Page 540 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

528 FLUID THERAPY

sinusoid is more leaky than other capillary beds. Conse- BOX 21-6 Causes of Azotemia in
quently, considerable protein can pool in the peritoneal
cavity of a cardiac patient with ascites, and the protein Heart Failure
concentration in ascitic fluid can exceed 3.5 g/dL.
Repeated abdominal paracentesis also can contribute to Renal Disease
total body depletion of protein. Plasma volume contrac- Preexisting renal disease
tion after diuretic therapy usually increases serum protein Renal thromboembolism (feline cardiomyopathy,
concentration, but total serum protein concentration bacterial endocarditis)
may remain subnormal or in the low-normal range. Heartworm disease (glomerulonephritis, amyloidosis)
HypoproteinemiaindogswithCHFcausedbyheartworm Inadequate Renal Blood Flow
disease may be related to glomerular injury and renal Dehydration
protein loss. Dramatic proteinuria has been observed in Anorexia and hypodipsia
heartworm-infected dogs with concurrent renal Vomiting
amyloidosis. Water restriction (by the client or veterinarian)
There are a number of clinical consequences of Severe heart failure (low cardiac output, hypotension)
hypoproteinemia in CHF. Effective plasma volume Drug Related
is decreased further when moderate to severe
Volume contraction resulting from diuretics
hypoalbuminemia develops. As demonstrated in experi- Angiotensin-converting enzyme inhibitors (hypotension,
mental studies of dogs with left atrial hypertension, edema efferent arteriolar vasodilatation)
is more likely to occur at lower venous pressures when Vasodilator therapy (hypotension)
60
there is hypoalbuminemia. Marked protein loss through Digitalis intoxication (secondary to anorexia or vomiting)
the gut may indicate a need for additional nutritional
support. Hypoalbuminemia also predisposes to metabolic
alkalosis (see Chapter 10). Infusions of plasma may be
required in the patient with severe hypoalbuminemia
and may promote a substantial diuresis. THERAPY OF HEART FAILURE
The initial goals of therapy in CHF include increasing
RENAL FUNCTION TESTS arterial PO 2 , reducing oxygen demand, establishing a

The blood urea nitrogen (BUN) and serum creatinine diuresis, and unloading the ventricles while supporting
concentrations may increase in CHF, indicating reduced ABP, tissue perfusion, and renal function. Inotropic
support is also beneficial in many patients with acute
glomerular filtration. There are several reasons for devel-
CHF. Long-term treatments are aimed at preventing
opment of azotemia in heart failure, but the most
fluid retention, load reduction, maintaining cardiac out-
common are preexisting renal disease, reduced cardiac
put to support exercise and organ perfusion, and blunting
output, and iatrogenic problems (i.e., overzealous use
progressive neurohormonal injury to cardiac and vascular
of diuretics and ACE inhibitors). Common causes of azo-
tissues.
temia in dogs or cats with CHF are listed in Box 21-6.
Approximately 25% of dogs with CHF are azotemic at HOSPITAL THERAPY
the time of admission. 12 The magnitude of azotemia gen-
The first goals are attained with supplemental oxygen
erally is mild to moderate. Renal function should be
therapy and sedation as needed to reduce distress or air
assessed both before and after initiation of therapy. Azo-
hunger. Traditionally, dogs in heart failure have been
temia is common in patients with dilated cardiomyopathy
sedated with morphine (initial dosage of 0.05 to
and cardiogenic shock and may improve only after aggres-
0.1 mg/kg intramuscularly), but vomiting after mor-
sive therapy with inotropic agents and reestablishment of
hydration (see Therapy of Heart Failure section). The phine injection occasionally precipitates cardiac arrest.
development of azotemia in a patient with previously nor- For this reason, we prefer butorphanol (0.2 to 0.3 mg/
mal renal function suggests overzealous diuresis, an kg, intramuscularly) as an effective and safer sedative
adverse reaction to an ACE inhibitor, inappropriate water for dogs in CHF. Stress in cats can be alleviated with an
restriction, or a worsening of heart failure. Return of acepromazine-butorphanol combination (0.05 to
serum creatinine concentration to normal after intrave- 0.1 mg/kg acepromazine and 0.25 mg/kg butorphanol
nous or subcutaneous administration of a crystalloid intramuscularly). In hypothermic or hypotensive cats,
solution or after reduction of the drug dosage indicates butorphanol is used but without acepromazine. In the
a prerenal or drug-induced cause of azotemia. Acute renal presence of moderate to severe pleural effusion,
failure that responds promptly to intravenous administra- thoracocentesis is performed to decrease pulmonary atel-
tion of a crystalloid solution has been observed in some ectasis. Tense ascites, sufficient to impair ventilation, is
reduced by abdominocentesis. About one third to one
dogs treated with ACE inhibitors.