Heatstroke: a new look at an ancient disease

pH-Assisted multichannel heat shock monitoring in the endoplasmic reticulum with a pyridinium fluorophore

Heat shock is a global health concern as it causes permanent damage to living cells and has a relatively high mortality rate. Therefore, diagnostic tools that facilitate a better understanding of heat shock damage and the defense mechanism at the sub-cellular level are of great importance. In this report, we have demonstrated the use of a pyridinium-based fluorescent molecule, PM-ER-OH, as a 'multichannel' imaging probe to monitor the pH change associated with a heat shock in the endoplasmic reticulum. Among the three pyridinium derivatives synthesized, PM-ER-OH was chosen for study due to its excellent biocompatibility, good localization in the endoplasmic reticulum, and intracellular pH response signaled by a yellow fluorescence (λ max = 556 nm) at acidic pH and a far red fluorescence (λ max = 660 nm) at basic pH. By changing the excitation wavelength, we could modulate the fluorescence signal in 'turn-ON', single excitation ratiometric and 'turn-OFF' modes, making the fluorophore a 'multichannel' probe for both ex vitro and in vitro pH monitoring in the endoplasmic reticulum. The probe could efficiently monitor the pH change when heat shock was applied to cells either directly or in a pre-heated manner, which gives insight on cellular acidification caused by heat stress.

Computational insights into survival durations and prehospital interventions in accidental cold-water immersion: A comprehensive analysis of fresh and saltwater temperatures

This study examines the complex relationship between scenarios of cold-water immersion, survival durations, and prehospital interventions. It utilizes computational modeling methods to shed light on how different water temperatures affect individuals facing accidental cold-water immersion incidents. The analysis reveals significant variations in survival times based on water temperature. For example, subjects immersed in water at temperatures of 5 °C, 2 °C, and 0 °C had average survival times of 136, 113, and 100 min, respectively, under stable conditions. In flowing water at the same temperatures, survival times decreased to 119, 92, and 81 min, indicating the impact of water movement on cooling rates and survival durations. Likewise, individuals immersed in saltwater at temperatures of 5 °C, 2 °C, 0 °C, and -2 °C showed average survival times of 111, 88, 80, and 66 min, respectively, in static conditions. In flowing saltwater at the same temperatures, survival times decreased to 98, 74, 68, and 57 min, highlighting the influence of water flow on cooling rates and survival durations. A comparison between immersion in pure water and saltwater at 2 °C revealed survival times of 113 and 88 min under stable conditions and 92 and 74 min under dynamic conditions, emphasizing the role of water composition in survival outcomes. The study also challenges the notion that the demise of the Titanic's passengers and crew resulted from hypothermia, asserting instead that severe thermal shock was the primary cause. These numerical findings underscore the importance of considering water temperature, flow dynamics, and prompt medical responses in cold-water emergencies to enhance survival prospects. The study identifies water within the range of 41-43 °C as the most effective active external rewarming fluid for critical hypothermal conditions. By quantifying the impact of these variables on survival times, the study provides data-driven recommendations to improve emergency protocols and outcomes for individuals facing cold-water immersion incidents.

Heatstroke presentations to urban hospitals during BC's extreme heat event: lessons for the future

BACKGROUND

Climate change is leading to more extreme heat events in temperate climates that typically have low levels of preparedness. Our objective was to describe the characteristics, treatments, and outcomes of adults presenting to hospitals with heatstroke during BC's 2021 heat dome.

METHODS

We conducted a review of consecutive adults presenting to 7 hospitals in BC's Lower Mainland. We screened the triage records of all patients presenting between June 25th and 30th, 2021 for complaints related to heat, and reviewed the full records of those who met heatstroke criteria. Our primary outcome was in-hospital mortality. We used Mann-Whitney U tests and logistic regression to investigate associations between patient and treatment factors and mortality.

RESULTS

Among 10,247 consecutive presentations to urban hospitals during the extreme heat event, 1.3% (139; 95% confidence intervals [CI] 1.1-1.6%) met criteria for heatstroke. Of heatstroke patients, 129 (90.6%) were triaged into the two highest acuity levels. Patients with heatstroke had a median age of 84.4 years, with 122 (87.8%) living alone, and 101 (84.2%) unable to activate 911 themselves. A minority (< 5, < 3.6%) of patients presented within 48 h of the onset of extreme heat. Most patients (107, 77.0%) required admission, and 11.5% (16) died in hospital. Hypotension on presentation was associated with mortality (odds ratio [OR] 5.3).

INTERPRETATION

Heatstroke patients were unable to activate 911 themselves, and most presented with a 48-h delay. This delay may represent a critical window of opportunity for pre-hospital and hospital systems to prepare for the influx of high-acuity resource-intensive patients.

