I know that Peter Deilmann's Deutschland offers this service in its medical centre (or at least it did 4 years ago) but dont know if any UK or USA ships do so.I would contact Peter Deilman if I were you, or one of the Agents who sell that ship. I know Bath Travel (Bournemouth based)_do so, if you are having trouble finding an agent who does( it's not a "mass market" ship so may not be too widely available in this country.) It is a very good quality cruise experience but bear in mind that the majority of fellow cruisers will be German. We found that no problem at all and we speak very little German.
I would suggest you email the cruise lines that you are interested in and ask them. I know that ship's medical centres are very good because my father had a bad attack (emphysema) and they had the equipment for him, but I'm not sure if they offer the type of treatment you require.
Contact dialysisatsea.com and they will advise what cruise lines they work with.
Visit www.dialysisholidays.co.uk they are a company specialising in haemodialysis cruises based in the UK. My friend booked through them and said they are really helpful and professional.