The HD machine has two delivery systems. What are they and what do they do?

• A. Blood delivery: circulates the patient's blood; Dialysate delivery: mixes and circulates dialysate
• B. Blood delivery: circulates dialysate; Dialysate delivery: circulates the patient's blood
• C. Blood delivery: filters air; Dialysate delivery: circulates the patient's blood
• D. Blood delivery: circulates dialysate; Dialysate delivery: circulates air

Answer: (A)

In hemodialysis, two separate fluid circuits do the work. The blood delivery system pulls the patient’s blood into the machine, runs it through the extracorporeal circuit and the dialyzer, and returns it to the patient under carefully controlled flow and pressure with anticoagulation as needed. The dialysate delivery system, on the other hand, creates and circulates the dialysate fluid that flows on the opposite side of the dialyzer membrane. By providing fresh dialysate, it establishes a concentration gradient across the membrane so wastes and excess fluid diffuse from the blood into the dialysate, which is then discarded. The blood and dialysate remain separate; the dialysate does not circulate the patient’s blood, and the blood does not circulate dialysate.