Department of Health

Extreme heat - information for clinicians

Key messages

  • Everyone is at risk of heat-related illness.
  • Some people are more at risk of heat-related illness including those who are old or young, or have co-morbidities, cognitive impairment and poor social support.
  • Some medicines can increase the risk of heat-related illness, or may be less effective or more toxic when stored at high temperatures.
  • Health professionals can help reduce heat-related illness by identifying at-risk people and implementing strategies to reduce risk.
  • Advance planning may help to reduce heat-related effects on patients, clients and staff.

Extreme heat and heatwaves can negatively affect at-risk members of the community.

Clinicians, particularly those in general practice, emergency departments and pharmacies, have a key role in preventing and managing heat-related illness.

Heatwave – definition

There is no single internationally accepted definition of a heatwave. The definition is dependent on factors such as:

  • humidity
  • demographics
  • urban or rural design issues 
  • acclimatisation.

These factors mean that similar temperatures may have a different impact in different environments or communities.

In Victoria, a heatwave is generally defined as a period of abnormally and uncomfortably hot weather that could impact on human health, community infrastructure and services.

The department has a definition of a heatwave based on the average daily temperature that is likely to impact on the health of a community.

The effects of a heatwaves are multifactorial. In addition to direct health effects, infrastructure failure or other natural emergencies can add to stress on people and services. For example, power outages stop people using air conditioners and public transport disruptions prevent people from reaching a cooler location. Bushfires occurring in association with heatwaves can affect air quality, which can exacerbate respiratory illness.

Heat – how it affects the body

In extreme heat, body temperature regulation is affected:

  • The body can lose heat to, and gain heat from, the environment.
  • Heat loss is controlled by the flow of blood to the skin and evaporation of sweat.
  • When the environment is hot, sweating is the main means by which the body can increase heat loss.
  • Sweating and heat loss can be impaired by humidity, excess fat, skin disorders and excessive layers of clothing.
  • Heat loss can be helped by wind or fanning, and water.

Dehydration is another side effect of extreme heat:

  • It is possible to sweat up to 15 litres per day.
  • Thirst does not match all fluids lost by sweating, even if fluids are freely taken.
  • Mild to moderate dehydration increases cardiac work and reduces fluid available for sweating.
  • Even mild dehydration is associated with increased risk of injury, heat stress illness and poorer performance of complex tasks.

Some illnesses or conditions can occur as a direct result of excessive heat, such as heat rash, cramps, exhaustion, heat stroke and exertional heat stroke.

Heat may also exacerbate existing medical conditions such as heart disease. Clinicians should consider the possible contribution of heat to other more common clinical presentations during a heatwave.

The following conditions may be precipitated or worsened by dehydration:

  • altered mental state
  • cardiovascular impairment
  • electrolyte disturbances
  • renal impairment
  • urolithiasis
  • falls.

The following may also occur due to heatwaves:

  • exacerbation of asthma and other respiratory illness
  • gastroenteritis, mostly due to poor food handling and storage.

Table 1: Direct heat-related illnesses




Heat rash

Inflammation of the sweat glands

Erythematous papular rash, pruritis, secondary infection

Heat cramps

Loss of salt in sweat affects muscle relaxation

Cramps in the abdomen, arms or legs

Heat exhaustion

Dehydration with poor blood flow affecting the brain and heart

Flushed or pale complexion and sweating, tachycardia, muscle cramps, weakness, dizziness, headache, nausea, vomiting, syncope

Exertional heat stroke

Core temperature rise precipitated by intense or prolonged exercise in hot weather

As for heat stroke, plus rhabdomyolysis, renal failure

Heat stroke

Core temperature rise with widespread organ injury

As for heat exhaustion, plus hyperthermia, shock, arrhythmia, dry skin with no sweating (skin may be damp from earlier sweat), altered mental state, ataxic gait, convulsions, unconsciousness, death

Heatwaves and medicines

Some prescribed medicines can increase the risk of heat-related illness or may be less effective or more toxic when exposed to high temperatures. Most drugs need to be stored below 25 °C, particularly emergency drugs such as:

  • antibiotics
  • adrenergic drugs
  • insulin
  • analgesics
  • sedatives.

