What Is Hypothermia?

Hypothermiais a potentially dangerous drop inbody temperature, usually caused by prolonged exposure to cold temperatures. The risk of cold exposure increases as the winter months arrive. But if you're exposed to cold temperatures on a spring hike or capsized on a summer sail, you can also be at risk of hypothermia.

Normal body temperature averages 98.6 degrees. With hypothermia, core temperature drops below 95 degrees. In severe hypothermia, core body temperature can drop to 82 degrees or lower.

What Causes Hypothermia?

Possible causes of hypothermia include:

Cold exposure.When the balance between the body's heat production and heat loss tips toward heat loss for a prolonged period, hypothermia can occur. Accidental hypothermia usually happens after cold temperature exposure without enough warm, dry clothing for protection. Mountain climbers on Mount Everest avoid hypothermia by wearing specialized, high-tech gear designed for that windy, icy environment.

However, much milder environments can also lead to hypothermia, depending on a person's age, body mass, body fat, overall health, and length of time exposed to cold temperatures. A frail, older adult in a 60-degree house after a power outage can develop mild hypothermia overnight. Infants and babies sleeping in cold bedrooms are also at risk.

Other causes.Certain medical conditions such asdiabetesandthyroidconditions, somemedications, severe trauma, or using drugs or alcohol all increase the risk of hypothermia.

How Does Cold Exposure Cause Hypothermia?

During exposure to cold temperatures, most heat loss -- up to 90% -- escapes through yourskin; the rest, you exhale from yourlungs. Heat loss through the skin happens primarily throughradiationand speeds up when skin is exposed to wind or moisture. If cold exposure is due to being immersed in cold water, heat loss can occur 25 times faster than it would if exposed to the same air temperature.

The hypothalamus, thebrain's temperature-control center, works to raise body temperature by triggering processes that heat and cool the body. During cold temperature exposure, shivering is a protective response to produce heat through muscle activity. In another heat-preserving response -- called vasoconstriction --bloodvessels temporarily narrow.

Normally, the activity of theheartandliverproduce most of your body heat. But as core body temperature cools, these organs produce less heat, in essence causing a protective "shut down" to preserve heat and protect thebrain. Low body temperature can slowbrainactivity, breathing, andheart rate.

Confusion andfatiguecan set in, hampering a person's ability to understand what's happening and make intelligent choices to get to safety.

What Are the Risk Factors for Hypothermia?

People at increased risk for hypothermia include:

  • The elderly, infants, and children without adequate heating, clothing, or food
  • People withmental illness
  • People who are outdoors for extended periods
  • People in cold weather whose judgment is impaired by alcohol or drugs

What Are the Symptoms of Hypothermia?

Hypothermia symptoms for adults include:

  • Shivering, which may stop as hypothermia progresses (shivering is actually a good sign that a person's heat regulation systems are still active.)
  • Slow, shallow breathing
  • Confusion andmemory loss
  • Drowsiness or exhaustion
  • Slurred or mumbled speech
  • Loss of coordination, fumbling hands, stumbling steps
  • A slow, weak pulse
  • In severe hypothermia, a person may be unconscious without obvious signs of breathing or a pulse

Hypothermia symptoms for infants include:

  • Cold-to-touch, bright red skin
  • Unusually low energy

How Is Hypothermia Diagnosed?

Recognizing the symptoms is the first step in diagnosing hypothermia. A specialized thermometer, available in most hospital emergency rooms, can detect very low core body temperatures and confirm a diagnosis.

Temperatures for mild, moderate, and severe hypothermia generally range from:

Mild hypothermia:89-95 degrees Farenheit

Moderate hypothermia:82-89 degrees Farenheit

Severe hypothermia:Lower than 82 degrees Farenheit

Because response to hypothermia varies among individuals, temperatures may differ.

What Is the Treatment for Hypothermia?

Hypothermia is a potentially life-threatening condition that needs emergency medical attention.

If medical care isn't immediately available:

  • Remove any wet clothes, hats, gloves, shoes, and socks.
  • Protect the person against wind, drafts, and further heat loss with warm, dry clothes and blankets.
  • Move gently to a warm, dry shelter as soon as possible.
  • Begin rewarming the person with extra clothing. Use warm blankets. Other helpful items for warming are: an electric blanket to the torso area and hot packs and heating pad on the torso, armpits, neck, and groin; however, these can cause burns to the skin. Use your own body heat if nothing else is available.
  • Take the person's temperature if a thermometer is available.
  • Offer warm liquids, but avoid alcohol andcaffeine, which speed up heat loss. Don't try to give fluids to an unconscious person.

If the hypothermic person is unconscious, or has no pulse or signs of breathing, call for emergency help right away. CPR (cardiopulmonary resuscitation) should be given immediately if a pulse can’t be felt and there is no sign of breathing. Feel for the pulse for up to a whole minute before starting CPR, because the heart rate may be extremely slow and you should not start CPR if there is any heart beat present.

CPR should be continued, in the absence of signs of breathing or a pulse, until paramedics arrive or the person is taken to a hospital.

In cases of advanced hypothermia, hospital treatment is required to rewarm the core temperature. Hypothermia treatment may include warmed IV fluids, heated and humidified oxygen, peritoneal lavage (internal "washing" of the abdominal cavity), and other measures. Complications during recovery can includepneumonia, heart arrhythmias, ventricular fibrillation (a dangerous "fluttering" rhythm of the heart), cardiac arrest (a sudden stopping of the heartbeat), and death.

