Hypothermia occurs when the body’s core temperature falls below its normal level of 98.6°F to 95°F or cooler. It is the opposite of fever, when the body’s temperature is above normal.
Hypothermia is dangerous because it affects the body’s core – the brain, heart, lungs, and other vital organs. Even a mild case of hypothermia affects your physical and mental abilities, and increases the risk of accidents. Severe hypothermia causes loss of consciousness and may result in death.
Cold water is especially dangerous because loss of body heat occurs 25 times faster in cold water than in cold air. How quickly you become hypothermic depends on many factors, including your behavior, environmental factors, how you are dressed, and your physical condition.
Everyone reacts differently to the cold, even under the same conditions. Generally, children lose body heat more quickly than adults. Thin people lose body heat faster than heavier people.
The expected survival times in Table 1 are guidelines for the average adult, showing the rapid onset of hypothermia as water temperatures drop.
Expected Time Before Exhaustion or Unconsciousness
|Expected Time of Survival|
Under 15 minutes
3 hours to indefinite
Symptoms of Hypothermia
As conditions worsen, your mental attitude and level of consciousness change. Resisting help and acting in an irrational or confused manner are common indicators of hypothermia. As your core temperature drops dangerously low (from 90°F to 82°F), you become semiconscious, then unconscious. Stress, shock, and low core temperatures may cause cardiac and respiratory failure.
Hypothermia symptoms intensify as your core temperature drops. Since each individual reacts differently, the severity of hypothermia is best measured by taking a core temperature reading using a rectal thermometer. Oral measurements do not accurately measure changes in the core temperature.
Hypothermia and the Diving Reflex
Hypothermia and the Diving Reflex
When a person’s face comes into sudden contact with very cold water, the “mammalian diving reflex” may be triggered. This lowers the heart rate, increases blood pressure, and shuts down blood circulation to all but the body’s core. The result is a lowered metabolism, so the body can conserve oxygen. This may help survival in cold water, since oxygen in the blood is carried to the brain and vital organs where it is needed most.
As a result of the dive reflex, people submerged for more than four minutes (when brain damage usually occurs) have been successfully resuscitated. The chances for surviving such a near-drowning depends on water temperature (colder is better), length of time under water, age of the person (younger is better), and rescue efforts.
The dive reflex and hypothermia can lead to fatal cardiac or respiratory arrest. Survival depends on prompt first aid and medical assistance. Cold water near-drowning victims have been revived after as long as one hour under water. Professional medical care is needed to resuscitate these victims, but rescuers should not give up on victims of extended cold water submersion.
Persistence in first aid and rescue efforts is also critical for cold air hypothermia victims. According to hypothermia researcher Dr. Larry Wittmers, “You aren’t dead until you’re warm and dead.”
Choose first aid methods based on the severity of hypothermia symptoms and the field conditions. Decide if artificial respiration or cardio-pulmonary resuscitation (CPR) is needed, assess the severity of the hypothermia, and re-warm the victim.
During all first aid efforts, watch for changes in the victim’s temperature and vital signs. “After drop” is a danger when re-warming hypothermia victims because cold blood in the extremities returns to the body core, lowering the core temperature further. See below for techniques to minimize the effects of “after drop.” These general procedures assume a rescuer has no special medical training or equipment, will prevent further heat loss, and will get professional medical help for the victim as soon as possible.
