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Feeling the heat of the summer? Is the resolution of the pandemic moving at a glacial pace? How about the recent heat of politics in an election year- Ready to chill out? In this episode of the WMS Technology column, we are going to explore some old and new technology in backcountry temperature management. Often, in the midst of the summer heat, our patients are finding themselves in a predicament of too much heat or strangely in some cases, not enough…. The daytime temperatures of the Pacific Northwest Cascade volcanoes (ie, Mt. Hood, Mt. Saint Helens, Mt. Adams) can often reach 80 degrees F only to plummet to freezing temperatures in the evening. As we move through the dog days of summer into the shoulder season, those temperature variances can be an increasing threat for the ill-prepared recreationalist.

 Many of you may recall lectures from your AWLS course or the curriculum of a DiMM program discussing the mechanisms of heat loss. To briefly review, physiological heat loss occurs by four mechanisms: conduction, convection, evaporation, and radiation. Hyperthermia or hypothermia may occur when environmental influences exceed the physiological capabilities of the individual to self- regulate temperature. In caring for patients in the backcountry, mitigation and treatment strategies have capitalized on these four mechanisms of heat loss to help restore a patient to homeostatic temperature. In many cases, this presents a challenge in a resource depleted austere environment. The ability to accurately assess temperature in the backcountry is also frequently a technical challenge and heavily relies on clinical findings from the patient care provider. Forthcoming in our discussion of this topic are some various technologies to help facilitate both the diagnosis and care of patients with altered temperature regulation. As in all of our reviews, an effort to discuss the strengths and weakness of these technologies will also be considered.


In recent trends, diagnosis of hypothermia and hyperthermia have relied on clinical findings vs. actual temperatures as the ability to assess backcountry core temperatures has proven logistically challenging or clinically unreliable. In regard to hypothermia, the International Commission for Alpine Rescue (ICAR) cited “Swiss Staging System” has capitalized on the presence or absence of shivering in conjunction with level of consciousness. Hyperthermia, similarly, relies heavily on clinical findings such as presence or absence of diaphoresis and level of consciousness. Both entities have various spectrums of temperature citing clinical correlation. Until now, temperature diagnostics included oral, esophageal, temporal, skin, rectal, pulmonary artery (PA) catheter each including a host of accuracy or logistical difficulty for backcountry temperature assessment.

Entering the scene is the 3M Bair Hugger Temperature Monitoring System (formerly 3M SpotOn System) which utilizes “zero-heat flux thermometry” to accurately measure core temperature via their proprietary 4.5 ounce control unit monitor:

Source: 3M

In essence, the system has an adhesive backed sensor which incorporates their flex circuit and thermistor along with insulation allowing temperature assessment that rivals the accuracy of the PA catheter. The company’s two studies highlighting the device’s precision are quite compelling:


Source: multimedia.3m.com/mws/media/878163O/spoton-system-brochure.pdf

Looking for wilderness clinical applications and proof of concept, I turned to my colleagues at the University of New Mexico (UNM) Diploma in Mountain Medicine (DiMM) program and their hypothermia lab. Buried in tubs of ice, their highly motivated DiMM students orchestrated a lightweight power source (USB Battery Pack) that provided the monitor with hours of core temperature assessment. 

This implementation was hardly a “MacGyver” move as USB power packs are readily available through retailers like Amazon and are frequently deployed to the wilderness environment.

While the 3M BearHugger Temperature Monitoring System is certainly lightweight and has been shown to withstand the basic rigors of testing by the UNM team, further anticipated limitations, yet to be determined, are present in the viability of an LCD display and portable battery in austere conditions.

While making the diagnosis is an important priority, the WMS clinical practice guidelines on the Out-of-Hospital Evaluation and Treatment of Accidental Hypothermia wisely quote the proverb that “an ounce of prevention is worth a pound of cure.” Again, looking to the four mechanisms of heat loss, the literature suggests a role for both treatment and prevention when addressing temperature management strategies.


