You are on a ski trip with a VIP, a 45 year old male, when he falls and breaks his leg. He is unable to walk, let alone ski. He is diabetic and not particularly fit. You have been skiing in the backcountry all day and are tired and hungry. The weather is poor and night is closing in fast. You are informed that helicopter rescue is impossible due to the white-out conditions. The principle is shivering uncontrollably and complaining of being extremely cold. In this situation hypothermia is a very real risk that, unless recognised and managed effectively, can easily lead to serious injury and death.
What is hypothermia?
Our bodies work within a very tight core temperature range. Within this range we are happy; chemical processes in our body work efficiently and our vital organs function effectively. The body works hard to maintain this stable core temperature; a process called thermoregulation. Thermoregulation can be summed up in a simple equation:
Core Temperature = metabolic heat +/- environmental heat
This means core temperature is a balance between the heat we produce ourselves through metabolic processes and the heat we gain or lose to the environment. In response to changes in the environment and the heat we produce, the body has different mechanisms with which to either conserve or shed heat. Hypothermia occurs when the body starts losing the battle to conserve heat.
Hypothermia is defined as a core body temperature of 35⁰C or less and can be thought of as a continuum; a downward slope towards death. As the core temperature drops, the body’s thermoregulatory mechanisms begin to conserve and produce heat:
- Blood is drawn away from the limbs and the peripheries towards the core, increasing the insulation properties of the muscles and so conserving core temperature
- Metabolism is increased and combined with shivering increases the body’s own production of heat
- Conscious and sub-conscious behavioural responses, such as putting on clothes and seeking shelter, mean we can also conserve and create heat
Swiss Staging of hypothermia (fig 1)
| Mental Status | Core Body Temperature | Shivering? | Breathing? | Stage |
| alert | >35°C (>95°F) | yes | yes | 0 |
| alert | 32−35°C (89.6−95°F) | yes | yes | I |
| drowsy | 28−31.9°C (82.4−89.5°F) | no | yes | II |
| unconscious | 24−27.9°C (75.2−82.3°F) | no | yes | III |
| unconscious | <24°C (<75.2°F) | no | no | IV |
Recognition
Classically, hypothermia has been classified by core body temperature level. This is useless in a pre- hospital environment, as measuring accurate core body temperature is extremely difficult and needs invasive temperature probes placed in the bladder, rectum or gullet. The Swiss Stages of Hypothermia[1] (fig 1) is particularly useful as it describes the downward spiral of hypothermia and helps with the early recognition. Recognising the early stages is far more important than classification, especially in hostile environments. Part of this recognition is not just being able to recite the classic signs and symptoms but to have an understanding of how hypothermia takes hold and who is susceptible. Hypothermia can be acute, sub-acute or chronic – the terms are not important but the mechanisms are. Acute hypothermia affects those who are suddenly immersed in cold water or fall down a crevasse. In these situations, the cold rapidly takes grip and the patient progresses through the Swiss categories with little chance of effective management or survival. Sub-acute would be those who are in the great outdoors but who have inappropriate clothing on or who are injured and unable to find adequate shelter – they are losing heat to the environment but are unable to conserve or produce enough heat. They will move more slowly through the Swiss stages but with early recognition and good management the hypothermia process can be reversed. Chronic hypothermia occurs when body temperature falls slowly over time and is most common in older people living in poorly heated houses. Combined with the mechanism, being able to identify those who are at risk is vital to early recognition.
