C. Equipment

Dialysis Machine: The dialysis machine is controlled by an integral computer,
which controls the mixing and monitoring of the dialysate. The machine also
monitors the flow of your blood while it is outside of the body. Through a system
of alarms that go off from time to time, the machine lets us know that something
needs to be checked. It keeps track of blood flow, blood pressure, how much fluid
is removed and other vital information. The dialysis machine also has a blood
pump that keeps the blood flowing by creating a pumping action on the blood
tubes that carry the blood from the body to the dialyzer and back to the body.

Extracorporeal Circuit: The external blood-delivery system, or extracorporeal
blood circuit, circulates a portion of the patient’s blood through the dialyzer and
returns it to the patient. It consists of tubing, pumps, pressure monitors, air foam
or bubble detectors, and alarms to keep blood moving safely from the blood
access device and accessories for hemodialysis to the blood compartment of the
dialyzer and back to the patient

Dialyzer: known as an artificial kidney, the dialyzer is a disposable component in
which solute exchange, or clearance, takes place. It is a hollow plastic tube about
a foot long and three inches in diameter that contains many tiny filters. There are
two sections in the dialyzer: the section for dialysate and the section for the blood.
A semipermeable membrane divides the two sections to prevent the dialysate and
blood from mixing together. The semipermeable membrane has microscopic holes
that allow only some substances to cross the membrane; thus the membrane
allows water and waste to pass through, but does not allow blood cells to pass
through.

Dialysate: a solution of purified water with an electrolyte composition similar to
that of blood. This fluid helps remove the unwanted waste products from the
blood. It also helps get your electrolytes and minerals to their proper levels in the
body, such as sodium, potassium, bicarbonate, chloride, calcium, magnesium and
phosphate.

Needles: A patient with a vascular access, either an AV fistula or AV graft, will
get two needle sticks in their access. The thin needles are inserted and taped into
place. One needle will slowly remove blood and transfer it to the dialyzer of the
dialysis machine, while the other needle receives the clean blood and puts it back
in the body.
D. Mechanism of Flow
In hemodialysis, blood is removed from the body and circulated through the
extracorporeal fluid circuit, removing it outside the body from the first needle. The blood
is passed through a dialyzer for solute and fluid removal, which is where the blood is
cleaned. The dialyzer contains a selectively permeable membrane, which is a filter that
allows fluids and waste to pass through, but prevents the exchange of blood components,
microorganisms and endotoxins. The fluid used to clean the blood, or dialysate, flows in
the opposite direction to the blood on the opposite side of the membrane, while waste and
extra fluid are removed from the blood and end up in the dialysate by controlling three
processes: diffusion, ultrafiltration and osmosis. The used dialysate fluid is pumped out
of the dialyzer, and the filtered blood is passed back into the body through the second
needle.
The mechanical parts of the blood pump do not contact directly with the blood;
they propel the blood along the tubing by squeezing the tube from outside using rollers.
Similarly, the sensors, which measure pressure in the blood at various points along the
blood pathway, are separated from the blood by multiple membranes and, in some cases,
an air gap is placed to prevent direct contact between blood and machine.
E. Process
Before hemodialysis can start, an access point must be available for blood to be
removed and returned, usually through an arteriovenous fistula (AV fistula). The
operation to create the AV fistula is usually carried out around four to eight weeks before
hemodialysis begins, allowing time for the tissue and skin surrounding the fistula to heal.
Generally, hemodialysis is done three times a week, and takes up to about four
hours each session. These sessions are delivered while the patient is sitting in a chair, or
overnight while the patient is asleep. The patient is hooked to the dialysis machine via
needle insertion through the AV fistula, and goes through the blood cleansing process of
dialysis. During the procedure, a person may experience dizziness, muscle cramps, or
feeling of sickness. This is caused by the rapid changes in blood fluid levels that occur
during the treatment. Usually, the procedure is not painful or uncomfortable and does not
require an anesthetic. Hemodialysis requires trained operators, specialized equipment and
supplies. It can be performed in a patient’s home, while transportable equipment is
available.
After the dialysis session, the needles are removed and a plaster is applied to
prevent bleeding. If treated in hospital, the patient can usually go home shortly
afterwards. To prevent transfer of blood-borne viruses between patients, and to simplify
cleaning, the entire blood pathway (consisting of blood tubing, dialyzer and any needles)
is discarded after a single treatment. The dialysis machine itself can be used for multiple
patients if cleaned between patients.
References
“Dialysis - How It's Performed.” NHS Choices, NHS,
www.nhs.uk/Conditions/Dialysis/Pages/How-haemodialysis-is-performed.aspx.
“Dialysis: It's a Lifesaver.” Dialysis Overview and Resources - DaVita,
www.davita.com/kidneydisease/dialysis/treatment/whatishemodialysis?%2Fe%2F
1350.
“Haemodialysis.” Renal Medicine: Haemodialysis,
www.renalmed.co.uk/database/haemodialysis.
How Hemodialysis Works: Dialysis Machine, Medical, Extracorporeal, Diffusion,
Ultrafiltration, Osmosis, Hydraulic Engineering, Blood Filtration,
www.toltec.biz/how_hemodialysis_works.htm.
S., Joe. “How Does a Dialysis Machine Work?” DaVita, DaVita Inc. ,
www.davita.com/treatment-options/hemodialysis/in-center-hemodialysis/howdoes-a-dialysis-machine-work?/t/5596.
http://www.who.int/medical_devices/innovation/hemodialysis_unit.pdf