Dialysis
Dialysis may be indicated in oliguric ARF, intoxication with dialyzable
substances such as ethylene glycol, fluid overload and in the decompensated
CRF patient to reestablish compensation. All animals with suspected ARF
should be given a trial of fluid
and diuretic therapy
(unless already overhydrated) in attempt to reestablish urine flow (and
to rule out prerenal azotemia) prior to starting dialysis. If the patient
has life threatening
hyperkalemia it
should be treated prior to placing the implant for dialysis which may
require general anesthesia.
Principles of Dialysis:
Dialysis is defined as the transfer of solutes across a semipermeable
membrane by the process of diffusion. The semipermeable membrane in
peritoneal dialysis is the parietal and visceral peritoneum. Whether or not
a particle will leave the blood and cross the peritoneal membrane depends on
the size of the particle, the size of the pores in the peritoneum, and the
composition of the dialysis solution in the peritoneal cavity. The
differences in composition between blood and the dialysis solution
establishes the concentration gradient. For any solute that can pass through
the pores in the membrane, movement will occur from an area where it is
present in high concentration to an area of low concentration. When there
are equal amounts of solute in both solutions, there is no additional net
transfer.
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Peritoneal Catheters
: There are several designs of peritoneal catheters on the market for
human use. Many of these have been investigated in dogs and cats and there
are several catheters for use in dogs and cats that enjoy limited use within
the institution at which they were developed. Two commercially available
catheters that I have used in dogs include the Impersol catheter, so called
acute catheter and the column disc catheter. The acute catheter is a
polyethylene tube with multiple fenestrations on the tip, that is inserted
with a metal stylet. An acute catheter can be used for short-term dialysis,
usually less than 1-2 days. Because it is a free floating, tubular structure
in the abdominal cavity, it is quickly invested by omentum. In obese animals
with a lot of intra-abdominal fat, this catheter may fail to drain at all.
Acute catheters are placed with the animal in dorsal recumbency. A small
skin incision is made and the styleted catheter is introduced on the midline
just caudal to the umbilicus with the tip of the catheter directed caudal
and off to the left or right. To reduce the chance of trauma to bowel or
other visceral structures, a needle or a standard IV catheter may be
introduced into the abdominal cavity, and the abdominal cavity filled with
air, CO2, or saline prior to placing the styletted catheter. The
column disc catheter was developed at Purdue University. This catheter
offers the advantage of being fixed to the inner surface of the abdominal
cavity, minimizing the chance of omental entrapment of the catheter. The
negative side of this catheter is that it requires general anesthesia for
surgical placement. Partial omentectomy may be performed at the time of
catheter placement to reduce the chance of obstruction. Unfortunately the
column disk catheter is no longer sold.
Dialysis Technique: The volume of
dialysis solution infused into the peritoneal cavity is dependent on patient
size. The abdomen should be mildly distended ; an approximate volume of 40
ml/kg.
In large critical care facilities, peritoneal dialysis is often performed
with a peritoneal dialysis cycler machine which rapidly instills and removes
small volumes of dialysis solution several times an hour. A more practical
approach is that of CAPD, continuous ambulatory peritoneal dialysis. In CAPD
the abdominal cavity always contains dialysis solution so there is a
continual movement of waste products from the blood to the dialysis
solution. CAPD is most easily performed with dialysis solution contained in
plastic bags. The peritoneal catheter is attached to either a standard
intravenous fluid set (10 drops/ml), or a short solution transfer set. All
the connections and disconnections of the catheter and attached lines should
be done as aseptically as possible, wearing sterile gloves and scrubbing all
the connection sites with an antiseptic solution, such as betadine, prior to
connection or disconnection. Barring any contamination of the system, the
catheter is never changed, the tubing between the catheter and bag of fluids
is changed once per week, and the bag of fluids is changed as directed by
the dialysis schedule. All connections that will eventually be broken should
be wrapped in an antiseptic solution soaked gauze, then wrapped with dry
gauze and taped securely in place.
Transfer of Dialysis Solution:
Dialysis solution should be changed a minimum of 3-4 times per day. Early in
the course of dialysis, a rapid reduction in urea nitrogen and creatinine,
and potassium can be made by hourly exchanges of dialysate. Approximately
98% of urea (60 daltons) and potassium (39 daltons), equilibrate when
dialysis solution has been in the abdominal cavity for one hour. Creatinine
(113 daltons) and phosphate (95 daltons) are about 60-80% equilibrated in an
hour. The decision on how frequent to change the dialysis solution is often
made on the basis of economics and labor availability. Too rapid reduction
in BUN can lead to dialysis disequilibrium characterized by neurologic
dysfunction. To change the dialysis solution, any clamps on the line should
be opened and the empty dialysis bag laid on the floor on a clean towel
allowing dialysate to drain by gravity into the empty bag. With a well
functioning catheter, a liter of solution should drain within a period of
approximately 10 minutes without needing to manipulate the patient's
position. If the catheter is partially obstructed, it might necessitate
changing the patient's position to remove the used dialysis solution. Once
the dialysis solution stops flowing, the bag containing the waste dialysate
is clamped at the neck and removed and a fresh bag of dialysis solution is
attached to the tubing, the neck of that bag wrapped with antiseptic
solution soaked gauze, the fresh bag suspended over the patient on an IV
hook and let flow into the patient by gravity. The line is then clamped and
the empty bag is folded or rolled, the extra IV tubing is rolled around the
bag, and the bag and tubing are attached to the patient until the next time
dialysis solution is changed.
The just drained bag of dialysate should be measured or weighed (1 ml =
approx. 1 g) Flow sheets should be kept to assess the volume status of the
patient: are you removing more fluid from the patient than you are
instilling or visa versa.The dialysis flow chart will be used to plan the
remainder of the patient's fluid therapy.
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Complications: Major complications
associated with peritoneal dialysis include peritonitis, obstruction of the
dialysis catheter, infection of the subcutaneous tract, subcutaneous leakage
of dialysate, and loss of body proteins. Often, even the most depressed, ill
animal will attempt to chew out their catheter. The catheter, the empty bag,
and the interposed tubing should be securely fastened to the patient to
prevent chewing, but not so excessively bandaged that it is difficult to get
to. Old t-shirts or body shirts of stockinette work well as "packages" in
which to "house" the dialysis apparatus between periods of use. This
procedure appears so simple that one may become careless in technique and
introduce bacteria into the abdominal cavity. The peritoneal cavity is not
forgiving. It is very difficult to resolve peritonitis, especially with a
catheter in place, as the catheter itself becomes colonized with bacteria.
It is much better to prevent peritonitis, than to treat peritonitis. If
contamination is known to occur, an aseptic solution can be instilled in the
dialysis solution for several exchanges. The one I have had the best
experience with is a dilute chlorhexadine solution--solution, not scrub.
Although antibiotics can be placed in the dialysis solution, they are no
more effective than parenterally administered antibiotics, most of which
will penetrate into the peritoneal fluid. Some patients may develop an
infection of the subcutaneous tract. This may be an extension of
contamination of the peritoneal cavity, or may localized. The site that the
catheter exits from the abdomen should be evaluated daily and cleaned with
an antiseptic solution. Protein loss is massive in the face of peritonitis.
A substantial amount of protein can be lost even in the absence of
infection. The patient's serum proteins need to be monitored closely and in
some cases, when an animal resumes alimentation, it may be necessary to
increase the protein content of their diet to offset the loses in the
peritoneal fluid.
Last Edited: May 06, 2008 1:02 PM
