Hypothermia Prevention: Survival in Cold Water

Hypothermia is a risk for anyone who enjoys activities like boating, fishing, swimming, hiking, or skiing. It can occur quickly and it can be fatal.

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 personality and 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 overweight people. The expected survival times the table below are guidelines for the average adult, showing the rapid onset of hypothermia as water temperatures drop.

The Risk

Minnesota’s inland lakes and streams are generally colder than 70°F in winter and spring. Water this cold always presents the danger of hypothermia. Some northern Minnesota lakes are cold year-round. For example, temperatures in western Lake Superior seldom exceed 70°F, except in some bays and shallow beach areas.

Symptoms of Hypothermia

When you first fall into cold water you gasp, your skin begins to cool, and your body constricts surface blood vessels to conserve heat for your vital organs. Blood pressure and heart rate increase. Muscles tense and shiver; this produces more body heat, but results in a loss of dexterity and motor control. As your body’s core temperature drops further, blood pressure, pulse, and respiration rates all decrease.

As conditions worsen, your mental attitude and level of consciousness change. Resisting help and acting irrational or confused 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

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, 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 depend 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.”

First Aid

Minimize the victim’s physical exertion when removing her or him from cold water. Rescuers may have to enter the water to get the victim. Once out of the water, gently remove wet clothing and cover the person with dry clothing or blankets. Protect the victim from wind, especially around the head and neck. Get her or him into a warm environment promptly and avoid re-exposure to the cold.

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 Table 2 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.

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.

Hypothermia Prevention: Methods and Equipment

Conserving body heat is essential for survival and for increasing your chances 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 the table below 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.

First

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.

Second

The more energy you use in cold water, the more your body cools off. To minimize your heat loss, use a personal flotation device and do not swim unless shore, a life raft, or an overturned boat is nearby. Swimming decreases survival time, and attempting to swim more than three-quarters of a mile accelerates heat loss and hypothermia. Remaining still in the water increases your survival time.

Third

If you cannot climb out of the water, conserve body heat by remaining as still as possible and reducing the amount of your body exposed to the water. Protect your critical heat loss regions: the head, sides, armpits, and groin.

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.

Fourth

For the greatest protection against hypothermia, insulate the critical regions of your body with specifically designed PFD. A vest PFD offers more protection than a collar-type, and will improve your chances of survival. Insulated flotation jackets protect more of your body than vest or collar-type PFDs. A hood protects the head and neck area, and a removable seat panel reduces heat loss in the groin area.

Clothing made of modern water-tight materials like nylon and Gore-Tex help keep warm in and cold water out. While these water-tight fabrics decrease contact with cold water, they require carefully selected underclothing since the garments may not have built-in insulation. If flotation materials are not used, then a PFD must be worn in addition to water-tight clothes.

Regardless of what you use to prevent hypothermia – life vest, float coat, industrial work suit, survival suit, or drysuit – 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, or emergency position indicating radio beacon (EPIRB) will increase your chance of being rescued.

It's more than just duck hunters! Minnesota requires boaters to carry a Coast Guard-approved PFD for each person in the boat. Even though the law requires merely having a PFD in the boat, wearing it is recommended. Trying to put on a PFD after falling into cold water is almost impossible.

By Chad P. Dawson, 1987