Prehospital amputations are performed rarely; usually, enough tools / hands can be assembled to lift whatever obsturction is pinning the extremity and free the victim. That having been said, I recall reading about some prehospital amputations being lifesaving (I cannot find any links).
In some cases people have done it themselves to save their own lives (life over limb). According to CNN:
MOAB, Utah (AP) — A Colorado climber amputated his own arm Thursday, five days after becoming pinned by a boulder, and he was hiking to safety when he was spotted by searchers, authorities said.
Aron Ralston, 27, of Aspen, was in serious condition late Thursday at a hospital in Grand Junction, Colorado.
Ralston was climbing Saturday in Blue John Canyon, adjacent to Canyonlands National Park in far southeastern Utah, when a 200-pound boulder fell on him, pinning his right arm, authorities said.
He ran out of water on Tuesday and on Thursday morning, he decided that his survival required drastic action.
Using his pocketknife, he amputated his arm below the elbow and applied a tourniquet and administered first aid.
He then rigged anchors, fixed a rope and rappelled to the canyon floor.
Wow. This fellow is exceptional, and is to be congratulated.
From what I have read, prejhospital amputations aren’t really all that difficult: the hard part is in making the decision, which isn’t taken lightly, but if it’s to be done it should be done in time to save the life of the patient.
Disclaimer: this is not medical advice. Don’t do this. The technique involves cutting through basically two different tissue densities: skin/fascia/muscle/nerve/artery/vein are going to be no match for a good strong pocket knife. The bone is an entirely different matter; the most practical device I’ve seen recommended is a flexible saw (like is used on tree limbs), which they still use in the OR, I hear. If there’s no way to cut through bone, plan to go through a joint. All of this tissue is well enervated (meaning everything hurts), so be prepared. Place a tourniquet prior to starting; when free, move like the wind to help!
In the case of our climber, I have to wonder if he didn’t have bones broken in his forearm, or already had a partial amputation he completed. Time will tell. And he did the right thing: he’s alive to tell the tale.
Update: Of course, I mean innervated, not ennervated.