Category Archives: cold

Maybe clothing technology really hasn’t gotten better

Early in the 20th century, explorers were busy trying to reach the poles and climbing mountains, simply because they were there. The casual observer from modern times must wonder how they were able to tolerate such cold temperatures without the high-tech fabrics available today. The mental images of Amundsen, Scott, Peary, and other cold weather explorers are often viewed as men laden with incredibly bulky furs and wool garments. How on earth could they achieve anything wearing that kind of clothing?

Credit: National Geographic/The Wildest DreamThat question has particular merit when considering the legacy of George Mallory and Andrew Irvine. They died in 1924 while attempting to summit Mt. Everest, almost 3 decades before Hillary and Norgay were able to do it successfully. Mallory’s remains were found in 1999 at 8157m, and his clothing was removed for testing before he was buried. After 3 years of intense study using multiple methods, they were finally able to definitively say what he was wearing.

But that only answers part of the question. Now that we know what he was wearing, was it enough to keep him warm but still allow freedom of movement needed to climb mountains? To test this, they simply replicated the fabrics, which were layers of silk, cotton, and wool. This was then covered with an outer layer of gabardine, faithful to the original made by Burberry.

(As an aside, many readers may not be aware of Burberry’s prowess in making clothing for polar expeditions. Like Abercrombie and Fitch, the clothing you can buy today is nothing in comparison to the rugged outdoor items one used to be able to purchase.)

So with that part answered, all that was left was for someone to climb Everest wearing the replica clothing. And Graham Hoyland did just that in 2006. He didn’t summit, but he did learn that the fabrics were light, comfortable, and more importantly, warm enough to use during the day. They were not, however, thick enough to survive a bivouac on the mountain in his opinion.

The part that made the outfit ingenious was the different fabrics of the alternating layers. This allowed decreased the friction between the layers, allowing movement with much less energy expenditure. This was demonstrated when tests comparing Scott’s to Amundsen’s layered garments showed a 20% decrease in said energy doing the same activity when more “slippery” fabrics were used (silk and furs versus wools). The same scientist also showed that Mallory’s fabrics would have been able to protect all the way down to -30C in calm weather.

Sadly, calm weather they did not have. A blizzard came upon them as they approached the summit, and they were last seen on one of the Three Steps. Whether this storm made them turn back or not, it certainly would have predisposed them to hypothermia. As to whether Mallory and Irvine actually summitted? We may never know, unless someone finds Howard Somervell’s camera with proof.

While these findings have done away with the myth that Mallory’s expedition was ill-prepared (based on photos from base camp), what they really show is that modern synthetic fabrics have only incrementally made gains in thermal protection, weight, and function. The argument can be made that tailoring them to fit properly is as important as the material itself.

I wouldn’t try to climb Everest in any modern garment made by Abercrombie or Burberry though.

Mountain Clothing and Thermoregulation: A Look Back
http://www.ncbi.nlm.nih.gov/pubmed/22441098

Additional Readings
http://www.alpinejournal.org.uk/Contents/Contents_2007_files/AJ%202007%20243-246%20Hoyland%20Clothing.pdf
http://www.independent.co.uk/news/world/asia/mystery-at-the-top-of-the-world-did-george-mallory-make-it-to-the-summit-of-everest-before-he-died-2063196.html
http://news.bbc.co.uk/2/hi/science/nature/5076634.stm
https://dspace.lboro.ac.uk/dspace-jspui/handle/2134/9716
http://thewildestdream.com/

Wear the helmet anyway

CC-BY-2.0 Søren HovenHelmets continue to be recommended or required by multiple ski resorts worldwide. The main thinking is that prevention of traumatic causes of death will directly reduce mortality from avalanches and other alpine trauma. That being said, the authors of this study wanted to see if perhaps wearing a helmet also slowed progression of hypothermia by nature of insulating the head.

It makes sense. We are taught starting in grade school that most heat is lost from the head. Since we now know this statement by itself isn’t true, you move on to the real meaning of the statement, which is: you lose most of your heat through any part of the body that is uncovered. Thus, if you wore a hat but no pants, you would lose most of your heat through your legs. See how fun this is?

So the theory behind covering the only part of your body left uncovered while skiing isn’t too far out there. But does it slow cooling of simulated avalanche victims or not? Of note, their secondary hypothesis was how closely the temperatures between 3 different probes (esophageal, capsule, and rectal) would correlate.

Unfortunately, this study can’t tell us the answer to the first question. Their power calculation required 11, they only got 9 participants, and only used data from 7. 1 declined to be buried a second time for the control, and another had a poorly functioning temperature probe, and apparently could not swallow the esophageal probe, limiting data collection.

While their data does not show a significant difference in temperature between insulated participants and those without, there are possible confounding variables. Most people who aren’t sedated will hold their head off the snow, creating an air pocket of insulation. This is likely the reason for the difference between this study and an earlier one using water, as you can’t keep a submerged head out of contact with water. Also, they still had a Gore-Tex hood protecting their head from snowmelt, likely also reducing heat loss. The participants without helmets subjectively rated their experience as “colder”, for what it’s worth. Let’s not kid ourselves though. Nobody advocates using helmets solely for thermal insulation.

