Page 361 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

CHAPTER • 15

Technical Aspects of Fluid Therapy

Bernie Hansen

Hospitalized veterinary patients frequently require paren- composition of fluid administered subcutaneously
teral fluid therapy for several days, sometimes with com- should ideally be comparable with that of extracellular
plex combinations of intravenous fluids and drugs that fluid because electrolyte-free or hypertonic fluids are
require specialized catheters and delivery techniques. associated with higher complication rates. 2,24,68 In
This chapter will provide an overview of the technical humans, subcutaneous fluids can be supplemented with
aspects of delivering fluids and mediations to patients potassium at a concentration up to 40 mEq/L and in
by parenteral routes, with emphasis on intravenous the author’s experience this concentration is usually
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techniques. There have been only a few reports of clinical well-tolerated by companion animals.
studies comparing therapy methods or identifying The potential for pain, inflammation, and electrolyte
complications in veterinary patients, and many of the imbalances from a large volume of subcutaneous electro-
principles described in this chapter are adapted from lyte-free fluid may be a realistic concern in small animals;
human medical practice, extrapolated from experimental therefore it is prudent to avoid subcutaneous administra-
work on animal models, or based on the author’s experi- tionoflargevolumesoflow-sodiumfluidstocatsandsmall
ence in a veterinary teaching hospital intensive care unit. dogs. Other potential complications include infection
resulting in subcutaneous cellulitis and skin necrosis from
ROUTES OF FLUID caustic or hypertonic fluids or fluids administered under
ADMINISTRATION high pressure into an unyielding subcutaneous space.
The volume administered at any single site is limited by
The most frequently used routes of parenteral therapy are the distensibility of subcutaneous tissue. Therefore fluids
intravenous, intraosseous, and subcutaneous. Intraperi- are usually administered in the subcutaneous space over
toneal administration of fluids is potentially hazardous the dorsal neck and cranial trunk, where loose connective
and offers no significant advantages over other routes; tissue is abundant. Although the addition of hyaluroni-
therefore it is not discussed further. The route of paren- dase to fluids for hypodermoclysis therapy in humans
teral fluid administration is chosen based on the underly- increases the rate of absorption of fluid, there is no evi-
ing disorder and its severity, therapeutic goals, fluid dence that the addition of this enzyme improves patient
composition, and characteristics of the patient, including tolerance. 12,68 However, it may be of value in dogs and
species, size, age, and accessibility of veins. cats with limited distensibility of their subcutaneous tis-
sue when rapid administration is necessary because of
SUBCUTANEOUS time constraints. The fluid should be warmed to body
Subcutaneous fluid administration (hypodermoclysis) is a temperature before administration to limit patient dis-
convenient and inexpensive route of maintenance fluid comfort and enhance local blood flow and absorption.
therapy for patients that do not require vascular access The skin should be cleansed with a cotton ball and alcohol
for other purposes. It should be reserved for relatively to remove debris from the surface. Fluid may be
stable animals because peripheral vasoconstriction in ill- administered with a syringe and 22-gauge needle in small
ness may limit absorption of fluids and prevents successful animals or by gravity flow with a fluid administration set
use of the subcutaneous route. The fluid should be nearly through a 20- to 18-gauge needle in larger animals. One
isotonic (200 to 400 mOsm) to limit discomfort and company markets a subcutaneous catheter (Endo-Sof,
complications. Although sodium-free or low-sodium Global Veterinary Products, New Buffalo, Mich.)
fluids are tolerated by many human patients, the designed to be implanted for repeated use. Although

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