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Dialysis
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| Kidney anatomy |
Kidney - blood and urine flow |
Alternative names
Artificial kidneys; Hemodialysis;Peritoneal
dialysis; Renal replacement therapy;
Definition
Dialysis is a method
of removing toxic substances (impurities or wastes)
from the blood when the kidneys are unable to
do so. Dialysis is most frequently used for patients
who have kidney failure, but may also be used
to quickly remove drugs or poisons in acute situations.
This technique can be life saving in people with
acute or chronic kidney failure.
How
the test is performed
PERITONEAL DIALYSIS
Peritoneal dialysis works by using the peritoneal
membrane inside the abdomen as the semipermeable
membrane. Special solutions that facilitate
removal of toxins are infused in, remain in
the abdomen for a time, and then drained out.
This form of dialysis can be performed at home,
but must be done on a continuous everyday basis.
HEMODIALYSIS
Hemodialysis works by circulating the blood
through special filters. The blood flows across
a semipermeable membrane (the dialyzer or filter),
along with solutions that help facilitate removal
of toxins. Before hemodialysis can be performed,
there needs to be adequate access to the vascular
system. The access needs to support a blood
flow of 250 milliliters per minute (ml/min),
and a normal venous peripheral IV will not support
that volume of blood flow. A special type of
arterial and venous access is therefore established.
The access can be either external or internal.
External access involves two catheters -- one
that is placed in an artery, and one in an adjacent
vein, or two catheters positioned within
different parts of a large vein. External access
is typically only used in emergency situations.
Internal access can be either an arteriovenous
(AV) fistula or AV graft. An AV fistula involves
the surgical joining of an artery and vein under
the skin. The increased blood volume stretches
the elastic vein to allow a larger volume of
blood flow.
After the 4 to 6 weeks the fistula needs to
heal, needles can be placed so that arterial
blood can be pulled off for dialysis, and the
cleansed blood returns through the dilated vein.
Turbulent blood flow over the AV fistula is
commonly felt and termed a thrill.
An AV graft may be used for people whose veins
are not suitable for an AV fistula. This procedure
involves surgically grafting a donor vein from
the patient’s own saphenous vein (in the leg),
a carotid artery from a cow, or a synthetic
graft from an artery to a vein.
After there is adequate access with two ports,
a hemodialysis machine is connected. The port
from the artery leads into the machine, and
the port returning from the machine leads into
the vein. Inside the machine, your blood is
run through tubes with semipermeable membranes,
and the tubes are bathed with solutions that
help remove specific soluble materials from
your blood.
In children, hemodialysis is used as preparation
for kidney transplant, rather than for chronic
care. In adults with chronic kidney failure,
hemodialysis is typically performed over 3 to
4 hours three times a week.
How
to prepare for the test
Blood pressure medications
are frequently withheld 6 to 12 hours before hemodialysis,
as are water soluble vitamins. Also, it is best
to eat before treatment, since dialysis can take
4 to 5 hours, and you will not be permitted to
eat during the procedure.
Just before your health care provider begins the
hemodialysis procedure, the following assessments
will be made:
- Blood pressure
- Temperature
- Heart rate
- Respiratory rate
- Weight
- Chest assessment
- Examination of venous access
- If you need the procedure explained
How
it feels
Since dialysis takes several
hours, it may become tedious. With children, it
is especially important to have games, something
to read, or other distractions.
Risks
Immediate risks include:
- Shock
- Emotional distress
- Infection
- Electrolyte imbalance
Long term risks include:
- Anemia
- Hypotension
- Growth retardation
- Neurologic complications
- Pericarditis
- Osteodystrophy
- Severe psychological problems
- Peritonitis (for peritoneal dialysis)
- Peritonitis; dialysis associated
Why
the test is performed
This procedure is performed
to remove contaminants from the blood that could,
and eventually would, result in death in the absence
of kidney function.
The kidneys function as filters for the blood,
removing products of amino acid breakdown. More
than that, they serve to reclaim and regulate
body water, maintain electrolyte balance, and
ensure that the blood pH remains between 7.35
and 7.45. Without the function of the kidney,
life is not possible.
Dialysis serves to replace some of the functions
of the kidney. Since dialysis is not a constant
ongoing process, it cannot serve as a constant
monitor as do normal functioning kidneys, but
it can eliminate waste products and restore electrolyte
and pH levels on an as needed basis.
Special
considerations
Take the following precautions
if you have internal angioaccess (access to a
vein through a fistula or AV Graft):
- When you sleep, avoid placing pressure on
the extremity with the access
- Do not allow anyone to take a blood pressure
on the extremity with the access
- Observe the access site after dialysis watching
for swelling, infection, or bleeding
- Do not wear tight clothing around the access
site
- Routinely check the access site for the
thrill indicating that the AV site is still
functioning (if the thrill disappears, call
your health care provider immediately)
- Do not use creams or lotions over the access
site
If you have an external access, take additional
precautions:
- Avoid physical activity that might dislodge
the access, which could result in excessive
bleeding, and air entering the circulatory
system (if this happens, call 911 and get
immediate medical attention)
- If the color in the tubes changes color
and becomes a dark red, call your health care
provider immediately (the blood may be clotting)
- Always keep a clamping tool on hand -- in
the event that the tubing comes unclamped,
you can use the tool to clamp off the tube
and stop the bleeding (if this happens call
your health care provider immediately)
- Call your health care provider immediately
if your have a fever or other sign of infection
- Do not allow the site to become wet (protect
it with plastic if you are to bathe)
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