Department of Health

Extreme heat - information for clinicians

Key messages

  • Everyone is at risk of heat-related illness.
  • Those at greatest risk include older persons, infants and young children, those who have co-morbidities, cognitive impairment, limited social support, or poor thermal protection in their homes and outdoor workers.
  • 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 is likely to help 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.

Extreme 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.

Dehydration

Dehydration is a potential consequence of exposure to extreme heat. Mild to moderate dehydration increases cardiac work and reduces the fluid available for sweating. Dehydration is associated with an increased risk of injury, heat-related illness and impaired cognition.

The following conditions may be precipitated or worsened by dehydration:

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

Some illnesses or conditions can occur as a direct result of excessive heat (Table 1). These include heat rash, heat cramps, heat exhaustion, and heatstroke, which is a medical emergency.

Table 1: Direct heat-related illnesses

Illness

Cause

Symptoms

Heat rash

Inflammation and/or blockage of the sweat glands

Erythematous papular rash, pruritis, secondary infection

Heat cramps

Loss of salt from sweating affects muscle relaxation

Muscle cramps predominantly in the abdomen, arms and legs

Heat exhaustion

Dehydration with poor blood flow affecting the brain and heart

pale skin, sweating, tachycardia, muscle cramps, weakness, dizziness, headache, nausea, vomiting, syncope

Heatstroke

Core temperature rise with widespread organ injury

Hyperthermia, altered mental state, dry skin with no sweating (skin may be damp from earlier sweat), circulatory shock, arrhythmia, nausea, vomiting, ataxic gait, seizures, acute renal failure, unconsciousness, death

Exertional heatstroke

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

As for heat stroke, plus rhabdomyolysis

Heat may also indirectly affect health, by precipitating or exacerbating existing medical conditions such as heart and kidney disease. Clinicians should consider the contribution extreme heat has played in the clinical presentations of their patients during a heatwave.

Heatwaves and medicines

Prescribed medicines should generally be stored below 25 °C. Planning for periods of extreme heat should include how best to use and store medicines during a heat wave.

Medications can increase the risk from extreme heat through a number of differing mechcanisms (Table 2).

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

Mechanism

Drug class or subclass

Examples of drugs

Reduced vasodilation

Beta-blockers

Atenolol, metoprolol, propranolol

Triptans

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
Stimulants Amphetamines, cocaine, thyroxine
Decreased thirst Antipsychotics Haloperidol, droperidol
Angiotensin-converting enzyme (ACE) inhibitors Enalapril, perindopril, ramipril
   
Dehydration Alcohol  
Diuretics Frusemide, hydrochlorothiazide, acetazolamide, aldosterone

Stimulant laxatives

Senna extract, bisacodyl

Aggravation of heat illness by worsening hypotension in at-risk patients All antihypertensives, particularly vasodilators such as nitrates and calcium channel blockers

Nitrates: glyceryl trinitrate, isosorbide mononitrate

Calcium channel blockers: Amlodipine, felodipine, nifedipine

Increased toxicity for drugs with a narrow therapeutic index in dehydration

Various

Digoxin, immunosuppressants, lithium, metformin, warfarin

At-risk groups include those with the following circumstances.

Individual characteristics

This group includes:

  • people over the age of 65 years
  • 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
  • people living with a disability.

Conditions that impair sweating

People that have a condition or are using 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 from other causes
  • infection.

Impairment of activities of daily living or ability to communicate

This group includes people with:

  • physical disabilities, 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 and are reluctant to use their air conditioner due to cost
  • are homeless or live in homes that are poorly insulated, have limited shading, or lack air-conditioning or adequate ventilation
  • are non-English-speaking who may not be able to understand heat warnings or have reduced access to appropriate health or support services.

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
  • outdoor workers or those that work in an otherwise hot environment.

Steps to take to prevent and mitigate heat-related illness When seeing patients who may be at-risk of heat-related illness, clinicians can take the opportunity to provide education, assess supports and optimise medical management. Consider including heat advice and a pre-summer medical assessment into routine care for at-risk people. 

Ask patients how they will know when it is hot

Ask patients how they will access the weather forecast and how they will know how hot it is inside their homes. You can suggest purchasing an inexpensive thermostat or thermometer for their homes, and monitoring the local weather conditions on the daily news (TV, radio) or on the Bureau of Meteorology’s 7-day forecast website . Patients and their caregivers can also receive warnings of forecast extreme heat and heatwaves from the Vic Emergency Platform.

