History and exam
Key diagnostic factors
common
cold exposure and body temperature <95°F (<35°C)
Those inappropriately dressed for a cold climate and outside for a considerable amount of time may be hypothermic, as assessed by measurement of a body temperature <95°F (<35°C).[27]
impaired mental status
Confusion, apathy, and impaired judgment. Typically seen in people with moderate hypothermia (core temperature of 82°F to 90°F [28°C to 32°C]).
shivering
Patient may be shivering, or there may be a history of shivering.
Note that shivering will be absent once the patient’s core temperature drops below a certain level; the threshold varies between patients but is typically 82°F to 90°F (28°C to 32°C).[48] May also be absent in patients with hypoglycemia.
frostbite
Occurs when the skin and subcutaneous tissue freeze, causing cellular damage.
See Frostbite.
Other diagnostic factors
common
tachypnea, tachycardia, hypertension
Usually seen in people with mild hypothermia (core temperature of 90°F to 95°F to [32°C to 35°C]). Note that tachycardia may progress to bradycardia, even in mild hypothermia.
respiratory depression, bradycardia, hypotension
Usually seen in people with moderate hypothermia (core temperature of 82°F to 90°F [28°C to 32°C]). However, note that tachycardia may progress to bradycardia, even in mild hypothermia.
coma and apnea
Usually seen in people with severe hypothermia (core temperature of <82°F [<28°C]). Some patients may have weak signs of life at temperatures <82°F (<28°C).
Beware of diagnosing death in a patient with hypothermia, even when the patient has fixed pupils or early signs of rigor mortis; signs of life may be minimal if the patient has severe hypothermia.[49]
cold-induced diuresis
Occurs with progression of hypothermia as the kidney loses its ability to concentrate urine.[11]
Risk factors
strong
trauma
drowning
general anesthetic use
Evidence suggests that during general anesthesia, especially after anesthetic induction, there is an internal redistribution of heat from the core to the peripheral compartment resulting in a linear drop in body temperature (i.e., 0.9°F to 1.8°F [0.5°C-1.0°C] per hour). Although unclear, it appears that this phase may last as long as there is a difference between energy metabolic production and heat loss. Long surgical procedures may also be associated with low body temperature.[30][31]
[ 
]
Active prewarming of patients for at least 30 minutes before general anesthesia is recommended to prevent hypothermia and reduce shivering.[32][33]
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substance misuse
Alcohol causes vasodilation, impairs judgment, and causes somnolence and a subjective feeling of warmth, so that measures to prevent hypothermia are not taken. Other drugs such as cannabis impair judgment and restrict shivering, thereby limiting the ability to respond appropriately to cold temperatures. Substance misuse is common among homeless hypothermic patients and is an important risk factor for death.[14][15][16]
impaired cognition
Patients with impaired cognition (e.g., Alzheimer disease, Parkinson disease, stroke) may be at increased risk. If the ability to judge temperature is impaired, patients may dress inappropriately for weather conditions. Getting lost or even stranded is a frequent occurrence and, as a result, patients are at a high risk for hypothermia.
hypothyroidism
Decompensated hypothermia may present with hypothermia, depressed vital signs, and altered mental status.[34]
stroke
Stroke may impair thermoregulation as a result of central nervous system failure.[19]
Parkinson disease
Parkinson disease may impair thermoregulation as a result of central nervous system failure.[19]
homelessness
A well-established risk factor for accidental hypothermia. Hypothermia associated with homelessness is a significant risk factor for hypothermia-related death.[16]
extremes of age
Older adults are at particular risk, most commonly due to acute medical illness, which may interfere with the body's ability to regulate temperature.[13][35]
Children have a larger body surface area relative to body size compared with adults. Relative to the rest of their body, the head is large and therefore dissipates heat rapidly.[36] Newborns are particularly at risk as they lack an effective mechanism for heat production.
gram-negative septicemia
Release of bacterial toxins can cause peripheral vasodilation, impairing the ability to preserve heat by vasoconstriction, thereby increasing the risk of hypothermia.
immobility
Patients who are immobile (e.g., due to illness or injury) are at increased risk of hypothermia.[37]
weak
use of certain drugs
Although rare, hypothermia may be a life-threatening adverse effect of antipsychotics. One systematic review found that hypothermia was reported most commonly with olanzapine, haloperidol, and risperidone.[38] Although the mechanism is unclear, it is hypothesized that antipsychotic-induced hypothermia may be due to peripheral vasoconstriction inhibition and central thermoregulation failure.[38][39]
Hypothermia may also manifest secondary to overdose with opioids, tricyclic antidepressants, phenothiazines, barbiturates, benzodiazepines, and sedatives/hypnotics.[40][41]
Hypothermia has been reported with metformin overdose as a result of systemic vasodilation secondary to acidemia.[35][42][43]
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