The session was led off by Zbylut J.
Twardowski, MD, PhD, University of
Missouri, Columbia, Missouri, with a
review of currently available catheters for
hemodialysis. There are several types of
catheters for chronic hemodialysis: dual
lumen, single lumen, Ash Split Cath
TM
, and
Dialock
TM
. No clear advantage of any
catheter could be ascertained as there are
no comparative studies.
Dr. Twardowski emphasized that,
according to Poiseuille’s equation, the flow
in a tubing at a given pressure difference is
proportional to the 4th power of radius,
and inversely proportional to the length of
the tubing and the fluid viscosity. The
influence of catheter diameter on blood
flow is paramount. The length of the
catheter, however, cannot be neglected.
While the internal length is determined by
the distance from the insertion site to the
right atrium, it is prudent to keep the
external length as short as possible. When
companies make claims regarding the flow
of their catheters, it is worthwhile to
remember the Poiseuille equation. One
may make catheters with higher flows by
increasing the diameter; however, the larger
the diameter, the higher the risk of
thrombotic and infectious complications.
All hemodialysis catheters have side
holes at the tip in the belief that this will
provide blood flow if the catheter tip is
occluded. Dr. Twardowski questioned the
wisdom of this design for several reasons:
(1) anticoagulant is leached out through
the holes, predisposing to intraluminal
clot formation; (2) if the arterial lumen
tip is occluded, the flow through side holes
sucks the vein intima, causing damage
and predisposing to mural thrombi;
(3) multiple scanning electron microscopy
pictures clearly show that side holes are
drilled and have rough surfaces, which are
thrombogenic; (4) several pictures of
catheters showed that side holes firmly
anchor clots, making them difficult to strip.
W. Kirt Nichols, MD, University of
Missouri, Columbia, Missouri, presented
surgical aspects of catheter implantation.
He stressed the need for good mapping of
the veins where the catheter is to be
implanted. Most of the time, but not
always, the jugular vein is located to the
front of the carotid artery, but positions
may vary. Good mapping reduces the risk
of puncturing the carotid artery, with consequent
local hematoma or hemothorax.
Other possible insertion complications
include catheter malposition, pneumothorax,
and air embolus. Flouroscopic control
of the tip position and postprocedure chest
x ray to assess possible complications are
mandatory. To avoid an air embolus, insertion
with the patient in Trendelenburg
position is recommended.
Daniel Golwyn, MD, Radiology
Consultants of Lynchburg, Lynchburg,
Virginia, presented aspects of catheter
implantation and care from the perspective
of the interventional radiologist.
Interventional radiology literature indicates
that, in 1% of patients, the jugular
vein is located behind the carotid artery. In
his opinion, real time ultrasonography is
the best method to avoid accidental puncture
of the artery. In cases of massive fibrin
sheath causing catheter malfunction, Dr.
Golwyn prefers to exchange the catheter
through the same tunnel, instead of stripping,
for several reasons: the procedure is
not more time consuming, is not more
expensive, and catheter function after
replacement is better and lasts longer.
After catheter removal, the fibrin sheath
should be disrupted with a balloon before
a new catheter is implanted. Dr. Golwyn
does not place patients in the
Trendelenburg position
for catheter procedures
and has not encountered
related complications.
Gerald Beathard, MD,
Austin Diagnostic Clinic,
Austin, Texas, stressed
that catheter-associated
infections are late complications.
The main source
of infection is contamination
of the hub or lumen at the time of
manipulation in the dialysis unit. Exit or
tunnel infection accompanies bacteremia
in one third of cases. In cases of positive
blood culture, immediate and prolonged
antibiotic treatment is essential. Antibiotic
therapy must be specific, based upon the
results of cultures. The important question
is how to manage the catheter. There are
several choices: leave the catheter in,
change the catheter over a guide wire,
change the catheter over the guide wire
with a new tunnel, or remove the catheter
and delay replacement. Action depends on
the presence of exit tunnel infection, the
need for a catheter, and severity of symptoms.
Dr. Beathard’s experience indicates
that, in most cases, cure may be achieved
by catheter replacement over a guide wire
after 24 – 48 hours of antibiotic treatment
in patients without exit or tunnel infection.
Andrew Davenport, MD, Royal Free
Hospital, London, England, pointed out
that although fistulas and/or arteriovenous
(AV) grafts are the preferred methods of
blood access for hemodialysis, not all
patients have suitable vessels for AV access
or cannot wait for AV access maturation,
and therefore need intravenous catheters.
Unfortunately, catheters have inherent
problems. Most important are thrombosis,
infection, and venous stenosis. In recent
years, Dr. Davenport has used intraluminal
catheter brushing for clot removal and
obtaining cultures. Generally, the results
with catheters are steadily improving;
therefore, intravenous catheters are here to
stay. Further progress is needed — mainly
prevention of colonization of the catheter
hub and more-biocompatible surfaces to
prevent thrombin deposition.