A century of exercise physiology: concepts that ignited the study of human thermoregulation. Part 3: Heat and cold tolerance during exercise

In this third installment of our four-part historical series, we evaluate contributions that shaped our understanding of heat and cold stress during occupational and athletic pursuits. Our first topic concerns how we tolerate, and sometimes fail to tolerate, exercise-heat stress. By 1900, physical activity with clothing- and climate-induced evaporative impediments led to an extraordinarily high incidence of heat stroke within the military. Fortunately, deep-body temperatures > 40 °C were not always fatal. Thirty years later, water immersion and patient treatments mimicking sweat evaporation were found to be effective, with the adage of cool first, transport later being adopted. We gradually acquired an understanding of thermoeffector function during heat storage, and learned about challenges to other regulatory mechanisms. In our second topic, we explore cold tolerance and intolerance. By the 1930s, hypothermia was known to reduce cutaneous circulation, particularly at the extremities, conserving body heat. Cold-induced vasodilatation hindered heat conservation, but it was protective. Increased metabolic heat production followed, driven by shivering and non-shivering thermogenesis, even during exercise and work. Physical endurance and shivering could both be compromised by hypoglycaemia. Later, treatments for hypothermia and cold injuries were refined, and the thermal after-drop was explained. In our final topic, we critique the numerous indices developed in attempts to numerically rate hot and cold stresses. The criteria for an effective thermal stress index were established by the 1930s. However, few indices satisfied those requirements, either then or now, and the surviving indices, including the unvalidated Wet-Bulb Globe-Thermometer index, do not fully predict thermal strain.

Therapeutic potential of traditional Chinese medicine on heat stroke

As global warming progresses, heat waves are becoming increasingly frequent and intense, meanwhile the incidence of heat stroke (HS) has increased sharply during the past decades. HS is typically associated with significant morbidity and mortality, and there is an urgent need for further research to solve this difficult issue. There currently exists difficulties regarding on-site emergency treatment methods and limited in-hospital treatment approaches, and better treatments are required as soon as possible. Theories and therapies from various traditional Chinese medicine (TCM) academic groups have been widely reported. Therefore, an exploration of prevention and protection methods should consider TCM experiences as an alternative. This article primarily reviews TCM herbal therapies and external therapies that have been described in various clinical reports and demonstrated in relevant studies. Herbal therapies, including herbal formulas, Chinese patent medicines (CPMs), single Chinese herbs, and associated extracts or monomers, are summarized based on the shared perspectives of the underlying mechanisms from TCM. In addition, external therapies including acupuncture, bloodletting, cupping, Gua sha and Tui na that have rarely been rarely mentioned and considered in most cases, are introduced and discussed to offer a unique perspective in the search for novel interventions for HS. In summary, TCM may provide abundant potential clinical benefits and research directions in the fight against HS.

Current clinical application of dantrolene sodium

Dantrolene sodium (DS) was first introduced as an oral antispasmodic drug. However, in 1975, DS was demonstrated to be effective for managing malignant hyperthermia (MH) and was adopted as the primary therapeutic drug after intravenous administration. However, it is difficult to administer DS intravenously to manage MH. MH is life-threatening, pharmacogenomically related, and induced by depolarizing neuromuscular blocking agents or inhalational anesthetics. All anesthesiologists should know the pharmacology of DS. DS suppresses Ca2+ release from ryanodine receptors (RyRs). RyRs are expressed in various tissues, although their distribution differs among subtypes. The anatomical and physiological functions of RyRs have also been demonstrated as effective therapeutic drugs for cardiac arrhythmias, Alzheimer's disease, and other RyR-related diseases. Recently, a new formulation was introduced that enhanced the hydrophilicity of the lipophilic DS. The authors summarize the pharmacological properties of DS and comment on its indications, contraindications, adverse effects, and interactions with other drugs by reviewing reference articles.

Recent progress of organic small molecule-based fluorescent probes for intracellular pH sensing

Fluorescent probes along with fluorescence microscopy are essential tools for biomedical research. Various cellular ubiquitous chemical factors such as pH, H₂O₂, and Ca²⁺ are labeled and traced using specific fluorescent probes, therefore helping us to explore their physiological function and pathological change. Among them, intracellular pH value is an important factor that governs biological processes, generally ∼7.2. Furthermore, specific organelles within cells possess unique acid-base homeostasis, involving the acidic lysosomes, alkalescent mitochondria, and neutral endoplasmic reticulum and Golgi apparatus, which undergo various physiological processes such as intracellular digestion, ATP production, and protein folding and processing. In this review, recently reported fluorescent probes targeted toward the lysosomes, mitochondria, endoplasmic reticulum, Golgi apparatus, and cytoplasm for sensing pH change are discussed, which involves molecular structures, fluorescence behavior, and biological applications.

Monitoring of the decreased mitochondrial viscosity during heat stroke with a mitochondrial AIE probe

Heat stroke is a fatal condition which usually results in central nervous system dysfunction, organism damage and even death. The relationship between heat stroke and mitochondria is still relatively unknown due to a lack of suitable tools. Herein, an aggregation-induced emission (AIE) probe CSP, by introducing a pyridinium cation as the mitochondria-targeted group to an AIE active core cyanostilbene skeleton, is highly sensitive to viscosity changes due to the restriction of intramolecular motion (RIM) and inhibition of twisted intramolecular charge transfer (TICT) in high-viscosity systems. As expected, with the viscosity increasing from 0.903 cP (0% glycerol) to 965 cP (99% glycerol), CSP exhibited a significant enhancement (more than 117-fold) in fluorescence intensity at 625 nm, with an excellent linear relationship between log I _{625 nm} and log η (R² = 0.9869, slope as high as 0.6727). More importantly, using CSP we have successfully monitored the decreased mitochondrial viscosity during heat stroke for the first time. All these features render the probe a promising candidate for further understanding the mechanism underlying mitochondria-associated heat stroke.