- Shivering, with cold hands and feet
- Still alert and able to help self
- Numbness in limbs, and loss of dexterity, clumsiness
- Pain from cold
- Primary task is to prevent further heat loss and allow body to re-warm itself
- Give warm, sweet drinks – no alcohol
- Apply gentle heat source to stabilize temperature
- Help victim exercise to generate heat
- Keep victim warm for several hours, with head and neck covered
- Shivering may decrease or stop
- Same as above
- Limit exercise
- Offer sips of warm, sweet liquids only after victim is fully conscious, begins to re-warm, and is able to swallow – no alcohol
- Shivering decreases or stops
- Confusion, abnormal behavior, i.e., loss of reasoning and recall
- Victim appears drunk; very clumsy, slurs speech, denies problem and may resist help
- Victim is semiconscious to unconscious
- Muscular rigidity increases
- Obtain medical advice as soon as possible, using your radio if necessary
- Assist but avoid jarring victim – rough handling may cause cardiac arrest or ventricular fibrillation of heart
- No food or drink – no alcohol
- Ignore pleas of “Leave me alone, I’m OK.” Victim is in serious trouble – keep a continuous watch
- Treat as for shock – lay down in bunk, wedge in place, elevate feet
- Apply external mild heat to head, neck, chest, and groin – keep temperature from dropping, but avoid too rapid a temperature rise
- Transport gently and quickly to hospital
(82°F, 28°C or below)
- Unconscious, may appear dead
- Little or no apparent breathing
- Pulse slow and weak, or no pulse found
- Skin cold, may be bluish-gray color
- Pupils may be dilated
- Body is very rigid
- Always assume patient is revivable; don’t give up
- Handle with extreme care
- Tilt the head back to open the airway – look, listen and feel for breathing and pulse for one to two full minutes
- If there is any breathing or pulse no matter how faint or slow, do not give CPR, but keep a close watch for changes in vital signs
- Stabilize temperature with external heat sources; also use naked chest-to-back warming by others (leave legs alone), and/or use rescuer’s breath exhaled in victim’s face in unison with victim’s breathing
- If no breathing or pulse is detected for one to two minutes, begin CPR immediately. Medical help is imperative – hospitalization is needed
To re-warm hypothermia victims in the field:
- Use the body heat of a rescuer through maximum direct body contact. Both rescuer and victim should remove outer clothing and be wrapped in a dry sleeping bag or blanket to conserve body warmth. It is best to place the victim between two rescuers.
– Apply hot water bottles or hot, wet cloths to the victim’s head, neck, trunk, and groin. Change the water periodically to ensure a constant temperature. The water should be 110-115°F to prevent burning.
– Exhale into the victim’s face as s/he inhales.
- Two additional re-warming methods require more equipment than usually available in field situations. These are best left to trained medical personnel: (1) administer heated, humidified oxygen to the victim at a temperature of 102-112°F, (2) provide a warm bath of 100-115°F water. Immerse the victim’s trunk but keep the arms and legs out of the water. These methods should be used only on people without major injuries, who do not need resuscitation, and who have been hypothermic for less than 12 hours.
Hypothermia victims with moderate to critical symptoms should always be treated by medical professionals as soon as possible. After medical treatment, victims should be protected from the cold and kept warm.
Conserving body heat is essential for survival and for increasing the chance of being rescued. The rate at which a body cools varies with body size, age, gender, water and air temperature, waves, wind, water currents, and other factors. See Table 3 for examples of how different situations affect survival time for an average sized, lightly clothed adult in 50°F water. Four important prevention principles are illustrated.
|Situation AND Predicted Survival Time||(Hours) in 50°F Water|
|Without flotation device worn|
|With personal flotation device (e.g., vest or collar-type PFD)|
|Huddling with Others||4|
|With hypothermia prevention Equipment|
|Insulated Flotation Jacket (float coat)||3 to 9|
The more body area you keep out of the water, the better your chances for survival. The drown proofing technique of repeatedly lowering your head into the water and floating causes substantial heat loss, and is not recommended in cold water. If you have no personal floatation device and nothing to climb onto, tread water. If possible, climb onto your capsized boat or pull yourself out of the water onto floating object to increase your chances of survival.
The Heat Escape Lessening Posture (H.E.L.P.) can be used only if you are wearing a personal flotation device (PFD). Hold your arms tightly against your sides and across your chest, pull your legs together and up toward your chest. The H.E.L.P. position can be difficult to maintain due to wave conditions, PFD design, and body size. A group of two or more people wearing PFDs can huddle together to conserve body heat, offer moral support, and provide a larger target for rescuers.
Regardless of what you use to prevent hypothermia – life vest, float coat, industrial work suit, survival suit, or dry-suit – flotation and insulation are important in increasing your survival time. PFDs designed to prevent hypothermia are recommended for anyone who spends time on or near cold water. To increase your visibility in the water, add reflective tape to your PFD. A strobe light, whistle, VHF Radio, or emergency position indicating radio beacon (EPIRB) will increase your chance of being rescued.
The source of this information was found at the Minnesota Sea Grant website in an article by Chad P. Dawson