Page 345 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

Introduction to Fluid Therapy 337

exceeded. The main advantages of colloids are that more potassium, 71 mEq/L chloride, and 33.5 g/L dextrose.
of the administered solution remains in the plasma com- It would provide 133 kcal/L and have an osmolality of
partment and there generally is thought to be less risk of 328 mOsm/kg. An alternative maintenance solution
edema in patients with an intact endothelium. Colloids may be made by mixing one part lactated Ringer’s solu-
are discussed in detail in Chapter 27. tion with two parts 5% dextrose and adding 20 mEq KCl
Crystalloid solutions are equally effective in expanding per liter of final solution. This solution has the following
the plasma compartment, but 2.5 to 3.0 times as much approximate composition: 43 mEq/L sodium, 21 mEq/L
crystalloidsolutionmustbegiven(comparedwithacolloid potassium, 56 mEq/L chloride, 1 mEq/L calcium,
solution) because the crystalloid is distributed to other 9 mEq/L lactate, and 33.5 g/L dextrose. It would provide
sites(e.g.,interstitialcompartment,intracellularcompart- 133 kcal/L and have an osmolality of 317 mOsm/kg.
ment). 26,27,39 Pulmonary capillaries normally are more Another commonly used crystalloid is 5% dextrose.
permeable to protein, resulting in a higher interstitial Administering 5% dextrose is equivalent to giving water
concentration of protein and more resistance to leakage because the glucose is oxidized to CO 2 and water. In fact,
of fluid from capillaries. 30 Peripheral edema is more likely the main reason for giving 5% dextrose is to correct a pure
to occur after crystalloid administration because muscle water deficit. Except in very small animals, administration
and subcutaneous capillaries are less permeable to protein. of 5% dextrose cannot be relied on to maintain daily caloric
Crystalloid solutions also can be classified as replace- needs because 5% dextrose contains only 200 kcal/L.
ment or maintenance solutions. The composition of Consider a normal, active 10-kg dog. Its maintenance
replacement solutions (e.g., lactated Ringer’s, energy requirement (MER) is approximately 740 kcal:
Normosol-R, Plasma-Lyte 148) resembles that of ECF
(Figure 14-2). Maintenance solutions (e.g., Normosol- MER ðkcalÞ¼ 60 body weight ðkgÞþ 140
M, Plasma-Lyte 56) contain less sodium (40 to 60
mEq/L) and more potassium (15 to 30 mEq/L) than To provide this number of kilocalories from 5% dextrose
replacement fluids. A simple maintenance solution can (200 kcal/L), almost 4 L of fluid must be administered
be formulated by mixing one part 0.9% NaCl with two per day. Such a volume is almost seven times more than
parts 5% dextrose and adding 20 mEq KCl per liter of the daily maintenance requirement for fluid in this dog.
final solution. The approximate composition of such a Administration of 4 L of 5% dextrose over a 24-hour
fluid would be 51 mEq/L sodium, 20 mEq/L period would initiate a diuresis that would impair use of

600
300

500
250 Glucose

Solution (mEq/L) 200 HCO – K + K + 400 H 2 O (mOsm/kg)

300
150
3
++
++
Ca
Ca
200
100 Lactate – Lactate –
Na + Cl – Na + Cl – Glucose Na + Cl – Na + Cl –
100
50
HPO 4 =
SO =
4
K + Org.Ac. =
Mg ++ Ca ++ Prot n+
0 5% Dextrose Lactated 5% Dextrose 0
Name Plasma Normal
saline in water Ringer’s in lactated
Ringer’s
Composition 9 g NaCl 50 g Glucose 50 g Glucose per
in 1 L of in 1 L of liter of lactated
solution solution Ringer’s solution
Synonyms Isotonic Saline 5% D/W Ringer’s lactate
Figure 14-2 Comparison of electrolyte composition of plasma with that of commonly used crystalloid
solutions. (From Muir WW, DiBartola SP. Fluid therapy. In: Kirk RW, editor. Current veterinary therapy VIII.
Philadelphia: WB Saunders, 1983: 30.)