Optimization of a Rhabdomyolysis Model in Mice With Exertional Heat Stroke Mouse Model of EHS-Rhabdomyolysis

Exertional heat stroke (EHS) is a life-threatening disease characterized by high mortality and incidence of rhabdomyolysis (RM). It would therefore be valuable to establish a stable EHS-induced RM model that accurately reflects the clinical characteristics of EHS patients and provides an objective animal model for further study of the pathogenesis of RM. In the current study, 8∼9-week-old, male, wild-type C57BL/6J mice, at the stage of sexual maturity, were randomly divided into four groups: the EHS group, the classical heat stroke (CHS) group, the sham heat exercise group, and sham heat rest group. The survival rate of mice was determined under relatively high levels of temperature and humidity (37.5°C, 65% relative humidity (RH); 37.5°C, 70% RH; 39.5°C, 65% RH; and 39.5°C, 70% RH) as well as a high core temperature (Tc; 42, 42.5, and 43°C). Results showed that the environmental condition of 39.5°C and 65% RH was most suitable for EHS modeling. The end point of EHS evaluation was exhaustion or an individual’s core temperature reaching 43°C. The survival rate of mice in the EHS group within 24 h under these conditions was 37.34%, which is consistent with the high mortality characteristics noted in EHS patients. Severe RM was observed in the EHS group by H&E staining and transmission electron microscopy. Creatine kinase levels in the EHS group mostly exceeded 10,000 U/L, which was approximately 10 times higher than that in the sham heat rest group. Renal tubules of the EHS group exhibited severe necrosis, and calcium overload in the skeletal muscles of this group was also observed using intravital 2-photon microscopy. In conclusion, we made improvements to a stable EHS-induced RM animal model to truly reflect the clinical characteristics of EHS patients. This new model should be helpful in the further study of RM pathogenesis.

A photostable Si-rhodamine-based near-infrared fluorescent probe for monitoring lysosomal pH during heat stroke

Heat stroke is a symptom of hyperthermia with a temperature of more than 40 °C, which usually leads to all kinds of physical discomfort and even death. It is necessary to study the mechanism of action of heat stroke on cells or organelles (such as cytotoxicity of heat) and the processes of cells or organelles during heat stroke. Recent studies have shown that there is a certain correlation between heat stroke and lysosome acidity. In order to clarify their relationship, Lyso-NIR-pH, a photostable Si-rhodamine-based near-infrared fluorescent probe, was developed for sensing pH changes in lysosomes during heat stroke in this paper. For Lyso-NIR-pH, a morpholine group is employed as the lysosome-targeting unit and a H⁺-triggered openable deoxylactam is employed as the response unit to pH. Lyso-NIR-pH can detect pH with a high selectivity and a sensitivity, and its pK_a is 4.63. Lyso-NIR-pH also has outstanding imaging performances, such as excellent lysosome-targeting ability, low autofluorescence and photostable fluorescence signal, which are in favor of long-term imaging of pH with accurate fluorescence signals. Moreover, we successfully applied Lyso-NIR-pH to monitor lysosomal pH increases induced by chloroquine and apoptosis in live cells. Finally, we successfully applied Lyso-NIR-pH for monitoring changes of lysosomal pH during heat stroke. These results confirmed that Lyso-NIR-pH is a powerful tool to monitor pH change in lysosomes and study its possible effects.

Heat Sepsis Precedes Heat Toxicity in the Pathophysiology of Heat Stroke-A New Paradigm on an Ancient Disease

Heat stroke (HS) is an ancient illness dating back more than 2000 years and continues to be a health threat and to cause fatality during physical exertion, especially in military personnel, fire-fighters, athletes, and outdoor laborers. The current paradigm in the pathophysiology and prevention of HS focuses predominantly on heat as the primary trigger and driver of HS, which has not changed significantly for centuries. However, pathological and clinical reports from HS victims and research evidence from animal and human studies support the notion that heat alone does not fully explain the pathophysiology of HS and that HS may also be triggered and driven by heat- and exercise-induced endotoxemia. Exposure to heat and exercise stresses independently promote the translocation of lipopolysaccharides (LPS) from gram-negative bacteria in the gut to blood in the circulatory system. Blood concentration of LPS can increase to a threshold that triggers the systemic inflammatory response, leading to the downstream ramifications of cellular and organ damage with sepsis as the end point i.e., heat sepsis. The dual pathway model (DPM) of HS proposed that HS is triggered by two independent pathways sequentially along the core temperature continuum of >40 °C. HS is triggered by heat sepsis at Tc < 42 °C and by the heat toxicity at Tc > 42 °C, where the direct effects of heat alone can cause cellular and organ damage. Therefore, heat sepsis precedes heat toxicity in the pathophysiology of HS.

