| Second:
Dialysis:
This may be instituted as a form of
renal replacement therapy. There are two types of dialysis.
Hemodialysis:
This is usually performed in a dialysis
center. Blood must be pumped from the patient’s circulation.
Uremic toxins are removed usually by diffusion across a semipermeable
membrane. Fluid is removed by ultrafiltration dependent upon a
pressure gradient between the blood and dialysate. Children require
artificial kidneys which hold less volume and have a controlled
urea filtration rate. Artificial kidneys which remove uremic toxins
too efficiently may produce dialysis disequilibrium and potentially
cerebral edema. Dialysis lines are adapted to child to allow slower
blood flow rates and hold less volume. Children usually do not
tolerate more than 10% of their blood volume outside their body
at any one time. Fluid removal (ultrafiltration) is also limited
when the total extracorporeal blood volume is close to or exceeds
10% of the blood volume. When performed in-center dialysis sessions
usually last from 3-4 hours three days a week. Hemodialysis may
be performed at home in a stable patient with a partner. Then
dialysis sessions may be performed more frequently for shorter
periods to simulate normal renal function.
Peritoneal dialysis:
This is essentially always performed
at home. A parent is trained in the dialysis technique. An older
child or an adolescent is given increasing degrees of responsibility
and may become completely independent. The technique is easier
to learn than hemodialysis and requires less sophisticated equipment.
Both toxins and water are removed by diffusion across the peritoneal
membrane. The dextrose concentration of the dialysate is varied
to remove more or less water. The dialysis is done nightly at
home using an automated cycler. This technique is called continuous
cycling peritoneal dialysis (CCPD). Sometimes a cycler is not
used and dialysate bags are simply exchanged between pass. This
is called continuous ambulatory peritoneal dialysis (CAPD). The
process is less efficient than hemodialysis and hence there is
virtually no danger of dialysis disequilibrium. Since peritoneal
dialysis is done much more often and for longer periods it gives
about the same degree of uremic control especially in smaller
individuals.
Both methods require access created to
the vascular system or to the peritoneum.
Access to the vascular compartment may
be through a central catheter usually inserted into the jugular
vein. An A-V fistula may be surgically created for cannulation.
The most frequently used site is the radial artery and vein. Other
fistulas may be created in the groin or upper arm. Synthetic grafts
may be used (e.g. Gortex®) when vessels are not large enough.
In peritoneal dialysis catheters are surgically inserted into
the peritoneal cavity through the abdominal wall. Central catheters,
A-V fistulas, and synthetic grafts may become clotted and are
at varying degrees of risk for infection. Peritoneal dialysis
catheters may become occluded with fibrin or omentum. They may
also develop infections along the tunnel and at the exit sight.
Peritonitis is a potentially serious complication of peritoneal
dialysis. The bacteria are usually introduced by contamination
during the set-up of the cycler or a bag exchange. They may also
be introduced from a tunnel or exit sight infection. Infections
of any of the various accesses for peritoneal and hemodialysis
are always potentially very serious and can result in the loss
dialysis assess. Also peritonitis especially recurrent episodes
can result in loss of the peritoneal membrane for dialysis. All
such infections must be treated promptly and sometimes require
the removal of access devices.
|