Keeping The Casualty Warm...

Posted by Jeremy Windsor on Apr 11, 2019

With cold weather finally arriving in the UK, we asked Arav Gupta and Mike Greene to take a look at a recent publication that tested the insulating devices that are currently available to the UK's mountain rescue teams.

Arav is an FY2 in South Manchester who is hoping to go into a career in anaesthetics and critical care. When not working he can be found plotting his FY3 year or cycling in the Peak District.

"With the number of visitors to our hills and mountains increasing each year, MRT's are busier than ever. Adverse weather conditions at the time of rescue will often impact upon the core temperature of the patient and lead to an impaired physiological response to injury or illness. One can imagine, therefore, that minimising heat loss leads to better patient outcomes and is a clinical priority.

Recently, Chris Press and his colleagues at Edale MRT compared six commonly used insulation systems and studied their effectiveness in minimising heat loss over a period of 130 minutes. 

For their study they filled a supine thermal manikin with 32L of water heated to 42 degrees C. 

The MCI Man™ MedicTech thermal manikin

This was placed inside six different insulating devices and laid on a Bell Mountain Rescue Stretcher.


Bell Mountain Rescue Stretcher 

Heat loss in the manikin was then measured at 10 minute intervals. Each study was conducted in still, dry conditions at an ambient temperature of between 11 and 13 degrees C.

The best performing method was the Full Body Splint (Vacuum Mattress) combined with a Pertex/Fibrepile blanket. This resulted in heat loss of 3.2 C over 130 minutes. 

The Full Body Splint (Vacuum Mattress) and Pertex/Fibrepile blanket was the most effective insulating device losing only 3.2 degrees C over 130 minutes.

The addition of a Wiggy Bag did not result in any improvement in insulation.

The Wiggy Bag

Alone, a Wiggy Bag or Mountain Equipment (ME) Heavyweight Casualty Bag both resulted in heat loss of 4.2C, whilst a Blizzard (Foil) Bag (5.4C) and a plastic survival bag (frequently carried by walkers) (9.5C) led to even greater falls in temperature. 

The Mountain Equipment Heavyweight Casualty Bag (4.2 degrees C), Blizzard Bag (5.4 degrees C) and Plastic Orange Survival Bag (9.5 degrees C) all resulted in greater heat loss than the Full Body Splint (Vacuum Mattress) and Pertex/Fibrepile blanket.

Thankfully, all were significantly better than no insulation at all, in which the poor manikin lost 12.2C in total!

The greatest fall in water temperature was seen in the Control (12.2 degrees C). The Plastic Orange Survival Bag (9.5 degrees C) and Blizzard Bag (5.4 degrees C) also experienced significant heat loss. The ME Casualty Bag and Wiggy Bag both resulted in heat loss of 4.2 degrees C.

The main limitations are well acknowledged by the authors and all stem from the fact that this is clearly not a "real life" test. The manikin cannot generate de novo heat and unavoidable variants on the hillside such as rain, wind and the victim's physical characteristics are not accounted for. Understandably, this sort of study on human subjects has enormous ethical implications and this is referred to in the discussion section of the study.

My main take-home message as a layman is that a plastic survival bag is better than nothing. It’s cheap and will likely limit heat loss and shield the user from the elements in the time it takes for the MRT to arrive with better equipment! It goes without saying, however, that comprehensive trip preparation to minimise the risk of needing the MRT is the ‘gold standard’ approach!"

A volunteer wrapped in a Full Body Splint (Vacuum Mattress) combined with a Pertex/Fibrepile blanket. The most effective means of insulation found in this study

Mike Greene is a former Consultant in Emergency Medicine and is currently the Programme Clinical Lead for the Diploma in Mountain Medicine organised by the Royal College of Surgeons (Edinburgh). He is Medical Officer for England and Wales Mountain Rescue and in 2014 was awarded an MBE for his services to medicine. Here's what he had to say,

"This review draws our attention to the need for good quality temperature control.  A recent review article endorsed by International Commission for Alpine Rescue (ICAR) provides an up-to-date summary of the assessment and treatment of the cold patient. The wet cold and windy environment of the British hills presents a significant physiological challenge. Injured patients are at particular risk and mortality increases three fold when they are hypothermic.  Shivering is the most important physiological mechanism to maintain temperature but fails when oxygen is prioritised to maintain vital functions. The absence of shivering and change in conscious level are simple clinical tools that can be used in the field to make treatment decisions (Swiss Classification). In addition to the insulation the importance of providing a vapour barrier (1,2) to minimise heat loss through continued evaporation is critical in the wet British climate. Without this layer heat loss continues and many insulation layers become ineffective. The “triple wrap” of a weather-proof layer, insulation and a vapour barrier, is a good way to remember what is needed on the hill. Once shivering has stopped adding heat to the package to prevent a further fall in temperature can be seen as “active insulation” and may minimise cardiac instability. All patients need protection from the elements.  This is an essential part of First Aid and Medical Care in the mountains and can save lives." 

1 Henriksson et al. Wilderness & Environmental Medicine, (2015) 26, 11–20.

2 Thomassen et al. Scandinavian Journal of Trauma, Resuscitation and Emergency Medicine, (2011), 19:41

Thanks to Arav and Mike for contributing to the blog!

2 thoughts on “Keeping The Casualty Warm...

Alun Thomas commented 1 year, 10 months ago
Accepting that the aim is to reduce the rate of inevitable heat loss in an immobile casualty,are there any similar studies which gather the evidence for heat packs (armpits and crotch) to supplement vapour wrapping? The combination of major trauma, coagulopathy and hypothermia is now well recognised as increasing morbidity, and there are recommendations for heat packs, but what about hypothermia alone? They don't to get a mention on LR or MR trg sessions from my experience.
Dave Gregory commented 2 years ago
I find it quite a common thing that people Neill give a patient a nice big jacket that has been in there rucksack, great! However this is generally cold, pulling heat away from the patient. Better idea is to give them your nice warm jacket and you, the warm uninjured person put on the cold one... From a chilly tent on hillside above Langdale 06:30.....

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