Hypothermia is when our body gets colder than 98.6º, and operates less efficiently. At the onset of hypothermia our muscles don’t respond with their full strength, we might loose our grip on things like paddles and ropes. As we get colder, involuntary shivering reduces coordination, and we loose mental abilities and don’t realize it, so we make faulty decisions and react slowly. As we get even colder we loose consciousness.
Hypothermia is seldom the direct cause of death of a paddler, but it often a contributing factor in numerous accidents and even drowning. It is therefore an important issue for boaters. Since Alaskan paddling is often done in less than ideal weather and frequently in cold water, it is an even more important topic for us than for most boaters.
Hypothermia can be caused by gradual lowering of the body’s core temperature due to environmental factors. This can take hours or sometimes even days. This is called sub-acute hypothermia and is often overlooked as it is seldom anticipated by boaters. This will sometimes occur with paddlers wearing a wet wetsuit, as the constant evaporation gradually cools the body faster than it can generate heat. Paddlers in wet jeans are also sometimes victims of sub-acute hypothermia for the same reasons. Time is an important factor, as the body gradually fatigues and looses the ability to keep up with the cold.
Acute hypothermia is more commonly noted by paddlers, and is usually caused by rapid cooling from exposure to cold water. This can happen in a matter of just a few minutes. Often the body’s core temperature is still sufficient, but the arm and leg muscles lose strength for self rescue, or even for holding onto a boat or rescue rope. Acute hypothermia happens a lot faster if the body has been pre-cooled from sub-acute hypothermia. So stay warm when boating in dangerous conditions.
Prevention of Hypothermia
Hypothermia is best dealt with by preventing it from ever starting. A drysuit is the usual first defense for Alaskan paddlers. If you can afford one, it will be a great investment.
A wet suit will delay hypothermia, but will often not prevent it. If your paddling is a short trip in moderate weather, a wetsuit should be fine, but if you might be wet for more than a couple of hours, or the weather is cool, a wetsuit will often not be a good solution. The problem with a wetsuit is that after it once gets wet it will hold water for hours, all the while causing evaporative cooling. It is certainly an improvement while you’re in the water, but once you’re back in the boat, you start to cool off, and continue to cool off for hours. Wearing a rain suit over the top of a wetsuit will reduce this evaporative cooling and make a wet wetsuit much warmer.
Boots, socks and gloves should be made of material that will continue to provide warmth when wet. Neoprene works well. Some people hate wet feet. I don’t mind it if I can keep them warm. I can usually do without gloves, but others find them necessary.
In cool weather, a hat should be worn. Once you are clothed properly, 80 to 90% of your body's heat loss can be through an unprotected head. Helmet liners can work great for this.
Layering is a good technique for river wear. Synthetic underwear, a fleece or nylon mid-layer, with a water & windproof outer layer.
Cotton kills. Don’t wear it on the water. As soon as it gets wet it stops being an insulator and starts being a conductor. It holds too much water and takes forever to dry out. Fleece is good insulation even when wet. It holds little water and dries fast. For warmer weather, nylon and other synthetics work well. Some people prefer wool, but synthetics are lighter, warmer and retain less water.
Another way to prevent hypothermia is to paddle in waters that are not beyond your abilities. Once you take a swim you often start to loose the battle with hypothermia. You get cold, and your body doesn’t function as well, and in your sluggishness you are not able to generate enough activity and the heat to re-warm yourself. Another causative factor in hypothermia is exhaustion. If you get tired & fatigued, you will get cold faster & easier.
Also, some boats are wetter and colder than others. For example, an inflatable kayak is a very wet boat, and your legs will continually get re-wetted even in gentle rapids. The cure is to wear warm pants under a drysuit even in warm weather. A cataraft is also generally wetter than a conventional raft, so plan your clothing appropriately.
Another factor in the prevention of hypothermia is keeping up your rate of metabolism. You need to eat foods that convertto glucose at a sufficient rate. Low carbohydrate diets are seldom a good idea if hypothermia is a consideration. Few foods convert to energy faster than refined grains. By some estimates bread converts to glucose faster than pure sugar. But by the same token these foods also get burned up faster, leaving you without reserves after only a couple of hours. Often the best solution is to keep additional food handy and continue to eat.
One thing that many people stop doing while boating is drinking sufficient liquids. Without enough water, metabolism slows down and you start to get cold. Many people reduce fluids when boating because; the lack of privacy, additional clothing layers and being on a moving boat makes urinating difficult. But this has to be weighed against the likelihood of dehydration aggravating hypothermia. The rule of thumb is; if your urine looks yellow, you’re not drinking enough water.
Dealing with Hypothermia
Early detection is the primary key. Often hypothermic victims are the last to know, so keep watching for hypothermic signs from others in your party; shivering, slurred speech, uncoordinated actions, quietness, lethargy, etc. After a swim or even a splashing, keep asking everyone if they are getting cold. At the first indication of possible hypothermia, pull over and deal with it.
Often exercise is the easiest & most expedient action to take if the paddler isn’t too cold. Get them walking briskly. Climb up & down the bank a dozen times. You may have to help them along to keep them at it long enough to do any good. Keep going long after the shivering stops. You need to get the core temperature up to a full 98.6 degrees.
If the victim’s clothes are wet, get them off & put dry clothes on. If it’s windy or rainy, get a rain suit on over the dry clothes. Fleece by itself is a poor cold weather material if it’s windy.
Other things to do: Start a fire to get warm. You might try to fire warm some PFDs & keep switching them on the victim. Use disposable heat packs. Climb into a sleeping bag with the victim. Eat fast carbohydrates (breads & sugars, etc.) Drink warm liquids.
Once the core drops below 90º, field re-warming techniques probably won’t work. Get professional help ASAP. Cardiac arrest and ventricular fibrillation is often induced by rough handling a hypothermic victim, so be gentile.
If the victim stops breathing, ventilate at half the normal rate. Use chest compressions only if you are certain that the victim’s heart has stopped, and if CPR does not slow the evacuation. People have been successfully revived with a core temperature of under 65º, but it’s probably not going to happen in the field, so get help fast.
Don’t drink alcohol. It dilates the surface blood vessels, making you feel warmer, while it actually cools the body and reduces heat generation ability.
Hypothermia Kit
In a drybag keep; fleece suit (jacket, pants, hat and socks), lightweight rain suit, emergency sleeping bag, survival blanket, a really good/simple fire starter kit. I also take a thermos with hot, sweet liquids. If it’s too hot I dilute at the river.
Hypothermic Symptoms
Moderate
> 95º Conscious & alert, but cold & probable violent shivering.
90º-95º Conscious with mental impairment - less shivering.
Severe
86º-90º Unconscious or severe mental impairment - rigid muscles - no shivering.
80º-86º Unconscious with shallow respiration
< 80º Barely detectable respiration & pulse
Skin will look pale and feel cold to the touch.
Pupils begin to dilate at approximately 92º and are fully dilated by approximately 86º.
Pulse will often be hard to detect. Check in the neck at the carotid artery.
