An excellent source of information on hypothermia is:
Hypothermia is the lowering of the body's core temperature. There are two types of hypothermia, acute and chronic. Acute hypothermia is the rapid lowering of the body's core temp. Chronic hypothermia is the slow lowering of the body's core temp. If the temperature drop occurs in less than 4 hours it is acute, otherwise it is chronic. Acute hypothermia is also called immersion hypothermia and typically occurs when a person is in cold water. It is important to note the difference between the two since treatment will be different. Hypothermia is considered severe when the body's core temperature drops below 90 degrees F and mild from normal body temperature to 90 degrees F.
A difference between acute and chronic hypothermia is the severity of something called afterdrop. This is the continued dropping of the body's core temperature after the person has been brought to a warm place. Afterdrop complicates treating severe hypothermia.
Hypothermia is the biggest killer of sea kayakers. Many of its victims are unprepared for the cold water exposure that induces it. Water conducts heat away at 20-25 times the rate that air removes heat. This is one reason why an exposure to cold water at a certain temperature is more traumatic than exposure to air at the same temperature.
Sometimes a person will not know they are hypothermic since people typically do not notice it in themselves. It is important for people in a group to keep an eye on their companions for signs of hypothermia (this includes group leaders and guides). Sometimes a person will appear physically and mentally okay and will refuse treatment because they claim they are okay.
Exposure to cold does not automatically induce hypothermia, it typically will take time to develop unless there is exposure to very cold water or there is no protection (wetsuit/drysuit) against the cold.
It can be difficult to tell if someone is hypothermic without actually measuring their core temperature. Measuring a persons core temperature in the field requires a rectal thermometer and is typically not practical. Therefore symptoms must be relied on. Hypothermia affects people in different ways and no one symptom is reliable to indicate if a person is hypothermic.
The following lists the body core temperature and its typical signs and symptoms. Not all hypothermia victims exhibit all of these symptoms, it varies from person to person. Note symptoms will change as the person's core temperature changes.
signs and symptoms
99 to 97F
(37 to 36C)
Normal temperature range, Shivering may begin
97 to 95F
(36 to 35C)
Cold sensation, goose bumps, unable to perform complex tasks with hands, shivering can be mild to severe, skin numb
95 to 93F
(35 to 34C)
Shivering intense, muscle incoordination becomes apparent, movements slow and labored, stumbling pace, mild confusion, may appear alert, unable to walk 30 ft. line properly
93 to 90F
(34 to 32C)
Violent shivering persists, difficulty speaking, sluggish thinking, amnesia starts to appear and may be retrograde, gross muscle movements sluggish, unable to use hands, stumbles frequently, difficulty speaking, signs of depression
90 to 86F
(32 to 30C)
Shivering stops in chronic hypothermia, exposed skin blue or puffy, muscle coordination very poor with inability to walk, confusion, incoherent, irrational behavior, BUT MAY BE ABLE TO MAINTAIN POSTURE AND THE APPEARANCE OF PSYCHOLOGICAL CONTACT.
86 to 82F
(30 to 27.7C)
Muscles severely rigid, semiconscious, stupor, loss of psychological contact, pulse and respiration slow, pupils can dilate
82 to 78F
(27 to 25.5C)
Unconsciousness, heart beat and respiration erratic, pulse and heart beat may be inapparent, muscle tendon reflexes cease
78 to 75F
(25 to 24C)
Pulmonary edema, failure of cardiac and respiratory centers, probable death, DEATH MAY OCCUR BEFORE THIS LEVEL
Lowest recorded temperature of chronic hypothermia survivor
This table is from a book by Wm. Forgey called _Hypothermia-Death by Exposure_.
Mild shivering and cold hands/feet does not indicate you are severely hypothermic. These signs do mean you are losing more heat than you are producing and your body is adjusting its temperature. Shivering is one way your body produces heat to warm itself. Cold hands and feet indicate your body is fighting the cold by reducing the flow of blood to the extremities. Reduced blood flow to the extremities helps to reduce heat loss and helps maintain the body's core temperature. Do take these signs as a warning.