Seek immediate medical help for anyone with hypothermia.Call 911if you suspect severe hypothermia.

WebMD Medical ReferenceReviewed byMelinda Ratini, DO, MSon January 02, 2015

What is Hyperthermia--Heat Stroke?

Heat strokeis the most serious form of heat injury and is considered a medical emergency. If you suspect that someone hasheat stroke-- also known as sunstroke -- call 911 immediately and givefirst aiduntil paramedics arrive.

Heat stroke can kill or cause damage to thebrainand other internal organs. Although heat stroke mainly affects people over age 50, it also takes a toll on healthy young athletes.

Heatstrokeoften occurs as a progression from milder heat-related illnesses such asheat cramps, heat syncope (fainting), andheat exhaustion. But it can strike even if you have no previous signs of heat injury.

Heatstrokeresults from prolonged exposure to high temperatures -- usually in combination withdehydration-- which leads to failure of the body's temperature control system. The medical definition of heatstrokeis a corebody temperaturegreater than 104 degrees Fahrenheit, with complications involving the centralnervous systemthat occur after exposure to high temperatures. Other common symptoms includenausea,seizures, confusion, disorientation, and sometimes loss of consciousness orcoma.

Symptoms of Heat Stroke

The hallmark symptom of heat stroke is a core body temperature above 104 degrees Fahrenheit. But fainting may be the first sign.

Other symptoms may include:

  • Throbbingheadache
  • Dizzinessand light-headedness
  • Lack ofsweatingdespite the heat
  • Red, hot, anddry skin
  • Muscleweaknessorcramps
  • Nausea and vomiting
  • Rapid heartbeat, which may be either strong or weak
  • Rapid, shallow breathing
  • Behavioral changes such as confusion, disorientation, or staggering
  • Seizures
  • Unconsciousness

First Aid for Heat Stroke

If you suspect that someone has a heat stroke, immediately call 911 or transport the person to a hospital. Any delay seeking medical help can be fatal.

While waiting for the paramedics to arrive, initiatefirst aid. Move the person to an air-conditioned environment -- or at least a cool, shady area -- and remove any unnecessary clothing.

If possible, take the person's core body temperature and initiate first aid to cool it to 101 to 102 degrees Fahrenheit. (If no thermometers are available, don't hesitate to initiate first aid.)

Try these cooling strategies:

  • Fan air over the patient while wetting his or herskinwith water from a sponge or garden hose.
  • Apply ice packs to the patient's armpits, groin, neck, and back. Because these areas are rich withbloodvessels close to the skin, cooling them may reduce body temperature.
  • Immerse the patient in a shower or tub of cool water.
  • If the person is young and heathy and suffered heat stroke while exercising vigorously -- what’s known as exertional heat stroke -- you can use an ice bath to help cool the body.

Do not use ice for older patients, young children, patients with chronic illness, or anyone whose heat stroke occurred without vigorous exercise. Doing so can be dangerous.

If emergency response is delayed, call the hospital emergency room for additional instructions.

Risk Factors for Heat Stroke

Heat stroke is most likely to affect older people who live in apartments or homes lacking air conditioning or good airflow. Other high-risk groups include people of any age who don't drink enough water, have chronic diseases, or who drink excessive amounts of alcohol.

Heat stroke is strongly related to the heat index, which is a measurement of how hot you feel when the effects of relative humidity and air temperature are combined. A relative humidity of 60% or more hampers sweat evaporation, which hinders your body's ability to cool itself.

The risk of heat-related illness dramatically increases when the heat index climbs to 90 degrees or more. So it's important -- especially during heat waves -- to pay attention to the reported heat index, and also to remember that exposure to full sunshine can increase the reported heat index by 15 degrees.

If you live in an urban area, you may be especially prone to develop heat stroke during a prolonged heat wave, particularly if there are stagnant atmospheric conditions and poor air quality. In what is known as the "heat island effect," asphalt and concrete store heat during the day and only gradually release it at night, resulting in higher nighttime temperatures.

Other risk factors associated with heat-related illness include:

Age.Infants and children up to age 4, and adults over age 65, are particularly vulnerable because they adjust to heat more slowly than other people.

Health conditions.These includeheart,lung, orkidney disease,obesityor underweight,high blood pressure,diabetes,mental illness,sickle celltrait,alcoholism,sunburn, and any conditions that cause fever.

Medications.These includeantihistamines,diet pills, diuretics, sedatives,tranquilizers, stimulants, seizure medications (anticonvulsants), heart andblood pressure medicationssuch as beta-blockers and vasoconstrictors, and medications for psychiatric illnesses such asantidepressantsand antipsychotics. Illegal drugs such ascocaineandmethamphetaminealso are associated with increased risk of heat stroke.

People withdiabetes-- who are at increased risk of emergency room visits, hospitalization, and death from heat-related illness -- may be especially likely to underestimate their risk during heat waves, according to a recent study presented at the Endocrine Society's annual meeting by researchers from the Mayo Clinic in Arizona, the National Ocean and Atmospheric Administration, and the National Weather Service.

Check with your doctor to see if your health conditions and medications are likely to affect your ability to cope with extreme heat and humidity.

WebMD Medical ReferenceReviewed byCarol DerSarkissianon September 18, 2016