Develop a plan with them, and their caregivers, on what they should do when extreme heat is forecast.

Advise patients on how to stay cool

Patients can also stay cool by reducing excessive clothing, using electric fans, applying cool damp towels to their skin, and taking cool showers. Patients should close the curtains to block the sun, and open the windows for ventilation when the air outside is cooler than inside (and if it is safe to do so).

Ask patients if they have access to air conditioning and advise them to use it during periods of heat. Suggest that they use the air conditioning in the room that they spend the most time in and close off other rooms to contain the cool air.

Advise patients that they may be eligible for a concession on electricity bills related to medically-required cooling.

If clients don’t have access to air conditioning, or are unable to use it, suggest that they spend time in an air-conditioned public space during the heat, including any public heat refuges provided by the local council, local shopping centres, places of worship, neighbour’s homes or community centres.

Assess patients’ risk from medications and medical conditions

Certain medications and medical conditions can affect sweating, dehydration and thermoregulation, which can increase their risk of heat-related illness. Advise patients on any changes to their medication dosage and fluid restrictions during periods of extreme heat.

Assess patients’ risk and need to travel during the heat

Patients may need to travel to obtain medications, laboratory tests or attend appointments. Suggest that they reschedule their travels to a cooler day, ask a family member to collect their medication, or switch appointments to Telehealth, where appropriate. If they must travel on hot days, suggest that they do so in the early morning or late evening when it is cooler.

Advise patients to drink appropriately to stay hydrated

Make drinking recommendations to patients that are appropriate to their health status. If they are unable to communicate thirst, advise their caregivers to provide them with water at regular intervals throughout the day.

Advise that fluids are not just limited to water; they can be icy poles, fruit, juice or cordial.

Remember salt tablets and sports drinks offer no benefits and may be harmful because of high osmotic load and drinking excessive amounts of pure water can lead to hyponatraemia.

Consider recommending self-monitoring of hydration status to at-risk patients, where appropriate. Patients can consciously plan their water intake goal for the day, record how many drinks they have taken, how many times they have passed urine, or even its colour.

Cooking during periods of extreme heat

Suggest to patient they eat small easy to digest meals such as fruit, salads or sandwiches, and not to cook using their oven. In addition, mention the importance of good food storage and handling, during these times and if there is a power outage

Advise patients that power supply may be compromised during heatwaves

Patients who rely on electricity for life-sustaining equipment should register with their energy supplier, so that restoration of power to their home can be prioritised. Patients should also consider a battery back-up, and should charge all medical equipment and communication devices if extreme heat or heatwave is forecast.

Provide patients with written information

Provide patients and their caregivers with take home resources which are available in a range of community languages.

Provide patients with contact information

Provide patients and their caregivers with details of support services, help lines and emergency services, including Nurse-On-Call (1300 60 60 24). 

Arrange referrals for at-risk patients

Considering registering appropriate patients who have consented with Red Cross’ Telecross service to receive a daily telephone call to check on their wellbeing and with their local government's vulnerable persons register.

Consider refer high-risk patients for urgent respite or additional home support where appropriate.

Review your practice's planning and systems

Primary health care services should consider appointing a person responsible for your practice’s preparedness and response to extreme heat. This includes:

  • Conducting yearly training to refresh staff knowledge on the risk factors for heat-related illness, the signs and symptoms of heat related illness and how to initiate proper cooling and resuscitative measures.
  • Arranging team meetings prior to Summer to discuss the practices’ response to periods of extreme heat, including a review the triage policy.
  • Appointing a person responsible for monitoring the extreme heat and heatwave forecast, and a communication process to keep staff informed.
  • Ensuring that the practice is heat-friendly for patients and staff.
  • Arranging maintenance for cooling systems, vaccine fridges, windows and curtains prior to Summer.
  • Developing a business continuity plan in case the power supply fails.
  • Holding an evaluation meeting with staff to discuss how they dealt with it, what worked well, what needs improvement.

For detailed guidance of heatwave planning for health services, see Heat health preparedness guidance for health and community services.

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 15 December 2022

Health.vic

Contact details

Emergency Management Branch

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