Acute liver failure and hepatic encephalopathy in exertional heat stroke

A 31-year-old man was brought to Accident & Emergency after collapsing during a race. On presentation, the patient had a temperature of 41.7°C (rectal). External cooling was started immediately. The patient was intubated in view of a Glasgow Coma Scale of 7 and was transferred to theintensive therapy unit. Laboratory results revealed an acute kidney injury, rhabdomyolysis, disseminated intravascular coagulopathy and acute liver failure. The patient was encephalopathic, jaundiced and difficult to sedate. His liver function continued to deteriorate with alanine aminotransferase (ALT) levels reaching 9207 U/L. King's Hospital Liver Centre, London was contacted for a possible liver transplant, and they advised an infusion of N-acetylcysteine. The following day liver function tests improved; thus, transplantation was not performed. The patient failed multiple sedation holds and required a tracheostomy. He continued to spike a fever. Despite no source of sepsis being found, the patient remained on broad spectrum antibiotics to cover for any potential infective causes until day 27. After 15 days, the patient's encephalopathy gradually improved. He was weaned off the ventilator and underwent intense physiotherapy. The patient was discharged from hospital one month after admission.

Pinpoint Diagnostic Kit for Heat Stroke by Monitoring Lysosomal pH

Heat stroke is one of the most serious causes of mortality. To prevent the situation, it is fundamental to research the mechanism of heat cytotoxicity. The preliminary results revealed that heat stroke and the change of lysosome acidity had some certain correlation. To further clarify their relationship, herein, we report a highly selective and sensitive fluorescence probe (NT1) for turn-on sensing of the pH value. NT2 was synthesized as control compound. Compared to NT2, NT1 showed accurate lysosome target ability. In addition, the suitable pK_a value (5.67) allows NT1 to response to the changes of lysosomal pH values. Most importantly, NT1 could be used to study the correlation between the change of lysosomal pH and heat stroke. It was shown that the lysosomal pH value increasing with temperature during heat stroke. Thus, NT1 was an excellent candidate for research of the complex biological mechanism of heat stroke.

Sodium tanshinone IIA sulfonate improves inflammation, aortic endothelial cell apoptosis, disseminated intravascular coagulation and multiple organ damage in a rat heat stroke model

The aim of the present study was to investigate the effects of sodium tanshinone IIA sulfonate (STS) on inflammatory responses, aortic endothelial cell apoptosis, disseminated intravascular coagulation (DIC) and multiple organ damage in an animal model of classic heat stroke (CHS). The rats in the heat stroke (HS) and STS-treated heat stroke (STS-HS) groups were placed into a pre-warmed animal temperature controller (ATC) at 35°C. The moment at which the rectal temperature reached 43.5°C was considered as the time of onset of HS. In the HS groups, the rats were removed from the ATC and allowed to recover at 26°C for 0, 2, 6 or 12 h. In the STS-HS groups, the rats received femoral vein injections of 5–40 mg/kg STS immediately following the onset of HS and were subsequently placed at a temperature of 26°C to recover for 6 h. In the present study, the serum levels of tumor necrosis factor (TNF)-α, interleukin (IL)-1β and IL-6 were assessed using ELISA, and the numbers of apoptotic aortic endothelial cells were investigated using terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick-end labeling combined with immunofluorescence. In the HS groups, the serum levels of TNF-α, IL-1β and IL-6, as well as the numbers of apoptotic aortic endothelial cells were increased compared with the normothermic control group. Additionally, the plasma prothrombin time, activated partial thromboplastin time and D-dimer level were significantly increased in the HS group compared with the normothermic control group following recovery for 6 h. By contrast, the platelet count was decreased in the HS group compared with the normothermic control group. The serum levels of creatinine, blood urea nitrogen, alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase and lactate dehydrogenase were increased and histopathological damage to multiple organs was observed in the HS group following recovery for 6 h. In the STS-HS groups, cytokine levels and apoptotic aortic endothelial cell numbers were reduced compared with the HS group after 6 h recovery. STS (40 mg/kg) treatment additionally improved the serum levels of organ injury indicators and plasma indicators of coagulopathy, and prevented histopathological damage to multiple organs. These findings demonstrated that STS treatment may ameliorate multiple organ damage by attenuating inflammatory responses, aortic endothelial cell apoptosis and DIC in CHS. These results suggested that STS may hold potential as an alternative therapeutic strategy for the treatment of patients with HS.

A retrospective study of clinical profile and outcomes of critically ill patients with heat-related illness

Background and Aims:

Heat-related illness (HRI) due to high ambient temperatures is a common feature during the Indian summer. HRI often results in Intensive Care Unit (ICU) admissions and are associated with significant morbidity and mortality. However, published report on the effects of HRI among the Indian population is lacking. This study was undertaken to identify the profile of patients admitted to ICU with clinical features of HRI and study their clinical outcomes.

Methods:

This was a retrospective case series of patients admitted with features of HRI during the summer of 2012 in our multidisciplinary ICU. Data on demographics, co-morbid illness, admission severity of illness (Acute Physiology and Chronic Health Evaluation II [APACHE II]), organ failure scores (Sequential Organ Failure Assessment [SOFA]) and neuroimaging studies were collected. Outcome data studied included mortality, ICU length of stay (LOS), ventilator days and hospital LOS. Statistical analysis was performed using Student's t-test, Chi-square test and multivariate analysis.

