No safe time limit for leaving children in vehicles in hot weather

Because of physiological differences in body make-up and maturity, children are at high risk for heat-related illnesses.

The number of children affected by heatstroke has increased in recent years – heatstroke related to sitting in vehicles is now a leading cause of death among children.

An analysis of 171 child-vehicle heatstroke fatalities in the United States between 1995 and 2002 found that in 75 per cent of cases the child was unattended in a car.

The study also revealed that just over half of the cases occurred in children who were unintentionally forgotten and left in the car by mistake. Of the instances where children were intentionally left in the vehicle, many were due to carers being unaware of how hot the vehicle would become.

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Heat illness includes a spectrum of maladies, ranging from a mild but irritating “prickly heat” rash to severe and potentially life-threatening cases of heatstroke. Hyperthermia or heatstroke occurs when a child’s core body temperature exceeds about 40 degrees – the longer the exposure, the greater the chance of the child dying.

Our adaptation to heat is dependent on the body’s ability to act as a natural cooling system. Human beings maintain an internal temperature within a narrow range of about 37 degrees. The main ways in which the body eliminates heat during thermal stress are through sweat production, increased cardiac output and redirection of blood flow to the skin.

Regulatory centre

Temperature regulation occurs in a part of the brain called the hypothalamus. This regulatory centre keeps our body temperature in a normal range by balancing the excess heat production that occurs in our muscles and liver with heat dissipation via the skin and lungs. Hyperthermia occurs when, despite a normally functioning regulatory centre, the body’s ability to lose heat is overwhelmed.

Children are particularly vulnerable to heatstroke injuries and fatalities due to having an underdeveloped temperature-regulation system and, compared with adults, having a large surface area-to-mass ratio – which means they absorb a greater amount of ambient heat.

Heat exhaustion precedes heatstroke and typically occurs when people exercise in a hot, humid place and body fluids are lost through sweating, causing the body to overheat. Heatstroke develops when the person’s internal body temperature rises to the point where damage to the brain and other internal organs occurs.

A child with hyperthermia will experience seizures and delirium, as well as organ failure and cardiac arrhythmia. Even with prompt medical care some 15 per cent of heatstroke cases are fatal.

Heat exhaustion typically produces symptoms such as excessive thirst, nausea and vomiting and muscle cramps. Signs that it is progressing to heatstroke include heavy sweating that suddenly stops; a rapid heart rate and rapid breathing; and neurological symptoms such as confusion and a loss of co-ordination.

Is there a safe time limit within which parents can leave a child unattended in a car on a hot day?

Despite the inconvenience of unstrapping or waking an infant and carrying them while you dash in to pay for petrol, the answer is no.

A combination of an extremely rapid temperature increase within a car and the physiological differences in young children mean such calculations are both unpredictable and dangerous.