Page 363 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

Technical Aspects of Fluid Therapy 353

TABLE 15-2 Suggested Intravenous safety mechanisms to limit the risk of operator injury
Catheter Gauges and exposure to patient blood. Safety catheters irrevers-
ibly retract or cover the needle after the vein is punctured
Jugular Vein Limb Vein and can be used for only one attempt.
(Through- (Over - Over-the-needle catheters are useful for short
Weight the-Needle) the-Needle) procedures such as anesthesia and for intravenous fluid
administration for 48 to 72 hours. These catheters are
Maintenance Therapy usually positioned in the cephalic, accessory cephalic,
<5 kg 22 24-20 medial and lateral saphenous, or femoral veins. Any other
5-15 kg 22-19 22-18 accessible superficial vein may be satisfactory (e.g., ear
>15 kg 19-16 20-18
veins in rabbits or dogs with pendulous ears).
Resuscitation There are several disadvantages associated with over-
<5 kg 22-19 22-18 the-needle catheters. They may fray or splinter at the
5-15 kg 19-16 18-14 tip during insertion and cause excessive injury to the vein
>15 kg 16-14 16-10
with a high risk of thrombosis. They are difficult to secure
adequately and may slide in and out of the skin with limb
movement. This action increases the risk of trauma to the
WINGED NEEDLE CATHETERS
vein and may also facilitate entry of skin surface bacteria
Winged needle catheters may be used for short-term (sin- through the catheter wound and into the vein. When they
gle dose) administration of fluid or drugs into a periph- are located in distal limb veins, fluid flow through these
eral vein. They are available in needle sizes of 27 to 16 catheters is often affected by limb position (e.g., elbow
gauge and with various lengths of plastic tubing bonded flexion often stops gravity flow of fluids through a
to the needle and connecting to a Luer adapter. Plastic cephalic vein catheter). Several brands of these catheters
wings at the needle hub facilitate handling and securing are composed of stiff Teflon or irritating polypropylene
the needle. The risk of needle puncture of the vessel wall and are not suited for extended dwell periods in an exter-
and subsequent extravasation is high because the sharp nal jugular vein or in veins that cross a joint where motion
needle bevel is left exposed within the lumen of the vein. enhances catheter-induced vessel trauma.
Therefore these catheters are best used only for collection
of blood or for single infusions of nonirritating drugs or THROUGH-THE-NEEDLE CATHETERS
fluids under direct supervision. They are usually posi- Through-the-needle catheters are long (6 to 36 inches)
tioned in the cephalic vein, where there is less risk of dis- and are often used to gain deep or central venous access
placement by patient movement. They must be located from peripheral sites. These catheters are generally known
sufficiently distal to the elbow so that joint flexion will as midline catheters in human medicine because they are
not displace the needle through the vessel wall. Although designed to obtain access to proximal limb veins from dis-
these are not useful for long-term fluid administration, tant venipuncture sites. Because of the anatomy of the
they have two major advantages for emergency or critical external jugular and lateral saphenous veins in companion
care patients: (1) they may be inserted rapidly with little animals, these catheters work well to obtain central
or no skin preparation; and (2) in many operators’ expe- venous access. This allows the catheter tip to be posi-
rience they are the most effective device to obtain percu- tioned in a large central vein with rapid blood flow,
taneous venous access in cats (and occasionally small allowing safe administration of viscous or hypertonic
dogs) with poor peripheral perfusion, via cannulation solutions. It is often difficult to thread these catheters past
of the medial cutaneous saphenous vein under direct visu- the elbow and axillary regions of the forelimb; thus they
alization through the thin skin of the medial thigh. are of limited usefulness in cephalic veins.
Through-the-needle style catheters are usually long
OVER-THE-NEEDLE CATHETERS and provide several advantages over short, over-the-nee-
Over-the-needle catheters are well suited for easy inser- dle style catheters. Body position and movement do not
tion into peripheral veins in companion animals. The affect the rate of fluid flow when the tip of the catheter is
wide range of available gauge sizes allows flexibility in positioned in a deep or central vein. Multiple blood
vein selection and maximal flow rates. Some are designed samples may be withdrawn easily from these catheters.
for arterial cannulation (e.g., Arrow Radial Artery cathe- They may be anchored securely to the skin and tunneled
ter, Arrow International, Reading, Pa.) and incorporate a extensively through subcutaneous tissue and are there-
wire guide stylet that facilitates placement. Multilumen fore less likely to conduct surface bacteria into a vein than
catheters (e.g., the Arrow Twin Cath, Arrow Interna- are shorter catheters. 51,57 However, small vein cannula-
tional) allow infusion of incompatible solutions through tion is often more difficult than with over-the-needle
a single catheter. In the past 15 years there has been an catheters, and the risk of catheter or air embolization dur-
industry-wide move toward catheters that incorporate ing catheterization is greater.