Page 359 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

Introduction to Fluid Therapy 349

cardiovascular system to handle the fluid load effectively fever, or cardiac murmurs. If any of these signs are
and could result in pulmonary edema caused by left-sided observed, the catheter should be removed, its tip
heart failure. In addition to the volume of fluid cultured, the patient started on appropriate antibiotic
administered, other factors that may affect CVP include therapy, and a new catheter placed in another vein.
heart rate, vascular capacity, and cardiac contractility. A Complications related to catheter placement include bac-
reduction in any of these three parameters could cause terial endocarditis, thrombophlebitis, thromboembo-
an increase in CVP. lism, and migration of a catheter fragment. When not
The Frank-Starling curve (Figure 14-8) relates stroke in use, the catheter should be irrigated with a small vol-
volume (SV) to left ventricular end-diastolic pressure ume (<1 mL) of a solution containing between 1 and 5
(LVEDP). If there is no obstruction across the mitral U of heparin per milliliter of 0.9% NaCl (“heparinized
valve, left atrial pressure (LAP) should equal LVEDP, a saline”). The complications of fluid therapy are discussed
measure of cardiac function. PWP measured with a further in Chapter 16.
Swan-Ganz catheter is an estimate of LAP. Generally, WHEN SHOULD FLUID
there is a direct relationship between right atrial pressure
(RAP) and LAP. Thus measuring CVP gives an indirect THERAPY BE
indication of LVEDP. Without cardiac dysfunction, DISCONTINUED?
CVP correlates well with PWP and LAP. In one study,
pulmonary artery diastolic pressure and PWP increased Ideally, fluid therapy is discontinued when hydration is
before CVP in dogs receiving an infusion of lactated restored and when the animal can maintain fluid balance
Ringer’s solution. 8 on its own by oral intake of food and water. As the animal
recovers, fluid therapy usually is tapered by decreasing the
COMPLICATIONS OF FLUID THERAPY volume of fluid administered by 25% to 50% per day. If an
Signs of overhydration occur when fluid is administered animal remains anorexic for more than 3 to 5 days, enteral
too rapidly. These may include serous nasal discharge, or parenteral nutritional therapy must be considered. Par-
chemosis, restlessness, shivering, tachycardia, cough, enteral nutrition is discussed in Chapter 25.
tachypnea, dyspnea, pulmonary crackles and edema, asci-
tes, polyuria, exophthalmos, diarrhea, and vomiting. 8
Expected laboratory abnormalities include a reduction REFERENCES
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0
10 20 10. DiBartola SP. Disorders of fluid, acid-base, and electrolyte
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Figure 14-8 Frank-Starling law of the heart relating stroke volume (contemporary issues in small animal practice). New York:
(SV) to left ventricular end-diastolic pressure (LVEDP). (From Rose Churchill Livingstone; 1985. p. 137.
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