How long should you wait to cut off a trapped limb?

Answers to your questions about the news.
Sept. 1 2011 6:19 PM

A Timetable for Disarmament

If your limb gets trapped, how long should you wait before cutting it off?

James Franco in 127 Hours. Click image to expand.
James Franco in 127 Hours, about a man who cut off his arm to survive a hiking accident

A Colorado man got stuck under a six-ton trailer on Aug. 19 and decided to cut off his toes to free himself after just 30 minutes of squirming and shouting for help. The man played by James Franco in the film 127 Hours waited more than 250 times as long to cut off his arm. If one of your limbs is pinned down by a boulder or truck, how long should you wait before hacking it off?

A day, at least. Longer, if you can stand it. Having a limb trapped under a weight isn't immediately life threatening, but cutting it off can be. There are two arteries in your foot. If you sever one of them and are unable to stanch the flow of blood, you could die within 30 minutes. So don't even consider cutting anything off until you're convinced that no one is going to find you, and death is imminent. Fortunately, most people lost in the American wilderness are found within 24 hours, and the main threats to survival move more slowly than that. Hypothermia rarely kills in less than a day, unless you're soaking wet. If it's warm outside, dehydration will be the most immediate danger, and it usually takes three days to kill.

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You may not want to wait until you're at the verge of death, however. Signs of an imminent demise include lethargy and a loss of coordination, both of which could make self-amputation and the slow hike to safety more difficult. When you decide that you can't hold out any longer, cut only as much as is necessary to get free of the weight, and let the surgeon worry about the damaged tissue around the point of compression.

As any third-year medical student can tell you, slicing through skin, muscle, and ligaments takes more force than you'd expect. Even with a sharp knife, you'll have to press hard. (You might pass out from the pain, but you'll come to fairly quickly.) It's nearly impossible to cut through the bone itself with a pocket knife, so you might have to find a way to break it. Aron Ralston, the real-life mountain climber portrayed in 127 Hours, used the weight that pinned him down as a fulcrum and relied on leverage to snap his arm.

Once the cut is made, bleeding is your biggest concern. First, cover the stump with a cloth and apply direct pressure. If that doesn't work—and it probably won't—fashion a tourniquet out of whatever is available and hope that does the trick.

If you hold off on amputation and are eventually rescued, your trapped limb still might not make it. Without blood supply, your limbs and extremities become unsalvageable after six to eight hours. In some cases, however, enough blood can flow around the obstruction to extend that deadline.

Your best chance of keeping all of your limbs intact, in any case, is to always tell someone where you're going to be and when you'll return.

Got a question about today's news? Ask the Explainer.

Explainer thanks Loren Greenway of the Wilderness Medical Society, Thomas Kirsch of the American College of Emergency Physicians and the Johns Hopkins University School of Medicine, Eric Lavonas of the American College of Emergency Physicians and Denver Health Medical Center, and Grant Lipman and Eric Weiss of the Wilderness Medicine Fellowship at the Stanford School of Medicine.

Brian Palmer writes about science, medicine, and the environment for Slate and the Natural Resources Defense Council. Email him at explainerbrian@gmail.com. Follow him on Twitter.

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