Hypothermia is a condition in which the body’s core temperature drops below 35ºC (95ºF) and cannot function properly: the blood circulation reduces significantly, especially in the small vessels in the skin. It can occur when a person is exposed to extreme cold, such as in mountainous regions in the winter. Other factors that intensify the risk of hypothermia are living in homes that lack heating, the use of alcohol or drugs or pre-existing mental health conditions (BMJ, 2014). Some conditions reduce people’s ability to recognise when they have lost a significant amount of heat.
Good practice points
- People experiencing hypothermia should be treated with care, removed from the cold source and have any wet clothes removed. If the person is moderate to severely hypothermic, clothes should be cut off to minimise their movement.
- A person experiencing hypothermia, who is responsive and shivering vigorously, should be warmed passively using a sleeping bag. If no sleeping bag is available, a blanket (e.g. fleece, 100% polyester) can be used, if possible, in combination with a thermal isolation blanket. The head and body should be covered to minimise convective and evaporative heat loss. Alternative equipment may be used including warm, dry clothing or reflective or metallic foil.
- If the person is not shivering, the first aid provider should actively warm them preferably using an electric heating blanket. As an alternative, hot water bottles, heating pads or warm stones may be used. Do NOT apply warm stones directly to the skin to avoid burning the person. Do NOT rub the person’s skin, as this may damage the skin and underlying muscles.
- Care should then be taken to insulate the person by placing a barrier between them and the ground (e.g., a tarp and sleeping bag) to minimise conductive heat loss.
- If the person is responsive and able to swallow, the first aid provider should give them a warm sugary drink (e.g., chocolate) or some high-energy food.
- For all cases of hypothermia, emergency medical services (EMS) or equivalent should be accessed and the person’s airway, breathing and circulation should be monitored.
Chain of survival behaviours
Prevent and prepare
- Wear appropriate cold-weather clothing.
- Keep clothing dry. If clothing gets wet, change into dry clothing as soon as possible.
- In cold weather, check on those in insecure housing, or without heating to ensure they have ways to keep themselves warm.
- Eat high-energy foods and drink high-calorie drinks, as well as water, to prevent dehydration.
- Avoid alcohol.
- If possible, take regular breaks from the cold to allow the body to warm up.
- When planning to visit a remote, cold area, check how to access local emergency services and take appropriate signals and contact details with you.
- Ensure someone knows when you are venturing to a remote place, the route you plan to take, and when you expect to return.
Early recognition
Symptoms will depend on the temperature and whether the person is experiencing mild or severe hypothermia. Take into account the surrounding environment, for example, if the person is in a cold environment or wearing wet clothing, they are at a higher risk of hypothermia.
The person may have the following:
- shivering
- poor coordination
- slow movements
- mild confusion
- skin becomes paler, ashen or loses its colour
- bluish colouring to lips, ears, fingers and toes.
As their condition worsens, they may show the following:
- no shivering
- disorientation, lack of memory
- exposed skin becomes blue and swollen
- the person may become incoherent or behave irrationally
- coordination continues to worsen; the person cannot walk or use their hands.
First aid steps
- Remove the person from the cold or protect them from cooling down further.
- Have the person remove any wet clothes (or help them if they are unable to do so). Carefully dry off the person if they are wet. Cover them with a blanket.
- If a person is responsive and shivering, let them warm up using a sleeping bag, or alternatively a blanket. If they can swallow, give them a warm, sugary drink (e.g., hot chocolate) or some high-energy food.
- If the person is in an altered state of responsiveness and is not shivering, gradually warm them using an electric heating blanket, or alternatively hot water bottles, heating pads or warm stones.
- Reassure them and monitor their breathing and level of response.
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CAUTION
- Do not rub the person’s skin, as this may damage it and the underlying muscles further.
- Do not apply warm stones directly to the skin as this may burn the person.
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NOTE
If the person becomes unresponsive, open their airway and check for breathing. See Unresponsiveness.