Uncontrolled shivering does mean you are hypothermic. A lack of shivering does not mean you are not hypothermic since a symptom of severe hypothermia (core temperature less than 90 degrees F) is the lack of shivering.
Mild hypothermia where the body core temperature is greater than 90F can be treated by warming the person up. This can be exercise, replacing of wet clothing with dry clothing, getting to a warm place, getting the victim out of the wind, etc. One way of treating hypothermia in the field is to strip the clothes off of the victim and place them into a sleeping bag with one or two other stripped people. This provides the victim with a source of heat that will gradually warm them up. If wet clothing cannot be replaced, cover them with a layer of non-breathing material such as a rain suit and then cover them with a dry layer of insulation. Covering them with a rain suit will prevent further cooling by evaporation and keep the dry layer of insulation from getting wet.
Even though materials such as polypropelene, capilene, polyester fleece, wool, etc. do insulate when wet, they are not as efficient when compared to dry clothing. There is heat loss due to evaporation and conduction when these clothes are wet. Stay away from cotton clothing, cotton kills in cold environments because it does not insulate when wet.
Severe hypothermia is where the body's core temperature is below 90F. A person with severe hypothermia needs to get to a hospital as soon as possible. They should be considered a stretcher case and handled very carefully. Rough handling can induce an irregular heartbeat that can kill them. If they cannot be taken right away, then treat them like you would somebody with mild hypothermia. The one thing that will not help them is exercise because at this stage they have depleted their energy reserves so much that they cannot even shiver. Exercise may even kill them by inducing an irregular heartbeart.
A hypothermia victim should not be considered dead unless they are warm and dead. Even though a hypothermia victim may appear lifeless, get them to an emergency room as quickly as possible. Their pulse and breathing maybe so shallow that they cannot be detected.
Be prepared. Wear clothing that is appropriate for immersion in the water and not the air temperature. Eat properly to keep your energy levels up, get enough rest and drink enough water to maintain proper hydration. Fatigue and dehydration help to induce hypothermia when exposed to cold. Most kayakers that get hypothermia did not expect to end up in the water. Be prepared for cold water immersion when paddling on cold water.
Stay off the water if you are unsure the conditions may exceed your abilities. This includes your ability to do a self rescue or assist in the rescue of another paddler. Be aware of the weather forecast and what the weather is currently doing. A weather forecast is not always 100% accurate.
Remember that extremely cold water can cause your hands to become useless in a relatively short time (less than 20 minutes) even while properly dressed. This will complicate operating a pump, pulling on a spray skirt, firing off flares, radioing for help, etc. This may result in your inability to signal for help, do a self rescue or assist in your rescue or the rescue of others.
Vertigo is not hypothermia but it is related to cold water exposure. Vertigo is the sudden loss of balance and orientation to one's surroundings.
Vertigo is caused when one ear drum is at a different temperature than the other and since your inner ear affects your balance, different inner ear temperatures affect your balance. A vertigo study was done where they would induce vertigo by injecting cold water into a persons ear. The head position they found that induced vertigo the most is the position of your head when you are starting your roll. Vertigo can be prevented by ear plugs and it can be cured by allowing your inner ears regain equal temperatures which occurs after a few minutes. Vertigo does not occur in all immersions into cold water.
Vertigo can cause your roll to fail no matter how good it is. Have a backup rescue method to your roll. If your roll fails, are you prepared to wet exit and be exposed to cold water?
Cold shock is not hypothermia but it is caused by sudden immersion in cold water. It is an involuntary gasp reflex followed by hyperventilation. These affect the ability to breath normally and can cause the breathing in of water that can result in drowning. Typically, there is one gasp reflex. The hyperventilation can last 10 to 15 minutes. It does not occur in all cold water immersions.
Cold shock can complicate a rescue. The gasp reflex can interfere with ones roll due to the involuntary breathing in of water. The hyperventilation will prevent a person from holding their breath for very long complicating the ability to do a reentry and roll. The hyperventilation can also cause panic in some people due to the inability to breath properly and/or the breathing in of water in rough seas.
No, but it is meant to help educate people on the dangers of cold water. This will hopefully result in the people who do paddle in cold water to realize the risk they are taking and to take the proper precautions.
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