Results:

Twenty-six patients met the diagnostic criteria for HRI. Fifteen were males. The mean age was 53.12 ± 18.6 years. Mean APACHE II score was 19.6 ± 7.7 and mean SOFA score was 7.5 ± 2.6. The common presenting symptoms were fever with neurological impairment (100%) and gastrointestinal symptoms (30%). Major organ systems involvement include neurological (100%), renal (57%), hepatic (34%) and coagulation abnormalities (26%). Most common metabolic abnormality noted was hyponatraemia (73%). Magnetic resonance imaging findings suggestive of heat stroke were seen in 5 of 26 patients. Mortality rate was 34%. 8 of 17 survivors had residual neurological impairment.

Conclusion:

HRI carries a high mortality and significant neurological morbidity.

Repeated muscle damage blunts the increase in heat strain during subsequent exercise heat stress

PURPOSE

Exercise-induced muscle damage (EIMD) has recently been shown to increase heat strain during exercise heat stress (HS), and represents a risk factor for exertional heat illness (EHI). We hypothesised that a repeated bout of EIMD blunts the increase in rectal temperature (T re) during subsequent endurance exercise in the heat.

METHODS

Sixteen non-heat-acclimated males were randomly allocated to EIMD (n = 9) or control (CON, n = 7). EIMD performed a downhill running treatment at -10 % gradient for 60 min at 65 % [Formula: see text]O2max in 20 °C, 40 % RH. CON participants performed the same treatment but at +1 % gradient. Following treatment, participants rested for 30 min, then performed HS (+1 % gradient running for 40 min at 65 % [Formula: see text]O2max in 33 °C, 50 % RH) during which thermoregulatory measures were assessed. Both groups repeated the treatment and subsequent HS 14 days later. Isometric quadriceps strength was assessed at baseline, and 48 h post-treatment.

RESULTS

The decrease in leg strength 48 h post-EIMD trial 1 (-7.5 %) was absent 48 h post-EIMD trial 2 (+2.9 %) demonstrating a repeated bout effect. Final T re during HS was lower following EIMD trial 2 (39.25 ± 0.47 °C) compared with EIMD trial 1 (39.59 ± 0.49 °C, P < 0.01), with CON showing no difference. Thermal sensation and the T re threshold for sweating onset were also lower during HS on EIMD trial 2.

CONCLUSION

The repeated bout effect blunted the increase in heat strain during HS conducted after EIMD. Incorporating a muscle-damaging bout into training could be a strategy to reduce the risk of EHI and improve endurance performance in individuals undertaking heavy exercise with an eccentric component in the heat.

Heat stress presenting with encephalopathy and MRI findings of diffuse cerebral injury and hemorrhage

Background

Heat stress results in multiorgan failure and CNS injury. There a few case reports in the literature on the neurological consequences of heat stress.

Case presentation

We describe a patient with heat stress presenting with encephalopathy and bilateral cerebral, cerebellar, and thalamic lesions and intraventricular hemorrhage on MRI.

Conclusion

Heat stress should be in the differential diagnosis of patients presenting with encephalopathy and elevated serum inflammatory markers especially if the history suggests a preceding episode of hyperthermia.

Electrical vagus nerve stimulation attenuates systemic inflammation and improves survival in a rat heatstroke model

This study was performed to gain insights into novel therapeutic approaches for the treatment of heatstroke. The central nervous system regulates peripheral immune responses via the vagus nerve, the primary neural component of the cholinergic anti-inflammatory pathway. Electrical vagus nerve stimulation (VNS) reportedly suppresses pro-inflammatory cytokine release in several models of inflammatory disease. Here, we evaluated whether electrical VNS attenuates severe heatstroke, which induces a systemic inflammatory response. Anesthetized rats were subjected to heat stress (41.5°C for 30 minutes) with/without electrical VNS. In the VNS-treated group, the cervical vagus nerve was stimulated with constant voltage (10 V, 2 ms, 5 Hz) for 20 minutes immediately after completion of heat stress. Sham-operated animals underwent the same procedure without stimulation under a normothermic condition. Seven-day mortality improved significantly in the VNS-treated group versus control group. Electrical VNS significantly suppressed induction of pro-inflammatory cytokines such as tumor necrosis factor-α and interleukin-6 in the serum 6 hours after heat stress. Simultaneously, the increase of soluble thrombomodulin and E-selectin following heat stress was also suppressed by VNS treatment, suggesting its protective effect on endothelium. Immunohistochemical analysis using tissue preparations obtained 6 hours after heat stress revealed that VNS treatment attenuated infiltration of inflammatory (CD11b-positive) cells in lung and spleen. Interestingly, most cells with increased CD11b positivity in response to heat stress did not express α7 nicotinic acetylcholine receptor in the spleen. These data indicate that electrical VNS modulated cholinergic anti-inflammatory pathway abnormalities induced by heat stress, and this protective effect was associated with improved mortality. These findings may provide a novel therapeutic strategy to combat severe heatstroke in the critical care setting.

