10 - Other Medical Considerations

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Dehydration, Sun Stroke, Heat Exhaustion, Hyponatremia, Cold Shock, Trench Foot


Dehydration is the loss of water from the body that occurs during respiration (breathing) or the body's attempts to cool itself by perspiration (sweating). Perspiration is the most frequent cause of dehydration but respiration can be a significant factor in cold dry climates. In warm humid conditions, the loss is most obvious as the sweat is visible and voluminous. But in dry conditions, the loss of water can be as much even though the skin stays completely dry as the sweat evaporates in the dry air.

With exercise, the muscles create many times more heat than when resting. This heat must be dissipated in order to keep the body chemistry working properly. Sweating moistens the skin and allows evaporation to cool the blood in the capillaries just under the sub-dermal fat layer. (The same ones affected by cold shock) The capillaries expand and more blood is sent to the capillaries in order to assist in the heat transfer and cooling process. Water is removed from the blood and the blood actually becomes thicker if this water is not replaced. This makes your heart pump harder to move the sludge around in your arteries and veins. A loss of 2% of your body weight will cause this loss of performance. At higher levels of water loss, you can experience additional problems as described below.

Some people think that most water is lost through the urinary system, but in fact the kidneys can make adjustments to greatly reduce the amount of water loss. The kidney's function is to remove the by products of combustion in your muscles. These waste products are carried by the blood to the kidneys where they are filtered out. If the blood is low on water, the kidneys do not remove much water from the blood and the concentration of waste products to water goes up. Thus the frequency, amount and color of urination is a great indicator of the hydration of your blood. If the amount of urine as near normal and the color is clear or slightly yellow, then all is well. The darker the yellow and the smaller the amount the more dehydrated you are. If you can only squeeze out a few ounces of brown urine, you are severely and dangerously dehydrated.

Water loss during exercise can range from 1 to 3 liters per hour. One liter of water weighs 1 Kilogram (2.2 pounds). A 200 pound man loses 1% to 3% of his weight per hour. That means that a during heavy exercise or extremely hot conditions, dehydration can be causing performance problems in just 30 minutes and a serious situation can develop in less than two hours.

Treatment for minor dehydration is to drink water and/or electrolyte replacement drinks.

Warm Weather

Heat Rash

Heat rashes are quite common for those engaged in physical activities in hot working conditions. Often known as “prickly heat,” heat rashes manifest themselves in the form of red papules (bumps) that can be extremely itchy. Heat rashes are most often caused by un-evaporated sweat caught on the skin by restrictive clothing. Generally, when the area is dried and cooled, the rash dissipates.

Heat Cramps

With a loss of 4% of your body weight, dehydration can cause heat cramps. The symptoms are headaches while in motion and muscle cramps or spasms when resting.

Treatment for minor dehydration is to drink water and electrolyte replacement drinks

Heat Exhaustion

Heat exhaustion is a more serious result of dehydration that occurs around a 6% loss of body weight. Symptoms include malaise, headache, weakness, nausea, loss of appetite, vomiting, dizziness when standing after sitting or sitting after standing. While suffering from heat exhaustion, the victim will still be sweating and be coherent and coordinated.

Treatment for heat exhaustion is to stop all exercise immediately (this might mean a tow), move to a shady spot (probably not possible), douse with water and fan with air to reduce core temperature to 100 degrees F or less. For paddlers, the easiest source of relief may be the water. Splash water onto clothing and wet the victim's head. Administer water and electrolyte replacement drinks.

Heat Stroke

Heat stroke occurs at 7% of body weight loss. At this point the brain is being affected by the change in blood chemistry. Internal temperatures have risen to 105 degrees F and the brain is in danger of cooking. It is a life threatening situation even on land. Paddling on the water makes it much more dangerous. Symptoms are confusion, disorientation, bizarre behavior, coma, seizures, rapid heart rate, low blood pressure, rapid breathing. Frequently, the victim is no longer sweating.

Treatment for heat stroke is to cool the victim as soon as possible with whatever method is available. For paddlers this is limited to dousing with water and fanning. Immersion in the water is not recommended because of the risks from disorientation and debilitation of the victim. If somewhat lucid, administer saline solution. Do not use water or electrolyte drinks if saline is available. Use one part sea water to 4 parts fresh water or a teaspoon of table salt in a liter of water. Vomiting or aspiration is a risk with this procedure. Use small amounts with frequent administration. Stabilization of the victims boat is probably necessary. Towing will be required. Get the victim to a hospital as soon as possible.


Hyponatremia occurs when heavy water loss is occurring through sweating but water, and only water, is being replaced. During sweating certain salts (electrolytes) are also excreted. Drinking replaces the water that is lost, but not the electrolytic salts. Once again the blood chemistry is changed. Now the body finds there is too much water in the blood and water is excreted into the brain and lungs. This condition comes about after four or more hours of heavy exercise with plenty of water taken in. This condition can cause death. Treatment with plain water makes the problem worse. The symptoms are respiratory distress (trouble breathing), nausea, disorientation or red sputum.

Treatment is to use an electrolyte replacement drink or saline solution (or diluted sea water 1 part sea water to 4 parts fresh).


Sea kayakers sometimes have to exert themselves for long periods in warm conditions with no shade or relief from the sun. They may need to overdress for the air temperature because of the water temperature. Keeping properly hydrated is an important ingredient to avoiding dangerous heat related medical conditions. Drink plenty of fluids including those with electrolyte replacements. Keep cool by splashing water on yourself. Learn to lower your whole body into the water and roll back up or use another boat's bow to lower your torso all the way into the water in order to cool off. This is the easiest and best solution when overdressed because of water temperatures. Do not remove clothing because of heat in cold water. Wear a hat to keep the sun off of your head and neck. Dip your hat in the water and put it on wet in order to keep your head cool.

