Page 94 - Small Animal Internal Medicine, 6th Edition

66 PART I Cardiovascular System Disorders

sodium fluid (such as 0.45% NaCl with 2.5% dextrose) with moderate activity is encouraged, as long as excessive respira-
added KCl is administered at a conservative rate (for example, tory effort or fatigue is not induced. Bursts of strenuous
VetBooks.ir 15 to 30 mL/kg/day IV). Alternatively, 0.45% NaCl with activity should be avoided.
2.5% dextrose or LRS can be administered subcutaneously.
DIURETICS
Potassium supplementation at a maintenance rate is pro-
vided by 0.05 to 0.1 mEq/kg/h (or more conservatively, Diuretic therapy remains fundamental for the long-term
0.5-2 mEq/kg/day). For animals with hypokalemia, higher management of CHF because of its ability to decrease car-
+
rates are used: 0.15 to 0.2 mEq/kg/h for mild K deficiency; diogenic pulmonary edema and effusions (see Table 3.3).
0.25 to 0.3 mEq/kg/h for moderate deficiency; and 0.4 to Furosemide (and other loop diuretics) interferes with ion
+
0.5 mEq/kg/h for severe deficiency. Serum K concentration transport in the loop of Henle and has the potent ability to
measurement in 4 to 6 hours is advised when supplementing promote both salt and water loss. Diuretics of other classes,
for moderate to severe deficiency. Hyponatremia and wors- such as potassium-sparing agents and thiazides, are some-
ened fluid retention can develop after administering low- times combined with furosemide for more intense diuresis
sodium IV solutions in some patients. These require a more in patients with advanced heart failure. Given to excess,
balanced crystalloid solution. Other supportive therapies for diuretics promote excessive volume contraction and activate
CHF and any underlying disease(s) depend on individual the renin-angiotensin-aldosterone cascade. Diuretics also
patient needs. Parenteral fluid administration is discontin- can exacerbate preexisting dehydration or azotemia. There-
ued as the animal is able to resume oral food and water fore the indication for their use in such animals should be
intake. clearly established, and the lowest effective dose should be
used.
MANAGEMENT OF CHRONIC Furosemide
HEART FAILURE Furosemide is the loop diuretic used most widely for cats
and dogs with heart failure (also see p. 61). It acts on the
GENERAL CONSIDERATIONS ascending limb of the loop of Henle to inhibit active Cl , K ,
−
+
+
A general approach to chronic heart failure therapy is pre- and Na cotransport, thereby promoting excretion of these
+
++
++
sented in this section. Additional information is found in the electrolytes and H ; Ca and Mg are also lost in the urine.
chapters describing different diseases. Long-term heart Loop diuretics also can increase systemic venous capaci-
failure management in dogs with chronic mitral valve disease tance, possibly by mediating renal prostaglandin release. In
or DCM generally involves a combination of furosemide, addition, furosemide may promote salt loss by increasing
pimobendan, an ACEI (usually enalapril or benazepril), and total renal blood flow and preferentially enhancing renal
the addition of spironolactone. A diet moderately reduced in cortical flow. The loop diuretics are well absorbed when
salt also is recommended for most heart failure patients. given orally. After oral administration, diuresis occurs within
Therapy is tailored to the individual animal’s needs by adjust- 1 hour, peaks between 1 and 2 hours, and may last for 6
ing dosages, adding or substituting drugs, and modifying hours. Furosemide is highly protein bound; about 80% is
lifestyle or diet. Pleural effusion and large-volume ascites actively secreted unchanged in the proximal renal tubules,
that accumulate despite medical therapy should be drained with the remainder excreted as glucuronide.
to facilitate respiration. Likewise, pericardial effusion that Although aggressive furosemide treatment is indicated
compromises cardiac filling must be drained (see Chapter 9). for acute, fulminant pulmonary edema, the smallest effective
As heart disease progresses, more aggressive therapy usually doses should be used for chronic heart failure therapy. The
is necessary. dosage will vary depending on the clinical situation. Respira-
Exercise restriction helps reduce cardiac workload regard- tory pattern, hydration, body weight, exercise tolerance,
less of heart failure etiology. For animals with active CHF, renal function, and serum electrolyte concentrations are
no exercise should be allowed until all signs of congestion used to monitor response to therapy. Furosemide (or other
have been well controlled. Strenuous exercise can provoke diuretic) alone is not recommended as the sole treatment for
dyspnea and potentially serious cardiac arrhythmias even in chronic heart failure because it can exacerbate NH activation
animals with compensated CHF. However, regular mild to and reduce renal function.
moderate activity (as tolerated) is thought to be beneficial Adverse effects usually are related to excessive fluid and/
for patients with no clinical signs of congestion (i.e., com- or electrolyte losses. Lower doses are used in cats because
pensated heart failure). Chronic heart failure is associated they are more sensitive to the drug than dogs. Although
with skeletal muscle changes that lead to fatigue and dyspnea. hypokalemia is the most common electrolyte disturbance, it
Physical training is known to improve cardiopulmonary is unusual in dogs that are not anorexic. Excessive diuresis
function and quality of life in human patients with chronic can result in hyponatremic, hypochloremic alkalosis.
heart failure. This is partly mediated by improvement in
vascular endothelial function and restoration of flow- Other Loop Diuretics
dependent vasodilation. Although it is difficult to know how Other more potent loop diuretics are sometimes used
much exercise is best, regular (not sporadic) mild to instead of furosemide. Torsemide (dosed initially at one