Recombinant thrombomodulin prevents heatstroke by inhibition of high-mobility group box 1 protein in sera of rats

Heatstroke, a severe inflammatory response disease, is a medical emergency characterized by high body temperature. The protein C anticoagulant system inhibits inflammation resulting from various causes. Thrombomodulin (TM), a widely expressed glycoprotein originally identified in vascular endothelium, is an important cofactor in the protein C anticoagulant system. We tested the hypothesis that TM could prevent acute inflammation induced by heat stress in a rodent model. Male Wistar rats received a bolus of 1 mg x kg of body weight of TM or saline injected into the tail vein, followed by heat-stress treatment (exposure to 42°C for 30 min). Serum concentrations of cytokines (IL-1β, IL-6, and TNF-α), NO, and high-mobility group box 1 (HMGB1) protein were measured at various time points after treatment. We observed a decrease in the levels of cytokines and HMGB1 protein in sera of TM-treated animals over time. Inhibition of NO overproduction by recombinant TM was observed during heat stress-induced inflammation. Because of the decline in inflammatory marker levels, TM ameliorated injury to various organs in the rat model of heat stress-induced acute inflammation. As TM exhibited a strong anti-inflammatory effect in a rat model of acute inflammation induced by heat stress, TM represents a potential therapeutic for heatstroke prevention or management in patients.

Multiple Organ Failure Following Near Fatal Exertional Heat Stroke

We describe the clinical features of a patient with near-fatal heat stroke who was admitted to our intensive care unit. A 14-year-old girl became convulsive and hyperthermic when participating in a strenuous hike under direct sunlight in a hilly area in Venezuela on a very hot and humid day. During the following days, she developed multiple organ failure, including neurological impairment, acute renal failure, disseminated intravascular coagulation, and extensive hepatic and muscle damage. Treatment consisted of ventilatory support, hemodialysis, corticosteroids, and enteral nutrition. This case of multiple organ failure following near-fatal heat stroke illustrates that although there are no specific techniques and measures for the treatment of this condition, intensive care management and conservative strategies can result in patient survival and complete recovery.

Case report: severe heat stroke with multiple organ dysfunction - a novel intravascular treatment approach

Introduction

We report the case of a patient who developed a severe post-exertional heat stroke with consecutive multiple organ dysfunction resistant to conventional antipyretic treatment, necessitating the use of a novel endovascular device to combat hyperthermia and maintain normothermia.

Methods

A 38-year-old male suffering from severe heat stroke with predominant signs and symptoms of encephalopathy requiring acute admission to an intensive care unit, was admitted to a ten-bed neurological intensive care unit of a tertiary care hospital. The patient developed consecutive multiple organ dysfunction with rhabdomyolysis, and hepatic and respiratory failure. Temperature elevation was resistant to conventional treatment measures. Aggressive intensive care treatment included forced diuresis and endovascular cooling to combat hyperthermia and maintain normothermia.

Results

Analyses of serum revealed elevation of proinflammatory cytokines (TNF alpha, IL-6), cytokines (IL-2R), anti-inflammatory cytokines (IL-4) and chemokines (IL-8) as well as signs of rhabdomyolysis and hepatic failure. Aggressive intensive care treatment as forced diuresis and endovascular cooling (CoolGard^® and CoolLine^®) to combat hyperthermia and maintain normothermia were used successfully to treat this severe heat stroke.

Conclusion

In this case of severe heat stroke, presenting with multiple organ dysfunction and elevation of cytokines and chemokines, which was resistant to conventional cooling therapies, endovascular cooling may have contributed significantly to the reduction of body temperature and, possibly, avoided a fatal result.

The roles of exercise-induced immune system disturbances in the pathology of heat stroke : the dual pathway model of heat stroke

Heat stroke is a life-threatening condition that can be fatal if not appropriately managed. Although heat stroke has been recognised as a medical condition for centuries, a universally accepted definition of heat stroke is lacking and the pathology of heat stroke is not fully understood. Information derived from autopsy reports and the clinical presentation of patients with heat stroke indicates that hyperthermia, septicaemia, central nervous system impairment and cardiovascular failure play important roles in the pathology of heat stroke. The current models of heat stroke advocate that heat stroke is triggered by hyperthermia but is driven by endotoxaemia. Endotoxaemia triggers the systemic inflammatory response, which can lead to systemic coagulation and haemorrhage, necrosis, cell death and multi-organ failure. However, the current heat stroke models cannot fully explain the discrepancies in high core temperature (Tc) as a trigger of heat stroke within and between individuals. Research on the concept of critical Tc as a limitation to endurance exercise implies that a high Tc may function as a signal to trigger the protective mechanisms against heat stroke. Athletes undergoing a period of intense training are subjected to a variety of immune and gastrointestinal (GI) disturbances. The immune disturbances include the suppression of immune cells and their functions, suppression of cell-mediated immunity, translocation of lipopolysaccharide (LPS), suppression of anti-LPS antibodies, increased macrophage activity due to muscle tissue damage, and increased concentration of circulating inflammatory and pyrogenic cytokines. Common symptoms of exercise-induced GI disturbances include diarrhoea, vomiting, gastrointestinal bleeding, and cramps, which may increase gut-related LPS translocation. This article discusses the current evidence that supports the argument that these exercise-induced immune and GI disturbances may contribute to the development of endotoxaemia and heat stroke. When endotoxaemia can be tolerated or prevented, continuing exercise and heat exposure will elevate Tc to a higher level (>42 degrees C), where heat stroke may occur through the direct thermal effects of heat on organ tissues and cells. We also discuss the evidence suggesting that heat stroke may occur through endotoxaemia (heat sepsis), the primary pathway of heat stroke, or hyperthermia, the secondary pathway of heat stroke. The existence of these two pathways of heat stroke and the contribution of exercise-induced immune and GI disturbances in the primary pathway of heat stroke are illustrated in the dual pathway model of heat stroke. This model of heat stroke suggests that prolonged intense exercise suppresses anti-LPS mechanisms, and promotes inflammatory and pyrogenic activities in the pathway of heat stroke.

