Page 545 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

Fluid and Diuretic Therapy in Heart Failure 533

volume should be infused slowly and distributed evenly determined, but it seems prudent to limit daily sodium
over 24 hours to reduce the risk of pulmonary edema intake to less than 12 mg/kg/day in dogs with end-stage
and pleural effusion. The choice of fluid depends largely cardiac failure. The average sodium content of Feline Pre-
on concerns about sodium retention. The intravenous scription Diet H/d (Hill’s Pet Nutrition) is about
route of administration is preferred, but either 0.45% 354 mg per 14.25-oz can (70 mg/100 kcal; 506 kcal/
NaCl in 2.5% dextrose or lactated Ringer’s solution can can), and a 5.5-oz can of CV-Formula contains about
be given subcutaneously if necessary. When the patient 112 mg of sodium (50 mg/100 kcal; 223 kcal/can). Die-
can drink, fluid therapy is tapered, low-sodium fresh tary sodium requirements for cats with CHF are not avail-
water is supplied ad libitum, and dietary sodium intake able and their acceptance of sodium-restricted diets
is regulated while ensuring a palatable diet. appears lower than for many dogs.
The CHF patient continues to retain sodium, and The clinician also must be mindful of the sodium con-
diuretics must be given concurrently to prevent untoward tent of crystalloid solutions. Normal saline solution (0.9%
retention of sodium derived from the diet or crystalloid NaCl) contains 154 mEq of sodium per liter. Therefore
therapy. Although it may seem paradoxical to administer 500 mL of 0.45% NaCl in 2.5% dextrose contains
diuretics to a patient receiving fluid therapy, these drugs 37.5 mEq (862 mg) of sodium, an amount that conceiv-
are important adjuncts to the overall fluid and electrolyte ably represents the minimal daily requirement for a
management in treatment of the edematous cardiac normal 75-kg dog. If severe metabolic acidosis in a
patient. 64,75,142 Diuretic therapy also promotes redistri- cardiac patient must be treated with sodium bicarbonate,
bution of extracellular water from edematous sites to an additional sodium load is imposed because there are
the venous system. Furosemide also acts initially to 23 mg of sodium per milliequivalent of sodium bicarbon-
increase GFR (possibly by releasing vasodilating ate. Metabolic acidosis in those with CHF often is caused
prostaglandins). After diuresis and contraction of the by lactic acidosis, a condition that may not be responsive
plasma volume, however, cardiac filling and GFR to bicarbonate treatment, and is best treated by
decrease unless the patient drinks adequately or receives improving cardiac output (see Chapter 10).
supplemental fluid therapy. A fine balance is required, Based on these concepts, either 5% dextrose or 0.45%
and the clinician must learn to control the risk of edema NaCl in 2.5% dextrose, supplemented with potassium
while preventing an increase in BUN or serum creatinine chloride, is recommended when routine fluid therapy is
concentration. Human BNP (nesiritide) may represent required for rehydration, maintenance of hydration, or
another option for preventing fluid retention in cardiac drug infusions in patients with CHF. Unfortunately, ther-
patients receiving fluid therapy; however, this drug also apy with 5% dextrose or 0.45% NaCl in 2.5% dextrose is
increases the serum creatinine in some human patients. sometimes associated with inadequate free-water excre-
tion, weight gain, hyponatremia, and hypokalemia, espe-
Sodium cially when 5% dextrose is administered. These electrolyte
Dogs with cardiac failure do not respond normally to a disturbances are similar to those observed when some
sodium load, and after saline infusion, marked retention dogs and cats with severe CHF are treated with diuretics
9
of sodium and water can occur. Healthy dogs can main- and given free access to water. Development of
tain normal serum sodium concentration with a diet hyponatremia in this clinical setting is especially common
containing sodium at only 0.5 mEq/kg/day (11.5 mg/ in cats. Because of the potential for hyponatremia, either
kg/day). 100,106 This amount is equivalent to approxi- 0.45% NaCl in 2.5% dextrose or a balanced crystalloid,
mately 175 mg of sodium or 435 mg of sodium chloride such as lactated Ringer’s solution or Plasmalyte, is used
per day for a 15-kg dog. In Canine Prescription Diet H/d as a replacement fluid for cardiac patients with dehydra-
(Hill’s Pet Nutrition, Topeka, Kan.), there are approxi- tion. The short-term use (<12 hours) of such sodium-
mately 23 mg of sodium and 542 kcal in a 418-g serving replete fluids usually is well tolerated, provided the
of canned food. The H/d dry product contains about volume is small and the rate of infusion is slow (e.g.,
15 mg of sodium and 407 kcal in a 99-g serving. Another 2.5 to 5 mL/kg/hr). Therapy of hyponatremia is
highly sodium-restricted diet, CV-Formula (Nestle ´ discussed later and in Chapter 3.
Purina PetCare Co., St. Louis), contains about 20 mg
of sodium and 638 kcal in a 354-g serving. Early Cardiac Potassium Supplementation
Support Diet (Royal Canin) delivers 61 mg of sodium Potassium (as the chloride salt) is administered routinely
and 300 kcal in a 73-g, dry food serving. A 2.5-oz jar to cardiac patients receiving fluid therapy. Administration
of chicken baby food contains approximately 40 to of glucose-containing, salt-poor solutions, especially dur-
60 mg of sodium. A number of over-the-counter dog ing diuretic therapy of anorexic patients, tends to
foods also are relatively restricted in sodium (e.g., Cycle decrease serum potassium concentration. Typical intrave-
Senior [Del Monte, San Francisco], Alpo Senior [Nestle ´ nous potassium dosages of 0.5 to 2.0 mEq/kg/day are
Purina PetCare Co.]). The extent of dietary sodium given using accepted guidelines for intravenous adminis-
restriction required in animals with CHF has not been tration of potassium (see Chapter 5). For hypokalemic