Hypothermia is defined as a core body temperature below 35 degsC. The condition is divided into mild (35-32 degsC), moderate (32-28 degsC) and severe (below 28 degsC).
Mechanisms such as shivering and an increase in metabolism, heart rate and cardiac output try to correct any fall in body temperature.
As cooling continues, these mechanisms are overwhelmed; shivering stops and heart rate, metabolism and cardiac output slow. Below 28 degsC there is a risk of arrhythmias and cardiac arrest.
The ability of the body's compensatory mechanisms to prevent hypothermia has been demonstrated by the extreme swimmer Lewis Pugh, who, in 2007, swam 1km at the North Pole,1spending about 20 minutes in water that was -1.7 degsC.
|Case study one: Homeless alcoholic patient|
During an evening surgery in January, a GP saw a 55-year-old patient who was known to be an alcoholic and of no fixed abode. She smelt of alcohol during the consultation. The GP diagnosed a chest infection and prescribed a course of antibiotics.
Later that night, she was found unresponsive, lying in a doorway. On admission to A&E, her core temperature was 33.4 degsC and her blood sugar was 3mmol/L. She was warmed with a forced-air warming blanket and given IV glucose. By the next morning, her temperature had returned to normal and she was alert and orientated.
|Case study two: Shivering and slurred speech|
A GP on a charity trek in Africa was asked by the trek leaders to review a participant who had been trekking late into the night as she had fallen behind the rest of the group. Her temperature (measured using a tympanic membrane thermometer) was 34.5 degsC and she was shivering and complaining of feeling cold. She was orientated, but her speech was slurred and her gait unsteady.
The GP arranged for her to be dressed in additional layers and put into a sleeping bag. She was given hot, sugary drinks and hot-water bottles were put in her sleeping bag. Her temperature stayed below 35 degsC for the next few hours, but then gradually normalised. She was able to rejoin the trek the following day.
Signs and symptoms
- Patients may complain of feeling cold but awareness can be reduced in the elderly
- Cold, pale skin (especially notable on the usually warm abdomen)
- Problems with gait, co-ordination and speech
Rectal thermometers, ECGs and blood tests can be useful, but are unlikely to be available to the GP.
- Prolonged exposure to cold
- Inadequate clothing or room temperature
- Chronic disease, for example, diabetes, heart failure, Parkinson's disease, malnutrition, dementia
- Acute illness, for example, pneumonia, sepsis
- Drugs, for example, alcohol, sedatives, opioids
- Old age, poverty or debility may prevent elderly people from taking measures such as turning up the heating or putting on adequate clothing. Physiological mechanisms, such as shivering and peripheral vasoconstriction, can be impaired. An elderly person who has fallen is at particular risk of hypothermia
- Exposure to severe cold or immersion in water
If low-reading core temperature thermometers are not available, symptoms can help to grade severity.
- Complaining of feeling cold
- Possibly muddled, but consciousness normally unaffected
- Appropriate behavioural responses, such as putting on extra clothing
- Tachycardia, tachypnoea, diuresis
Moderate and severe hypothermia
- Not shivering
- Confusion and reduced consciousness
- Patient may feel warm and start to remove clothing or open windows
- Bradycardia, arrhythmia, reduced respiratory rate
Mild hypothermia in a patient who is normally well can be managed by replacing wet clothing with multiple warm and windproof layers, and using external sources of heat, such as heaters or hot-water bottles.
Exercise (where practicable) will also help to warm the patient. Calories are necessary to fuel shivering. The danger of warming the patient too quickly is probably overstated, but immersion into hot water could be dangerous.2
Older patients and those with physical and mental health problems are at higher risk of worsening hypothermia, so the threshold for admission should be lower for people in these categories.
Consider environmental factors, such as the support network, housing and heating, in deciding whether a patient is likely to deteriorate if left at home.
When these patients return home, their medications and chronic diseases might need reviewing to reduce the risk of future episodes.
Patients with symptoms or signs of moderate or severe hypothermia should be managed in hospital where possible. The initial pre-hospital management is the same as for mild hypothermia, but severely hypothermic patients should be handled very gently and kept flat, to minimise the risk of precipitating VF. The guideline for rewarming is 1 degsC per hour.3
- Dr Jopling is a GP in London. Thanks to Dr Nicholas Ramscar for reviewing this article
1. Lewis Pugh: achieving the impossible. North Pole 2007: (1km): 18 min 50 sec.
2. Frozen Mythbusters. Wilderness Medicine Newsletter
3. Nolan J, Soar J, Lockey A et al. Advanced Life Support (sixth edition). London, Resuscitation Council (UK), 2011.
- Mallet ML. Pathophysiology of accidental hypothermia. QJM 2002; 95(12): 775-85.