If in a limited resource setting, create a heat source (campfire) to warm the person and build a shelter to protect them from the cold. Ensure there is a layer, such as a blanket, between the person and the ground.
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Access help
For all cases of hypothermia, the first aid provider should access emergency medical care immediately.
Recovery
Most healthy people with mild to moderate hypothermia will recover fully. However, if signs and symptoms continue or additional ones appear, access medical care.
Education considerations
Context considerations
- Learners in or visiting cold climates may benefit from learning how to prevent hypothermia and Frostbite, (including winter conditions in any setting, and specific settings such as the mountains).
- Include information on accessing help in rural or remote environments. (See Remote context.)
- Programme designers should consider that hypothermia can also occur in the home (e.g., older people who are unable or choose not to turn on the heat in cold weather, or people who slip on icy steps and cannot help themselves up).
- Hypothermia can even occur in warm temperatures if a person is wet and inactive.
- In some contexts, learners may benefit from learning about reducing the risk of experiencing an avalanche, including familiarisation with local avalanche warning signs and safe behaviours to follow (e.g., avoid closed ski slopes).
Facilitation tips
- Make learning contextual; facilitating a session outside in cold conditions can reinforce the reality of what a learner may experience in this type of emergency.
- Plan to include environmental conditions at the end of a session as this will allow you to integrate other first aid education (e.g., preventative actions to take or additional symptoms to look for when in a cold environment).
- Recommend individuals review any medication with their healthcare provider as some medical conditions and medications affect the body’s ability to regulate its temperature.
Facilitation tools
Scenarios or games can be used to reinforce key learning points, such as a focus on early recognition. For example:
- Divide learners into small groups and set the scene (e.g., going on an overnight hiking trip). Ask them to write a list of what they will take and what they must do to prepare as a group.
- Add in a complication such as a change in the weather or the group must cross a river and the water is cold.
- Encourage the group to assess what is happening and decide what they will do. Refer them back to their equipment and preparation lists.
- You can also include complications that allow learners to use other first aid skills. For example, one of the group members sprains their ankle and cannot walk on it. Now learners must provide care for the ankle, decide how they will prevent the person from getting hypothermia and determine how they will evacuate the area.
Learning connections
- In some contexts, this topic could be combined with Frostbite.
- Communicate that hypothermia can occur as the result of cooling a Burn. First aid providers should focus their cooling efforts on the burn site (rather than the entire body) and monitor the person during the cooling process.
Scientific foundation
Systematic reviews
We looked at the systematic evidence summary from the Centre of Evidence-Based Practice (CEBaP).
Body-to-body contact
There is limited evidence from two non-randomised controlled (within-subject) trials neither in favour of using a blanket or insulated bag in combination with body-to-body rewarming nor using a blanket or insulated bag alone. In two studies, a difference in the rate of rewarming, afterdrop temperature and length of afterdrop could not be demonstrated when combining body-to-body contact with using an insulated bag or a blanket, compared to an insulated bag or blanket alone. Evidence is of low to very low certainty and results cannot be considered precise due to limited sample size and lack of data.
Heating pads
There is limited evidence from one non-randomised controlled (within-subject) trial in favour of using a blanket in combination with heating pads. It was shown that using a blanket in combination with heating pads resulted in a statistically significant increase of the rectal rate of rewarming, compared to using a blanket alone. Evidence is of low to very low certainty and results cannot be considered precise due to limited sample size.
Heating pads versus body-to-body
When comparing the use of heating pads in combination with using a blanket to body-to-body contact in combination with using a blanket, a difference in the rate of rewarming, afterdrop temperature and length of afterdrop could not be demonstrated. Evidence is of very low certainty and results cannot be considered precise due to limited sample size.
