The Australian and New Zealand Committee on Resuscitation (ANZCOR) makes the following recommendations in summary for 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. 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 minutes.
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 feasible.
4. ANZCOR suggests preventing further heat loss using barriers that use a combination of an insulation layer, such as woollen blankets, and a vapour barrier, such as plastic wrap.
5. ANZCOR suggests that the rescuer should begin active rewarming if the person is not shivering.
6. ANZCOR suggests that a person with hypothermia who is shivering will also benefit from active rewarming (comfort, reduced cardiovascular stress).
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.
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.
3. ANZCOR suggests NOT to rub the affected tissue, use radiant heat, or break blisters.
4. ANZCOR suggests avoiding walking on affected feet. Rest with the feet elevated.
5. ANZCOR suggests ensuring that refreezing does not occur. Once the skin’s colour and consistency have been restored, the person can safely resume normal activity, provided they increase their insulation and take precautions against recurrence.
Exposure to cold conditions can lead to generalised body cooling, hypothermia, or localised cold injury. For the 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 independently.
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 rewarm. Cold injury may be freezing cold injury (frostbite), non-freezing cold injury (NFCI), or trench foot.
Hypothermia
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. 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 benefit those with severe hypothermic cardiac arrest where uninterrupted CPR is impossible. To accomplish passive rewarming, the person’s body temperature regulation mechanisms must be intact, and they need adequate energy stores to create their own body heat through shivering.
Shivering during mild hypothermia can increase heat production by three to five times. Drinks with a high-carbohydrate content will fuel shivering and thus heat production, minimising or preventing further core cooling. Warm drinks will not provide a significant thermal benefit to the body’s core. 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.
In general, when external heat is applied to people who are vigorously shivering (mildly hypothermic), skin warming inhibits shivering heat production. 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.
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.
Hypothermia Prevention
Hypothermia may occur due to unavoidable circumstances, but it can be prevented in many cases. When planning outdoor activities, ensure:
• Adequate equipment and protection from cold, wind and moisture. Wear appropriate clothing, stay dry, and be aware of the ‘wind chill’ potential.
• A regular intake of food and non-alcoholic drinks. Eat appropriate energy food such as fruit or warm sweet fluids, if available, and drink regularly.
• Have a plan for the terrain and environment and ensure that everyone is adequately trained and has experienced leadership.
For further information on preventing accidental hypothermia, refer to New Zealand Mountain Safety Council or Snow Safe or your regional weather bureau website for advice on expected weather conditions and any risk factors that might result in cold weather injuries.
Hypothermia And Frostbite Recognition
If temperature measurement is not possible, rescuers should use the following criteria to assess the hypothermic status of the affected person:
Mild hypothermia (32-35°C):
• Shivering
• Pale, cool skin
• Impaired coordination
• Slurred speech
• Responsive, but possibly with delayed responses.
Moderate (28-32°C) to severe (less than 28°C) hypothermia:
• Absence of shivering
• Increasing muscle stiffness
• Confusion and or a progressive decrease in responsiveness
• Slow/irregular pulse
• Low blood pressure.
There may be dangerous heart rhythms and cardiac arrest in more severe cases. The person may have fixed and dilated pupils and appear dead, particularly if they have a weak, slow pulse.
Management Strategies
• Rescuers perform CPR for those who are unresponsive and not breathing normally. This should continue until ambulance or rescue personnel take over
• 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 minutes.
• 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 feasible.
• Moving the person to a warm, dry shelter as soon as possible. Keep the person lying flat and minimise their physical activity.
• Removing any wet clothing and replacing it with dry clothes to protect the person against wind and draughts. The ambient temperature should be raised to reduce further heat loss whenever possible.
• Send for an ambulance or rescue team.
• Preventing further heat loss using barriers that use a combination of an insulation layer, such as woollen blankets, and a vapour barrier, such as plastic wrap.
• If the person is responsive, they should be given glucose-containing (“sugary”) oral fluids and food, avoiding alcohol and caffeine.
• If the person is not shivering, the rescuer should begin active rewarming.
Active rewarming may include:
• The use of body-to-body contact maximises skin-to-skin contact between the back of the hypothermic person and the front of a person with a normal temperature.
• Chemical heat packs applied inside insulation/vapour barrier material. Charcoal-burning air-activated heat packs or hand warmer sachets that stay warm for 10 hours, hot water bags and electrical heating blankets may also be used safely. External heat should be applied to the armpit and on the chest or back (if possible) as these are the locations that provide the most efficient heat transfer. Some external rewarming methods risk burning the skin if they are applied directly. The manufacturer’s directions must be followed, especially those suggesting appropriate insulation between the heat source and the skin.
• Active rewarming should also be applied to people with hypothermia who are shivering due to the benefits of increased comfort, decreased energy requirements and reduced cardiovascular stress.
• Rescuers should be aware of their own risk of developing hypothermia in cold environments and should monitor their own status and that of any companions as well as that of the affected person.
Cold Injury
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 farther away from the body core and normally has 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
Some conditions 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 party 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 the lining of small blood vessels, leading to poor or no blood flow.
Management
• Applying general management principles regarding shelter, ambient temperature, and sending for help, as outlined in the management of hypothermia above
• If possible, remove jewellery from the affected area and elevate the affected part.
• 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 reheated on the warm abdomen (under clothing) of a companion.
• DO NOT rub the affected tissue, use radiant heat, or break blisters. Avoid walking on affected feet. Rest with the feet elevated.
• Ensuring that refreezing does not occur. Once the skin’s colour and consistency have been restored, the person can safely resume normal activity, provided they increase their insulation and take precautions against recurrence.
For those specifically trained in rescue in cold environments (alpine, polar, tundra), ANZCOR suggests:
• Rewarming of deeply frozen body parts only if there is no risk of refreezing. For severe frostbite, rewarming should be accomplished within 24 hours.
• If tissue is frozen, best tissue outcomes can be achieved by placing the injured part in warm water with circulating water at 37 – 39°C until the affected part thaws. This may take 30 minutes or more and is best achieved under hospital conditions where infection control and adequate pain relief can be provided.
• Chemical warmers should not be placed directly on frostbitten tissue as they can reach temperatures that can cause burns. Following rewarming, efforts should be made to prevent frostbitten parts from refreezing and quickly evacuate the person for further care.
• If the tissue has spontaneously thawed (as is often the case), the water bath is not required, but affected tissue can be cleaned and bathed at a more comfortable temperature (30-35°C).
