Heatstroke/Sunstroke Diagnosis

  • Diagnosis

    Heatstroke occurs when your body's thermostat cannot keep your body cool. Your body relies on water evaporation to stay cool. As your temperature rises, your body reacts by sweating. When this sweat evaporates, it cools your body. The amount of moisture in the air (humidity) determines how readily sweat evaporates. In very dry air, sweat evaporates easily, quickly cooling your body; but in very humid air, sweat does not evaporate. It may collect on the skin or run off your body without affecting your body's climbing temperature.

    Extremely warm and humid temperatures can quickly overwhelm your body's cooling system—particularly when the air is not circulating. When sweating can no longer keep you cool, body temperature quickly rises, causing the symptoms of heat-related illness.

    Sunstroke is a type of heatstroke. Heatstroke is a condition that occurs after exposure to excessive heat. In sunstroke—also called heat illness, heat injury, hyperthermia, heat prostration, and heat collapse—the source of heat is the sun. Other types of heatstroke occur after exposure to heat from different sources.

    Heatstroke—including sunstroke—is considered to be the most severe of the heat-related illnesses. Heat can have punishing effects on your body. After excessive exercise or physical labor, your body can overheat, and you may suffer heat exhaustion. Heat cramps occur after excessive loss of water and salt; usually resulting from excessive sweating, or after strenuous exercise or labor. During heat exhaustion and heat cramps, the heat-controlling system is still intact, but can be overwhelmed. If this happens, heat exhaustion can progress to heatstroke, a life-threatening medical condition. In severe cases, heatstroke can even cause organ dysfunction, brain damage, and death.

    Sunstroke is caused by a failure in your body's cooling system. When its cooling system fails, your body is overwhelmed by excess heat; this is when sunstroke occurs. Anything that disrupts your body's thermostat can increase the likelihood of sunstroke. These may include such factors as underlying medical conditions, medications, physical characteristics, or age.

    Dehydration contributes to sunstroke. Dehydration happens when your body excretes more water than it takes in. For example, increased water loss through excessive urination is a common side effect of caffeine, alcohol, and many prescription and over-the-counter medications. When the water supply in your body is low, cells begin to pull water from the bloodstream, forcing organs to work harder. Dehydration can also affect the skin's ability to cool the body efficiently. The heart must pump an adequate supply of blood to the skin in order for the skin to cool the body. When you are dehydrated, the blood's volume is reduced, so the cooling process becomes less effective. The taxing effect on the body escalates into the symptoms of heat-related illness.

    Prolonged exposure to the sun contributes to sunstroke. When body fluids are not adequately replenished, sun exposure can cause rapid dehydration. Even on mild or overcast days, the sun can have dangerous health effects. The heat index is a measure calculated by the National Weather Service. It indicates how hot it "feels" outside in the shade when both the air temperature and the relative humidity are considered. In the direct sun, the heat index rises even higher. The following heat indices are associated with these heat-related conditions:

    • 80°F-90°F: Fatigue possible after prolonged physical activity or sun exposure.
    • 90°F-105°F: Heat exhaustion, heat cramps, and sunstroke possible after prolonged physical activity or sun exposure.
    • 105°F-130°F: Heat exhaustion, heat cramps, and sunstroke likely after prolonged physical activity or sun exposure.
    • 130°F and higher: Sunstroke likely with sustained exposure to the sun.

    Symptoms of sunstroke can occur suddenly Table 01. Once your body loses its ability to regulate heat, body temperature can rise quickly. Symptoms of sunstroke include sudden headache, dizziness, weakness, or fainting. Because your body's thermostat is malfunctioning, you will only sweat a little bit or not at all. The skin is hot and dry. Body temperature can rise to 102°F (38.9°C) or higher. In severe cases, repeated vomiting and coma can occur.

    Table 1.  Symptoms of Sunstroke

    Sudden dizziness, weakness, or faintness
    Sudden headache
    Little or no sweating
    Hot and dry skin
    High body temperature, typically 102?F (38.9?C) or higher
    Rapid heartbeat
    Muscle cramps
    Vomiting
    Coma

    Young children and the elderly are at an increased risk for heatstroke and sunstroke Table 02. Young children who rely on others to modify their environments—for example, to remove extra blankets or heavy clothing—may be sensitive to rising temperatures. Elderly adults are less sensitive to changes in temperature, so their thermostats work less efficiently. People with excess body fat are also more likely to retain heat.

