Page 544 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

532 FLUID THERAPY

intestinal malabsorption of furosemide. Low dosages of medically, and allow the patient’s kidneys to correct any
furosemide (e.g., 1 to 2 mg/kg every 12 hours or every fluid and electrolyte disturbances. This approach may lack
24 hours), in combination with an ACE inhibitor and technical sophistication, but it often works well in the
pimobendan, are quite effective in patients with mild clinical setting. Aside from mild hypochloremia, dogs
heart failure. However, patients with renal failure or are especially resilient to the complications of diuretic
low cardiac output may require higher dosages to deliver therapy provided their intake of water and food is ade-
sufficient amount of active drug to the renal tubules. 55 quate. In fact, it is common to observe a dog or cat begin
In the case of furosemide, gradually increasing the dose drinking shortly after receiving successful therapy for life-
and frequency from 2 mg/kg every 12 hours to 6 mg/kg threatening pulmonary edema or pleural effusion.
every 8 hours may be sufficient to maximally inhibit renal Some patients with heart failure do develop problems
tubular chloride and sodium reabsorption. Once this that require fluid and electrolyte supplementation.
“ceiling” effect is achieved, no further diuresis develops Indications for fluid therapy in the patient with CHF
with increasing the dosage. 142 This “ceiling” effect is include persistent anorexia, dehydration, renal failure,
especially apparent with loop diuretics (e.g., furosemide, moderate to severe hypokalemia, digitalis intoxication,
bumetanide, torsemide), which typically have a short drug-induced hypotension, gastroenteritis, anemia, and
duration of action (see previous Diuretics section). Furo- serious metabolic (e.g., diabetes mellitus), neoplastic,
semide may be poorly absorbed by a congested intes- or infectious diseases. Another indication is the need
tine, 174 and subcutaneous administration of furosemide for intravenous infusion to deliver drugs such as
in patients with refractory ascites and pleural effusion dobutamine, sodium nitroprusside, or lidocaine. Ventric-
should be considered. Frequently, the same dose, given ular filling is impaired in pericardial disease, and this
subcutaneously instead of orally, leads to substantial abnormality may demand volume expansion with paren-
diuresis. We have taught clients to administer one of teral fluid therapy along with pericardiocentesis. When
the daily doses of furosemide subcutaneously to their animals with heart disease undergo general anesthesia, a
animals every other day, and such therapy can be benefi- catheter should be placed and intravenous fluids
cial when used chronically. Combination diuretic therapy administered although at a reduced rate. Hypertrophied
with sequential nephron blockade represents another ventricles may be more difficult to distend unless CVP is
option for the patient with refractory edema or effu- maintained at a normal to slightly increased level. How-
sion. 65,112,115,142 The combination of three diuretics ever, overinfusion of fluids can lead to peracute pulmo-
(furosemide, hydrochlorothiazide, and spironolactone) nary edema in dogs and in cats with marked left
acting on different segments of the nephron (see ventricular hypertrophy, and care must be taken.
Figure 21-5) may be effective in treating dogs with pro- Thus a number of situations may necessitate fluid ther-
gressive ascites or pleural effusion. However, apy in the cardiac patient. What fluid should be infused?
hyponatremia (<130 mEq/L) and hypokalemia are The following recommendations are based on our clinical
contraindications to thiazide diuretics, and thiazide experience and theoretical considerations for fluid, elec-
diuretics often induce profound hyponatremia. When trolyte, and diuretic therapy in patients with CHF. Con-
hydrochlorothiazide is prescribed, the initial dosage trolled, prospective evaluations of such therapy in dogs
should be low, approximately 1 to 2 mg/kg orally every and cats are unavailable. The following discussion
48 hours. Renal function and serum electrolyte considers basic principles of therapy; selection of fluids,
concentrations should be evaluated within 1 week of additives, and rates of administration; monitoring of
treatment before the dosage is increased. the patient (including Swan-Ganz catheterization); and
our approach to some specific problems related to fluid
THERAPY OF FLUID AND therapy in the cardiac patient.
ELECTROLYTE IMBALANCES
IN CONGESTIVE HEART PARENTERAL SOLUTIONS
Fluid Volume
FAILURE
The daily fluid volume is guided by the current state of
edema, estimated maintenance needs (40 to 60 mL/
INDICATIONS kg/day), hydration status, body weight, oral fluid intake,
The cardiac patient, in contrast to many other sick estimated urine output, total serum protein concentra-
animals, is not an ideal candidate for parenteral fluid ther- tion, serum sodium concentration, serum creatinine con-
apy. Volume expansion poses substantial risks in terms of centration, and, when available, CVP and pulmonary
increasing venous pressures, sodium retention, and capillary wedge pressure. It is prudent to consider a mini-
edema. In managing cardiac patients, we prefer to offer mal fluid infusion initially (e.g., no more than 30 to
water (of low sodium content) ad libitum, provide a 40 mL/kg/day) and to assess the effect of fluid therapy
sodium-restricted but palatable diet, treat CHF on the patient and serum biochemical values. The daily