Heat Stroke – Definition, Causes, and Prevention.

Overview – Heat stroke

Heat stroke is a form of hyperthermia or heat-related illness, an abnormally elevated body temperature with accompanying physical symptoms including changes in the nervous system function. Unlike heat cramps and heat exhaustion, two other forms of hyperthermia that are less severe, heat stroke is a true medical emergency that is often fatal if not properly and promptly treated. Heat stroke is also sometimes referred to as heatstroke or sun stroke. Severe hyperthermia is defined as a body temperature of 104 F (40 C) or higher.

The body normally generates heat as a result of metabolism and is usually able to dissipate the heat by radiation of heat through the skin or by evaporation of sweat. However, in extreme heat, high humidity, or vigorous physical exertion under the sun, the body may not be able to sufficiently dissipate the heat and the body temperature rises, sometimes up to 106 F (41.1 C) or higher. Another cause of heat stroke is dehydration. A dehydrated person may not be able to sweat fast enough to dissipate heat, which causes the body temperature to rise.

Heat stroke is not the same as a stroke. “Stroke” is the general term used to describe decreased oxygen flow to an area of the brain.

Heat stroke – Pathophysiology

Despite wide variations in ambient temperatures, humans and other mammals can maintain constant body temperature by balancing heat gain with heat loss. When heat gain overwhelms the body’s mechanisms of heat loss, the body temperature rises, potentially leading to heat stroke. Excessive heat denatures proteins, destabilizes phospholipids and lipoproteins, and liquefies membrane lipids, leading to cardiovascular collapse, multiorgan failure, and, ultimately, death.

The exact temperature at which cardiovascular collapse occurs varies among individuals because coexisting disease, drugs, and other factors may contribute to or delay organ dysfunction. Full recovery has been observed in patients with temperatures as high as 46°C, and death has occurred in patients with much lower temperatures. Temperatures exceeding 106°F or 41.1°C generally are catastrophic and require immediate aggressive therapy.

Heat may be acquired by a number of different mechanisms. At rest, basal metabolic processes produce approximately 100 kcal of heat per hour or 1 kcal/kg/h. These reactions can raise the body temperature by 1.1°C/h if the heat-dissipating mechanisms are nonfunctional. Strenuous physical activity can increase heat production more than 10-fold, to levels exceeding 1000 kcal/h. Similarly, fever, shivering, tremors, convulsions, thyrotoxicosis, sepsis, sympathomimetic drugs, and many other conditions can increase heat production, thereby increasing body temperature.

Causes of heat stroke

There are many factors which can cause heat stroke and heat-related illness, including:

• Dehydration – to keep healthy, our body temperature needs to stay around 37°C. The body cools itself by sweating, which normally accounts for 70 to 80 percent of the body’s heat loss. If a person becomes dehydrated, they don’t sweat as much and their body temperature keeps rising. Dehydration may happen after strenuous exercise (especially in hot weather), severe diarrhea or vomiting, drinking too much alcohol, taking certain medications (for example, diuretics), and not drinking enough water.
• Lack of airflow – working in hot, poorly ventilated or confined areas.
• Sun exposure – especially on hot days, between 11 am and 3 pm.
• Hot and crowded conditions – people attending large events (concerts, dance parties, or sporting events) in hot or crowded conditions may also experience heat stroke that can result in illness.
• Bushfires – exposure to radiant heat from bushfires can cause rapid dehydration and heat-related illness. Bushfires usually occur when the temperature is high, which adds to the risk.

Some drugs, such as ecstasy and speed, also raise the body’s temperature, which can lead to heat stroke.

Risk factors of heat stroke

Certain factors can increase your risk for heat exhaustion and heat stroke, though anyone can develop either condition.

The following factors can increase your risk for heat sensitivity:

• Infants and children under the age of 4 and adults aged 65 and older are at increased risk for heat-related illnesses. That is because your ability to regulate temperature is more difficult at these ages.
• Prescription medications. Some medications used to treat high blood pressure or heart conditions may reduce your ability to stay hydrated. Dehydration can cause heat exhaustion and heat stroke.
• Your body retains more heat when you weigh more. It can also be more difficult to cool your body down if you are overweight.
• Sudden temperature changes. When you rapidly move from a colder to a warmer climate, such as going on vacation in a hotter location, your body may not be able to adjust to the warmer weather. You may have more difficulty regulating your body temperature as a result.
• A high heat index. The heat index is a measurement that factors in humidity along with the outside temperature to determine how hot it feels to you and your body. If the humidity is high, your sweat evaporates more easily and you may have a harder time cooling yourself down. If the heat index is greater than 91°F (32.8°C), you should focus on prevention methods.