    Conditions or medications that cause dehydration can increase your risk for sunstroke Skin disorders such as scleroderma can interfere with your ability to sweat. Dehydrating medications; for example, the diuretics furosemide (Lasix) or hydrochlorothiaszide (Esidrix) make less water available in the body for sweat, thereby crippling your body's cooling system.

    Sunstroke is typically diagnosed on the basis of symptoms alone. To get the best measure of your body's core temperature, your doctor may use a rectal thermometer. Your doctor may also take your blood pressure and ask for a blood or urine sample.

    Your doctor may perform tests to rule out conditions with symptoms similar to those of sunstroke. Irregular heartbeats, a heart attack, a fever-causing infection, fluid loss related to medications, or cocaine intoxication can mimic sunstroke by causing elevated blood pressure and body temperature.

    Table 2.  Risk Factors for Sunstroke

    Very old or very young age
    Low level of physical activity
    Obesity
    Smoking, drug, and alcohol use
    Heart disease
    High blood pressure
    Diseases of the skin, kidney, or liver
    Decreased ability to sweat, such as in scleroderma and cystic fibrosis
    Medications that can aggravate sunstroke, including water pills (diuretics), allergy pills (antihistamines), tranquilizers, anticholinergics, and amphetamines
    Heavy, restrictive clothing
    Poor ventilation or lack of air conditioning in home
    High humidity

    Drink plenty of fluids Table 03. Keeping the body well-hydrated is the easiest and most reliable way to prevent heat-related illness. Under normal conditions, you should consume at least eight 8-ounce glasses of water per day. During strenuous activity, it is essential to replenish fluid at least every 20 minutes, even if you are not thirsty. Avoid caffeinated and alcoholic drinks; these act as diuretics and dehydrate the body

    Avoid exposure to excessive heat. Stay in shaded, cool, or air-conditioned areas whenever possible. In addition, schedule your activities to avoid being outside during the hottest times of the day (from 10am to 6pm). When you must be outside, wear loose-fitting, lightweight, light-colored clothing. Wear a hat that shades your face, neck, and ears.

    Avoid strenuous activity in warm climates. If you want to exercise outside, do so during the early morning, which is the coolest part of the day.

    Table 3.  Strategies for Preventing Sunstroke

    Drink plenty of non-caffeinated, non-alcoholic fluids during the day, even if you are not thirsty.
    Replenish water lost through sweat by drinking at least every 20 minutes during exercise.
    Stay in cool, shaded, or air-conditioned areas.
    Avoid being outside during the hottest hours of the day (10 AM to 6 PM)
    Wear cool, non-restrictive, light-colored clothing.
  • Prevention and Screening

    Drink plenty of fluids Table 03. Keeping the body well-hydrated is the easiest and most reliable way to prevent heat-related illness. Under normal conditions, you should consume at least eight 8-ounce glasses of water per day. During strenuous activity, it is essential to replenish fluid at least every 20 minutes, even if you are not thirsty. Avoid caffeinated and alcoholic drinks; these act as diuretics and dehydrate the body

    Avoid exposure to excessive heat. Stay in shaded, cool, or air-conditioned areas whenever possible. In addition, schedule your activities to avoid being outside during the hottest times of the day (from 10am to 6pm). When you must be outside, wear loose-fitting, lightweight, light-colored clothing. Wear a hat that shades your face, neck, and ears.

    Avoid strenuous activity in warm climates. If you want to exercise outside, do so during the early morning, which is the coolest part of the day.

    Table 3.  Strategies for Preventing Sunstroke

    Drink plenty of non-caffeinated, non-alcoholic fluids during the day, even if you are not thirsty.
    Replenish water lost through sweat by drinking at least every 20 minutes during exercise.
    Stay in cool, shaded, or air-conditioned areas.
    Avoid being outside during the hottest hours of the day (10 AM to 6 PM)
    Wear cool, non-restrictive, light-colored clothing.

Recommended Reading

Meet the Pharmacists

I'm Shereen A. Gharbia, PharmD. Welcome to PDR Health!

Check out my latest blog post on antidepressants

Heatstroke/Sunstroke Related Drugs

    Heatstroke/Sunstroke Related Conditions