Who does this guideline apply to?

This guideline applies to adults, children and infants but excludes newborns in the first minutes to hours following birth.

Who is the audience for this guideline?

This guideline is for use by bystanders, first aiders and first aid training providers.

Recommendations

The Australian and New Zealand Committee on Resuscitation (ANZCOR) makes the following recommendations in managing those who have, or may have, hypothermia:

1. ANZCOR recommends rescuers perform cardiopulmonary resuscitation (CPR) for those who are unresponsive and not breathing normally (ANZCOR Guideline 8). This should continue until ambulance or rescue personnel take over.
2. ANZCOR suggests for those with severe hypothermia who are unresponsive and not breathing normally, where it is not possible to start CPR (for example if initially moving the person to a safer location), rescuers may consider delaying the onset of CPR for up to 10 minutes⁴ [Good practice statement].
3. ANZCOR suggests for those with severe hypothermia who are unresponsive and not breathing normally, only where it is not possible to maintain the continuity of CPR (for example during transport), performing periods of at least 5 minutes of CPR with periods of no more than 5 minutes without CPR. Uninterrupted CPR should be resumed as soon as feasible⁴ [Good practice statement].
4. ANZCOR suggests preventing further heat loss using barriers that use a combination of an insulation layer, such as woollen blankets, and a vapor barrier such as plastic wrap ^5,6,7 [Good practice statement].
5. ANZCOR suggests that if the person is not shivering the rescuer should begin active rewarming.⁸ [Good practice statement].
6. ANZCOR suggests that a person with hypothermia who is shivering will also derive benefits (comfort, reduced cardiovascular stress) from active rewarming⁸ [Good practice statement].

The Australian and New Zealand Committee on Resuscitation (ANZCOR) makes the following recommendations in managing those who have, or may have, cold injury:

1. ANZCOR suggests, if possible, remove jewellery from the affected area and elevate the affected part [Good practice statement].
2. ANZCOR suggests rewarming the affected part immediately. Affected fingers may be placed in the opposite armpit, the armpit of a companion, or a warm hand over a frostbitten cheek or ear. Feet can be rewarmed on the warm abdomen (under clothing) of a companion [Good practice statement].
3. ANZCOR suggests NOT to rub the affected tissue, use radiant heat, or break blisters⁹ [Good practice statement].
4. ANZCOR suggests avoiding walking on affected feet. Rest with the feet elevated⁹ [Good practice statement].
5. ANZCOR suggests ensuring that re-freezing does not occur. Once colour and consistency of the skin have been restored the person can safely resume normal activity provided they increase their insulation and take precautions against recurrence [Good practice statement].

Abbreviations

Exposure to cold conditions can lead to generalised cooling of the body, hypothermia, or localised cold injury.  For normal function of most body systems and organs the human body temperature is kept controlled between narrow limits (about 37°C). Hypothermia occurs when the body gets very cold and cannot warm up on its own. 

Shivering is a mechanism that the body uses to prevent hypothermia. A person who is cold and shivering with a core temperature above 35°C is cold stressed but does not have hypothermia. Those that are cold stressed and able to move should reduce further heat loss and take active steps to rewarm³.

Cold injury may be either freezing cold injury (frostbite) or non-freezing cold injury (NFCI) or trench foot.

Hypothermia occurs when the body temperature is below 35°C. As the body temperature falls, systems and organs progressively fail until death occurs. Infants and elderly people are at greater risk. Hypothermia may develop acutely, for example by falling into icy water. More commonly hypothermia is a gradual process, an example of this is those who have prolonged exposure to cold conditions such as cold weather or lying on a cold floor without adequate protection.

Cooling reduces the resting oxygen consumption of most human tissues, and can protect the brain from injury due to low oxygen levels. There are reports of people with normal oxygen levels before they became hypothermic making a full recovery, even after extended periods of cardiac arrest.³ For those in cardiac arrest due to hypothermia, immediate uninterrupted CPR is the objective, but this is not always possible or may be suboptimal when evacuating a person on a stretcher, transferring into and out of a vehicle, and at altitude. Delayed and interrupted CPR may be of benefit to those with severe hypothermic cardiac arrest where uninterrupted CPR is impossible.^3,4

To accomplish passive rewarming the person’s body temperature regulation mechanisms must be intact and they need adequate energy stores in order to create their own body heat through shivering.¹ Shivering during mild hypothermia can increase heat production by three to five times.²  Drinks with a high-carbohydrate content will fuel shivering and thus heat production, which will minimize or prevent further core cooling. Warm drinks will not provide a significant thermal benefit to the body’s core. In fact, a warm drink may temporarily inhibit shivering through the competing responses of increasing comfort in contrast to its effectiveness, which results in a decreased heat balance.⁸

In general, when external heat is applied to people who are vigorously shivering (mildly hypothermic), skin warming inhibits shivering heat production by approximately the same amount of heat that is donated, such that core rewarming rates are similar between shivering only and external warming. If external heat is available there is a benefit of increased comfort, decreased energy requirements and reduced stress on the heart and other body systems.⁸

 People with severe hypothermia who are not shivering have a greatly reduced ability to produce their own body heat. Wrapping methods can reduce further heat loss, however, active rewarming methods are required to rewarm the person’s core temperature effectively.¹

Freezing Cold Injury (Frostbite)

Frostbite occurs when tissues freeze. This happens in cold environments when blood vessels constrict and reduce blood flow and oxygen to the tissues. Frostbite usually affects body parts that are farther away from the body core, and therefore normally have less blood flow. These include the feet, toes, hands, fingers, nose, and ears. However, it can affect any part of the body. When there is less blood flow and internal heat delivered to body tissue this results in ice crystals forming in cells, which causes cell death. Damage to the affected tissue is worst when there is prolonged cold weather exposure and the tissue slowly freezes.

Frostbite injury is classified as either superficial or deep, depending upon the depth of injury. Deep frostbite extends beyond the superficial skin tissues and involves tendons, muscles, nerves and bone.

Non-Freezing Cold Injury

There are some conditions that occur without freezing the skin, such as chilblains and frostnip. Prolonged exposure of limbs to low temperatures above zero degrees may lead to “trench foot” or “immersion foot”. The injured part may be pale, pulseless, immobile and lack feeling, but is not frozen. Although there is no formation of ice crystals in the tissue, the cold temperature alone may cause damage to nerves and to the lining of small blood vessels, leading to poor or no blood flow.

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