Things to know about ACCIDENTAL HYPOTHERMIA
Hypothermia is a decrease in the body temperature to an abnormally low level. The severity of hypothermia and the danger involved depends on the degree to which the body temperature is lowered. There are "safe," "transitional," and "danger" zones of hypothermia. In the "safe" zone, the body's normal heat-producing and heat-conserving mechanisms are still intact. In the "danger" zone, these mechanisms are no longer functioning. The "transitional" zone is in between and extends from about 33 to 30 C (91.6 to 86.F).
In any discussion of temperature and heat loss, it is necessary to understand the concept of the body's "core" temperature. Temperature varies very little within the warm, central "core," which includes the contents of the head, chest, and abdomen and some of the deeper tissues of the arms and legs. Rectal temperatures are closer to the actual core temperature than are oral readings, but still may not be entirely accurate. For practical purposes, rectal temperatures are usually used.
The falling body temperature passes through three levels of considerable importance. At 35 to 32 C (95 to 90 F), the body reacts by attempting to produce and retain more heat. Vessels in the skin contract. Shivering may increase heat production by two to five times. At 32.2 to 24 C (90 to 75.2 F), tissue metabolism progressively slows down. Blood vessels are still constricted but shivering has stopped. At body temperatures under 24 C (75.2 F), the body's mechanisms for heat conservation are lost. Survival is uncommon when core temperatures drop below 24 C.
In the field, the early stages of hypothermia may be quite subtle. The victim may become tired and apathetic. Slight personality changes, such as impaired judgment and unnecessary recklessness, may appear. The pace of a hiker usually slows. Shivering occurs only in the early stages, and may be violent then. Further personality changes, such as aggressive or uncooperative behavior, may occur. Muscle weakness increases with cramps, clumsiness, and loss of sensation in the legs. Later, the victim becomes exhausted and incoherent and collapses in a state of partial consciousness or stupor. As death approaches, he is 'unconscious and extremely pallid. In the later stages, there is also generalized muscle rigidity. Muscle rigidity is lost and pulses can no longer be felt in the final stages. Death may ensue as quickly as one or two hours after the onset of hypothermia.
mild hypothermia 32-35 C (89.8-95 F)
moderate 30-32 C (86-89.8F)
severe Less than 30 C (86 F)
Hypothermia victims who appeared to be quite dead have survived with rewarming, especially young and fit persons. The only way that death can be definitely distinguished from hypothermic cardiac arrest is by rewarming the victim.
Factors Predisposing to Hypothermia
I t is clear that people who are old, unhealthy, in poor physical condition, inadequately clothed, tired, injured, or wet are most likely to suffer hypothermia. Certain drugs, especially alcohol, can also increase the likelihood of hypothermia. A number of diseases have been found to predispose to hypothermia. Not only do these diseases increase the fall in body temperature, but they also seem to decrease the likelihood of recovery. Individuals who are physically fit are able to maintain a more vigorous pace, and therefore produce more body heat. Exhaustion may be associated with a considerable fall in body energy stores. A decrease in circulation and blood vessel tone regularly occurs.
The importance of wearing adequate clothing and keeping dry in the prevention of hypothermia are clear. Air that is entrapped within the clothing provides excellent insulation. However, much of a garment's insulating ability is lost if these layers of air move within the clothing. Considerable amounts of heat are also lost when moisture evaporates from the body or clothing. In the cold, and especially if the ambient air is damp, water that has evaporated from the body will often condense in the clothing; most of the heat initially required to evaporate this water is lost, and more heat is lost as the water evaporates from the clothing.
When clothing becomes damp, it is more easily compressed. Moisture and compression displaces much of the dead air in the clothing, so that it is much less insulating. Since water conducts heat at rates 26 times greater than air, much heat may be lost by increased conduction. Clothing should be windproof and water repellent. A wind of 10 knots is equivalent to a fall in temperature of about 30 C on the skin. It is also important, though, that the fabric not be so tightly woven that water vapor from the body cannot escape through it. Otherwise, the vapor will condense and wet the body and clothing. The total insulation of clothing that is' thoroughly wet and exposed to a strong wind is very small, and about the same as if the individual is nude at the same ambient temperature but at a lower wind velocity.
