Most anesthesiologists are aware of the adverse effects
associated with mild hypothermia in the perioperative period (e.g. increased
risk of wound infection, cardiac morbidity, and PACU stay). However, in the ICU
population, some of whom are exposed to environmental extremes, the
manifestations of hypothermia become more numerous.
Hypothermia is classified as mild (core temperature
32-35C), moderate (28-32C), and severe (< 28C), and leads to multiple
physiologic derangements, including in the CNS (fatigue, ataxia, reduced gag
reflex, coma, decreased EEG activity), cardiovascular system (hypovolemia
[secondary to diuresis], arrhythmias [including asystole]), pulmonary system
(respiratory depression, apnea, pulmonary edema), kidneys (“cold diuresis”),
and immune system (immunosuppression).
The mortality rate of hypothermic patients is
approximately 17% (based on a multicenter review of over 400 non-operative
cases)
In 2002, two large, prospective trials demonstrated that
mild hypothermia after resuscitation from cardiac arrest and maintained for 12
to 24 hours improved survival and neurologic outcome in patients suffering from
VF/VT arrest [Hypothermia after Cardiac Arrest Study Group. NEJM 346: 549,
2002; Bernard SA et al; NEJM 346: 557, 2002]. Additional studies have suggested
that therapeutic hypothermia may be beneficial following respiratory arrest,
electrical mechanical dissociation, and asystole, provided that it is initiated
within 25 minutes [Oddo M et al. Crit Care Med 36: 2296, 2008].
In 2005, the IHAST trial demonstrated that therapeutic
hypothermia was safe in patients undergoing aneurysm surgery (craniotomy) but
resulted in no improvement in neurologic outcome [Todd MM et al. NEJM 352: 135,
2005], thus hypothermia cannot be recommended for intraoperative
neuroprotection
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