Estimating the incidence of heat-related deaths among immigrants in Pima County, Arizona

Widespread media reports have described an increase in heat-related deaths among illegal immigrant border crossers in Southern Arizona in recent years. We conducted a retrospective case series review of heat-related deaths reported by a large border county medical examiner office in an attempt to estimate the occurrence and distribution of these deaths for the years 1998-2003. United States Border Patrol apprehension data were also collected and used in the analysis to estimate the size of the population of border crossers. An increase in the total heat-related deaths has occurred since 1999 in Pima County Arizona and has continued to date. Precise estimates of rates are not possible but appear to have increased as well. Implications for understanding the complexity of researching this public health issue including the definition of cases and population at risk are discussed.

Heat fatalities in Pima County, Arizona

The most common cause of heat fatalities is environmental exposure during heat waves. Deserts of the southwestern USA are known for temperatures that exceed 32 degrees C for 30 days or more; yet, heat-related fatalities are rare among residents of the region. We compiled data from the National Weather Service and the Office of the Medical Examiner in order to determine the relationship between temperature and occurrence of heat fatalities in Pima County, AZ. Logistic regression indicated that for each degree of increase in temperature (degrees C), there was a 35% increase in the odds of a heat fatality occurring (p<0.001).

An observational study on the spectrum of heat-related illness, with a proposal on classification

During operations in subtropical areas over the summer months of 2001 and 2003 the authors audited 80 patients with heat-related illness, with the intention of defining the nature and distribution of the underlying pathophysiology. Haematological, biochemical and clinical data were gathered prospectively and patients allocated to diagnostic categories on the basis of the combination of clinical findings and investigations. Four basic types of heat-related illness could be distinguished: (1) excessive salt loss with hyponatraemic dehydration, (2) hypokalaemic alkalosis with low serum bicarbonate, (3) haemodilution associated with excessive water intake in stressed individuals, and (4) loss of normal thermoregulation, characterised by high core temperature and paradoxical cessation of sweating. Most of the patients fell clearly into a single distinct category, but there was a degree of overlap. Reduction of extracellular fluid volume was a common central mechanism. Common provoking factors identified were: gastrointestinal upset, history of previous heat intolerance (35%) environmental temperatures exceeding 45 degrees C, short period of acclimatisation (55%), travel, sleep loss, hard physical work especially if directly preceded by a period of sleep, work in confined humid spaces (45%), and lack of additional salt intake. When several of these factors were present together admission rate over one 24-hour period reached 3% of persons at risk per day. Patients are often more ill than they appear. To reduce the incidence of heat illness during future operations the following measures are proposed: 1. Avoidance of physical exertion during the heat of the day for the first 7-10 days. 2. Progressive gentle exercise in the early morning or late evening over the same period. 3. Increase in daily salt intake to 15-20gm for the first 2-3 weeks. 4. Only sufficient water intake to relieve thirst and to ensure the flow of abundant dilute urine.

Dantrolene--a review of its pharmacology, therapeutic use and new developments

Human malignant hyperthermia is a life-threatening genetic sensitivity of skeletal muscles to volatile anaesthetics and depolarizing neuromuscular blocking drugs occurring during or after anaesthesia. The skeletal muscle relaxant dantrolene is the only currently available drug for specific and effective therapy of this syndrome in man. After its introduction, the mortality of malignant hyperthermia decreased from 80% in the 1960s to < 10% today. It was soon discovered that dantrolene depresses the intrinsic mechanisms of excitation-contraction coupling in skeletal muscle. However, its precise mechanism of action and its molecular targets are still incompletely known. Recent studies have identified the ryanodine receptor as a dantrolene-binding site. A direct or indirect inhibition of the ryanodine receptor, the major calcium release channel of the skeletal muscle sarcoplasmic reticulum, is thought to be fundamental in the molecular action of dantrolene in decreasing intracellular calcium concentration. Dantrolene is not only used for the treatment of malignant hyperthermia, but also in the management of neuroleptic malignant syndrome, spasticity and Ecstasy intoxication. The main disadvantage of dantrolene is its poor water solubility, and hence difficulties are experienced in rapidly preparing intravenous solutions in emergency situations. Due to economic considerations, no other similar drugs have been introduced into routine clinical practice.

