Page 387 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

Technical Aspects of Fluid Therapy 377

is scrubbed with antiseptic solution and carefully cleaned AIR EMBOLISM
with alcohol. When the alcohol has dried, the catheter is Air embolism may occur whenever a catheter is within a
removed aseptically, and the catheter tip is cut off with a
vein, but the risk is probably highest during insertion of
sterile blade and dropped into a sterile tube containing
central venous catheters. When the catheter tip enters the
either sterile saline (to keep it moist before transfer to
thoracic cavity it is exposed to negative intrathoracic pres-
culture medium) or culture medium broth for direct bac- sure during inspiration, and aspiration of air occurs if the
teriologic evaluation. 47 If the catheter is suspected to be
free end of the catheter is exposed to the atmosphere.
the cause of infection in a bacteremic animal but the cath-
This risk may be higher in dogs with extrathoracic airway
eter cannot be easily replaced (e.g., catheters inserted
obstruction (e.g., brachycephalic breeds) because the
surgically in animals with limited venous access), differen- obstruction produces markedly negative intrathoracic
tial bacteriologic culture may be performed. In this pressure during a relatively long inspiratory phase. Clini-
procedure, cultures are performed on blood drawn simul- cally significant air embolism during catheterization is
taneously through a peripheral vein and through the cath-
avoided by completing the procedure and sealing the
eter. In humans, if the catheter blood sample shows a
Luer end as rapidly as possible.
sevenfold increase in identical bacterial colonies
Air embolism may also result from problems with the
compared with the peripheral vein blood culture, the fluid administration setup such as accidental disconnec-
catheter is probably the source of the bacteremia. 20 Pre-
tion of tubing or presence of air within the fluid path,
vention of infection is assisted by using sterile technique
as may occur with vented fluid administration sets or fluid
during catheterization, tunneling the catheter subcutane-
containers that hold an excessive volume of air. The risk
ously before venipuncture, using needleless connection
may be reduced substantially by using collapsible plastic
devices, avoiding tubing disconnections, properly containers and nonvented administration sets.
maintaining the catheter dressing, and carefully manag- Small air emboli are trapped in the pulmonary vascula-
ing injection ports and fluid containers. 48,57,80 Antibiotic ture and usually go unnoticed. Administration of a bolus
therapy does not appear to alter the risk of catheter of air produces an air lock in the right ventricular outflow
infection but is used to treat infections after catheter
tract and circulatory obstruction. Larger emboli mark-
removal.
edly increase pulmonary vascular resistance and cause
CATHETER EMBOLISM respiratory distress and pulmonary edema. 30 A slow
infusion of air into the vascular space of dogs increases
Catheter embolism occurs when a fragment of the cathe-
pulmonary artery and CVPs and produces a progressive
ter becomes free and is carried by blood flow until it
decrease in arterial blood pressure. Ultimately, arterial
lodges in the heart or a pulmonary artery. This may occur
blood pressure is markedly reduced, and cardiovascular
in any of the following circumstances: collapse occurs.
1. The catheter is accidentally cut during bandage The best approach to treatment of air embolism is to
removal. immediately attempt to aspirate air from the right atrium
2. A through-the-needle catheter is advanced, then
and ventricle if a central venous catheter is in place. If this
pulled back into the needle shaft and sheared off by
is not possible, the animal may be positioned in left lateral
the needle bevel.
recumbency to trap gas in the right ventricular apex and
3. The needle within an over-the-needle catheter is par-
allow blood to flow through the right ventricular outflow
tially withdrawn and then reinserted while the catheter
tract. However, one group found that no one position
tip is still within the vein. If the flexible catheter tip is
was better than another to resuscitate dogs with air
bent to the side, the needle catches on the catheter 26
embolism. Standard cardiopulmonary resuscitation
shaft and amputates the end of the catheter.
procedures should be instituted if the animal develops
4. The catheter shaft disconnects from the catheter hub. 79
respiratory or cardiac arrest.
If catheter amputation is observed, a tourniquet is
immediately applied proximal to the venipuncture site EXSANGUINATION
to hold the embolus and prevent further migration.
If the catheter is made of radiopaque material, the area Exsanguination is possible whenever the unobserved ani-
is radiographed to identify the embolus position, and it mal disconnects the catheter or administration tubing.
is removed surgically if possible. Long fragments that Metal floor grates pose a unique threat: they can snag
have migrated to the right ventricle may be removed with and separate tubing connection sites, and during the
a transvenous loop snare under fluoroscopic guid- resulting hemorrhage, blood dripping to the cage floor
ance. 15,23 Catheter embolization is best prevented by underneath the grate may be difficult to see.
careful technique during catheter insertion and removal. Disconnections are particularly likely in dogs that change
A misplaced catheter is never withdrawn while the needle position frequently. Blood loss may be most severe
is left in place; instead, the catheter and needle are through cephalic vein catheters when an animal is in ster-
withdrawn together as a unit. nal recumbency with its elbows flexed. Anchoring the