Final answer:
Hemodialysis is a medical procedure used to filter waste products and excess water from the blood of patients with kidney failure. The frequency of hemodialysis sessions is necessary to regularly remove waste materials from the bloodstream.
Step-by-step explanation:
Hemodialysis is a medical procedure used to filter waste products and excess water from the blood of patients with kidney failure. It is usually done on an outpatient basis in a hospital or dialysis clinic. The frequency of hemodialysis sessions, typically 3 to 4 hours, 3 times a week, is necessary because waste materials are constantly building up in the bloodstream and need to be removed regularly to maintain the patient's health.