Hyperthermia (Heat-Related Illness)

Hyperthermia is the condition where the body’s temperature is elevated beyond the normal range of 36 to 37.7 degrees C (96.8 to 99.9 degrees F).

Hyperthermia (heat-related illness) definition

Hyperthermia is the condition where the body’s temperature is elevated beyond the normal range of 36 to 37.7 degrees C (96.8 to 99.9 degrees F).

Elevated temperature may be due to a fever in response to an infection or an autoimmune disease, or because of exposure to a medication or illicit drug, or because of the body’s failure to cool itself adequately in a hot environment.

This article will primarily look at heat-related illness related to hot environments.

There are many types of heat-related illness that range from inconvenient, like heat rash, to life-threatening, like heat stroke.

Heat-related illnesses associated with activity like work or exercise include the following:

• Heat cramps
• Heat syncope
• Heat exhaustion
• Heat stroke

The body cools itself most efficiently by sweating and having that sweat evaporate. If sweating can’t meet the cooling demands of the body, heat-related illness can occur. This spectrum of conditions may be inconvenient with minor symptoms like prickly heat (heat rash), but can progress to heat cramps, then heat exhaustion, and finally to heat stroke, a life-threatening medical condition. Heat syncope is a poorly understood condition where people can pass out (faint) when exposed to excessive heat (brought on by suddenly standing).

The body has many cooling mechanisms like conduction, convection, and radiation, but the most effective way the body cools down is with evaporation.

Sweat on the skin evaporates and allows heat to dissipate. It requires that the body is adequately hydrated, that the skin is exposed to the environment, that there is a breeze to make sweating more efficient, and that the humidity is low enough so that the air can accept sweat as it evaporates.

When the relative humidity is high, the air is holding as much water as it can, and there is no room to accept sweat. When this happens, evaporation is ineffective even if sweat is present.

Most often, hyperthermia is related to exercise and work in a hot environment, the body becomes dehydrated and the ability of the body to cool itself is inadequate.

Medications can affect the temperature regulation, as can conditions like heart disease or infection. Drugs and alcohol increase the risk of heat-related illness.

Infants and the elderly are at higher risk, because their temperature regulation abilities can be limited.

The common risk factors for hyperthermia include:

• Aggressive exercise or work in a hot, humid environment
• Lack of acclimatization. The body has the ability to adjust to a hot environment by increasing blood flow to the skin, making more sweat, decreasing the amount of exercise that is needed to start sweating, and lower the body’s baseline temperature. This takes about 1-2 weeks of exposure.
• Dehydration
• Obesity
• Wearing heavy clothing like protective work clothing, military uniforms, or athletic padding
• Suffering from an illness
• Medications
  • Some high blood pressure medications including diuretics
  • Antihistamines and anticholinergic medicines affect sweating
  • Some anti-seizure medications
  • Anti-Parkinsonism medications
  • Psychiatric medication
• Alcohol, cocaine, ecstasy, and other drugs that change heart rate and metabolism

Those at greatest risk of hyperthermia include:

Infants and children are very sensitive to the effects of high temperatures and rely on others to regulate their environment, including clothing and fluid intake. They have a higher metabolic rate and inefficient sweating as compared to adults.

Older people may not be able to tolerate heat efficiently, and are less likely to sense and respond to changes in temperature. They are also at higher risk because of pre-existing medical conditions, and medications that can make them more vulnerable to dehydration.

Overweight individuals may be prone to heat-related illness because of their tendency to retain more body heat.

Some people have multiple risk factors. Imagine a worker in a foundry, wearing heavy protective gear, who takes high blood pressure medications, or a roofer on a metal roof who takes seizure medications.

Each heat-related illness may present with its own set of symptoms.

Heat rash

This occurs when the duct that leads from the sweat glands to the skin is blocked and sweat gets trapped under the skin causing inflammation.

The skin can become red with small, raised, itchy bumps that may or may not be fluid filled.

