Other than the first aid/medical portion of the US Sailing Safety at Sea class, here are First Aid/CPR at Sea all-day courses in the Seattle area that are primarily intended for commercial fishermen, but open to recreational boaters as well. Also, some other resources/on-line classes
Put on by North Pacific Fishing Vessel Owners' Association at Fishermen's Terminal, Seattle. Open to recreational boaters. About $135 (in 2018). I've taken this course, and can recommend it. More info email: email@example.com or call 206-285-3383. Schedule: npfvoa.og/class-schedule
Also offered at Fishermens' Terminal. Also all day, for commercial fishermen, but open to recreational boaters (about $100). I've taken this course, and can recommend it. Schedule: https://wsg.washington.edu/students-teachers/sign-up/#marine-safety-training More info/to be notified of future classes contact: Sarah Fisken <firstname.lastname@example.org>
https://fas.org/irp/doddir/milmed/ships.pdf A bit dated, but still nice to have free downloadable resource.
I've not taken this course (It's $280!), so can't comment on the quality. While I see value in on-line training, from my experience, hands on training under the supervision of a qualified instructor is important to build confidence and competence in this subject. But some may find this appealing: https://www.maritimetraining.com/Course/Medical-Emergencies-at-Sea