Page 365 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

Technical Aspects of Fluid Therapy 355

veins in dogs with pendulous ears. These veins may fill RISK OF THROMBOSIS
very slowly in animals with poor peripheral perfusion There is a risk of thrombosis whenever a vein is
and can be difficult to visualize or palpate. In this setting,
cannulated. Thrombosis is more likely in small veins with
the saphenous veins may be superior (lateral in dogs,
low blood flow or when the intravascular portion of the
medial in cats) because the relatively thin skin overlying
catheter traverses a mobile joint. Some specific diseases
them allows better visualization and control over catheter
such as preexisting phlebitis, glomerulonephritis, pro-
insertion. Catheterization may be facilitated by the vascu-
tein-losing enteropathy, autoimmune hemolytic anemia,
lar access procedures described in the following sections.
and any disorder that causes systemic inflammation are
THERAPEUTIC GOALS complicated by increased risk of serious thrombosis and
pulmonary thromboembolism. 21,37,42,62 Intravenous
Short-term administration of fluids may be accomplished catheterization in these animals is probably accompanied
using any vein, and choice of vein in this setting depends by a higher risk of clinically significant thrombosis than in
primarily on operator experience and catheter design.
other diseases. It may be advisable to avoid venous cath-
Central venous catheterization is preferred in patients
eterization in these animals when possible. When cathe-
that require long-term fluid administration or parenteral
terization is unavoidable, one should use short, soft,
nutrition, administration of hypertonic solutions or
small diameter catheters that are removed as soon as pos-
irritating drugs, frequent blood sampling, or central
sible. Compared with catheterization of peripheral veins,
venous pressure (CVP) monitoring. Central venous
catheterization of the jugular vein in companion animals
access is most easily accomplished by cannulation of the
is probably not an independent risk factor for venous
external jugular or saphenous veins. The right external
thrombosis and pulmonary thromboembolism, but the
jugular is preferred over the left because this vein joins consequences of thrombosis in that location are more
the cranial cava in a straighter line through the brachyce- apparent and severe. Cats with aortic saddle thrombi have
phalic trunk than does the left, facilitating catheter poor blood flow to their pelvic limbs and devitalization of
passage into the cranial vena cava.
those tissues. Pelvic limb vein catheterization in these
RISK OF INFECTION animals is associated with a high risk of venous
thrombosis and infection and must be avoided.
The risk of infection is increased in the presence of ban-
dage contamination. Catheters inserted into peripheral
veins that are likely to be soiled by vomiting, diarrhea, CATHETER PLACEMENT
or urine pose a greater threat. Therefore the saphenous
veins are not ideal choices in animals with diarrhea or SKIN PREPARATION
polyuria, and the cephalic vein is not a good choice in
an animal with frequent vomiting. There is a greater Healthy animals undergoing short-term catheterization
threat of infection of catheters inserted through a for elective procedures (e.g., anesthesia for ovariohys-
cut-down incision or through skin that is wounded or terectomy) rarely develop phlebitis or sepsis from sloppy
infected. Therefore unhealthy skin is avoided, and technique during catheter placement. In contrast, sick
catheters inserted through incisions are removed as soon animals with compromised immunity may not tolerate
as possible, ideally within 6 hours. even a minor breach of aseptic technique, and intravenous
catheters may quickly become colonized and serve as a
RISK OF DAMAGE TO THE CATHETER point source for bacteremia and septic phlebitis. With
Catheters located in limb veins are particularly accessible the exception of emergency venous access, these patients
to the animal’s teeth, and some animals chew at and dam- require careful aseptic technique for skin preparation and
age or remove the catheter. Catheters located in an ear catheter insertion. If an intravenous catheter is to remain
vein may prompt scratching and head shaking that even- in place for more than a few hours, the skin must be
tually dislodge the device. Some form of restraint, such as prepared as for any surgical procedure. Every effort must
an Elizabethan collar, may be necessary to prevent dam- be made to be thorough but gentle because abraded or
age to catheters located at these sites. The risk of catheter scarified skin is not healthy and will support colonization
damage is considerably lower when the jugular vein is by pathogenic bacteria. Key points include avoiding
used and bandaged adequately. Surprisingly, most sick clipper burn and avoiding rough cotton gauze for skin
dogs and cats do not disturb properly positioned, care- cleansing:
fully bandaged intravenous catheters. Animals that chew 1. A wide clip centered on the intended venipuncture site
or scratch at their catheters frequently do so because of is performed. A No. 40 blade is used to obtain a close
excessive irritation. Catheters and bandages that were cut. The clipper blade must be well lubricated and held
tolerated initially and subsequently provoke chewing or parallel to the skin (not raked across it) to limit clipper
scratching should be carefully inspected for evidence of burn, and the coat is clipped sufficiently far from the
tightness, wetness, or infection. point of insertion so that there is no risk the catheter