Man is homeothermic and maintains a constant internal temperature despite variations in the external environment and requires a nearly constant internal body temperature. When internal temperature deviates significantly from normal, metabolic functions usually deteriorate and death may result.Enzymatic reactions are highly temperature dependant. Mild hyperthermia increases the rate of enzymatic reactions. However excessive heat leads to an alteration in their chemical configuration (denaturation) and loss of activity. Lower body temperature is well tolerated, reducing the rate of reactions and slowing metabolism.Anesthetic – induced inhibition of thermoregulation combines with exposure to a cold operating room environment to make most unwarmed patients hypothermic.