Electric blanket
There is evidence from two randomised controlled trials in favour of using an electric blanket. It was shown that using an electric blanket resulted in a statistically significant increase of rewarming rate, thermal comfort and satisfaction with their care, as well as a statistically significant decrease of pain scores, shivering and anxiety levels, compared to a blanket alone. However, in the smallest of the two studies, a statistically significant decrease of shivering, using an electric blanket compared to a blanket alone, could not be demonstrated. Evidence is of moderate certainty.
Charcoal heater (heat pack)
There is limited evidence from one randomised controlled trial and two non-randomised controlled trials neither in favour of using an insulated bag (with or without a vapour barrier) in combination with a heat pack (on the head or torso) nor using only an insulated bag (with or without a vapour barrier). A statistically significant difference in rewarming rate, afterdrop, length of afterdrop, afterdrop recovery time, total recovery time, when comparing a charcoal heater with an insulated bag to an insulated bag alone, could not be demonstrated. Evidence is of moderate to low certainty and results cannot be considered precise due to limited sample size and lack of data.
Heat pack (torso) vs heat pack (head)
There is limited evidence from one non-randomised controlled trial neither in favour of using an insulated bag with a vapour barrier in combination with a heat pack wrapped around the upper torso nor using an insulated bag with vapour barrier in combination with a heat pack wrapped around the head. A statistically significant difference in rewarming rate, afterdrop and length of afterdrop, when comparing a charcoal heater placed on the upper torso compared to wrapped around the head, could not be demonstrated. Evidence is of low certainty and results cannot be considered precise due to limited sample size and lack of data.
Warm water immersion
There is inconclusive evidence from two randomised and one non-randomised controlled trials concerning the immersion of arms and legs (only) in warm water (42 or 45 °C) compared to using a blanket or an insulated bag. Evidence is of low to very low certainty and results cannot be considered precise due to limited sample size and lack of data.
There is limited evidence from two randomised and two non-randomised controlled trials in favour of immersing the whole body, excluding the head, arms and legs, in warm water. It was shown that warm water immersion resulted in a statistically significant increase of rewarming rate and a statistically significant decrease of rectal afterdrop and length of afterdrop, compared to a blanket. However, a statistically significant difference in oesophageal afterdrop, when comparing warm water immersion to using a blanket, could not be demonstrated.
In addition, it was shown that warm water immersion resulted in a statistically significant increase of (maximum) rewarming rate and a statistically significant decrease of the rectal afterdrop, the length of afterdrop and the time from the start of rewarming to the cessation of shivering, compared to an insulated bag. However, a statistically significant difference in rewarming rate, tympanic afterdrop, tympanic length of afterdrop, when comparing warm water immersion to using an insulated bag, could not be demonstrated. Evidence is of very low certainty and results cannot be considered precise due to limited sample size, lack of data and large variability of results.
Warm water immersion (excluding extremities) vs body-to-body
There is limited evidence from one non-randomised controlled trial in favour of immersing the whole body excluding head, arms and legs, in warm water. It was shown that warm water immersion resulted in a statistically significant increase of rewarming rate and a statistically significant decrease of length of afterdrop. However, a statistically significant difference in afterdrop temperature, when comparing warm water immersion to using a blanket and body-to-body contact, could not be demonstrated. Evidence is of very low certainty and results cannot be considered precise due to limited sample size.
Warm water immersion (excluding extremities) vs heating pads
There is limited evidence from one non-randomised controlled trial in favour of immersing the whole body excluding head, arms and legs, in warm water. It was shown that warm water immersion resulted in a statistically significant increase in rewarming rate and a statistically significant decrease in afterdrop temperature and length of afterdrop. Evidence is of very low certainty and results cannot be considered precise due to limited sample size.
There is limited evidence from three randomised and one non-randomised controlled trial in favour of immersing the whole body, excluding the head, in warm water. Compared to using a blanket, it was shown that warm water immersion resulted in a statistically significant increase of oesophageal, rectal and tympanic rewarming rates, and a statistically significant decrease of oesophageal, rectal and tympanic afterdrop temperature, as well as of oesophageal, rectal and tympanic length of afterdrop.
