Hemodialysis (HD) apparatus can be broadly divided into a blood circuit and a dialysis solution circuit, which meet at the dialyzer.
The blood circuit begins at the vascular access.
From there blood is pumped through an “arterial blood line” to the dialyzer.
Blood is returned from the dialyzer to the patient via a “venous blood line.”
These terms are used even though often only venous blood is being accessed (such as when using a venous catheter).
More precise would be to term these the “inflow” blood line and “outflow” blood line, but as often is the case, the traditional names rather than more correct terms continue to be used.
Various chambers, side ports, and monitors are attached to the inflow and outflow blood lines, and are used to infuse saline or heparin, to measure pressures and to detect any entrance of air.
The dialysis solution circuit includes the dialysis solution (dialysate) supply system, which makes dialysate online by mixing purified water with concentrated dialysate solutions.
The final dialysate is then pumped through the dialysate compartment of the dialyzer, the latter being separated from blood compartment by a semipermeable membrane.
The dialysis solution circuit includes various monitors that make sure that the dialysis solution is at the right temperature and has a safe concentration of dissolved components.
Also, a blood leak detector is present with the purpose of stopping dialysis if blood products are detected in the outflow dialysate.
