Sentence:  An artificial kidney these days still means a refrigerator-sized dialysis machine. Such devices mimic...real kidneys.... But they are nothing like as efficient, and can cause bleeding, clotting and infection—not to mention inconvenience for <WSD>patients</WSD>, who typically need to be hooked up to one three times a week for hours at a time. 
Meaning of the word marked with <WSD> tags:  A person or animal who receives treatment from a doctor or other medically educated person.