Monthly Archives: February 2014

Space blankets are worthless

Well, that’s not entirely true. They just aren’t good at being blankets. They fell out of favor quickly in hospital use, but survivalists still advocate for their use in wilderness settings. There’s at least one ultramarathon that makes participants carry one at all times. Why do they do this?

Space blankets came into vogue during the 60s and 70s, as a response to the “space race”. Anything that had to do with interstellar travel was popular, and out of that technology boom came the thin plastic coated with metal on one side.

They work quite well in space, since they’re small, weigh very little, and reflect radiated heat. Well, they work well on equipment, and only for keeping it cool. Heat from the sun is effectively reflected by the blankets. The problem is, humans don’t radiate much. Most heat loss is by convection, and the space blanket does little for this outside of being a wind break.

An even funnier consideration is referenced in the paper as well. The blankets only reflect heat on the size that has been metallized. Since this is usually only one side, and often clear plastic is used, you have a 50/50 shot of putting it on backwards if you’re not careful, and not reflecting any heat back to you. All of the negatives of looking silly without any of the benefits.

Now that the usefulness of the metal has been show to be invalid, let’s talk to the other putative benefits of space blankets. They can be made into shelters, rain catchers, water-repellent devices such as ponchos and boot liners, and all sorts of first aid items, from wraps to slings to wound dressings. Truth be told, a space blanket would probably work in that situation. A trash bag of any decent thickness would work just as well, and cost a whole lot less. You could get them in fancy colors if you wanted to use them as a signal in snow, and they come in multiple sizes.

Sure, the reflective side of the blanket could serve as a signal, but you’ve already got a mirror on you. (You DO have a signal mirror, don’t you?) If you’ve got one in your pack, don’t throw it out just yet though. You could always use it in a pinch, as long as it hasn’t become stuck to itself by prolonged storage. You might want to check before the next hike though.

So if your friend finishes a road race and is worried about getting cool too fast, give them a jacket. And if you’re in an emergency department and the patient is cold, give them a warm blanket.

Hypothermia and the use of space blankets: a literature review.

Preventing paresthesias when hiking

Appalachian trailParesthesthias commonly occur in long distance hiking, such as thru-hiking the Appalachian Trail (seen to the left) or the Pacific Coast Trail. They occur in both upper and lower extremities, and can certainly make hiking less fun. Of course, there can be serious causes to paresthesias, so care needs to be taken to not dismiss cerebrovascular accidents, toxidromes, and complications of diabetes. Once those are ruled out, the paresthesia is likely related to repetitive trauma or compression of nerves.

Shoulder straps from backpacks can cause ulnar paresthesias, and most commonly present as numbness or tingling of the ring and little fingers. Hip straps can cause numbness of the outer thigh, usually called meralgia paresthetica. It is also known as Bernhardt-Roth syndrome. Tarsal tunnel syndrome, or posterior tibial neuralgia, can be caused by footwear that compresses the area behind the medial malleous (known perhaps unsurprisingly as the tarsal tunnel). This usually causes numbness or pain of the sole, but can include the toes. If just the toes themselves are affected, then it is known as digitalgia paresthetica, and is commonly attributed to type of shoe padding.

Most of these are well known to long distance hikers, but they can happen to short distance hikers who are out of shape, as well as military recruits. Once they present, the first suggestion is to alter whatever piece of gear is the offending agent. This can mean adjusting or padding the straps of one’s pack, or changing footwear. This may stop it from getting worse, but may not makes symptoms go away.

The question is, can we prevent this? The neuropathy can last for months and be fairly debilitating. This article wasn’t trying to answer just that question, but was instead trying to determine prevalence and predictors of all injuries and illness in long distance hikers. They did this by anonymously surveying thru-hikers of the PCT and AT near the northern terminus of each trail. The responses were included if they had hiked at least 500mi in the last season, and were older than 18. Of the 143 surveys they received, only 15 were excluded.

Paresthesias were common, with 48% prevalence. The survey did allow for localization, but hikers were like most survey takers, and declined to input free text. Since the surveys did have sections asking about footwear and pack weight, the authors had enough of a sample size to analyze these factors.

Unsurprisingly, pack weight had a statistically significant affect on prevalence of paresthias, with packs between 10-20lbs having a ~30% rate of paresthesias, 21-30lbs at ~50%, and >31lbs having a nearly 70% prevalence. Obviously the take home message is to carry less with you if you want to prevent numbness or tingling. 

What is interesting is footwear. While never reaching significance, there was an obvious trend toward minimalist footwear as well. Hiking boots were worst, with ~70% paresthesias, then it drops sharply for low top hiking boots at ~40%. Running shoes were a little lower, and sandals were at the bottom with <30% prevalence of paresthesias. Maybe those guys with Chacos were doing it right all along.

So is ultralight the way to go? From this study, it seems to be a logical and healthy alternative to what many are doing.

Of note, there was also a 50% rate of wilderness-associated diarrhea, in line with earlier studies. I guess they should have washed their hands more.

The Impact of Footwear and Packweight on Injury and Illness Among Long-Distance Hikers

Ants as sutures?

You’ve probably heard of it, or seen pictures of it on various internet feeds. But how many references have you seen in the medical literature? They’re sparse at best, which is part of the reason I haven’t written about them yet.

Does this mean that their use hasn’t been recognized in the medical literature? Far from it. This paper from 1925 discusses much of the history (to that point) of using ant heads as wound closure devices. What may surprise you is how long it has been in the literature. You may also be surprised that it was written by an ichthyologist, who apparently just found this interesting and decided to publish it in JAMA.