In any discussion of temperature and heat loss, it is necessary to understand the concept of the body's "core" temperature. Temperature varies very little within the warm, central "core," which includes the contents of the head, chest, and abdomen and some of the deeper tissues of the arms and legs. Rectal temperatures are closer to the actual core temperature than are oral readings, but still may not be entirely accurate. For practical purposes, rectal temperatures are usually used.
The falling body temperature passes through three levels of considerable importance. At 35 to 32 C (95 to 90 F), the body reacts by attempting to produce and retain more heat. Vessels in the skin contract. Shivering may increase heat production by two to five times. At 32.2 to 24 C (90 to 75.2 F), tissue metabolism progressively slows down. Blood vessels are still constricted but shivering has stopped. At body temperatures under 24 C (75.2 F), the body's mechanisms for heat conservation are lost. Survival is uncommon when core temperatures drop below 24 C.
In the field, the early stages of hypothermia may be quite subtle. The victim may become tired and apathetic. Slight personality changes, such as impaired judgment and unnecessary recklessness, may appear. The pace of a hiker usually slows. Shivering occurs only in the early stages, and may be violent then. Further personality changes, such as aggressive or uncooperative behavior, may occur. Muscle weakness increases with cramps, clumsiness, and loss of sensation in the legs. Later, the victim becomes exhausted and incoherent and collapses in a state of partial consciousness or stupor. As death approaches, he is 'unconscious and extremely pallid. In the later stages, there is also generalized muscle rigidity. Muscle rigidity is lost and pulses can no longer be felt in the final stages. Death may ensue as quickly as one or two hours after the onset of hypothermia.
mild hypothermia 32-35 C (89.8-95 F)
moderate 30-32 C (86-89.8F)
severe Less than 30 C (86 F)
Hypothermia victims who appeared to be quite dead have survived with rewarming, especially young and fit persons. The only way that death can be definitely distinguished from hypothermic cardiac arrest is by rewarming the victim.
Factors Predisposing to Hypothermia
I t is clear that people who are old, unhealthy, in poor physical condition, inadequately clothed, tired, injured, or wet are most likely to suffer hypothermia. Certain drugs, especially alcohol, can also increase the likelihood of hypothermia. A number of diseases have been found to predispose to hypothermia. Not only do these diseases increase the fall in body temperature, but they also seem to decrease the likelihood of recovery. Individuals who are physically fit are able to maintain a more vigorous pace, and therefore produce more body heat. Exhaustion may be associated with a considerable fall in body energy stores. A decrease in circulation and blood vessel tone regularly occurs.
The importance of wearing adequate clothing and keeping dry in the prevention of hypothermia are clear. Air that is entrapped within the clothing provides excellent insulation. However, much of a garment's insulating ability is lost if these layers of air move within the clothing. Considerable amounts of heat are also lost when moisture evaporates from the body or clothing. In the cold, and especially if the ambient air is damp, water that has evaporated from the body will often condense in the clothing; most of the heat initially required to evaporate this water is lost, and more heat is lost as the water evaporates from the clothing.
When clothing becomes damp, it is more easily compressed. Moisture and compression displaces much of the dead air in the clothing, so that it is much less insulating. Since water conducts heat at rates 26 times greater than air, much heat may be lost by increased conduction. Clothing should be windproof and water repellent. A wind of 10 knots is equivalent to a fall in temperature of about 30 C on the skin. It is also important, though, that the fabric not be so tightly woven that water vapor from the body cannot escape through it. Otherwise, the vapor will condense and wet the body and clothing. The total insulation of clothing that is' thoroughly wet and exposed to a strong wind is very small, and about the same as if the individual is nude at the same ambient temperature but at a lower wind velocity.
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