Whether you are out walking in the Brecon Beacons or traversing the Cairngorms plateau this winter, it is important to have an awareness of how to keep warm and reduce the risk of hypothermia. This short article will cover some common pitfalls and explore how to manage a cold casualty out in the field.
As shown in figure 1 below, there are four main mechanisms by which humans lose heat: Radiation, Conduction, Convection and Evaporation.
Figure 1: The Four Mechanisms of Heat Loss
The way in which we dress for cold conditions is designed to minimise the impact of these four mechanisms. For example, a suitable wicking base-layer will reduce the amount of heat lost through evaporation when individuals sweat. Mid-layers and insulating jackets aim to reduce convective heat loss by trapping warm air between multiple layers. Staying as dry as possible for as long as possible is vital, and a good pair of Gore-Tex trousers and a jacket are essential. Hard-shell layers also reduce the impact of wind chill, whilst gloves, hats, thick socks, and walking boots focus on minimising conductive heat loss. The potential impact of wind chill cannot be understated. As wind speed increases, the apparent temperature drops significantly, as shown in figure 2.
It is vital to remember that there is a temperature drop of approximately 1C per 100 metres of elevation and appreciate that whilst it may be a relatively warm day in the valleys, it may be very different on the summits.
Figure 2: The Impact of Wind Speed on Temperature
Propper planning, and understanding these principles, is fundamental to enjoying a safe day out on the hill, however despite our best efforts, individuals can get cold, whether this is due to injury, poor equipment, or underlying health conditions.
Over 13% of mountain rescue callouts occur due to cold and exhausted hill walkers.
The human body is designed to operate at a fixed temperature range of 36.5 to 37.5C. Once our core body temperature drops outside of this range, we will start to exhibit symptoms of hypothermia. Individuals frequently start to behave differently from usual, they may become quiet and withdrawn, have problems walking, become confused or have difficulty completing simple tasks such as zipping up their jacket.
An easy way to remember these common symptoms to think of the “Umbles” as shown in Figure 3 (mumbles, stumbles, fumbles, and grumbles).
Figure 3: The “Umbles”
Several different methods exist to classify, or stage, hypothermia, however a pragmatic way to approach a cold casualty is to use the Canadian Cold Card, which was developed by Professor Gordon Giesbrecht and is shown in Figure 4. This handy aide-memoire can be used by both lay and medical professionals, and therefore certain details, such as giving intravenous fluids, are beyond the scope of practice for an outdoor instructor. Nevertheless, it provides a really useful overview of the key symptoms and subsequent management strategies, for a cold casualty in an austere setting.
Figure 4: Canadian Cold Card
Depending on an individual’s condition, it may be necessary to call Mountain Rescue, however there are some simple measures that you can try in the interim whilst waiting for help to arrive:
Providing an individual is conscious and able to swallow, giving them a hot drink and something to eat can help provide the calories and energy required for them to generate some endogenous heat.
Putting up an emergency shelter and using a roll-mat to reduce heat loss into the ground, is an essential yet straightforward intervention.
Removing wet clothing and replacing these with dry items is also valuable if these are available.
Placing warmed fluids in a Nalgene, or similar watertight container, and applying these to the armpits, groins and near the neck can help warm the circulating blood volume, as these areas are where large arterial vessels pass closest to the skin.
The detailed medical assessment of a patient with hypothermia is beyond the scope of this article, however when a patient stops shivering or is no longer alert, this is a medical emergency. In such scenarios, indicative of the casualty should be handled gently and be kept still due to the risk of irregular heart rhythms developing, which can lead to subsequent cardiac arrest.
Early identification of mild to moderate hypothermia can prevent these compilations, and, as mentioned on the Cold Card, creating a vapour barrier or “burrito,” as shown in Figure 5, is a simple, yet potentially life-saving intervention, that can be accomplished with the kit you are carrying.
Figure 5: Creating a Vapour Barrier or Burrito
As with all potential medical emergencies, prevention is better than cure. Checking the weather forecast, performing an appropriate risk assessment, and ensuring you and your group have good quality gear is vital.
Hypothermia occurs frequently in the UK, particularly in wet conditions, and prompt identification and management can mean the difference between a safe trip and a mountain rescue call-out.
This article has provided a very brief overview of hypothermia for the outdoor professional, however if you are interested in finding out more, visit “Baby its cold outside” https://www.bicosurvive.com/ which includes relevant case studies, resources and more.
Disclaimer: This article does not constitute medical advice and should not be treated as such. You must not rely on the information published here as an alternative to medical advice from your doctor or other professional healthcare provider. You should never delay seeking medical advice, disregard medical advice or discontinue medical treatment because of information published in this article. If in doubt, please advise all participants to see their doctor for a comprehensive assessment and management plan.