There are two methods of removing wastes from the blood and
excess fluid from the body when the kidneys have failed. The
first, haemodialysis, may also be used as emergency treatment
in some cases of poisoning or drug overdose. It makes use of
an artificial kidney (or “kidney machine”) and can be carried
out at home. Peritoneal dialysis needs an abdominal incision,
which is performed in hospital but may also be done at home.
Access to the
bloodstream for
dialysis is obtained by a
shunt (in the shortterm
or in an emergency) or an
arteriovenous fistula,
which an artery is joined
surgically to a vein.
needle inserted into
the shunt or fistula
carries blood to the
machine. The machine
pumps the blood through
a filter attached to its
side. Once inside the
filter, the blood flows on
one side of a membrane,
and dialysate fluid flows
on the other. Waste
products and water pass
from the blood, across the
membrane, and into the
dialysate fluid. The filtered
blood returns from the
machine to the body via
another needle inserted
into the shunt or fistula.
V e in
S h u n t
S h u n t s e w n
A r t e r y
in t o b l o o d v e s s e l
A r t ific ia l
k i d n e y
m a c h i n e
B l o o d
fil t e r .
In people with damaged kidneys, the process of
maintaining the balance of electrolytes and water, and
of excreting waste products, may fail, causing harmful,
even life-threatening, effects. Dialysis can take
overthe function of the kidneys until they
start working normally again. Or dialysis
can function for the kidneys for the rest
of a seriously affected person’s life if a
kidney transplant is not performed.
Diseased kidney
The kidney at left was removed from a person
with adult polycystic kidney disease - one of
many disorders that may damage kidney function
to the extent that dialysis is needed.
The membrane separates the
patient’s blood from a special fluid
called dialysate. Wastes, toxic molecules,
and excess fluid pass across the membrane
from the blood into the dialysate.
D ia ly s a t e
t u b in g
small abdominal incision is made, and a catheter is
inserted into the peritoneal cavity. A
bag of dialysate is
attached to the catheter; the fluid passes into the cavity,
where it is left for several hours. Used fluid is then drained
out of the abdomen.
S p i n a l c o lu m n
I n t e s t in e
C a t h e t e r
D ia ly s a t e
t u b in g
Waste products, and excess
water from the blood vessels
lining the peritoneal cavity, seep
through the peritoneal membrane
into the cavity and mix with the
dialysate. The fluid is allowed to
drain out (by the release of a clamp)
through the catheter and into the
empty dialysate bag.
U s e d f l u i d
The bag is discarded and replaced with
a bag containing fresh dialysate. The
procedure, which takes about an hour, can
be performed during the day or overnight.
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