Clinical tips: Heat stroke and dehydration

woman drinking water

Dr Esther Lau and Professor Lisa Nissen take a look at our longer, hotter summers and how they impact dehydration and heat-related illness

Every year, we seem to be facing hotter and hotter summers. This has also seen an increase in heat related illnesses as average global temperatures are increasing as a result of climate change.

According to the therapeutic guidelines, the severity of heat related conditions sit along a continuum:

  • Heat cramps are painful involuntary muscle spasms after prolonged exercise, more often in non-acclimatised individuals. It is commonly caused by dehydration-induced volume depletion and significant sodium loss from sweating.
  • Heat exhaustion is another mild form of systemic heat illness. It is also typically associated with volume depletion but the body’s normal heat dissipation capacity is maintained.
  • Heat stroke is an uncommon but life-threatening condition, where organ system failure can occur when the core body temperature exceeds 40°C, and the body’s ability to dissipate heat is lost. It can be classified as:
  • classic (nonexertional)—typically occurs in the elderly and those with chronic disease, who may either have impaired normal thermoregulation or are unable to remove themselves from a hot environment
  • exertional—occurs in individuals engaging in strenuous exercise during periods of high ambient temperature and humidity.

Differential diagnosis is important as an elevation of core body temperature can be seen in other conditions e.g. sepsis, neuroleptic malignant syndrome, serotonin syndrome or toxicity, malignant hyperthermia. 

As we strive to keep cool in these sweltering hot summers, it is important to remind patients to stay hydrated to help prevent heat-related illnesses (and for pets too!). Mild to moderate dehydration can be managed by drinking more fluids, but immediate medical treatment is required for severe dehydration.

There is no reliable early sign/symptom that signals the body’s need for water. People, especially older people, do not start feeling thirsty until they are dehydrated. Signs and symptoms of dehydration also present differently in children compared to adults e.g.

Infants or young children: Dry mouth and tongue, no tears when crying, no wet diapers for three hours, sunken eyes and/or cheeks, sunken soft spot on top of skull, listlessness or irritability.

Adults: Extreme thirst, dry mouth, lips, tongue, headaches, less frequent urination, dark-coloured urine, fatigue, dizziness, confusion.

Pharmacists play an important role in reminding patients to make sure they drink enough water each day, and have extra to replace any fluid lost during hot weather, illness or exercise.

Also, patients need to be reminded that rather than guzzling down lots of water, they should be drinking small amounts of water regularly to give the body time to process it.

The general rule of thumb is males should drink 2.6 litres or ten cups of fluid each day, while females should drink 2.1 litres or 8 cups of fluid each day.

However, some patients may be taking medications or have medical conditions that require fluid restriction e.g. heart failure, so tailored advice is required for those specific patient cohorts.

Dr Esther Lau and Prof Lisa Nissen are from the School of Clinical Sciences, Queensland University of Technology.

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