One strategy for temperature preservation is already being utilized for its primary purpose by rescue teams across the country and abroad. Ever since the trend away from cervical collars and rigid backboards has been perpetuated widely in the wilderness medicine literature, a growing use of vacuum mattress splints has become more common place. Effectively providing spinal cord protection as well as splinting of various fractures in the extremities, the use of vacuum mattresses provides an excellent solution to heat loss through the “conduction” mechanism. Its implementation also partially executes coverage (posterior) of the convection, radiation, and evaporation mechanisms of heat loss. These “mattresses” provide stability to fractures by wrapping the extremity, pelvis, neck, etc. in a vinyl wrap filled with polyethylene or polystyrene “beads.” When the mattress is deflated via portable hand pump, semi-rigid stability of extremity fractures and protection of the cervical spine is achieved. Multiple companies, such as Hartwell Medical and Conterra, have similar product designs that incorporate carrying handles and carrying cases, but they also suffer the inevitable inconveniences that come from a relatively lightweight but inherently large device. The size alone is prohibitive for small groups but, nevertheless, the device is certainly a game changer for backcountry SAR teams seeking to stabilize a patient.

Once a patient has been reached, a diagnosis has been established, and mitigation strategies have been put into place, further treatment of hyperthermia and hypothermia are warranted. Two devices have caught our attention for their exemplary ability to treat hyperthermia and hypothermia, their relative portability, and their field proven reliability.


In the case of hyperthermia, such as seen in endurance racers or soldiers on the battlefield, field treatment strategies have often included placing the patient in the cool shade, applying cold water immersion, and even using cooled IV fluids. In many cases, these resources are unavailable or would be impractical for application and yet the severity of disease can have profound impact on morbidity/ mortality. When logistical limitations of the environment are coupled with a patient whose metabolic heat production is outpacing heat loss (transfer/ exchange), a timely response is warranted.

CoolVest, a product out of Australia, treats heatstroke immediately with no power or refrigeration required.


After application of the “vest” to a hyperthermic patient, the patient care provider introduces an eco-friendly chemical solution into the baffles of the vest which thereafter provides one hour of cooling and reduction of ambient temperature by 25 degrees Celsius. The vest is compatible with automatic CPR devices, defibrillation, and has not been shown to cause cold induced tissue injury. Proof of concept demonstrations and clinical trials have shown the device effective both for heat exhaustion and heat stroke patients as well as an adjunct therapy for out -of-hospital cardiac arrest in military, SAR, and race/event settings.

The device has a rather large price tag for one-time use and is about 15 lbs, so while it doesn’t seem to fit the bill for small party first aid kits, they obviously have a place for military, fire, and event planning where susceptibility to hyperthermic injury is more likely.

On the opposite end of the temperature spectrum and approaching a cost/ weight advantage to consider deployment with virtually any assigned wilderness medical provider is our final device review in hyper/hypothermia diagnosis and management. Earlier, our discussion highlighted the mitigation of heat loss by the vacuum mattress. The vacuum mattress is, indeed, very effective and can also work in conjunction with rescue litters and hypothermia .“burrito wraps” Hypothermia is one component of the nebulous “trauma triad” (the other two being coagulopathy and metabolic acidosis) with associated increases in mortality. When mitigation strategies and passive rewarming techniques for heat loss are insufficient, a more active field rewarming approach is required. In this situation, the wilderness medical provider should give strong consideration to the application of the “ready-heat” blanket, by Tech Trade, LLC. This blanket is one of my personal favorite adjuncts to my first aid kit when deploying with Portland Mountain Rescue.



Weighing in at 1.25 lbs and vacuum sealed in a nearly flat plastic wrap, the blanket package easily slips in the back of rescue pack. Upon opening, the chemical heat blanket is activated by air and provides 8 hours of heat at 100 degrees. Despite its dependence on air for chemical activation, it functions well in high altitude and low oxygen alpine environments. The blanket has a 5-year shelf life and costs only $12/ unit making it easy to understand why it has become a staple ingredient in military medical protocols since 2006.

In the difficult times of this pandemic and election, figuratively, we may see things “heating up” or needing to “chill out” but it is important for us to also consider the ongoing needs or our wilderness medicine patients. We are in the final days of the summer heat and quickly entering the shoulder season where future patients let their guard down in preparedness and estimation of risk. Being able to respond with some helpful tools in the toolbox to treat hyperthermia and hypothermia is paramount.

What are your favorite backcountry resources on this topic? Feel free to send an email to [email protected] or post in the comments on social media.

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