Epidemiology
Risk factors
Evidence suggests that during general anaesthesia, especially after anaesthetic 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., 0.5°C to 1.0°C [0.9°F to 1.8°F] 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.[16][17]
[ 
]
Active pre-warming of patients for at least 30 minutes before general anaesthesia is recommended to prevent hypothermia.[18][19]
[ ]
Older adults are at particular risk. Often, they have significant comorbidities (e.g., Alzheimer's disease) with various medications (e.g., beta-blockers) that may interfere with the body's ability to regulate temperature.
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. Newborns are particularly at risk as they lack an effective mechanism for heat production.
Patients who are immobile (e.g., due to illness or injury) are at increased risk of hypothermia.[20]
Alcohol causes vasodilation, impairs judgement, and causes somnolence and a subjective feeling of warmth, so that measures to prevent hypothermia are not taken. Other drugs such as cannabis impair judgement 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.[21]
Patients with impaired cognition (e.g., Alzheimer's disease) may be at increased risk. They may wander from home and may be unable to find their way back, thus leaving them vulnerable to cold weather.
Hypothyroidism results in cold intolerance, which is usually compensated for by behavioural mechanisms, such as overdressing, and intrinsic heat-saving mechanisms, such as shivering. If ambient temperature decreases further, or if the compensations are reduced (e.g., by central nervous system depression due to alcohol or muscle relaxation), hypothermia may occur.[9]
If a stroke affects a patient's cognition, this may impair their ability to judge temperature, and they may dress inappropriately for weather conditions. Impaired cognition can also put patients at risk of getting lost or stranded and, as a result, they are at a high risk for hypothermia.
If Parkinson's disease affects a patient's cognition, this may impair their ability to judge temperature, and they may dress inappropriately for weather conditions. Impaired cognition can also put patients at risk of getting lost or stranded and, as a result, they are at a high risk for hypothermia.
A well-established risk factor for accidental hypothermia. Hypothermia associated with homelessness is a significant risk factor for hypothermia-related death.[22]
Release of bacterial toxins can cause peripheral vasodilation, impairing the ability to preserve heat by vasoconstriction, thereby increasing the risk of hypothermia.
Induces vasodilation and suppresses the normal sympathetic response, such as shivering. Lower ambient temperatures amplify the hypothermic effects of these drugs.[23]
Induces vasodilation and suppresses the normal sympathetic response, such as shivering. Lower ambient temperatures amplify the hypothermic effects of these drugs.[23]
Induces vasodilation and suppresses the normal sympathetic response, such as shivering. Lower ambient temperatures amplify the hypothermic effects of these drugs.[23]
May impair the patient's ability to judge the effects of temperature.
Use of this content is subject to our disclaimer