The body can only absorb water at the rate of 1 liter per hour, yet it can lose water at the rate of 1 to 3 liters an hour. Thus with vigorous exercise in hot conditions, you will lose water and dehydrate. If you do not slow down, cool off and re-hydrate you will eventually experience heat related problems. Take at least 5 minute hourly breaks to cool down and replace water and salts.

Cold Weather

Cold Shock
Plunging your torso, head and neck into cold water (<50 degrees F <10 degrees C) can lead to a number of catastrophic debilitating physical reactions that can lead to immediate death. The colder the water, the more likely cold shock may affect you. Without a PFD on when you go over, you will not survive if cold shock occurs. Many PFDs typically worn by kayak paddlers will not save you either.

When your body is quickly immersed in cold water, it reacts with a sudden constriction of the capillaries under the fat just under your skin. This causes a sudden increase in blood pressure. Your heart rate rises dramatically, perhaps to its maximum. The following can happen:

  1. Immediate loss of consciousness. Without a PFD that will right your body and float your nose and mouth out of the water, or immediate assistance, you will drown. Most PFDs worn by paddlers (Class III ) will not right an unconscious body.
  2. Cardiac arrest from the strain placed on your heart. If your heart can not stand the sudden jump to maximum heart rate and the high blood pressure, it stops. Without immediate assistance, you are dead.
  3. Involuntary Gasping Reflex can cause you to inhale while you are underwater. You will not be able to prevent this reflex reaction. Cold water in the lungs or muscle contractions of the windpipe may prevent you from breathing should you regain the surface. If your PFD brings you back or keeps you at the surface, perhaps you live. No PFD, straight to the bottom with you.
  4. After gasping in a lung full of cold water, the temperature of you heart plunges, the muscles stop contracting and you die. Even if you manage to gain the surface or even land, you may still die if you can not empty your lungs quickly enough.

    So how do you prevent cold shock?

    1. Only paddle in warm water. Not a realistic option for most paddlers.
    2. Wear protective clothing - a neoprene wet suit or dry suit will protect the torso from the immediate effects of the cold water and reduce the possibility of cold shock. However, most paddlers still leave the head and neck areas exposed. Wearing a neoprene hood that covers the neck and head will greatly reduce the possibility of cold shock.
    3. Practice - immerse yourself in cold water in safe conditions with someone to rescue you if you need it. Tolerance can be built up. However, you can never be sure how your body will react each time, particularly regarding cardiac arrest.

Frostnip is a nonfreezing cold injury causing pain but seldom serious damage. Symptoms are red, swollen skin which is tender and hot to the touch and may itch. This can worsen to an aching prickly or pins and needles sensation, then eventually numbness. The inflammation is due to cold, damp weather that damages small blood vessels and nerves in the skin. Area may remain sensitive to cold.


Frostbite is the freezing of skin and surface tissues. Proper and prompt treatment can prevent any permanent damage. Symptoms of frostbite are white waxy skin that feels hard. Do not thaw frostbitten flesh if refreezing is a possibility. To treat frostbote, immerse body part in just warmer than normal body temperature water (100O F). If not possible warm bodypart with blankets or additional warm dry non-restrictive clothing. Sever frostbite may develop blisters. Leave blisters intact and cover with clean dry dressing.

Deep Frostbite

This is the most serious type of frostbite. In this stage, blood vessels, muscles, tendons, nerves and bone may be frozen. This can lead to permanent damage, blood clots and gangrene, in severe cases. No feeling is experienced in the affected area and there is usually no blistering. Serious infection and loss of limbs frequently occurs after frostbite reaches this stage. However, even with deep frostbite, some frozen limbs may be saved if medical attention is obtained as soon as possible.


Chillblains are small, itchy, red swellings on the skin, which can become increasingly painful, can swell and then dry out leaving cracks in the skin which expose the foot to the risk of infection.

Trench Foot/ Immersion Foot

Trench foot refers to injury to the tissues of the foot, resulting from prolonged exposure of feet to moisture in either cold conditions or prolonged periods in warmer conditions. This condition is also called immersion foot. It was a very large problem for soldiers in World War I in the trenches of France - hence the name. Trench foot is caused by a wet foot losing heat rapidly, blood circulation being reduced to the feet in order to slow the loss of heat in the body. With reduced blood flow, tissue in the foot suffers from a lack of oxygen and accumulation of waste products, leading to tissue damage, tissue death and gangrene. Symptoms are numbness, tingling pain, burning pain, itching, swelling, color change initally to pale and mottled then to dark purple, gray or blue, sometimes accompanied by red blisters.

Preventive techniques are to simply keep the feet dry and warm. Treatment is to get them clean, dry, warm and elevated to reduce swelling. Analgesics such as Ibuprofin will help with the pain. Do not walk on damaged feet or additional damage will occur. If further immersion is unavoidable try waterproofing the feet with Vaseline or other type of grease. Do not wear socks or booties that restrict circulation. If sweating is a problem, use foot powder.

Frozen lung

Frozen lung is a severe bronchial irritation that results from rapidly inhaling air faster than the airway can warm it. To prevent this, wear protection, a scarf over the mouth and nose, and reduce your level of effort to slow your breathing.

Search and Rescue Society of British Columbia on Hypothermia

Equipped to Survive

Surviving Outdoor Emergencies

Wilderness Medicine Institute

American Red Cross




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