Care planning for vulnerable people during hot weather should include consultation with their general practitioners and pharmacists about using and storing medicines.

Table 2: Mechanisms for medicine increasing the risk of heat-related illness


Drug class or subclass

Examples of drugs

Reduced vasodilation


Atenolol, metoprolol, propranolol


Sumatriptan, zolmitriptan

Decreased sweating

Anticholinergics – tricyclic antidepressants

Amitriptyline, clomipramine, dothiepin

Anticholinergics – sedating antihistamines

Promethazine, doxylamine, diphenhydramine

Anticholinergics –phenothiazines

Chlorpromazine, thioridazine, prochlorperazine

Other anticholinergics

Benztropine, hyoscine, clozapine, olanzapine, quetiapine, oxybutynin, solifenacin

Beta blockers

Atenolol, metoprolol, propranolol

Increased heat production

Antipsychotic drugs

Clozapine, olanzapine, quetiapine, risperidone


Amphetamines, cocaine, thyroxine

Decreased thirst


Haloperidol, droperido

Angiotensin-converting enzyme (ACE) inhibitors

Enalapril, perindopril, Ramipril



Not applicable


Frusemide, hydrochlorothiazide, acetazolamide, aldosterone

Stimulant laxatives

Senna extract, bisacodyl

Aggravation of heat illness by worsening hypotension in vulnerable patients

All antihypertensives, particularly vasodilators such as nitrates and calcium channel blockers

Nitrates: glyceryl trinitrate, isosorbide monnitrate

Calcium channel blockers: Amlodipine, felodipine, nifedipine

Increased toxicity for drugs with a narrow therapeutic index in dehydration


Digoxin, immunosuppressants, lithium, metformin, warfarin

Clinicians can provide education, assess supports and optimise medical management when seeing patients who may be at risk of heat-related illness,

At-risk groups include those with the following circumstances.

Individual characteristics

This group includes:

  • people over the age of 65
  • infants and young children
  • people who are overweight or obese
  • pregnant women and breastfeeding mothers
  • people who have low cardiovascular fitness
  • people who are not acclimatised to hot weather.

Chronic illness

Chronic illnesses and conditions that make people more at risk to negative effects of heat include:

  • heart disease
  • hypertension
  • diabetes
  • cancer
  • kidney disease
  • alcohol and other substance use
  • mental illness.

Conditions that impair sweating

People that have a condition or are on medicines that impair sweating are also at risk, such as:

  • heart disease
  • dehydration
  • extreme age (that is, very old or very young)
  • skin disorder
  • congenital impairment of sweating
  • cystic fibrosis
  • quadriplegia
  • scleroderma
  • medicines with anticholinergic effects.

Acute illness

Acute illnesses that can impair resilience to hot weather include:

  • dehydration
  • infection.

Impairment of activities of daily living

This group includes people with:

  • poor mobility
  • cognitive impairment.

Social factors

Social factors that affect heat resilience include people who:

  • live alone or are socially isolated
  • have a low socioeconomic status
  • are homeless.

Occupation and recreation

Some people in certain occupations and who participate in certain recreational activities are at risk, including those who:

  • exercise vigorously in the heat
  • work in a hot environment.


  • Identify patients at risk of heat-related illness.


  • Take the opportunity to educate those at risk how to manage their health during hot weather.
  • Advise them on how to adjust their behaviour, store and take medicine, and drink fluids during hot weather.
  • Encourage appropriate behaviour such as reducing excessive clothing and using cooling devices at home, and discourage avoidance of fluids due to continence issues.
  • Educate carers of children, older people and people with cognitive impairment or disability.
  • Provide written information, with details of support services, help lines and emergency services.
  • Consider including heat advice and a pre-summer medical assessment into routine care for vulnerable people with chronic diseases.

