الفهرس 
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Abstract
Severe hypothermia may be induced deliberately to
confer protection against tissue ischemia, specifically
during cardiac and , occasionally, neurosurgery.
Drugs such as barbiturates and volatile anesthetic
provide considerably less protection than even mild
hypothermia, temperatures as low as those deliberately
induced are usually lethal when unintentional. Deliberate
hypothermia is safe only because anesthesiologists
understand and treat the physiologic changes caused by
core temperatures 10 to 15º C lower than normal.
A- organ Function:
ischemia damages tissues because oxygen
deprivation forces cells to obtain energy anaerobically.
Because this mechanism is inefficient, it may not provide
adequate energy. Anaerobic metabolism also producer more
toxic metabolic waste products (e.g., lactate and superoxide
radicals) than does the Krebs cycle, a situation that is
particularly serious when these products are not removed by
circulating blood.
Hypothermia decreases the whole-body metabolic rate
by ≈8 percent/ºC, to approximately half the normal rate at
28ºC. whole-body oxygen demand diminishes, and oxygen
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consumption in tissues that have higher than normal
metabolic rates, such as the brain, is especially reduced. Low
metabolic rates allow aerobic metabolism to continue during
periods of compromised oxygen supply; toxic waste
production declines in proportion to the metabolic rate.
Although decreased metabolic rate certainly contributes to the
observed protection against tissue ischemia, other specific
actions of hypothermia (including ” membrane stabilization ” and
decreased release of toxic metabolites ) may be most
important..