To be perfectly honest, if you are single handed, and 1,500 miles offshore, it doesn't make a damned bit of difference - THERE'S NOTHING YOU CAN DO OTHER THAN HOPE FOR THE BEST!
Now, if you have a medical background, which I do, there are steps you can take to possibly make it to the nearest port and possibly obtain emergency medical help. Without that background, at best, it's a WAG (Wild Assed Guess) when it comes to the diagnosis. Sure, there are a few books for sailors to make an educated guess at what may or may not be going on, but by and large, it's a crap shoot and the odds are stacked against you making a proper diagnosis without having the tools onboard to do so. I carry a number of medications with me, including anticoagulants, beta blockers, alpha blockers, and good old Bayer Aspirin, which has saved more lives than anyone can imagine. I also carry a blood pressure cuff and a pulse oximeter. I also have a complete first aid kit, old military style, with needles and sutures, a wide variety of bandages, compression bandages, chemical cold packs, antibiotics, pain killers, etc... All that stuff should be on any boat traveling offshore.
Now, I can stitch up most wounds, even bad ones and get good results. I have the background and knowledge to diagnose most medical problems, but definitely, not all - including some of my own. For example, a week ago, while sleeping, I awoke at 3 a.m. with an excruciating pain in the bottom of my foot. I felt the spot that hurt and there was a huge lump. I figured I had ruptured a blood vessel in my foot, therefore, I immediately put an ice pack on my foot and wrapped it with an Ace bandage. The problem persisted and got worse and the following day I was unable to walk without the aid of a cane. I want to a local Doc In A Box, and the young man who examined me ordered some X-rays to be safe. After the X-rays, he did a preliminary exam of the foot, and said "My friend, you have the gout!" Now, I don't eat rich foods, etc..., the things associated with Gout. However, I discovered that sometimes it just happens. He gave me prescription for some tiny pills, said the problem will be gone in three days, and damned if he wasn't right.
So, if you have no practical medical experience whatsoever, my best advice is to carry a big first aid kit, get one of those first aid for sailors books and read it a couple times cover to cover, and stay close to shore.
Most medical problems at sea can usually be prevented by using nothing more than a bit of common sense. Hey, sailing is supposed to be fun. When it's no longer fun, find another hobby.
Gary
