer Olympics are projected to experience environmental heat stress that surpasses the environmental conditions observed in the Atlanta (1996), Athens (2004), Beijing (2008), and Rio (2016) Summer Olympics. This raises particular concerns for athletes who will likely to be exposed to extreme heat during the competitions. Therefore, in mass-participation event during warm season, it is vital for the hosting organization to build preparedness and resilience against heat, including appropriate treatment, and management strategies for exertional heat stroke (EHS). However, despite the existing literature regarding the evidence-based management of EHS, rectal thermometry and whole-body cold-water immersion are not readily accepted by medical professionals outside of the sports, and military medicine professionals. Current Japanese medical standard is no exception in falling behind on evidence-based management of EHS. Therefore, the first aim of this paper is to elucidate the inconsistency between the standard of care provided in Japan for EHS and what has been accepted as the gold standard by the scientific literature. The second aim of this paper is to provide optimal EHS management strategies that should be implemented at the Tokyo 2020 Summer Olympics from organizational level to maximize the safety of athletes and to improve organizational resilience to heat. The risk of extreme heat is often neglected until a catastrophic incidence occurs. It is vital for the Japanese medical leadership and athletic communities to re-examine the current EHS management strategies and implement evidence-based countermeasure for EHS to expand the application of scientific knowledge.

Use of the heat tolerance test to assess recovery from exertional heat stroke

Exercise or work in hot environments increases susceptibility to exertional heat illnesses such as exertional heat stroke (EHS). EHS occurs when body heat gain exceeds body heat dissipation, resulting in rapid body heat storage and potentially life-threatening consequences. EHS poses a dangerous threat for athletes, agriculture workers, and military personnel, as they are often exposed to hot environmental conditions that restrict body heat loss or contribute to body heat gain. Currently, there is limited guidance on return to activity (RTA) after an episode of EHS. While examining biomarkers in the blood is thought to be beneficial for determining RTA, they are not sensitive or specific enough to be a final determining factor as organ damage may persist despite blood biomarkers returning to baseline levels. As such, additional assessment tests to more accurately determine RTA are desired. One method used for determining RTA is the heat tolerance test (HTT, 120 minutes treadmill walking; 40°C, 40% relative humidity). Unfortunately, the HTT provides even less information about EHS recovery since it offers no test sensitivity or specificity even after years of implementation. We provide an overview of the HTT and the controversy of this test with respect to assessment criteria, applicability to tasks involving high metabolic workloads, and the lack of follow-up analyses to determine its accuracy for determining recovery in order to diminish the likelihood of a second EHS occurrence.

Cooling Rates of Hyperthermic Humans Wearing American Football Uniforms When Cold-Water Immersion Is Delayed

CONTEXT

Treatment delays can be contributing factors in the deaths of American football athletes from exertional heat stroke. Ideally, clinicians begin cold-water immersion (CWI) to reduce rectal temperature (Trec) to <38.9°C within 30 minutes of collapse. If delays occur, experts recommend Trec cooling rates that exceed 0.15°C/min. Whether treatment delays affect CWI cooling rates or perceptual variables when football uniforms are worn is unknown.

OBJECTIVE

To answer 3 questions: (1) Does wearing a football uniform and delaying CWI by 5 minutes or 30 minutes affect Trec cooling rates? (2) Do Trec cooling rates exceed 0.15°C/min when treatment delays have occurred and individuals wear football uniforms during CWI? (3) How do treatment delays affect thermal sensation and Environmental Symptoms Questionnaire responses?

DESIGN

Crossover study.

SETTING

Laboratory.

PATIENTS OR OTHER PARTICIPANTS

Ten physically active men (age = 22 ± 2 y, height = 183.0 ± 6.9 cm, mass = 78.9 ± 6.0 kg).

INTERVENTION(S)

On 2 days, participants wore American football uniforms and exercised in the heat until Trec was 39.75°C. Then they sat in the heat, with equipment on, for either 5 or 30 minutes before undergoing CWI (10.6°C ± 0.1°C) until Trec reached 37.75°C.

MAIN OUTCOME MEASURE(S)

Rectal temperature and CWI duration were used to calculate cooling rates. Thermal sensation was measured pre-exercise, postexercise, postdelay, and post-CWI. Responses to the Environmental Symptoms Questionnaire were obtained pre-exercise, postdelay, and post-CWI.

RESULTS

The Trec cooling rates exceeded recommendations and were unaffected by treatment delays (5-minute delay = 0.20°C/min ± 0.07°C/min, 30-minute delay = 0.19°C/min ± 0.05°C/min; P = .4). Thermal sensation differed between conditions only postdelay (5-minute delay = 6.5 ± 0.6, 30-minute delay = 5.5 ± 0.7; P < .05). Environmental Symptoms Questionnaire responses differed between conditions only postdelay (5-minute delay = 27 ± 15, 30-minute delay = 16 ± 12; P < .05).

CONCLUSIONS

Treatment delays and football equipment did not impair CWI's effectiveness. Because participants felt cooler and better after the 30-minute delay despite still having elevated Trec, clinicians should use objective measurements (eg, Trec) to guide their decision making for patients with possible exertional heat stroke.

