Health professionals play a vital role in helping people to prepare and stay healthy in the heat.
In a healthy person, the hypothalamus is responsible for regulating body temperature and keeping it within a range of 36.1 – 37.8 degrees Celsius.
The body can lose heat by:
When the temperature of the skin is higher than the air temperature, a healthy person can lose heat by radiation, conduction and convection. However, when the air is hotter than around 35 degrees Celsius, the body can only lose heat through sweating (evaporation). Sweating and heat loss can be impaired by humidity, excess fat, skin disorders and excessive layers of clothing. Heat loss can be improved with wind or fanning, applying cool water or cold packs.
The physiological response of the body to heat includes peripheral vasodilation, which increases blood flow to the skin. This results in large quantities of warm blood from the core of the body being carried to the skin in order to facilitate heat loss through radiation, convection and conduction. Peripheral vasodilation requires an increase in cardiac output. People with chronic medical conditions that affect peripheral vasodilation or who cannot increase their cardiac output accordingly will be most at risk during heat waves.
The body’s heat regulation system can be impaired in the elderly, the chronically ill and by certain medications. Young children are also more vulnerable as they produce more body heat, sweat less and have faster rising core temperatures.
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.
However, exacerbation of chronic conditions contribute to the majority of heat-related morbidity and mortality.
Even mild dehydration leads to an increased risk of injury, heat stress illness and poorer performance of complex tasks.
Cardiac work is increased by mild to moderate dehydration and leads to reduced fluid available for sweating. A person can sweat substantially, and it is important to note that thirst does not match fluids lost by sweating, even when fluids are freely taken.
Heat-related illness provides more details on symptoms and emergency treatment.
The majority of heat-related morbidity and mortality is due to exacerbation of existing chronic conditions.
Conditions that contribute to the most common causes of death during a heat wave include:
Dehydration and subsequent medication toxicity may exacerbate:
Everyone needs to take care in hot weather, but some people are at higher risk of heat illness.
This list should be used as a guide only.
The characteristics of people at higher risk include:
Some prescribed medications can increase the risk of heat-related illness.
Also, some medications can be less effective or more toxic when exposed to and stored in high temperatures. Most medications need to be stored below 25 degrees Celsius or in the fridge if indicated. This applies particularly to antibiotics, adrenergic drugs, insulin, analgesics and sedatives.
It is important for health professionals to discuss the correct use and storage of medications with people who take regular prescription medications as part of their care plan for hot weather.
Interference with sweating, caused by:
Interference with thermoregulation, caused by:
Decreased thirst, caused by:
Dehydration or electrolyte imbalance, caused by:
Reduced renal function, caused by:
Aggravation of heat illness by worsening hypotension, caused by:
Levels of drug affected by dehydration (possible toxicity for drugs with a narrow therapeutic index), caused by:
Identify your patients at risk and: