Page 339 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

CHAPTER • 14

Introduction to Fluid Therapy

Stephen P. DiBartola and Shane Bateman

She had apparently reached the last moments of earthly existence, and now nothing could injure her—indeed, so
entirely was she reduced, that I feared I should be unable to get my apparatus ready ere she expired. Having inserted
a tube into the basilic vein, cautiously—anxiously, I watched the effects; ounce after ounce was injected, but no
visible change was produced. Still persevering, I thought she began to breathe less laboriously, soon the sharpened
features, and sunken eye, and fallen jaw, pale and cold, bearing the manifest impress of death’s signet, began to
glow with returning animation; the pulse which had long ceased, returned to the wrist; at first small and quick, by
degrees it became more and more distinct, fuller, slower, and firmer, and in the short space of half an hour, when six
pints had been injected, she expressed in a firm voice that she was free from all uneasiness, actually became jocular,
and fancied that all she needed was a little sleep; her extremities were warm, and every feature bore the aspect of
comfort and health.
Thomas Latta, describing the first use of intravenous fluid therapy in a human patient with cholera in a letter to
the Lancet, 1832.

Fluid therapy is supportive. The underlying disease pro- 4. What type of fluid should be given?
cess that caused the fluid, electrolyte, and acid-base 5. By what route should the fluid be given?
disturbances in the patient must be diagnosed and treated 6. How rapidly should the fluid be given?
appropriately. Normal homeostatic mechanisms allow the 7. How much fluid should be given?
clinician considerable margin for error in fluid therapy, 8. When should fluid therapy be discontinued?
provided that the heart and kidneys are normal. This is
fortunate because estimation of the patient’s fluid deficit IS THE PATIENT SUFFERING
is difficult and may be quite inaccurate. The purpose of FROM A SHOCK SYNDROME
this chapter is to provide an overview of the principles
of fluid therapy. The composition and distribution of THAT REQUIRES IMMEDIATE
body fluids are discussed in Chapter 1, and the technical FLUID ADMINISTRATION?
aspects of vascular access are discussed in Chapter 15.
Fluid therapy potentially consists of three phases: resusci- Shock patients (see Chapter 23) urgently require fluid
tation, rehydration, and maintenance. Most patients in therapy. The presence of altered mental status and cool
shock (see Chapter 23) require rapid administration of extremities in association with tachycardia or severe bra-
a large volume of crystalloid, colloid, or other fluid to dycardia, mucous membrane pallor, prolonged or absent
expand the intravascular space and correct perfusion capillary refill time, reduced or absent peripheral pulses,
deficits. Dehydrated patients also require sustained and hypotension are among the most common physical
administration of crystalloid fluids for 12 to 36 hours examination findings in patients in shock. Such physical
to replace fluid losses from the interstitial and intracellular examination findings in association with a compatible
spaces. Patients with normal hydration unable to con- clinical history are the basis for the decision to institute
sume sufficient water to sustain fluid balance require a resuscitation phase of fluid therapy. Some forms of
maintenance fluid therapy with crystalloid solutions. In shock may be associated with variations in these physical
formulating and implementing a fluid therapy plan, eight examination findings, and it is crucial to understand the
questions should be considered 10,28 : different shock syndromes. (See Chapter 23 for more
1. Is the patient suffering from a shock syndrome that information on shock.)
requires immediate fluid administration? The shock syndromes most likely to respond to
2. Is the patient dehydrated? marked volume expansion of the intravascular space
3. Can the patient consume an adequate volume of water are hypovolemic and distributive shock states. Obstruc-
to sustain normal fluid balance? tive forms of shock often respond favorably to

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