Page 385 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

Technical Aspects of Fluid Therapy 375

COMPLICATIONS OF the pulmonary arteries. When small in mass, these emboli
INTRAVENOUS THERAPY usually go unnoticed, but some fibrin sheaths extend to a
larger thrombus hanging freely from the end of the
catheter and may embolize the lung with significant
EXTRAVASATION consequences (Figure 15-9). 77,87 Another, potentially
Extravasation of fluid and infiltration of surrounding tis- more damaging type of thrombus usually forms at contact 4
sue occur when a catheter is displaced out of the vein. points between the catheter and the vessel or atrial wall.
Needle catheters and stiff plastic catheters are more likely Endothelial injury at these points results in local inflam-
50
to perforate the vessel wall than softer polyurethane or sil- mation and thrombus formation. These thrombi are
icone catheters. Extravasation at a peripheral vein site is more likely to develop when stiff or reactive catheter
heralded by swelling and tenderness. Cooling of the skin materials are used, on long catheters that cross a joint
over the catheter tip may be palpated as a high-pressure or enter the right atrium, and on catheters with frayed
pocket of fluid impairs circulation, especially if room tem- tips. Mural thrombi may grow progressively and eventu-
perature fluids are being administered. If the intravenous ally obliterate the vessel lumen. Complications of these
solution contains irritating drugs such as thiobarbiturates thrombi may be both obvious and serious. 18,74,85 Hepa-
or thiacetarsamide, swelling may be accompanied by rin-bonded catheters result in less fibrin deposition on
increasing pain, heat, redness, and induration followed catheters used experimentally in dogs and reduce the
by necrosis and sloughing of skin and perivascular tissues. incidence of catheter-associated thrombosis in humans,
Signs of central vein extravasation may be absent until at least for a few days. 35,65
large quantities of fluid have been administered. THROMBOPHLEBITIS
Complications of central venous extravasation include
mediastinal or pleural fluid accumulation resulting in dif- Thrombophlebitis represents the most severe end of the
ficulty breathing. This may be identified by evaluation of spectrum of catheter-related vessel damage and may be
physical signs, thoracic radiographs, and fluid analysis. caused by mechanical, chemical, or infectious processes.
Penetration of the right atrium may occur with a catheter Damage to the endothelial lining of the vein initiates both
positioned too deeply in the chest, resulting in accumula- inflammation (phlebitis) and thrombus formation on
tion of blood and fluid in the pericardial sac and cardiac the vessel wall. Early signs of thrombophlebitis include
tamponade. tenderness and erythema of the skin over the vessel and
Extravasation of a short catheter at a peripheral site may palpable induration of the vessel itself. If left untreated,
be detected early by frequent inspection of the vein. Cath- these early signs progress, and the vessel may become
eter positioning and patency should be evaluated before completely thrombosed. This is recognized as severe
injecting any irritating substance. This may be accom- hardening of the vessel and may be accompanied by com-
plished by aspirating blood and administering a test injec- plete occlusion and inability to infuse fluids. Purulent dis-
tion of sterile saline while observing the perivascular area. charge may be noted from the catheter site. Systemic
To aspirate blood without disconnecting a fluid adminis- signs of inflammation including fever and leukocytosis
tration line, lower the fluid container below the level ofthe may be present, although some animals develop severe
catheter tip. Gravity flow pulls blood back until it is visible local reactions in the absence of systemic signs.
at the catheter hub or administration set tubing. Other Mechanical damage is minimized by selecting small
recommendations to minimize the risk of extravasation catheters and large veins; by using soft, inert catheter
include the following: (1) avoid winged needle catheters materials; and by securely anchoring the catheter to the
for prolonged infusions; (2) use the smallest and softest skin to minimize in-and-out motion. If an indwelling
catheter that will perform adequately; (3) select a large catheter crosses a joint, the limb should be immobilized
vein at a location well away from a joint; and (4) limit to limit trauma to the vascular endothelium. Irritating
movement of peripheral vein catheters located near joints drugs should be administered after adequate dilution
by immobilizing the limb with a heavy bandage or splint. and only into central veins with high blood flow rates
to minimize local endothelial injury. Hypertonic
THROMBOSIS solutions with an osmolality higher than 600 mOsm/
Thrombosis is a common complication of indwelling kg should be administered only into central veins when-
catheters. Catheters left in place for more than a few ever possible.
hours are covered with a fibrin sheath and platelets.
Within days, cells from the injured vessel wall invade this INFECTION
sheath. If left in place for a week or longer, this process Any intravenous catheter supports infection, and there
yields a sheath composed of smooth muscle and collagen are multiple routes for possible exogenous catheter con-
and covered by endothelium. 86 This sheath strips away tamination. In humans and experimental animal models,
from the catheter surface during catheter removal and catheter colonization has been documented from the skin
either is incorporated in the vessel wall or embolizes at the exit site, 3,13,36,73 contamination of the hub