Page 364 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

354 FLUID THERAPY

GUIDED CATHETERS AND material are coated with silicone elastomer to reduce their
PERIPHERALLY INSERTED CENTRAL reactivity. Catheter thrombogenicity is related not only to
CATHETERS chemical reactivity but also to the stiffness of the material
and the smoothness of its surface. 18,33 Teflon is the
Central venous catheters designed for insertion into a
stiffest material; polypropylene, PVC, and polyethylene
human internal jugular or subclavian vein use almost
are more flexible. Stiff catheters are easier to pass through
always use a guide wire placement technique to increase
the skin and subcutaneous tissues but are more prone to
the likelihood of successful cannulation. Because they
kinking and more likely to damage vessel walls and cause
are composed of soft material, they either incorporate a
thrombophlebitis. Polyurethane elastomer (e.g., Vialon,
wire stylet or are threaded over a preplaced guide wire
using the technique of Seldinger. 72 Some of the catheters Becton Dickinson, Franklin Lakes, N.J.) and silicone
marketed for use in humans are suitable for use in dogs elastomer catheters are much softer and more flexible.
and cats (e.g., Arrow Pediatric Central Venous Catheteri- Silicone elastomer catheters are so flexible that they
zation Sets, Arrow International). Some guide wire are difficult to introduce into a vein without a stylet or
guide wire.
catheters are marketed specifically for use in dogs and cats
Many brands of catheters are made radiopaque by the
(e.g., Mila International, Florence, Ky.; Global Veterinary
addition of heavy metal salts (barium or bismuth) to the
Products). The guide wire technique allows central vein
plastic. When mixed uniformly into the material, these salts
access via insertion into veins that may not be successfully
increase the roughness of the catheter surface and increase
cannulated otherwise. Other peripherally inserted central 33
the risk of thrombosis. If embedded within the wall
catheters (PICCs; Mila International, Global Veterinary
of the catheter, or if the catheter is coated with another, less
Products) are inserted through a short, larger introducer
thrombogenic material (e.g., silicon elastomer), this risk is
sheath with or without a guide wire. A major advantage of
these catheter designs is the availability of double or even lower. Heparin coating may significantly reduce catheter
67,74
triple lumen products that allow greater vascular access thrombus formation, at least for 1 to 2 days. Some
through a single catheter. manufacturers have developed antibiotic-coated catheters
that appear to reduce the risk of catheter-associated
sepsis. 27,43,45 Examples of antiseptics either coated onto
CATHETER COMPOSITION or impregnated into catheters include chlorhexidine-silver
sulfadiazine and rifampicin-miconazole. 27,43
Catheter composition affects handling characteristics
during insertion and influences the potential for throm-
bosis and phlebitis. Widely used catheter materials VEIN SELECTION
include polyvinyl chloride (PVC), polyethylene, polypro-
pylene, polyurethane, silicon elastomer (Silastic), Catheter site selection depends on several factors, includ-
tetrafluoroethylene (TFE Teflon), and fluoroethylene- ing operator experience, accessibility, therapeutic goals,
propylene (FEP Teflon) (Table 15-3). These materials risk of infection, risk of damage to the catheter, and risk
are chemically inert, but leaching of plasticizers of thrombosis.
and stabilizing agents from some plastics probably
contributes to the development of phlebitis, especially ACCESSIBILITY
in small veins with low blood flow. 63,75,85 Silicone elasto- Peripheral vein cannulation is most often performed in
mer catheters are the most chemically inert, whereas the cephalic and accessory cephalic veins of the thoracic
PVC, polypropylene, and polyethylene are the most limbs and the lateral saphenous vein of the pelvic limbs.
reactive. Teflon and polyurethane are intermediate in Other suitable veins include the medial saphenous (cats),
reactivity. Some catheters composed of more irritating the femoral veins (in some cats and dogs), and the ear

TABLE 15-3 Catheter Materials

Material Reactivity Stiffness Thrombogenicity

Teflon þþ þþþþ þþ
Polyether-based polyurethane þ þþ þ
Polyester-based polyurethane þþ þþþ þþ
Polyvinyl chloride þþþþ þþþ þþþ
Polyethylene þþþ þþþ þþþ
Polypropylene þþþ þþþ þþþ
Silicone elastomer þ þ þ

Relative values for each material: þ¼ minimal, þþ ¼ mild, þþþ ¼ moderate, and þþþþ ¼ high.