KISS: Heat-Related Illness

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Wilderness Medical Society Guidelines 2013, NHS Choices

A heat wave is considered as ≥2 consecutive days of average 30oC by day and 15oC overnight, during which there is a significant increase in the risk of people developing heat-related illnesses. These may also be seen in people undertaking strenuous exercise in lower temperatures.


  • Heat exhaustion
    • Mild>mod illness caused by exposure to high environmental heat or strenuous exercise
    • Headache, weakness, anorexia, nausea, cramps, excessive sweating, clammy skin, tachycardia/pnoea, intense thirst, discomfort, anxiety, dizziness, syncope
    • In children also consider if floppy and sleepy
    • Core temperature may be normal or slightly elevated - >37.0oC to <40.0oC
      • NB a rectal measurement is considered most accurate in heat-related illness
  • Heat stroke
    • More severe illness, characterised by a core temp >40oC & CNS abnormalities
    • Confusion, seizure, loss of consciousness, marked tachycardia/pnoea/SOB, dehydration, lack of sweating despite temperature


  • Core temperatures rising to critical levels results in thermoregulatory dysfunction, acute-phase response and heat shock protein response, the ensuing chain reaction culminating in circulatory shock
  • The acute phase response is similar to the inflammatory response seen in sepsis
  • Protective “heat shock proteins” fail, resulting in denaturation of normal protein and enzymes at a cellular level, resulting in end-organ dysfunction
  • Critical hyperthermia can cause direct tissue injury and death

Specific considerations

  • Various medications and illicit drugs can contribute, particularly:
    • Most antihypertensives, TCAs, antiepileptics, antipsychotics, phenothiazines, anticholinergics, laxatives, thyroid agonists, benzos, amphetamines, cocaine, alcohol


  • The NHS has some simple advice for managing people with heat exhaustion:
    • Move the person to a cool place
    • Lie the person down and slightly elevate their legs
    • Encourage plenty of water - sports/rehydration drinks are ok
    • Cool the person’s skin using a spray or sponge with cold water and fan - cold packs around the axillae and neck are also helpful
    • Monitor the person - they should improve within 30 minutes
  • Our role, as ever, is to identify those with severe illness or at increased risk
  • Heat stroke is a medical emergency - call 999 if any signs or a person fails to improve from heat exhaustion after 30 minutes despite the above interventions
Published on 25th July 2019

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