Page 352 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

342 FLUID THERAPY

alkalosis, but this does not occur in animals with relatively concentrations up to 30 to 35 mEq/L without irrita-
normal renal function because the kidneys can efficiently tion. 13 Approximately 10 mL/kg or 50 to 200 mL may
excrete the excess bicarbonate. be administered per site. 34 Fluid is administered under
Crystalloid solutions with preservatives must be the skin along the back from the area of the scapulae to
avoided in cats. Benzoic acid derivatives (e.g., benzyl the lumbar region. Volume overload is unlikely to occur
alcohol, methylparaben, propylparaben, ethylparaben) when fluids are administered subcutaneously in patients
have been added to some solutions for their antimicrobial with no underlying cardiac insufficiency. Furthermore,
effect. Clinical signs in cats receiving fluids with such some owners can use subcutaneous administration to give
preservatives have included behavioral changes, hypersal- fluids at home to animals with chronic disease problems
ivation, ataxia, muscle fasciculations, seizures, dilated (e.g., chronic renal failure).
nonresponsive pupils, coma, and death. 3,9,33 Young cats The subcutaneous route is not adequate for patients
may be at increased risk for these complications. with acute and severe losses (e.g., shock) and is not
recommended for extremely dehydrated or hypothermic
BY WHAT ROUTE SHOULD animals because peripheral vasoconstriction may reduce
FLUIDS BE GIVEN? absorption and dispersion of the administered fluid in
these settings. The volume that may be given is limited
The route of fluid therapy depends on the nature of the by skin elasticity, and this route is not useful in larger
clinical disorder, its severity, and its duration. animals requiring large volumes of fluids. Irritating or
hypertonic solutions must not be used subcutaneously;
INTRAVENOUS only isotonic fluids are recommended. Isotonic fluids
The intravenous route is preferred when the patient is containing bicarbonate precursors other than lactate also
very ill, when there has been severe fluid loss, or when are not recommended for subcutaneous administration.
the fluid loss has been acute. This route also is used dur- Although not harmful, they appear to cause mild local
ing anesthesia to maintain renal perfusion and vascular discomfort and are not well tolerated by veterinary
access for emergencies. The intravenous route provides patients. The subcutaneous administration of 5% dex-
rapid dispersion of water and electrolytes and allows trose in water should be avoided because equilibration
precise dosage. A large volume can be given rapidly, of ECF with a pool of electrolyte-free solution may lead
and hypertonic fluids can be given safely via a large vein. to temporary aggravation of electrolyte imbalance.
This route requires vascular access and close monitoring
during infusion to avoid complications such as ORAL
overhydration, infection, thrombosis, phlebitis, embo- The oral route is most physiologic, and fluids with a wide
lism, and impaired fluid delivery (e.g., obstruction of variety of compositions may be given. Oral fluid therapy is
the catheter by a change in the patient’s limb position). useful for administering hypertonic fluids with high calo-
The veins available for vascular access include the jug- ric density. Fluid can be administered rapidly with mini-
ular, cephalic, lateral saphenous, and femoral veins. There mal adverse effects, and caloric needs can be met.
are advantages and disadvantages of each, but the jugular However, this route should not be used in the presence
vein is most useful because it allows delivery of large of gastrointestinal dysfunction (e.g., vomiting, diarrhea).
volumes, administration of hypertonic or potentially The oral route also is inadequate in animals that have
irritating solutions, measurement of CVP, and repeated had acute or extensive fluid losses because dispersion
venous blood sampling. The cephalic vein also is and use of the administered fluid and electrolytes are
commonly used, but fluid delivery can be hindered by not sufficiently rapid. In anorexic animals without
flexion of the elbow, and extremely hypertonic vomiting or diarrhea, fluid can be administered orally
or irritating solutions should not be used. Intravenous using a number of different techniques (e.g., nasogastric
catheter function and the catheter-skin interface should tube, esophagostomy tube, gastrostomy tube).
be monitored routinely to detect complications.
Catheters that remain clean and free of complications INTRAPERITONEAL
need not be replaced at some routine interval. The types Intraperitoneal administration of fluid allows moderately
of catheters used and their placement are discussed in rapid absorption of large volumes. Only isotonic fluids
Chapter 15. can be used because administration of hypertonic fluids
results in further contraction of the extracellular compart-
SUBCUTANEOUS ment as water enters the peritoneal space by osmosis.
The subcutaneous route is convenient for maintenance Peritonitis also is a potential complication of this route.
fluid therapy in small dogs and cats. The subcutaneous The intraperitoneal route is not used commonly
space in dogs and cats can accommodate relatively large except to perform peritoneal dialysis as described in
volumes of fluid, and potassium can be used in Chapter 28.