a)    Define heat stroke and describe the two forms of heatstroke, highlighting the differences between these two conditions.                                   (20% marks) 
 
b)    Describe the clinical features of heatstroke and the biochemical and haematological changes that may occur.                                              (40% marks) 
 
c)    Discuss the cooling strategies in heat stroke.                      (40% marks) 
 

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College answer

a)    Heat stroke is defined as a core body temperature usually in excess of 40ºC with associated central nervous system dysfunction in the setting of a large environmental heat load that cannot be dissipated. Classic (nonexertional heat stroke) affects elderly individuals with underlying chronic medical conditions that impair thermoregulation, prevent removal from a hot environment, or interfere with access to hydration or attempts at cooling. These conditions include cardiovascular disease, neurologic or psychiatric disorders, obesity, anhidrosis, physical disability, extremes of age, and the use of recreational drugs and certain prescription drugs. Exertional heat stroke generally occurs in young, otherwise healthy individuals who engage in heavy exercise during periods of high ambient temperature and humidity.   (2 marks)         
 
b)    The first clinical signs are often neurological and may include restlessness, delirium, seizures and coma. Multiple organ involvement may occur including signs of distributive shock with a hyperdynamic profile with hypovolaemia as a consequence of dehydration and reduced organ perfusion and associated lactic acidosis. There may be hyperventilation with respiratory alkalosis and hypoxia from acute lung injury. The main biochemical abnormalities include hyperglycaemia, hypophosphataemia, raised hepatic and muscular enzymes and an elevation of acute phase proteins. The haematological findings include leucocytosis, thrombocytopenia and activation of coagulation and fibrinolysis.    (4 marks) 
 
c)    Cooling Strategies in Heat Stroke: 
Methods:  
Water and fan: Evaporative and convective cooling: 
Body sprayed with lukewarm water and fans are used to blow air over the moist skin. 
 
Suppression of heat: 
Agitated and shivering patient can generate heat. That can be suppressed with the use of benzodiazepines (such as lorazepam, midazolam) and chlorpromazine paralysing agents may be required 
 
Cold water immersion:  
Immersion of patient in ice water: non-invasive, rapid but makes patient monitoring difficult 
 
Application of ice packs: 
Ice packs can be placed in axillae, neck and groin: excellent method for intubated patient, poorly tolerated by non- intubated patients 
 
Cold compressors:  
Can be applied on smooth, hairless surfaces like: palms, cheeks, soles: rapid cooling 
 
Cold thoracic, gastric and peritoneal lavage: invasive but rapid 
 
Cooling catheters: invasive, rapid 
 
Cooling blankets: non-invasive, can set the temperature 
 
Cold IV fluids 
 
Cooling recommendations are primarily based on observation studies 
There is no definitive study supporting any particular approach to cooling in classic heat stroke 
Pharmacological agents like dantrolene are ineffective and not indicated in heat stroke 
Alcohol sponge baths should be avoided due to risk of absorption of alcohol through skin  
 

Discussion

Definition of heat stroke

  • Failure of thermoregulation due to impaired heat dissipation, characterised by severe hyperthermia, dry skin and a decreased level of consciousness

Exertional heat stroke

  • Increased body thermogenesis due to exercise, and the failure of otherwise normal healthy thermoregulatory mechanisms

Non-exertional heat stroke

  • Impaired thermoregulatory mechanisms and increased body temperature under condtionals of normal rates of thermogenesis

Clinical signs of heat stroke

  • Raised body temperature
  • Neurological dysfunction - restlessness, delirium, coma
  • Hyperdynamic circulation; distributive shock (Shahid et al, 1999)
  • Dry skin (usually)
  • Seizures

Characteristic laboratory findings in heat stroke

  • ABG: acidosis, probably mixed metabolic; as well as respiratory alkalosis and hypoxia
  • BSL: elevated (catecholamines)
  • FBC: haemolysis, thrombocytopenia, anaemia, raised white cell count
  • EUC: renal failure, hyperkalemia
  • CMP: hypophosphataemia and hypocalcemia (Knochel & Caskey, 1977)
  • LFTs: raised transaminases and bilirubin. Specifically, AST and LDH will be raised.
  • CK: elevated
  • Urinary myoglobin
  • Coagulopathy (DIC): raised PT and APTT
  • Raised acute phase inflammatory markers (CRP, ferritin)

Cooling strategies for heat stroke

  • Evaporation of cold water sponges
  • Ice packs
  • Immersion in ice water
  • Contact cooling by blankets and jackets
  • Iced gastric, colonic, bladder, or peritoneal lavage
  • Infusion of cold intravenous fluids
  • Invasive technique such as cooling of the dialysis circuit, or ECMO