We need to be alert to those who are not producing heat:
- Diabetics
- Patients in clinical shock e.g. from bleeding
- Malnourished
- Performing extreme physical exertion (extreme is relative to fitness)
- Extremes of age
- Inactivity and impaired shivering
Those with impaired thermoregulation:
- Nervous system disorders
- Diabetes
- Metabolic failure (e.g. infection)
- Toxicological effects (e.g. alcohol, cocaine use)
Those with increased heat loss due to:
- Immersion
- Shock (importantly hypovolemic shock secondary to trauma)
- Pharmacological effects (beta blockers and other medications effecting thermoregulation)
- Burns
- Psoriasis
- Cold fluid therapy
- Recurrent hypothermia
- Infections and infestations
If we now know which patients are going to be susceptible to hypothermia, we can start to look for the signs and symptoms. There is a long list of classic signs and symptoms that are not particularly useful in stressful or time pressured environments. What works are the ‘umbles’[2]
Does the patient
- Grumble – the cold affects peoples’ personality; those who were the light of the group become reclusive and begin to complain about their situation
- Mumble – the cold affects how we speak and the fine motor control muscles of speech
- Fumble – fine motor control is lost as our peripheries are starved of heat and blood; tying shoelaces, doing up zips, delicate tasks normally easily achievable become impossible.
- Stumble – proprioception is affected, as is the central nervous system, which means balance is also affected.
Management
Looking at our VIP, we can quickly see that he is at stage I of the Swiss Staging model – he is beginning to grumble and is shivering. More importantly he has a number of risk factors that make him more susceptible to heat loss:
- He has been skiing all day and isn’t particularly fit – he has probably depleted his energy supplies and now is running out of fuel to create heat
- He is diabetic – not only does this prevent glucose in the body being used as fuel but also affects how the body moves blood to the core
- He is injured – A fractured femur can cause shock, will reduce shivering due to the pain and render the VIP immobile
We need to move quickly to prevent our VIP losing more heat to the environment. Having already applied a traction splint to the femur, shelter then becomes the next priority. A bothy bag provides instant shelter, is lightweight and bright orange, making the team highly visible for rescue. Removing wet clothing and replacing with dry clothes is important but may not be an option and certainly removing your own clothing to keep the VIP warm is not a good idea. There are several options for keeping the patient warm – from survival bags and blizzard blankets through to sleeping bags and specialised thermal bags with their own heat source. In this situation the blizzard blanket would be the most useful as it is lightweight, relatively cheap and very effective. Since movement and exercise to create heat is now impossible, it is important to provide the body with the fuel to create its own heat. Hot SWEET drinks are ideal but in this situation it is unlikely that you have the kit to make hot drinks. At this point any food is important as is the management of the VIPs diabetes. This is where good planning is worth its weight in gold. Making the VIP aware of the risks, having a basic understanding of diabetes and ensuring that the VIP is carrying his medication may avert disaster.
If patients do not recover rapidly, consideration needs to be given to extrication as their management becomes more complex. It is likely that they will need to be carried during evacuation, which is time and resource intensive. They will need to be treated gently and most likely managed lying down thus reducing the risk of cardiac arrest and death. Advanced management such as warm humid air, warmed fluids, external heat sources and, as a last resort, heart-lung bypass machines may be required in highly advanced medical care facilities. If a patient appears dead then the old adage ‘they are not dead until they are not warm and dead’ still applies. However, the decision to begin and sustain CPR until the patient is able to be rewarmed at a hospital is a difficult one and will depend greatly on resources available and the environment. There is no right or wrong answer but the knowledge that you did all you could for the patient at the time or had the ability to make a phone call to a doctor, to help that decision making process, will lighten the moral and ethical load.
Key Points
Avoidance
Early Recognition
Effective management
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By: Tom Davies
Author – Tom Davies is one of Prometheus’ Senior Instructors and is a full-time Paramedic working with West Midlands Ambulance Service and Midland Air Ambulance.
Photograph – © Prometheus Medical Limited 2013
[1] European Resuscitation Council Guidelines for Resuscitation 2010, Section 8
[2] Is it hypothermia? Look for the “umbles” – stumbles, mumbles, fumbles, and grumbles. (2003) NIH News, U.S. Department of Health and Human Services, National Institutes of Health (Online) Available: www.nih/go/news/pr/jan2003
Emily H
December 29, 2016 at 5:37 PMThis is a very well written article. Where could I find more information about extreme physical exertion as risk factor for hypothermia?
Thank you, Emily H