Compared to using a blanket and vapour barrier, it was shown that warm water immersion resulted in a statistically significant increase of oesophageal and rectal rewarming rates. However, a statistically significant difference in oesophageal and rectal afterdrop temperature, when comparing warm water immersion to using a blanket and vapour barrier, could not be demonstrated.
Compared to shivering only, it was shown that warm water immersion resulted in a statistically significant decrease in tympanic length of afterdrop, as well as a statistically significant improvement in thermal sensation, thermal comfort sensation, shivering sensation, simple reaction time, two-choice reaction time and cognitive performance. However, a statistically significant difference in rectal and tympanic afterdrop temperature and rectal length of afterdrop, when comparing warm water immersion to shivering only, could not be demonstrated. Evidence is of low certainty and results cannot be considered precise due to limited sample size.
Warm water immersion (whole body) vs heating pads
There is limited evidence from one non-randomised controlled trial neither in favour of immersing the whole body, excluding the head, in warm water nor using only heating pads. A statistically significant difference in rectal and tympanic afterdrop temperature and rectal and tympanic length of afterdrop, using whole-body warm water immersion compared to using heating pads, could not be demonstrated. Evidence is of low certainty and results cannot be considered precise due to limited sample size and lack of data.
Warm water (45°C) vs warm water (42°C)
There is limited evidence from one non-randomised controlled trial in favour of immersing only the arms and legs in warm water at 45 °C. Evidence is of low certainty and results cannot be considered precise due to limited sample size.
Warm water immersion (excluding extremities) vs warm water immersion (extremities only)
There is limited evidence from one randomised controlled trial in favour of immersing the whole body excluding the head, arms and legs, in warm water. Evidence is of low certainty and results cannot be considered precise due to limited sample size.
Warm water immersion (whole body) vs warm water immersion (extremities only)
There is limited evidence from one randomised controlled trial in favour of immersing the whole body, excluding the head, in warm water. Evidence is of low certainty and results cannot be considered precise due to limited sample size.
Warm water immersion (whole body) vs warm water immersion (excluding extremities)
There is limited evidence from two randomised controlled trials in favour of immersing the whole body, excluding the head, in warm water. Evidence is of low to very low certainty and results cannot be considered precise due to limited sample size.
Exercise
There is limited evidence from one randomised and one non-randomised controlled trial in favour of shivering while covered only by a blanket or wearing a pile suit. Evidence is of low certainty and results cannot be considered precise due to limited sample size.
Exercise (pile suit) versus insulated bag (with a vapour barrier)
There is limited evidence from one randomised controlled trial in favour of using only an insulated bag with a vapour barrier. In making this evidence conclusion, we place a higher value on afterdrop over the length of afterdrop, rate of rewarming and total recovery time. It was shown that using only an insulated bag with a vapour barrier resulted in a statistically significant decrease in oesophageal afterdrop, compared to exercising while wearing a pile suit. Evidence is of low to very low certainty and results cannot be considered precise due to limited sample size and large variability of results.
Exercise (pile suit) vs heat pack
There is limited evidence from one randomised controlled trial in favour of using an insulated bag with a vapour barrier in combination with a heat pack wrapped around the torso. In making this evidence conclusion, we place a higher value on afterdrop over the length of afterdrop, rate of rewarming and total recovery time. It was shown that using an insulated bag with vapour barrier in combination with a heat pack wrapped around the torso resulted in a statistically significant decrease in oesophageal afterdrop, compared to exercising while wearing a pile suit. Evidence is of low to very low certainty and results cannot be considered precise due to limited sample size and large variability of results.
References
Systematic reviews
Centre for Evidence-Based Practice, Belgian Red Cross-Flanders. (2018). Evidence summary Hypothermia – Active or passive rewarming. Available from: https://www.cebap.org/knowledge-dissemination/first-aid-evidence-summaries/
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