Hello,
Thanks for writing to Health Care magic, I am Dr , Muhammad Ahmad , I have read your question closely, I understand your concern and will be helping you with your health related problem.
A metallic valve in the heart does not significantly break red blood cells ,to an extent that the person needs 18 pints of blood in a year, there must be some other cause to the blood loss.
All patients having a metallic heart valve in place are almost always getting an anticoagulant(blood thinner) which is in most cases
Warfarin. This might thin out your blood that that extent that it starts oozing out of minor ulcers or damaged mucosa places of patient's stomach and gut. This is probably the case with your mother, She is 88 so not making blood as efficiently as a young person and on the other hand she is losing blood most probably through her gut because of blood thinners.
I would advise you to discuss this problem of blood thinners with your doctor, after getting special monitoring tests like INR to see the extent to which blood has got thinned, the doctor can change the dose of warfarin and this can help with blood oozing eventually helping with the symptoms of your mother.
I hope this answered your question, If you have more queries I am happy to answer you.
Regards.
Dr.Muhammad Ahmad