Heat syncope (fainting)

Heat syncope is a mild form of heat exhaustion. Blood vessels dilate as the body attempts to cool itself. If a person stands for a longer period of time, blood can pool in the legs, and less blood is available to circulate to the brain and the victim faints.

Heat cramps

Heat cramps occur in people who exercise or work in a hot environment. Large muscles, like the quadriceps or hamstrings in the leg, can go into spasm after high intensity exercise, or if the person exercises to exhaustion. The onset of cramps may be delayed and do not always occur immediately during the activity.

Heat cramps are not well understood since they can occur when exercise occurs in a cold environment, like in hockey players. Some researchers suggest that the term should be exercise-related muscle cramps, but most often they are associated with activity in hot environments.

Heat edema

When a person stands or sits for a period of time in a hot environment, their hands and feet may swell because blood vessels have dilated. This is self-limited and resolves when the person begins to move.

Heat exhaustion

Profuse sweating, nausea and vomiting, headache, muscle cramps, and weakness are common. A low-grade fever may be present.

With dehydration, the victim may feel lightheaded when attempting to stand, and can potentially faint (syncope).

Heat stroke

Heat stroke is a medical emergency. The victim is usually markedly dehydrated, sweating has stopped, and the skin is warm, dry and flushed. The patient will have altered mental status with confusion or may be unconscious. Nausea, vomiting, rapid heart rate, and rapid breathing will be present. Temperature may spike to 106 degrees F (41 degrees C) or higher.

Heat rash

• Wear light, loose-fitting clothes
• Avoid creams or ointments that can block sweat ducts
• Should the rash occur, keep it clean and dry, use cool compresses to help with the itch
• The rash should resolve within a few days

Heat syncope (fainting)

• Move the patient to a cool area out of the heat
• Loosen clothing to help with air circulation
• Elevated their legs
• Provide fluids to help with rehydration
• Make certain that other causes of syncope are not present

Heat cramps

• Move the patient to a cooler area
• Actively stretch the muscle that is cramped or in spasm
• Provide fluids to rehydrate the patient

Heat edema

• Gentle exercise to encourage circulation
• When resting, elevate legs above the level of the heart

Heat exhaustion

• Move the patient to a cool area
• Loosen clothing to promote air circulation and cooling
• Spray the patient with a cool mist to support sweating and cooling
• Have the patient sip fluids for rehydration
• If the patient cannot tolerate fluids because of nausea or vomiting, seek medical attention

Heat stroke

• Heat stroke is a medical emergency. Call 911
• First aid:
  • Move the patient to a cool area (remember that care air-conditioned if needed)
  • Undress the patient to promote air movement
  • Use ice packs in the armpits and groin to try to bring down the temperature
  • At the hospital:
  • The patient will need to have his breathing and circulation evaluated and supported.
  • Many options are available for cooling include misting, cooling blankets, cool intravenous fluids.
  • Medications may be used to prevent seizures
  • Kidney function will be monitored

Hyperthermia should be preventable by understanding the risks when the weather gets hot or when working in a hot environment.

• If possible, avoid working during the hottest part of the day or in a hot environment. If it is unavoidable, take frequent breaks to cool down and drink fluids.
• If you have to wear protective clothing, remove them frequently to promote sweating and cooling.
• Drink enough fluids so that your urine is clear. It’s a way of measuring hydration. Concentrated urine means you need to drink more fluids.
• Wear light-colored, loose-fitting clothing
• Try to sleep in a cool environment. Many people cannot afford to pay for electricity to run air conditioners. Consider public cooling centers, or public air-conditioned buildings and spaces.
• Check on your neighbors, especially during heat waves. The elderly are susceptible to the heat.
• Infants and children need to be watched over carefully.
  • Never leave infants, children, or pets in a parked car.
  • Dress infants and young children in cool, loose clothing, and shade their heads and faces with hats or an umbrella.
  • Limit sun exposure during the mid-day hours and in places of potential heavy sun exposure, such as beaches.
  • Provide infants and children with enough fluids to drink.
• Don’t forget your pets!