The good news is that the three different probes did correlate in temperature as far as rate of change. The absolute values of temperature were different enough that there still needs to be further work towards finding the ideal method of measuring temperature. But since we aren’t using the gold standard of pulmonary artery temperatures, we might as well stop (or significantly reduce) doing rectal and esophageal probes, as the discomfort of these likely reduces study participants. As capsules become more reliable, expect them to become the overwhelming favorite for future temperature studies.

Effect of Head and Face Insulation on Cooling Rate During Snow Burial
http://www.ncbi.nlm.nih.gov/pubmed/25281588

Do they really have to be “warm and dead”?

The classic teaching is that nobody is dead until they are warm and dead. But as discussed last week, knowing which patients are likely to survive (and thus warrant lifesaving efforts) is difficult to ascertain. Unlike the avalanche patient who is hypothermic, the non-trauma accidental hypothermia patient typically has better outcomes as well. It’s especially hard to stop (or not start) when you consider that the authors of this study had previously reported successful ROSC in a patient who had a core temp of 13.7◦C after 6 hours and 52 minutes of resuscitation.

The study was done in northern Norway, where data collection is easier for a hypothermia study. They had 28 years of data that they broke down into 3 “eras”; the early years, after moving to the new hospital, and post ECLS. Unfortunately, they only included 34 patients in their analysis, 9 of which survived. The authors did not find statistically significant difference in survival based on mechanism of cooling, season, initial ECG-rhythm, transport time, or distance from the medical center.

Similar to the French study, the potassium level was significantly different between survivors and non-survivors. Specifically, the highest level for survivors was 5.9 mmol/L, but a normal K did not predict survival. Survivors and non-survivors also differed in length of stay, as would be expected. However, the longest stay for a non-survivor was 218 days! This was twice the length of the longest survivor at 106 days, and calls into question their statement that non-survivors consumed only modest resources, even though median length of stay for non-survivors was 0.35 days. They also did not have any survivors until the last time period, after ECLS was incorporated into their treatment.

The authors do state that their study supports the use of K>12 mmol/L as a decision to stop resuscitation. While I don’t disagree, I would argue that it supports the use of a lower level, perhaps 10 or even 7 mmol/L. However, barring external trauma incompatible with life, packed snow in the airway, or physically being frozen, if they have a K lower than whatever cutoff you choose to use, you have to resuscitate them until they reach 34◦C. It is a retrospective study, and low patient numbers limit application of their data, but it’s unlikely that anyone can do a prospective trial on such a topic.

“Nobody is dead until warm and dead”: Prolonged resuscitation is warranted in arrested hypothermic victims also in remote areas – A retrospective study from northern Norway
http://www.ncbi.nlm.nih.gov/pubmed/24882104

Of note, volume 85 of the journal Resuscitation had quite a few articles about wilderness topics. This is the second one in two weeks, but people interested should look into the other articles.

Predicting survival after avalanches

More than 150 people die each year after being buried in an avalanche, and mortality is greater than 50% for this condition. Unfortunately, a large amount of resources are used on patients who ultimately expire, so determining which ones are likely to survive can safe costs and allow better utilization of resources such as extracorporeal life support (ECLS) warming and air evacuation.

Of the 3 common causes of cardiac arrest after avalanche, only hypothermia is likely to have good outcomes. Trauma and hypoxia have poor outcomes. Most algorithms have providers stop resuscitation for severe trauma, and airways packed with snow. However, ascertaining hypoxia vs hypothermia is less obvious. Prior attempts used potassium >10 mmol/L or >12 as a surrogate marker for cellular death from hypoxia, but no other markers are used.

So these authors took 20 years of data from the North French Alps, which ended up being only 48 patients with cardiac arrest.  18 of them had ROSC pre-hospital, and only of those 2 were eligible for ECLS. 19 of the 30 without ROSC were also eligible for ECLS. In total, only 8 survived, 5 from the pre-hospital ROSC group, and 3 from the non-ROSC. Of the 8 survivors, only 3 had favorable neurologic outcomes.

All of these were patients with rescue collapse, that is loss of vital signs after extrication or transfer. 3 other patients with rescue collapse died however. Other indicators for survival in their analysis are the presence of a rescue pocket, K <4.3 (nobody survived above 4.2, but some nonsurvivors had levels below this), and coagulation disturbances. Interestingly, their data showed no overlap of prothrombin time between survivors and non-survivors, but they sadly did not give the values, only as ratios. Other values such as PaO2, PaCO2, lactate, and bicarb are not predictive.

Unfortunately, for such a long time period of collections, there were very few survivors. The retrospective nature also limits analysis. It does look like we need to reduce the cutoff for resuscitation from values of K from 10-12 mmol/L to a lower number (7?). Also, identification of coagulation abnormalities may help. Perhaps POC thromboelastograms may be a way to identify those that do not merit resuscitation.

Survival after avalanche-induced cardiac arrest
http://www.ncbi.nlm.nih.gov/pubmed/24971508