Symptoms and Signs

Heatstroke signs and symptoms include:

• High body temperature. A core body temperature of 104 F (40 C) or higher, obtained with a rectal thermometer, is the main sign of heatstroke.
• Altered mental state or behavior. Confusion, agitation, slurred speech, irritability, delirium, seizures, and coma can all result from heatstroke.
• Alteration in sweating. In heatstroke brought on by hot weather, your skin will feel hot and dry to the touch. However, in heatstroke brought on by strenuous exercise, your skin may feel dry or slightly moist.

• Nausea and vomiting. You may feel sick to your stomach or vomit.
• Flushed skin. Your skin may turn red as your body temperature increases.
• Rapid breathing. Your breathing may become rapid and shallow.
• Racing heart rate. Your pulse may significantly increase because heat stress places a tremendous burden on your heart to help cool your body.
• Your head may throb.

Complications of heat stroke

Heatstroke can result in a number of complications, depending on how long the body temperature is high. Severe complications include:

• Vital organ damage. Without a quick response to lower body temperature, heatstroke can cause your brain or other vital organs to swell, possibly resulting in permanent damage.
• Without prompt and adequate treatment, heatstroke can be fatal.

Diagnosis of heat stroke

It’s usually apparent to doctors if you have heat stroke, but laboratory tests can confirm the diagnosis, rule out other causes for your symptoms, and assess organ damage. These tests include:

Rectal temperature to check your core body temperature. A rectal temperature is the most accurate way of determining your core body temperature and is more accurate than mouth or forehead temperatures.

A blood test to check blood sodium or potassium and the content of gases in your blood to see if there’s been damage to your central nervous system.

A urine test to check the color of your urine, because it’s usually darker if you have a heat related condition, and to check your kidney function, which can be affected by heatstroke.

Muscle function tests to check for serious damage to your muscle tissue (rhabdomyolysis).

X-rays and other imaging tests to check for damage to your internal organs.

Treatment and Medications

4 First aid treatments for heat stroke

Victims of heat stroke must receive immediate treatment to avoid permanent organ damage. First and foremost, cool the victim.

• Get the victim to a shady area, remove clothing, and apply cool or tepid water to the skin (for example, you may spray the person with cool water from a garden hose), fan the victim to promote sweating and evaporation, and place ice packs under the armpits and groin.
• If the person is able to drink liquids, have them drink cool water or other cool beverages that do not contain alcohol or caffeine.

• Monitor body temperature with a thermometer and continue cooling efforts until the body temperature drops to 101 to 102 F (38.3 to 38.8 C).
• Always notify emergency services (911) immediately. If their arrival is delayed, they can give you further instructions for the treatment of the victim.

Heatstroke treatment centers on cooling your body to a normal temperature to prevent or reduce damage to your brain and vital organs. To do this, your doctor may take these steps:

• Immerse you in cold water. A bath of cold or ice water has been proved to be the most effective way of quickly lowering your core body temperature. The quicker you can receive cold water immersion, the less risk of death and organ damage.
• Use evaporation cooling techniques. If cold water immersion is unavailable, health care workers may try to lower your body temperature using an evaporation method. Cool water is misted on your body while warm air is fanned over you, causing the water to evaporate and cool your skin.
• Pack you with ice and cooling blankets. Another method is to wrap you in a special cooling blanket and apply ice packs to your groin, neck, back, and armpits to lower your temperature.
• Give you medications to stop your shivering. If treatments to lower your body temperature make you shiver, your doctor may give you a muscle relaxant, such as a benzodiazepine. Shivering increases your body temperature, making treatment less effective.

Can heatstroke be prevented or avoided?

There are many things you can do to prevent heat-related illnesses. Babies, children, and elderly people are more sensitive to heat and require extra attention. Don’t go outside when the temperature and heat index are high. If possible, stay indoors in air-conditioned areas. If you must go outside, take the following precautions.

• Wear lightweight, light-colored, loose-fitting clothing.
• Protect yourself from the sun by wearing a hat or using an umbrella.
• Use sunscreen with a sun protection factor (SPF) of 15 or higher.
• Drink plenty of water throughout the day. Dehydration and lack of salt contribute to heat-related illnesses. Some sports drinks can help replenish the salt in your body lost through sweating. Drink water or other fluids every 15 to 20 minutes, even if you don’t feel thirsty. If your urine is clear, you are probably drinking enough fluids. Dark-colored urine is a sign that you’re dehydrated.
• Avoid or limit drinks that contain caffeine (such as tea, coffee, and soda) or alcohol.
• Schedule outdoor activities for cooler times of the day — before 10 a.m. and after 6 p.m.
• Take frequent breaks from the heat and outdoor activities.
• Do not stay or leave a child in your car when it is hot outside. Even if you open the windows, the intense heat can be extremely dangerous.

Certain medicines can put you in danger of heatstroke. They affect the way your body reacts to heat. Talk to your doctor if you take any of these or have an ongoing health problem. They can help you manage the heat with your condition.