Be aware

  • Be aware of potential side effects of medicines and consider optimal dosing during periods of hot weather.
  • Be aware that high temperatures can adversely affect the efficacy of drugs.


  • Monitor fluid intake and drug therapy, especially in the older people and those with significant co-morbidities.

Assess and manage

  • Assess patients who are experiencing heat-related illness, and manage as appropriate (for example, give fluids, keep cool, observe them and advise about specific treatments).

Follow up or referral

  • Have a low threshold for admission to hospital, referral to emergency departments and/or urgent respite placement for vulnerable individuals.
  • Consider the need to optimise the home environment (for example, home temperature, cooling facilities) and available supports
  • Arrange follow-up for at-risk individuals.

Drinking recommendations

  • Know that, during hot weather, people need to drink even if they are not thirsty.
  • Make drinking recommendations to patients that are appropriate to their health status, particularly those who have a decreased perception of thirst.
  • Warn carers that they also need to maintain adequate hydration.
  • Advise that fluids are not just limited to water; they can be icy poles, weak tea or cordial.
  • Be aware that salt tablets, sports drinks or electrolytecarbohydrate supplements offer no benefits and may be harmful because of high osmotic load.
  • Be aware that drinking excessive amounts of pure water can lead to severe hyponatraemia, potentially leading to complications like stroke and death.

Review your knowledge

  • Understand the mechanisms of heat illnesses, clinical manifestations, diagnosis and treatment.
  • Recognise early signs of heatstroke, which is a medical emergency.
  • Be aware of how to initiate proper cooling and resuscitative measures.
  • Be aware of the risk factors in heat-related illness.

Review your practice and systems


  • Appoint a person responsible for planning a heatwave response. ·
  • Hold team meetings to:

discuss the practice response to a heatwave
develop a written policy • review the practice triage policy
conduct yearly heatwave meetings before summer to refresh practice staff

  • Develop and implement a communication policy to keep staff updated if a heatwave is forecast.
  • Plan for staff shortages during heatwaves.
  • Have a plan in case power goes out; for example, what to do with fridges storing vaccines.
  • Remember the practice is a community service that may have additional responsibilities during a heatwave.

For a detailed account of heatwave planning for health services, see ‘Heatwave planning’.

Clinical tools

  • Consider including heat-related content in assessment tools and management plans for vulnerable patients. For example, consider adding a question in the over-75 health assessment that asks a patient to consider their personal care during a heatwave.
  • Ensure the practice is heatwave-friendly for patients and staff with a cool waiting room, available water, blinds closed to block the sun and staff breaks for drinks.

Facility environment

  • Ensure the practice is heatwave-friendly for patients and staff with a cool waiting room, available water, blinds closed to block the sun and staff breaks for drinks.

Information and resources

  • Keep in contact with the Medicare Local for heat health alerts from the Chief Health Officer.
  • Have phone numbers of key resources within easy access – emergency departments, local Home and Community Care (HACC) services, Royal District Nursing Service (RDNS) and the department heatwave website.
  • Have up-to-date heatwave take-home resources for patients and their carers.

Discussion and evaluation

After the heatwave, have an evaluation meeting with staff to discuss how they dealt with it, what went well, what needs improvement and provide feedback to the Medicare Local.

Contacts and resources

Emergency respite

Commonwealth Respite and Carelink Centre

Careline 1800 052 222 (Business Hours) or 1800 059 059 (After-Hours Emergency Respite)

Veterans’ Home Care Agency assessment service

1300 550 450 (Business Hours) (for emergency after-hours respite call Careline above)

Annecto Emergency After-Hours Response Service (Victorian)

1800 72 72 80 (5pm–9am weekdays, 24 hours weekends and public holidays). Free short term personal care, respite crisis management, telephone and in home support for older people, people with disability or carers who do not have funded assistance.

Local government

Local governments often provide respite services

NURSE-ON-CALL – 24 hour health advice

1300 60 60 24

Reviewed 23 October 2021


Contact details

Emergency Management Branch

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