Page 34 - Color Atlas Of Pathophysiology (S Silbernagl Et Al, Thieme 2000)

Hypothermia, Cold Injury
If there is a danger of the core temperature ! Stage of paralysis (severe hypothermia, < ca.
dropping, (counter)regulatory heat production 288C): coma; no pupillary reflexes (but no sign
results (muscle tremor and movement) (→ A). of brain death); ultimately ventricular fibrilla-
Its narrow limits are usually not overstepped, tion, asystole, and apnea. The lower the tem-
because the risk of cooling triggers behavioral perature until cerebral blood flow ceases, the
changes, depending on the underlying cause(s) longer the brain will tolerate circulatory arrest
(protection against wind, added clothing, leav- (308C: 10–15 min; 188C: 60–90 min). This is
ing swimming pool, etc.). If this reaction does why some persons have survived extreme hy-
not occur—either because it is not possible to pothermia (< 208C). The long time of circula-
escape the situation for physical reasons, the tory arrest tolerated at low temperature is
danger is not realized, or there are metabolic, also of use in induced therapeutic hypothermia
hormonal, or neurological abnormalities—hy- (during open-heart surgery and preservation
Temperature, Energy at 5–108C can lead to hypothermia after only still be attempted even if the core temperature
pothermia develops, i.e., the core temperature
of organs for transplantation).
drops below 358C (→ A). Immersion in water
Rewarming of hypothermic patients should
10 minutes (depending on the amount of “pad-
has dropped below 208C. However, rewarming
may be associated with lethal complications,
ding”). Wearing wet clothing in a strong wind
especially if it is done externally and too rapid-
and in an ambient temperature of 08C can
hour. Both the elderly (restricted thermoregu-
(→ B). In stage I (> 328C), warming is done pas-
latory range) and infants (especially new-
sively and externally (warm room, blankets,
2 bring about hypothermia in less than one ly, i.e., more quickly than a few 8C per hour
borns), who have a relatively high body surface foil). In stage II, active warming must be under-
area to mass ratio, low resting heat production, taken (electric blankets, warm infusions, pos-
and a thin subcutaneous fat layer are particu- sibly hemodialysis with heat exchanger) under
larly at risk. While unclad young adults can careful monitoring. In stage III hypothermia
maintain a constant core temperature even with circulatory arrest, active warming by
when the ambient temperature drops to ca. means of extracorporeal circulation (heart–
278C because of their resting heat production, lung machine) is the most effective method of
hypothermia may develop in a newborn at an rewarming.
ambient temperature of < 348C. Long-term sequelae of successfully treated
The acute sequelae and symptoms of hypo- hypothermia include heart failure, liver and
thermia can be divided into three stages (→ A, kidney failure, abnormal erythropoiesis, myo-
I–III): cardial infarction, pancreatitis, and neurologi-
! Stage of excitement (mild hypothermia, cal disorders.
32–358C): maximal muscle tremor, resulting Frostbite. Even with mild hypothermia and/
in a marked increase in resting metabolic rate, or low ambient temperature the perfusion of
all sources of glucose are utilized (hyperglyce- skin and limbs is markedly reduced, with in-
mia), and O 2 consumption is increased up to termittent and brief increases (Lewis reaction:
sixfold. Tachycardia and vasoconstriction about every 20 min at a skin temperature
cause a rise in blood pressure; acral vasocon- < 108C). None the less, frostbite may occur:
striction causes pain. The person is at first fully 1st degree (at first pallor and loss of sensation;
awake, later confused and even apathetic, and swelling and pain after rewarming); 2nd de-
ultimately judgment becomes impaired. gree (blister formation after 12–24 h followed
! Stage of exhaustion (moderate hypother- later by healing); 3rd degree (after days and
mia, 32–288C): the sources of glucose become weeks: extensive tissue necrosis with healing
exhausted (hypoglycemia); bradycardia, ar- by scar).
rhythmia, and depressed breathing occur and
the person begins to hallucinate and to behave
24 perplexingly, soon losing consciousness and
no longer feeling pain.
Silbernagl/Lang, Color Atlas of Pathophysiology © 2000 Thieme
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