Can't say i have ever had any significant medical issues in literally many thousands of miles of paddling including in recreational paddling, racing and race training.
However I have been well prepared by having paddled with many highly trained professional medical people. I have often paddled the Yukon River and other canoe race events with some or all of these medically trained friends: a county clinical pathologiist, an active duty military combat medic fresh from recent duties iin Iraq and Afghanistan, a hospital surgical suite coordinator, a cardiac surgeon's physician's assistant, a physical therapist, and a hospice end of life care provider. Thankfully I have not needed the services while canoeing of either the first or the last person on that list, all interesting people and good to have their experiencess and skills on a remote wilderness trip.