There is not specific approach which is thought to be more effective than other approaches. For instance, in a letter to Intensive Care Medicine, Hadad et al (2005) pointed out that in the Israeli Defence Forces, with tap water and a fan one is able to achieve a core temperature rate drop of 1°C every 9 minutes. Costrini (1990), looking at different ways of cooling down overheated athletes, suggested ice water immersion to be the best method. A more detailed discussion of cooling methods is carried out in the chapter on inducing therapeutic hypothermia. The college, in their answer to Question 22 from the second paper of 2018,  mention alcohol sponge baths as a discredited alternative.  This practice has been discredited since the 1960s, when it killed children (Senz et al, 1959) and adults (Wise, 1969) by producing a surprising amount of alcohol absorption (they were using mainly isopropyl "rubbing" alcohol). On the other hand, if your objective is to achieve heroic levels of intoxication, percutaneous obsorption is a valid method (Puschel et al, 1981).

References

Bouchama, Abderrezak, and James P. Knochel. "Heat stroke." New England Journal of Medicine 346.25 (2002): 1978-1988.

Grogan, H., and P. M. Hopkins. "Heat stroke: implications for critical care and anaesthesia." British Journal of Anaesthesia 88.5 (2002): 700-707.

Glazer, James L. "Management of heatstroke and heat exhaustion." Am Fam Physician 71.11 (2005): 2133-2140.

Shahid, Maie S., et al. "Echocardiographic and Doppler study of patients with heatstroke and heat exhaustion." The International Journal of Cardiac Imaging 15.4 (1999): 279-285.

Bricknell, M. C. "Heat illness--a review of military experience (Part 1)." Journal of the Royal Army Medical Corps 141.3 (1995): 157-166.

Bricknell, M. C. M. "Heat illness-A review of military experience (Part 2)." Journal of the Royal Army Medical Corps 142.1 (1996): 34-42.

Buggy, D. J., and A. W. Crossley. "Thermoregulation, mild perioperative hypothermia and post-anaesthetic shivering." British Journal of Anaesthesia 84.5 (2000): 615-628.

Rowell, L. B. "Cardiovascular aspects of human thermoregulation." Circulation Research 52.4 (1983): 367-379.

Deschamps, A., et al. "Effect of saline infusion on body temperature and endurance during heavy exercise." Journal of Applied Physiology 66.6 (1989): 2799-2804.

Buckley, I. K. "A light and electron microscopic study of thermally injured cultured cells." Laboratory investigation; a journal of technical methods and pathology 26.2 (1972): 201.

Bynum, GAITHER D., et al. "Induced hyperthermia in sedated humans and the concept of critical thermal maximum." American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 235.5 (1978): R228-R236.

Leon, Lisa R., and Bryan G. Helwig. "Heat stroke: role of the systemic inflammatory response." Journal of applied physiology 109.6 (2010): 1980-1988.

Alzeer, Abdulaziz H., et al. "Serum enzymes in heat stroke: prognostic implication." Clinical chemistry 43.7 (1997): 1182-1187.

Bouchama, Abderrezak, Mohammed Dehbi, and Enrique Chaves-Carballo. "Cooling and hemodynamic management in heatstroke: practical recommendations." Crit Care 11.3 (2007): R54.

Misset, Benoît, et al. "Mortality of patients with heatstroke admitted to intensive care units during the 2003 heat wave in France: A national multiple-center risk-factor study*." Critical care medicine 34.4 (2006): 1087-1092.

BOUCHAMA, ABDERREZAK, et al. "Ineffectiveness of dantrolene sodium in the treatment of heatstroke." Critical care medicine 19.2 (1991): 176-180.

Adams, Tom, et al. "Exertional heat stroke." British Journal of Hospital Medicine 73.2 (2012): 72-78.

Hadad, Eran, Daniel S. Moran, and Yoram Epstein. "Cooling heat stroke patients by available field measures.Intensive care medicine 30.2 (2004): 338-338.

Costrini, Anthony. "Emergency treatment of exertional heatstroke and comparison of whole body cooling techniques." Medicine and Science in Sports and Exercise22.1 (1990): 15-18.

Senz, Edward H., and Donald L. Goldfarb. "Coma in a child following use of isopropyl alcohol in sponging." The Journal of pediatrics 53.3 (1958): 322-323.

Wise, Jr JR. "Alcohol sponge baths." The New England journal of medicine 280.15 (1969): 840-840.

Püschel, Klaus. "Percutaneous alcohol intoxication." European journal of pediatrics 136.3 (1981): 317-318.

Knochel, James P., and Jennifer H. Caskey. "The mechanism of hypophosphatemia in acute heat stroke." Jama 238.5 (1977): 425-426.