Hypothermia is a life threatening condition that may result in death. It is a drop in the core body temperature of less than 95°F (35° Celsius). This temperature is below what is required for normal metabolism and bodily function (Figure 1). The normal body temperature is between 97.7°F and 99.5°F (Fahrenheit) which is the same as 36.5°C and 37.5°C (Celsius). The body's thermoregulation mechanism adjusts to weather changes.
During extreme cold, the body receives a signal from sensory receptors. The signal will go up to the brain. The brain then sends a signal to the body to respond to the cold temperatures and attempts to maintain the core body temperature (Figure 2). This is necessary in order to provide the vital organs with the necessary heat to function properly. The brain will send a signal to the smooth muscle cells of the blood vessels of the skin and the skeletal muscles.
The smooth muscle cells line the arteries and arterioles (Figure 3). During cold, the signal from the brain causes vasoconstriction of the arterioles in the skin which allows the body to shift the blood to more vital areas of the body (Figure 4). Another signal from the brain goes to the skeletal muscles, which quickly contracts them causing shivering that helps to keep the body warm.
If the body is exposed to cold and the thermoregulation mechanism is unable to preserve the heat, a drop in the core body temperature will occur. As the body temperature drops, characteristic symptoms will occur such as shivering and mental confusion (Figure 5). Hypothermia can be mild, moderate, severe or profound. Heat is produced by the muscles, by the heart, as well as the liver and the body loses heat through the skin. The body heat increases 2-4 times more with contraction of the muscles from exercises of by shivering. Accurate core body temperature can be measured by a special low body temperature thermometer, which may not be available.
Hypothermia may also be associated with frostbite. Symptoms will depend on the degree of hypothermia. These symptoms include shivering, blushed lips and extremities (Figure 6), and an altered mental status due to decreased CNS electrical activity (such as confusion, poor judgment, etc.). The patient may slowly lapse into an unconscious state. ATTENTION! Cold hands, feet or skin, shivering and teeth chattering, or feeling cold does not necessarily mean you are experiencing hypothermia. Only a core body temperature below 95°F indicates hypothermia.
Causes of hypothermia include exposure to low temperatures, alcohol use during exposure to the cold, poor clothing, trauma, swimming or diving into cold water (heat is lost more in water than on land), patients who perform outdoor sports such a skiing or mountain climbing, patients who have had a major surgery, and people who have experienced excessive blood and fluid loss.
Alcohol consumption increases the risk of developing hypothermia and does not help with the symptoms. Alcohol is a vasodilator and it increases the blood flow to the skin and extremities (Figure 7). Alcohol may make the patient feel warmer, however it increases the heat lost by vasodilatation.
Elderly people are most prone to hypothermia because they are more fragile, have a lower body fat content, and are prone to a worse outcome if they have a cardiac history (Figure 8). Keep elderly individuals home and warm.
Children are also susceptible to hypothermia. Children have a smaller size and less body surface area. A child's head is larger relative to the rest of their body and a lot of heat is lost through their heads. When you are outside in the cold, make sure to cover up the heads of children.
Hypothermia and Paradoxical Undressing
A large percentage of deaths occur from hypothermia when the patient becomes confused and disoriented. They may remove their own clothing thinking they will feel better. When this occurs it only increases the rate of heat loss and the condition of hypothermia gets worse.
The heart rate may slow in patients with hypothermia. It may be difficult to find a pulse, so keep trying. Hypothermia increases the heart's need for oxygen and lethal cardiac arrhythmia may occur.
Hyperthermia is different from hypothermia. Hyperthermia occurs due to elevated body temperature that is present during heat exhaustion and heat strokes.
A proper diagnosis may saves lives and immediate action is required. The patient should be moved from water and to a safe place. Remove any wet clothing and wrap the patient with a warm, dry blanket. Do not apply dry heat and do not massage the patient. Warming of the patient should be done gradually. Treatment at the hospital usually begins with warm blankets followed by warm IV fluids and warm humidified oxygen. An EKG or blood warmer may also be used.
Any drop in body temperature will make a person feel cold. If you begin to shiver during exposure to cold, this is the point where you should get out of the weather and warm up. Prolonged exposure to the cold beyond this point can be dangerous and it is not a good idea to remain exposed to these cold temperatures.
Make sure you have a proper thermometer available, this is one that can measure lower temperatures. be aware of paradoxical undressing. The patient's life will be endangered unless you warm them up. The patient may resist warming, thinking that they are hot. Do not rely on what the talking tells you. Take their temperature and feel the patient's skin.
If this happens, it is an emergency. As a doctor, you may need to get additional assistance. The patient may need to be monitored in the ICU.
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