| MadSci Network: Medicine |
Reference: normal adult body temperature = 98.6*F or 37*C
Hypothermia is defined as: "A decrease in core (rectal, esophageal) body temperture below 35*C. or 95*F."
This condition is often graded as mild (body temperature=34-35*C), moderate (30-34*C), and severe (<30*C) based upon the measured body temperature. A special thermometer (not oral, like the ones you stick in your mouth) which can register as low as 25*C (77*F) is needed to monitor and treat hypothermia. Temperatures in the hypothermic range affect the body in many ways. The greatest effect of hypothermia is to decrease the body's rate of burning its nutrients (decrease metabolism); this amounts to 50% of the normal rate when the body temperature reaches 28*C!!! The low temperature decreases blood flow, constricting the blood vessels. This effect makes oral measurement of body temperature invalid. Irregularity in the heart beat (called ventricular fibrillation) is a major cause of death in hypothermia.
There is no simple single temperature at which death occurs in typical cases of clinical hypothermia. The individual's age, weight, amount of clothing being worn, concurrent disease (for example, diabetes, vascular heart disease, ashthma), the actual environmental temperature leading to hypothermia, the duration of exposure to the hostile temperature, and speed of diagnosis and treatment all play significant roles that affect the the person's outcome. Certainly active intervention by trained health care providers in a professional facility can prevent a fatal outcome; as can prompt help from the companions of a hypothermic person. Learn how to recognize and treat hypothermia under field conditions if you are going into such an environment.
As a practical example from my own Columbia River basin in SE Washington state: healthy, properly clothed, hunters and fishermen can die within 10-15 min or less if they fall into the water during the winter months (when Columbia river temperatures are often only 35-40*F) and are not rescued immediately.
Reference 1: Pathophysiology: Concepts of Altered Health States by Carol Porth, Third Edition, 1990.