Page 93 - Small Animal Internal Medicine, 6th Edition

CHAPTER 3 Management of Heart Failure 65

used concurrently with digoxin and a catecholamine but Arteriolar vasodilators can be detrimental in the presence
would seem redundant with pimobendan. of LV outflow obstruction, because afterload reduction pro-
VetBooks.ir infusion rate is reduced or the drug is discontinued. Cate- vokes greater systolic obstruction (see Chapter 8). However,
If arrhythmias develop during IV inotropic therapy, the
ACEIs at standard doses do not appear to worsen the LV
cholamine infusion is likely to increase the ventricular
soon as the animal begins eating again.
response rate in animals with atrial fibrillation (AF), by outflow gradient. Addition of an ACEI is recommended as
enhancing AV conduction. If dobutamine or dopamine is
deemed necessary for such a case, diltiazem (IV or oral) is MONITORING AND FOLLOW-UP
used to reduce the heart rate (see Table 4.2). Oral digoxin Repeated assessment is important for monitoring the effec-
with an initial loading dose is an alternative. Digoxin is not tiveness of therapy and for early detection of hypotension or
recommended intravenously; the only, and rare, exception severe azotemia caused by excessive diuresis. Mild azotemia
might be for a sustained supraventricular tachyarrhythmia is common. Hypokalemia and metabolic alkalosis also can
when other acute antiarrhythmic therapy is unavailable or occur after aggressive diuresis. Maintaining serum potas-
ineffective (see Chapter 4, p. 80). Acidosis and hypoxemia sium concentration within the mid- to high-normal range is
associated with severe pulmonary edema can increase myo- especially important for animals with arrhythmias. Serum
cardial sensitivity to digitalis-induced arrhythmias. biochemical testing every 24 to 48 hours is advised until the
patient is drinking well and beginning to eat.
Other Acute Therapy Arterial blood pressure should be monitored, usually by
Mild sedation (see Box 3.1) can reduce anxiety. Because indirect means because gaining arterial access can increase
morphine can induce vomiting, butorphanol is a better patient stress. Indirect measures of organ perfusion such as
choice in dogs. Morphine is contraindicated in dogs with capillary refill time, mucous membrane color, pulse oxime-
neurogenic edema because it can raise intracranial pressure. try, urine output, toe-web temperature, and mentation also
Morphine should not be used in cats. are useful. Body weight should be monitored, especially with
Some dogs with severe pulmonary edema and broncho- aggressive diuretic therapy.
constriction benefit from short-term bronchodilator therapy. Central venous pressure (CVP) does not adequately
Aminophylline, given slowly IV or IM, has mild diuretic and reflect left heart filling pressures. It should not be used to
positive inotropic actions as well as a bronchodilating effect; guide diuretic or fluid therapy in patients with cardiogenic
it also decreases fatigue of respiratory muscles. Adverse pulmonary edema. Although pulmonary capillary wedge
effects include increased sympathomimetic activity and pressure can reliably guide therapy, placement and care of an
arrhythmias. The oral route can be used when respiration indwelling pulmonary artery catheter require meticulous
improves because GI absorption is rapid. attention to asepsis and close monitoring.
Pulse oximetry is helpful for monitoring oxygen satura-
HEART FAILURE CAUSED tion (SpO 2 ). Supplemental O 2 should be given if SpO 2 is less
BY DIASTOLIC DYSFUNCTION than 90%; mechanical ventilation is indicated if SpO 2 is less
When acute CHF is caused by hypertrophic or restrictive than 80% despite O 2 therapy. Arterial sampling for blood gas
cardiomyopathy, thoracocentesis (if needed), diuretics, and analysis is more accurate but is stressful for the patient. Reso-
oxygen therapy are given as outlined previously. Cutaneous lution of radiographic evidence for pulmonary edema usually
nitroglycerin can also be used. For cats with a rapid tachyar- lags behind clinical improvement by a day or two.
rhythmia, persistent sinus tachycardia, or marked LV outflow After respiratory signs begin to abate and diuresis is
obstruction, a β 1 -blocker such as atenolol or IV esmolol can evident, drinking water is offered. Fluid administration
reduce the frequency of ectopic beats, control heart rate, and (either subcutaneously or intravenously) generally is NOT
reduce the LV outflow pressure gradient. However, propran- advised for patients with CHF. In most cases, gradual rehy-
olol (or another nonselective β-blocker) should be avoided dration by free choice water intake is preferred even after
in patients with fulminant pulmonary edema because β 2 - aggressive diuresis. However, cautious fluid therapy may be
blockade could induce bronchoconstriction. Pimobendan necessary for heart failure patients with advanced renal dys-
can be helpful in cats with reduced myocardial contractility, function, marked hypokalemia, hypotension, persistent
restrictive or end-stage cardiomyopathy, and recurrent or anorexia, digoxin toxicity, or other serious systemic disease.
progressive CHF from HCM. Whether pimobendan therapy Some animals require relatively high cardiac filling pressure
should be started at first-onset CHF in cats with HCM is to maintain cardiac output, especially those with myocardial
controversial; prospective clinical evidence is awaited to failure or markedly reduced ventricular compliance (as from
support or refute this use. In cats with hypertrophic obstruc- HCM or pericardial disease). Diuresis and vasodilation in
tive cardiomyopathy (HOCM), there is concern regarding such cases can cause inadequate cardiac output and hypoten-
use of pimobendan (as well as other positive inotropic or sion. For most patients with decompensated CHF that need
vasodilator agents). Because increased contractility and arte- a drug by CRI, the smallest fluid volume possible should be
rial vasodilation can worsen dynamic LV outflow obstruc- used. Careful monitoring and continued diuretic use are
tion and potentially cause hypotension, pimobendan is important to prevent recurrent pulmonary edema. When
theoretically contraindicated. additional fluid therapy is necessary, D 5 W or a reduced