The use of ants as sutures likely dates from prehistoric times. It seems fairly easy to go from “this big ant bit me and it pinched the skin” to “lets use this to close wounds”, but most facts that seem simple after being established generally weren’t. Since we have no evidence of the first use, we have to go to the first recorded use. This falls to the Artharva Veda, circa 1000 BC. However, they weren’t using ants for skin wounds, they were using them to suture intestinal wounds after surgeries. It goes without saying that they probably didn’t start with that, so it had likely been in practice for some time prior.

It is possible, then, that the use of ants in surgery in the Mediterranean was learned from the Indian practices. Arabian medicine had translated the Hindu literature by 600 AD, and many recorded uses into the middle ages were from Arabic physicians. From there it spread into parts of Europe. The use in surgery persisted until the early Renaissance.

What made them stop? This article contends that a few high-ranking surgeons decided against them for a myriad of reasons. Theodoric rejected Arabian medicine, de Chauliac felt that they were rejected by the body, di Vigo felt they were obsolete, Fabricius felt the mandibles relaxed too much after the ants died (and were also hard to source in winter), and Purmann ridiculed them in his books. Most of these manuscripts were published (or republished) around 1500. Gut suture had also become more common by then, and was much easier to obtain.

Their use in skin continued in austere environments. As South America was explored, use of ants by native peoples was noted from the 1800s on. Concurrent use was still occurring in Algeria and noted by the French Foreign Legion. Their use was also described in Greece in 1896, as wounds were still being dressed by barbers according to local customs. That one comes from the Journal of the Linnaean Society of London, so you may have missed it on your feedly.

So why don’t we see articles discussing it now? Because it’s an established fact at this point. You’d be hard pressed to get more than a case report out of using ants as sutures, unless you were going to write a review article. And since much of the literature (including this article) isn’t accessible on pubmed, it becomes a scavenger hunt to get enough sources. The author of the paper had to look at the originals at the New York Academy of Medicine. Many are written in other languages, so you have to trust that the translation is correct (or translate the original yourself) before citing it.

Now, if you want to use ants to close a wound, you’ll want the right kind. Generally you would ask locals what they’ve used in the past, as naming species is unlikely to help you. Driver ants, army ants, and bullet ants are a few of the types that have mandibles big enough to close a decent skin wound.

Eciton burchelli ants

The image to the left shows a bunch of the wrong type of ants, and one that is suitable, even though they’re the same species of army ant. Once you’ve found a suitable ant, pinch the wound closed, and hold the ant by the thorax (using something other than your fingers preferentially). You’ll want to be incredibly careful with the bullet ant, as it has the most painful sting of any hymenoptera, hence the name. The mandibles will usually be open in a defensive position if you’re holding it. Once the mandibles are near the skin, the mandibles will clamp shut, holding the wound closed. Then lift up the thorax and pinch off the body, leaving just the head and mandibles. Repeat as needed to close the wound, and there you have it. 

You’ll of course want to irrigate the wound with water clean enough to drink prior to closure, as has been discussed before here. Also, don’t try to suture intestines with ants. That is well beyond what I would recommend in the wild.

Stitching Wounds with the Mandibles of Ants and Beetles

Wilderness wound pitfalls

Wounds happen out there. Even with maximum preventive measures, they’re inevitable, so we should definitely know how to manage them appropriately.

This handy little report talks about a Grand Canyon boatman who injured himself at the beginning of a trip down the Colorado. It goes downhill from there, but it is a useful case to point out the things they didn’t do right, and did do wrong. The narrative is also mostly written by the river guide himself, and the style is quite humorous.

Serendipitously, or so he thought, there were two doctors on the trip, one of which whipped out his suture kit and fixed the rather large bleeding wound on his shin. I don’t have a problem with closing the wound, as it was large and likely to cause problems if left open. 

What did they do wrong? First, they didn’t irrigate the wound. It goes without saying that the raft, the pack, and the Colorado River were not sterile, and thus the wound wasn’t clean either. They also shaved his leg with a razor, because apparently JCAHO was going to make a trip to the park that day. Must have left the batteries out of the electric clippers. 

They correctly covered the wound with Tegaderm and Coban for protection on the first day, with subsequent dressing changes. 4 days later, the wound developed cellulitis, so he was started on Bactrim (TMP/SMX). It wouldn’t be my first choice for cellulitis, but it isn’t the worst drug to use as it covers Aeromonas. Levaquin (levofloxacin) would be great, or just adding Keflex (cephalexin) to the bactrim for better gram positive coverage coverage.

Two days later the cellulitis is progressing even with antibiotics, and now there is a pitting edema below the wound. Too late to evacuate that day, they elect to open the wound that evening. Anesthesia provided by gin and tonic. They irrigate using Betadine  and pack it with Betadine-soaked gauze. The tissue-toxic solution could certainly reduce wound healing, and I can’t recommend using it.  Using a squirt gun for higher pressure irrigation is a neat trick though. 

Azithromycin is added to the antibiotic regimen, likely because it’s all they had. The next morning he is flown out. The good news is that after a washout in the OR and two days of wound vac therapy, they get the skin closed and it heals nicely.

Recap of important points for austere wound therapy

  • Irrigate with clean water, but nothing toxic. You want to clean and promote healing, not kill tissue.
  • Consider prophylactic antibiotics for dirty wounds that can’t be cleaned, especially penetrating injuries in water.
  • Use occlusive dressings. They promote healing and decrease infection rates.
  • Wounds less than 1 inch do not need closure, as cosmesis and infection rates are similar open or closed. Close if in an area prone to reopening certainly. Sutures, adhesive strips, and skin glue are all similar in efficacy if used appropriately.

They Had Me in Stitches: A Grand Canyon River Guide’s Case Report and a Review of Wilderness Wound Management Literature.