Distribution and mitogen response of peripheral blood lymphocytes after exertional heat injury

To determine whether immune disturbances during exertional heat injury (EHI) could be distinguished from those due to exercise (E), peripheral lymphocyte subset distributions and phytohemagglutinin-stimulated CD69 mitogen responses as discriminated by flow cytometry were studied in military recruits [18.7 +/- 0.3 (SE) yr old] training in warm weather. An E group (3 men and 3 women) ran 1.75-2 miles. During similar E, 11 recruits (10 men and 1 woman) presented with suspected EHI. EHI (40.4 +/- 0.3 degrees C) vs. E (38.6 +/- 0.2 degrees C) body temperature was significantly elevated (P < 0.05). Heat illness was largely classified as EHI, not heatstroke, because central nervous system manifestations were generally mild. Blood was collected at E completion or EHI onset (0 h) and 2 and 24 h later. At 0 h (EHI vs. E), suppressor, natural killer, and total lymphocyte counts were significantly elevated, helper and B lymphocyte counts remained similar, and the helper-to-suppressor ratio was significantly depressed. By 2 h, immune cell dynamics between groups were similar. From 0 to 24 h, T lymphocyte subsets revealed significantly reduced phytohemagglutinin responses (percent CD69 and mean CD69 fluorescent intensity) in EHI vs. E. Thus immune cell dynamics with EHI were distinguishable from E. Because heat stress as reported in exercise or heatstroke is associated with similar immune cell disturbances, these findings in EHI contributed to the suggestion that heat stress of varying severity shares a common pathophysiological process influencing the immune system.

The role of the gut in the pathogenesis of death due to hyperthermia

Pathologic data from the gastrointestinal tract in heat-stroke victims, although documented, are confusing. The object of this study was to document the gastrointestinal changes observed during induced total body hyperthermia (42 degrees C) followed by cooling. An established heat-stroke model was used in a university animal laboratory. Group A underwent immersion hyperthermia for 1 hour, followed by cooling to normothermia. Group B underwent hyperthermia to cardiac arrest, followed by resuscitation plus cooling to normothermia. The postmortem findings in the gastrointestinal tract were evaluated. In group A, several hours after return to normothermia and stable vital signs, delayed secondary deterioration with massive gastrointestinal bleeding occurred. The postmortem findings revealed bleeding into the whole intestine and serosanguineous fluid in the peritoneal cavity. In group B, an adynamic gut was observed after 165 +/- 21 minutes (range 125-174) of heating when mean arterial pressure (MAP) decreased to 38 +/- 21 mm Hg (range 30-70). Cardiac arrest occurred at 178 +/- 26 minutes (range 140-208) of immersion. Eight monkeys could be resuscitated to spontaneous circulation with return of normal gut motility, then they rearrested at 158 +/- 68 minutes (range 45-228). The postmortem findings resembled those in group A. The Postmortem findings in the four monkeys in which restoration of spontaneous circulation failed, revealed only some intestinal wall edema and occasional petechial hemorrhages. It is concluded that after a hyperthermic event, tissue injury continues to develop. The pathologic findings are related to the time lapse between hyperthermia, cooling, and death. The similarity to the descriptions of septic shock, multiple organ failure, and the gut reperfusion syndrome is striking. An immunologic response as a mechanism for all these syndromes is discussed.

Severe liver failure in exertional heat stroke

Exertional heat stroke usually occurs in warm climates. Increased serum levels of liver enzymes is a common finding in this condition, whereas liver failure is a more rare event that carries a poor prognosis. Liver transplantation has been recommended as treatment in cases of severe liver failure, but no long-term survival after this procedure in exertional heat stroke has been described. We report the case of a 31-year-old man who had a heat stroke after running 5 km at 21 degrees C. He developed severe liver damage, with serum alanine aminotransferase (ALAT) activities increasing to 16,410 U/l (reference values, 10-50 U/l) after 48 h, concomitantly with a pronounced coagulation disturbance, with Normotest (NT) decreasing to 12% (international normalized ratio (INR) = 4.2) (reference values, 70%-130% for NT and 0.8-1.2 for INR). A liver biopsy on the 5th day after the incident showed extensive liver cell necrosis. The patient was referred to be considered for liver transplantation but recovered completely on conservative treatment. We conclude that exertional heat stroke is a diagnostic possibility also in temperate climates and that severe liver failure may ensue. The liver injury is reversible, and the indications for liver transplantation in this situation have not been clarified.

Disseminated zygomycosis due to Rhizopus schipperae after heatstroke

A 21-year-old woman suffered heatstroke and developed diarrhea while trekking across south Texas. The heatstroke was complicated by seizures, rhabdomyolysis, pneumonia, renal failure, and disseminated intravascular coagulation. The patient's stool and blood cultures grew Campylobacter jejuni. The patient subsequently developed paranasal and gastrointestinal zygomycosis and required surgical debridement and a prolonged course of amphotericin B. The zygomycete cultured was Rhizopus schipperae. This is only the second isolate of R. schipperae that has been described. R. schipperae is characterized by the production of clusters of up to 10 sporangiophores arising from simple but well-developed rhizoids. These asexual reproductive propagules are produced on Czapek Dox agar but are absent on routine mycology media, where only chlamydospores are observed. Despite multiorgan failure, bacteremia, and disseminated zygomycosis, the patient survived and had a good neurological outcome. Heatstroke has not been previously described as a risk factor for the development of disseminated zygomycosis.

MDMA induced hyperthermia: a survivor with an initial body temperature of 42.9 degrees C

A young male survived hyperpyrexia (42.9 degrees C) following MDMA ("Ecstasy") ingestion. He developed convulsions, rhabdomyolysis, metabolic acidosis, and respiratory failure. This was successfully managed by assisted ventilation, aggressive fluid therapy, and the early administration of dantrolene, in addition to cooling measures. This is the first report of a survivor with such a severe hyperpyrexia.