By Paul Henry / in , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , /

Dialysis is a therapy that artificially removes
wastes from the blood of patients whose kidneys can no longer perform this function adequately. There are two main types of dialysis: hemodialysis
and peritoneal dialysis. In hemodialysis, blood is filtered outside
the body, in a dialysis machine. The patient’s blood is pumped to the machine,
cleansed, then returned to the body. To prepare for regular hemodialysis treatments,
a one-time minor surgery is performed to create a vascular access, which is essentially a
large and strong vein, enough to sustain the high flow rate through the machine. This can be accomplished by fusing an artery
to a vein, forming a so-called fistula; or by adding a synthetic tube – a graft. For emergency treatment, a catheter can be
used for temporary access. Once inside the machine, blood flows within
tiny tubes surrounded by a dialysis solution, called dialysate. The walls of the tubes act as semipermeable
membranes that allow only small molecules, such as water, nitrogenous wastes and electrolytes,
to pass through. The filtration occurs by osmosis and diffusion,
where water and solutes move from higher to lower concentration. The dialysis fluid contains solutes at the
levels similar to those in healthy blood. Urea, potassium and other solutes that are
present at higher levels in patient’s blood, move out to the dialysate, which is constantly
replaced and discarded. At the same time, other substances can be
added to the dialysis fluid to be administered to the patient. These may include: bicarbonate, to adjust
the patient’s blood pH; erythropoietin, to compensate for its low production by the
failing kidneys; and certain medications. Because of the increased risks of blood clotting
associated with its contact with foreign surfaces, an anticoagulant such as heparin is usually
added. The composition of dialysis fluid is typically
prescribed by a nephrologist based on the patient’s needs. Hemodialysis is normally performed as 4-hour
treatments, 3 times a week, in a dialysis center. Complications include risks of blood infection,
thrombosis, and internal bleeding due to the added anticoagulant. In peritoneal dialysis, the dialysis fluid
is introduced into the patient’s abdominal cavity via a catheter. The lining of the abdomen, the peritoneum,
serves as the natural filtering membrane. The fluid remains in the body for several
hours, allowing exchange and equilibrium with the blood running in the underlying vessels,
before being discarded. The therapy can also be done automatically
at night during sleep. Peritoneal dialysis is less effective than
hemodialysis, but because it can be performed for longer periods of time, the result is
comparable. Peritoneal dialysis offers more flexibility,
is better tolerated by patients, and less expensive, but is more often complicated with
abdominal infections.

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