time is the enemy: ischemia and infarction

In many wilderness medicine curriculums a core area of focus is distal CSM. Distal being “away” (in this context from the heart) and CSM being circulation, sensation, and movement. Blood and nerves tend to be wires hanging out in the same conduit throughout your body, collectively known as neurovascular bundles. Slice one and the results are clear: blood pours out and everything south of the severed nerves now has no feeling and muscles don’t work. Pretty terrible. Definitely something to avoid.

nvb
The yellow and red stuff makes it so you get blood, can move muscles, and feel things. You generally don’t want to have that get trashed.

In wilderness medicine you additionally have to deal with those neurovascular bundles getting pinched or squeezed. Even something as common as a dislocation, definitely something with lots of trauma (like a fall) that jammed a bone into some weird position, can now be putting sufficient force on blood and nerves that it went from a nuisance problem potentially life threatening.

In search and rescue, time is always against you. Consider a typical situation:

  1. Someone slips on a rock when backpacking and plants their next foot into a hole, bending their ankle in a way that baby jesus never intended it to move. It’s now 0800 just after breakfast.
  2. The patient tries to move around a bit and see how bad it is. Yep, it hurts like hell. They confer with their friends and decide there’s no way they can walk out. They need help. It’s now 0815.
  3. The friends get to a mountaintop where they can get a cell signal out and call 911, explaining the situation. It’s now 1130.
  4. Search and rescue gets mobilized and a helicopter is put on alert status. 1140.
  5. SAR is staging at the trailhead a few miles from the patient, packing the right gear. The helicopter has been re-assigned to a case of massive head trauma. No chopper today. 1200.

I’ll stop there as even before the first boot step moves in the patient’s direction four hours has already elapsed. You can chop that time down by having a $250 satellite communicator (and $15/month service plan), but it’s still going to take a while for folks to get to that patient and really this article is written towards the folks providing that medical care.

DelormeInReach
My preferred satellite communication device these days. GPS, bad-but-useable text messaging, tracking with a map folks at home can see, an SOS feature, and a good amount of battery life.

My training has taught me that infarction (tissue death) happens within about two hours. It’s not the same for all tissues, but for the arms/legs/hands/feet I go with 120 minutes. Pinch that blood supply off for that length of time and the tissue distal from it is deader than Firefly.

Fortunately ischemia (restriction of blood flow) is typically not an all-or-nothing thing. A bone jammed up against a tube of moving blood might block it a little, a bit, a bunch, or entirely. Think of having a plastic bag over your head versus one with a small hole in it. With the sealed plastic bag, you’re pretty dead pretty fast. With the small hole in, you can eek out a few more moments of life. The more restriction, the bigger the problem. So maybe you’ve got more than two hours since the ischemia might not be so complete. That’s hardly wonderful news since rescue response times can be all over the map with “a few hours” being optimal if the patient’s position is known, authorities were alerted immediately, and the terrain is not too difficult. If a patient’s location is unknown, response times to the tune of days is not uncommon.

And then you have transport time, which of course is wildly dependent upon terrain, the patient’s injuries, available air assets, and the size and ability of the ground crew.

Time is the enemy in other ways as well. Hypothermia in some climates, hyperthermia in others. Increasing intracranial pressure, HAPE, HACE, and a host of other problems get worse the longer they are left untreated. And generally by the nature of the operation you can assume they already have gone untreated for a prolonged period of time. With some exceptions, a properly trained wilderness medical provider can slow or even reverse many of these life threatening conditions.

litterlower
There’s nothing easy about transport.

By constantly remembering the impact of time on our patients, both before we got there and after they are in our care, we can do several things:

  • Shorten the list of serious problems that higher levels of medical care need to focus on. Instead of clinical moderate hypothermia, a patient now might simply want a second blanket on arrival to the hospital due to your interventions.
  • Save a limb. The next time you hug a loved one or stand on two feet, imagine not being able to do that quite so easily. By ensuring proper perfusion our patients can fully live out their lives.
  • Provide more insight to higher levels of care. If our attempts at providing perfusion are inadequate (perhaps through manual alignment in accordance with your training and agency protocols), it’s a clear signal that other issues such as acute compartment syndrome might be at play.
  • Slice and dice between the the original chief complaint (an unstable and painful ankle) and new issues such as dehydration and heat illness from laying in an unshaded spot because of the ankle.

One way that time can be somewhat of your accomplice if not outright friendly:  keep track of things you may want to do during transport and execute them when appropriate. If a belay needs to be rigged, take some vitals. If the litter team is scouting a route, toss in some more heat packs.

And although an entirely separate conversation, haste can also be your enemy. Rigging a belay takes time, but is obviously better for the patient than chucking him or her down a cliff. We want to move fast, but only as fast as safety and the patient’s interests will allow.

Going back to the example of the injured ankle, if the ground team gets there at nightfall and a storm sets in, if perfusion isn’t an issue and there’s no immediate need of extraction would be it safer to set up camp for the night, wait out the weather, and then proceed with daylight and dry footing 12 hours later when potentially more rescuers are available as well? That’s a very big question and can’t be answered in a hypothetical: much more information is needed that only a real scenario would be able to address. I only bring it up to to balance against rapid transport as a rule, rather than a probable option.

My writing is commentary on my training and personal experience. I try as often as I can to discuss patient care with medical teams I interact with in order to learn where I can improve and provide better outcomes. Please don’t substitute my writing for comprehensive and recognized medical training.

 

 

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