Hypothermia is defined as a core, or internal, body temperature of less than 95 F (35 C). Normal body core temperature ranges from about 98 F to 100 F (36.6 C to 37.7 C); core temperature is best measured by a rectal thermometer; do not rely on an oral, ear, or axial (under the armpit) or skin temperature if hypothermia is suspected. Core body temperatures of 95 F (35 C) and lower can cause the heart and nervous system to begin to malfunction and can, in many instances, lead to severe heart, respiratory and other problems that can result in organ damage and death.
During 1999 to 2002 a total of 4067 death in the US were linked to hypothermia ( MMWR March 17th 2006 ). About half of the cases occurred in persons over 65 years of age.
Hypothermia has been a military problem ever since Hannibal lost nearly half of his troops while crossing the Pyrenees Alps in 218 B.C., and has continued to plague military campaigns through both world wars and the Korean War. The tragic tales of people falling into icy lakes are poignant examples of hypothermia. Anyone exposed to cold temperatures, whether for work or recreation, may be at risk of becoming hypothermic.
Today, with the popularity of an expanding number of winter sports and increasing at-risk populations, hypothermia has slowly become a civilian, urban problem.
Hypothermia has been used as a technique to help improve neurologic recovery for people in cardiac arrest. This topic can be further examined by readers looking into the references 2 and 3 as these topics are not covered in this article.
Normal body temperature is the reflection of a delicate balance between heat production and heat loss. Many of the chemical reactions necessary for human survival can occur only in specific temperature ranges. The human brain has a number of ways to maintain vital temperature. When these mechanisms are overwhelmed, heat loss happens faster than heat production, which results in hypothermia.
Primary hypothermia is due to exposure to a cold or frigid environment, with no underlying medical condition, causing disruption in temperature regulation:
The body loses heat by several major mechanisms that may occur at the same time.
The body also has a variety of methods to increase heat production. But at a certain low level, the body cannot continue heat production, and core body temperature drops quickly. From 98.6 F to 89.6 F (30 C to 32 C), the body begins to shiver, blood vessels contract, and hormones are released to facilitate the generation of heat.
When the core body temperature is 89.6 F to 75.2 F (32 C to 24 C), shivering stops and basic metabolism progressively slows down. At a body temperature lower than 75.2 F, almost every mechanism for heat conservation becomes inactive. Core body temperature continues to plummet. In primary hypothermia, the body is unable to generate heat fast enough to compensate for ongoing heat losses. This primarily is a disease of exposure.
Sometimes the body's temperature control can be altered by disease. In this case, core body temperature can decrease in almost any environment. This condition is called secondary hypothermia. In secondary hypothermia, something goes wrong with the body's heat-balancing mechanisms. People with such diseases as stroke, spinal cord injury, low blood sugar, and a variety of skin disorders can become hypothermic in only mildly cool air.
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