Page 362 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

352 FLUID THERAPY

the catheter material is inert and can stay in place for a INTRAVENOUS CATHETERS
long time, failure to adhere to strict aseptic technique will
result in bacterial contamination. Catheter product designs currently available include
winged needle, over-the-needle, through-the-needle,
INTRAVENOUS and those placed through an introducer or over a guide
Intravenous administration is the route of choice when wire (Table 15-1). Selection is influenced by operator
blood volume expansion is desired. It is clearly superior experience, availability, cost, and patient requirements.
to subcutaneous administration for any critically ill patient Smaller diameter catheters and those made of soft mate-
with poor perfusion of tissues. Indications for vein cannu- rial are less traumatic to veins than large or stiff catheters.
lation include administration of fluids, drugs, total paren- For routine maintenance therapy, the smallest gauge
teral nutrition, blood products, intravenous anesthetics, catheter that provides adequate flow should be used.
and as a precaution against the need for venous access in If rapid administration of fluid is required, the largest
the event of an emergency. gauge size possible should be used (Table 15-2). The
maximal fluid flow rate increases as the radius of the cath-
INTRAOSSEOUS eter lumen is increased. For small catheters (<14 gauge),
Intraosseous fluid administration provides access to the this relationship is linear, whereas for larger catheters,
vascularspace via the capillary beds ofthe medullary vascu- flow rate increases geometrically with size and is propor-
lar system. It is an excellent alternative to the intravenous tional to the lumen radius raised to the fourth power
4 25
route in neonates, (in whom vascular access is technically (r ). Short over-the-needle catheters are preferred for
difficult) or animals with circulatory collapse. This route is rapid intravenous access in emergencies because they
best suited for rapid, short-term administration of fluids, can be inserted rapidly and are available in sizes up to
blood products, or drugs in emergency situations. 8.5 French.

TABLE 15-1 Intravenous Catheter Design
Style Advantages Disadvantages

Winged steel needle Can be inserted rapidly with little to Suitable for short-term use only
no skin prep
High risk of extravasation
Over-the-needle (OTN) Well suited for peripheral vein Most brands cannot use for central
access
Inexpensive Cannot be tunneled very far
subcutaneously
Technically easy to use Stiff materials more damaging to veins
Multiple veterinary distributors Unreliable for aspirating blood
Fluid flow affected by limb position
Over-the-needle with guide wire Can be inserted into small/difficult veins Same as OTN
Arterial catheters useful for dorsal pedal artery More expensive than OTN
Through-the-needle (TTN) Can be used for central access Technically more difficult to insert
Useful for repeated blood collection Greater potential for hemorrhage than
OTN type
Can be tunneled subcutaneously More expensive than OTN
Made of softer/less irritating material
Less likely to produce thrombophlebitis
over time
Through introducer sheath with or Can be used to achieve central venous access Same as TTN, plus:
without guide wire
Can insert relatively large/multilumen Requires drape/sterile field/sterile
catheter gloves
Can create a long subcutaneous tunnel
Catheter material may be very soft (silicone,
polyurethane)
Can be placed in veins too difficult for
TTN-style catheter