Searched: "non-surgeon" emergency amputation, field surgery shoulder amputation, traumatic shoulder amputations, "how to" shoulder amputation (etc). I found a lot of results from field manuals for army surgeons, and some results for people on what to do if someone has a limb torn off and you need to stabilize them while waiting for help (which is helpful), and some results on doctors who aren't surgeons performing amputations with help via text message from surgeons, lol. But nothing on performing an amputation itself, for someone without medical training. Which I can understand.
Also read the Wikipedia article on "amputation" and some related articles.
Here's the background.
The island has been at war for a about a year, and an invasion was just successfully repelled in a bloody battle over the past couple of days. James, one of the foremost wizards specializing in warfare on the island, is reeling because his wife, a non-combatant, was killed, and he's now solely responsible for their young daughter (and since James only agreed to have a kid because his wife wanted one, this is messing with his head). He goes to a quiet, unpopulated part of the island to sort out his thoughts.
Sadly for James, there's someone lurking in this quiet unpopulated part of the island. It would take too long to explain what the actual disease is in story, but let's call what he has lycanthropy for ease of understanding. Not!Werewolf is badly injured and will probably die. He recognizes James, and knows he doesn't have any chance of killing him in his injured state. He attacks, but with one goal in mind--to bite him. Which he does, on James's hand. James had been attempting to capture him alive; after being bitten, he kills him.
James is in a bad fix. This infection, once spread throughout the body, is incurable, and like lycanthropy, has certain very undesirable social drawbacks. James would rather be dead. The only way to stop the infection from spreading is amputation (and it doesn't work all the time). The farther from the heart the bite was, and the sooner the amputation is performed, the better the chance that the infection did not spread.
However, he got to where he is by walking, and he knows it's a more than two hour walk to the nearest healer. Fortunately, the place where he is walking happens to be near the summer home and workshop of Rabbit. You could call Rabbit that world's equivalent of an engineer (in-world she's called a mechanic). When their country is not at war and school is in session, she teaches 16 to 18-year-olds something akin to shop class, so she both regularly trains in first aid and has occasions to use it (mostly on things like minor cuts), but she has no surgical training at all. Rabbit does a lot of experimenting, and her workshop has lots of tools, tables, and machines. It's attached to her bungalow, which is basically a little kitchen, bathroom, and place to sleep.
Rabbit at first wants to take her broom and go get a healer, but even that is going to take 40 minutes to go, gather help, and come back. James doesn't want to wait--remember, he'd rather die in an unsuccessful surgery then live in one that doesn't keep him from being infected. He also insists on doing it at the shoulder (rather than at the elbow) because it took him ten minutes to think of what to do and walk to her place. Reluctantly she agrees.
So, now we come to the problems. I understand that this will be very, very risky, and I want it to be so. If there's only a 5% chance for James to survive, that's fine. I just don't want to write it in a way that there would be zero chance for him to survive.
1. Biggest one, of course, is that neither Rabbit nor James are surgeons, and they can't be coached through it by one either. (I'm comfortable with them both having knowledge of anatomy, though, especially James.) They are approaching this with the attitude of "No other option, so do the best we can, and if he dies, well, we knew that was the overwhelming probability." But I need James to live.
2. I assume that they would do what I (a non-doctor like them) would think would be the easiest way to amputate at the shoulder, namely, put James on a table, dislocate the shoulder (James would know how to do this--would Rabbit do it with or without a tool? she's a pretty strong woman), cut the arm off as quickly as possible (she has power tools that can do this), and then staunch the bleeding as well as one can, turning James onto his side to raise the wound above his heart. Would this, in and of itself, totally kill him? Would a table saw-like device have any drawbacks that I wouldn't be aware of?
3. Infection (the germ kind). Magic can boil water instantly, and the tiny kitchen has running water. Would this be sufficient to clean and sterilize tools that she's been using to cut metal, wood, etc? Assume that Rabbit is keeping her tools in good condition.
4. Wound-staunching materials. This is basically a large workshop with tiny one-person bungalow attached. I imagine she has a first aid kit, but will that include enough materials for such a major wound as losing an arm at the shoulder? Rabbit is willing to sacrifice her sheets, towels, etc, but she only has an amount that would be reasonable for a tiny summer bungalow with one person in it. How much cloth is needed for a wound like that? Would she want to put medicine onto the wound or not?
5. Cauterization. She's got metal and the ability to heat it. Would this be a better idea than just bandaging it?
6. After she performs the amputation and does what she can to stop the bleeding (bandage or cauterize and bandage), she leaves, gets on her broom, and goes as fast as she can to the nearest healer (about 20 minutes), tells them the situation, they get their stuff together, and get on a faster mode of transportation and come back (probably another 20 minutes). Can James survive that 40 minutes without dying from exsanguination? How about shock?
For character development purposes I would rather have the situation go as described (Rabbit performing surgery by herself and leaving James alone while she gets help afterwards). But if that is untenable, would having another person there to go get the healer while Rabbit performed the amputation and stayed with James make the situation possible?
Again, I don't mind his survival being unlikely, I just don't want it to be impossible.
I know there have been cases where people with arms trapped under boulders while mountain climbing have amputated their own limbs and then made it to safety by themselves, so I assume that there has to be a way to do this...
Edit: To clarify: not a Harry Potter fanfic. Original work.