Effects of Intravenous Cold Saline on Hyperthermic Athletes Representative of Large Football Players and Small Endurance Runners

OBJECTIVE

To evaluate the cooling effects of intravenous (IV) cold normal (0.9%) saline on hyperthermic athletes.

DESIGN

Randomized crossover study design.

SETTING

Controlled research laboratory.

PARTICIPANTS

Twelve male participants who were representative of a collegiate cross-country (6) and American football (6) population.

INTERVENTIONS

Participants underwent body composition analysis using a BodPod. They were placed in an environmentally controlled chamber and brought to a Tc of 39.5°C with dynamic exercise. When temperatures were reached, they were treated with either 2 L of cold saline (CS) (4°C) or intravenous room temperature (22°C) saline (RS) over a ∼30-minute period. Tre was measured with a rectal temperature probe every minute during the treatment period.

MAIN OUTCOME MEASURES

Total ΔTre (ending Tre - starting Tre) and cooling rate (total change in Tre/time) were measured for each condition, and body composition variables calculated included body surface area (BSA), BSA-to-mass ratio (BSA/mass), lean body mass, and body fat percentage (%BF) (P < 0.05).

RESULTS

Statistically significant differences were found in the total ΔTre and cooling rate between the CS and RS trials. The cooling rate for the CS trials was significantly correlated to mass, BSA, BSA/mass, and %BF.

CONCLUSIONS

In hyperthermic athletes, core temperature was reduced more effectively using chilled saline during IV infusion. Body composition had a significant impact on overall cooling revealing that the smaller and leaner participants cooled at a greater rate. When indicated, CS infusion could be considered for cooling hyperthermic individuals when other methods are not available.

Effect of a Cooling Kit on Physiology and Performance Following Exercise in the Heat

Context: Exercising in the heat leads to an increase in body temperature that can increase the risk of heat illness or cause detriments in exercise performance. Objective: To examine a phase change heat emergency kit (HEK) on thermoregulatory and perceptual responses and subsequent exercise performance following exercise in the heat. Design: Two randomized crossover trials that consisted of 30 minutes of exercise, 15 minutes of treatment (T1), performance testing (5-10-5 pro-agility test and 1500-m run), and another 15 minutes of treatment (T2) identical to T1. Setting: Outdoors in the heat (wet-bulb globe temperature: 31.5°C [1.8°C] and relative humidity: 59.0% [5.6%]). Participants: Twenty-six (13 men and 13 women) individuals (aged 20–27 y). Interventions: Treatment was performed with HEK and without HEK (control, CON) modality. Main Outcome Measures: Gastrointestinal temperature, mean skin temperature, thirst sensation, and muscle pain. Results: Maximum gastrointestinal temperature following exercise and performance was not different between trials (P > .05). Cooling rate was faster during T1 CON (0.053°C/min [0.049°C/min]) compared with HEK (0.043°C/min [0.032°C/min]; P = .01). Mean skin temperature was lower in HEK during T1 (P < .001) and T2 (P = .05). T2 thirst was lower in CON (P = .02). Muscle pain was lower in HEK in T2 (P = .03). Performance was not altered (P > .05). Conclusions: HEK improved perception but did not enhance cooling or performance following exercise in the heat. HEK is therefore not recommended to facilitate recovery, treat hyperthermia, or improve performance.

Unexpected Human Fatality Associated with Bed Bug (Hemiptera: Cimicidae) Heat Treatment

Thermal insect treatments can be an effective method of controlling cryptic insect pests, particularly bed bugs, in residential settings. The treatments require high heat over a sustained timeframe. Residents are not present during treatment but return after completion. An unexpected death was investigated following heat treatment for bed bugs in the home of an elderly female, found with a postmortem axillary temperature of 106.2°F (41.2°C) approximately 8 h after returning home. The cause of death was classified as hyperthermia with a contributory cause of hypertensive cardiovascular disease. The manner of death was an accident. The decedent had medical history and medications that could have impaired her ability to dissipate heat. Furthermore, the air conditioning inside the residence was not functional following treatment. Recommendations including education regarding heat stroke and treatment, re-entry timeframes, and/or temperature thresholds are suggested to reduce the risk of heat-related injury or death in vulnerable populations.

Interactions of Gut Microbiota, Endotoxemia, Immune Function, and Diet in Exertional Heatstroke

Exertional heatstroke (EHS) is a medical emergency that cannot be predicted, requires immediate whole-body cooling to reduce elevated internal body temperature, and is influenced by numerous host and environmental factors. Widely accepted predisposing factors (PDF) include prolonged or intense exercise, lack of heat acclimatization, sleep deprivation, dehydration, diet, alcohol abuse, drug use, chronic inflammation, febrile illness, older age, and nonsteroidal anti-inflammatory drug use. The present review links these factors to the human intestinal microbiota (IM) and diet, which previously have not been appreciated as PDF. This review also describes plausible mechanisms by which these PDF lead to EHS: endotoxemia resulting from elevated plasma lipopolysaccharide (i.e., a structural component of the outer membrane of Gram-negative bacteria) and tissue injury from oxygen free radicals. We propose that recognizing the lifestyle and host factors which are influenced by intestine-microbial interactions, and modifying habitual dietary patterns to alter the IM ecosystem, will encourage efficient immune function, optimize the intestinal epithelial barrier, and reduce EHS morbidity and mortality.