Page 225 - Clinical Small Animal Internal Medicine

19 Management of Heart Failure 193

A common strategy in patients with refractory CHF is enemas, diuretic reduction, or cautious restriction of
VetBooks.ir to layer additional diuretics onto the existing furosemide water intake can be performed. Hyponatremia is consid-
ered a poor prognostic sign in dogs with chronic CHF.
therapy. This strategy of “sequential nephron blockade”
involves adding diuretics that act at sites other than the
loop of Henle. Addition of hydrochlorthiazide (0.5 mg/kg Additional Vasodilators
SID or 1 mg/kg q48 h) or, if not already being adminis-
tered, spironolactone (2 mg/kg/day) can be considered. Patients with refractory CHF might benefit from vasodi-
Adverse reactions to high‐dose or multiple diuretics lator therapy in addition to standard administration of
include severe azotemia, anorexia, dehydration, and ACEI. In these instances, use of arterial vasodilators
electrolyte abnormalities. This is particularly important such as hydralazine or amlodipine is occasionally consid-
in patients are partially anorexic or eating diets severely ered. Due to the perceived relationship between after-
restricted in sodium. load (which is approximated by the aortic systolic blood
Another option to improve diuresis is to replace furo- pressure) and degree of mitral regurgitation, arterial
semide with another diuretic such as torsemide (alterna- vasodilators are often considered in dogs with refractory
tive spelling, torasemide). Torsemide, like furosemide, is CHF due to MMVD, but their efficacy in reducing the
a loop diuretic. In humans, torsemide is characterized by degree of regurgitation is unknown. The limiting factor
more reliable gastrointestinal absorption, a longer half‐ in the administration of additional vasodilators is sys-
life, and adjunctive antialdosterone effects. In dogs, tor- temic hypotension, and vasodilators are not prescribed
semide has a longer half‐life and is well suited for both if the baseline systemic systolic blood pressure is
resolution and long‐term control of CHF. Torsemide is <100 mmHg. Amlodipine (0.–0.4 mg/kg PO BID in dogs
markedly more potent than furosemide and the recom- and cats) is a calcium channel blocker with potent anti-
mended dose range for treatment of CHF in dogs is 0.1– hypertensive properties. A starting dosage of 0.1 mg/kg
0.6 mg/kg SID. Dogs with mild CHF typically require BID and uptitrating over two weeks to the higher dosage
0.1–0.3 mg/kg SID and any increases in dose in response of 0.3–0.4 mg/kg BID is typically well tolerated. Prior to
to reoccurrence of clinical signs are done in 0.1 mg/kg/ the widespread use of amlodipine as an antihypertensive
day increments. In dogs with CHF refractory to existing agent in both dogs and cats, hydralazine was often used
doses of furosemide (typically >6 mg/kg/day), replace- in dogs and continues to be an option in refractory cases
ment of furosemide involves replacing the total daily of canine MMVD. Hydralazine (0.5–2 mg/kg PO BID) is
dose of furosemide with 1/10th to 1/20th the dosage of a direct‐acting vasodilator with a shorter half‐life and
torsemide. For example, if the existing furosemide dose more rapid onset of action than amlodipine. Thus, acute
was 25 mg BID, the equivalent torsemide dose would be hypotension and reflex tachycardia are more common
1/10th to 1/20th of 50 mg or 2.5–5 mg per day. There are than with amlodipine. In emergency situations where
limited reports of use of torsemide in cats. The dose acute arterial vasodilation is needed (i.e., acute life‐
range in cats is likely similar to that in dogs. Torsemide, threatening CHF or systemic hypertension), hydralazine
like all diuretics, requires close monitoring of renal func- is considered. Common adverse effects of hydralazine
tion, electrolytes, blood pressure, hydration status, and include hypotension and gastrointestinal signs.
body weight. Oral nitrate compounds such as sustained‐release
Clinicians might wish to consult with a specialist to isosorbide dinitrate or mononitrate (0.5–2.0 mg/kg PO
discuss individualized treatment and monitoring plans BID in dogs and cats) are infrequently used as a venous
in patients with refractory CHF. In general, the need for vasodilator. Administration is usually performed when
diuretics in addition to or in place of furosemide in signs of congestion persist despite diuretic usage or fur-
patients with refractory signs of CHF is considered a ther increases in diuretic usage are hindered by concom-
poor prognostic sign. itant azotemia or arterial hypotension. Due to rapid
Volume depletion is caused by high dose and potent development of tolerance, oral nitrates are typically
diuretics and affects renal excretion of other cardiac administered in two doses eight hours apart with a 16‐
drugs, such as digoxin, and close monitoring of such hour drug‐free interval. In humans who are intolerant of
drugs is needed. ACEI, hydralazine or amlodipine along with an oral
Thus, the risk for digoxin toxicity increases with wors- nitrate is administered, albeit with less clinical benefit
ening hypovolemia. In late stages of CHF, free water than ACEI.
retention by arginine vasopressin (antidiuretic hormone) Pulmonary hypertension (PHT) (see Chapter 23) is a
can result in severe hyponatremia and hypochloremia. common complication in patients with advanced heart
These electrolyte derangements can be difficult to treat. failure, especially those with MMVD. Signs of PHT
Occasionally, cautious addition of sodium chloride or include right‐sided heart failure, syncope, and persistent
potassium chloride to the diet, warm sodium chloride tachypnea in the absence of pulmonary edema.