While Googling a first aid question I had, I ran across the UK Maritime and Coastguard Agency website. In case anyone is interested, there's an online version of The Ship Captain's Medical Guide. There are links to PDF chapters in this guide. I only skimmed chapter 1, which covers your traditional first aid, but there are also chapters on general nursing, communicable diseases, and other topics that may be of interest to people.

In some ways, being stuck far out at sea with a medical situation sounds like it could be similar to what some people may face when cut-off from medical services for some time after a major earthquake, hurricane, or that next pandemic.