Dilated Cardiomyopathy: Acute Therapy

By | 2013-06-07

Treatment Goals

The treatment goals depend on the type and severity of the clinical signs. If severely dyspneic the initial goal is to make it easier for the cat to breathe by removing pleural effusion, by reducing pulmonary edema pharmacologically, or by administering oxygen. If the primary problem is a marked reduction in perfusion leading to hypothermia, the goal is to increase cardiac output, if possible, via the administration of an intravenous positive inotropic agent, such as dobutamine, and possibly the judicious use of intravenous fluid administration, especially if the cat is severely dehydrated.

Pleurocentesis

Pleurocentesis is often life saving in the severely dyspneic cat that has a large amount of pleural effusion. Thoracocentesis is described in posts.

Diuretic Therapy

Diuretic administration is the only reliable way to reduce pulmonary edema formation in a cat with severe dilated cardiomyopathy. Furosemide is used almost exclusively. The dose depends on the severity of the pulmonary edema, on whether the cat is currendy on furosemide for heart failure, and whether the situation is acute or chronic Cats in severe respiratory distress may need an initial dose as high as 2 mg/lb parenterally. Intravenous administration is preferred, but the drug should be administered intramuscularly if restraint for intravenous administration produces stress. Absorption half-life after intramuscular administration is around 5 minutes, so the entire dose is fully absorbed within 20 to 25 minutes. The duration of effect of furosemide after parenteral administration is probably 1 to 2 hours in a cat in heart failure. Consequently, another dose should be administered within that period if the cat is still in respiratory distress and is not severely dehydrated. A cat with a lesser amount of pulmonary edema and less respiratory distress needs a smaller dose of furosemide parenterally in the acute setting. Respiratory rate and character should be monitored carefully after diuretic administration with the cat in an oxygen-enriched environment.

Oxygen

Increasing the percent concentration of oxygen delivered to the alveoli is critical in cats in respiratory distress. This can be accomplished using a face mask, standard oxygen cage, a pediatric incubator, or nasal insufflation. Generally the goal is to increase fraction of inspired oxygen (FIO2) to at least 40% (normal is 21%). If the cat resists a face mask, it should not be used. When placed in a confined space, especially a small space like an incubator, it is mandatory to keep the environmental temperature and the carbon dioxide concentration within reasonable levels. Failure to do so can cause death. A canister containing sodium lime or barium hydroxide lime controls carbon dioxide level in an oxygen cage, and a refrigeration unit controls temperature. Carbon dioxide concentration is usually controlled in an incubator by maximizing the flow rate of oxygen (and therefore flushing out the carbon dioxide).

Inotropic Support

Beta-adrenergic agonists, usually dobutamine or dopamine, can be used for acute inotropic support in a cat widi severe dilated cardiomyopathy and severe heart failure. However, conscious cats have more side effects with these drugs than do dogs. They often appear agitated and may even seizure. The half-life of these drugs is around 1 minute, so stopping the drug infusion results in rapid cessation of adverse effects. The infusion rate for dobutamine and dopamine in a cat is less than that used in a dog and is generally in the range of 1 to 2.5 Mg/lb/min.

Nitroprusside

Nitroprusside is a potent dilator (i.e., smooth muscle relaxant) of systemic arterioles and systemic veins. It can only be used in cats with dilated cardiomyopathy that are not in cardiogenic shock (systolic systemic arterial blood pressure over 100 mm Hg). If systemic pressure is adequate, the drug can be used in one of two ways: (1) empirically at a dose of 2 µg/lb/min or (2) titrated using blood pressure starting at a dose of 1 ug/lb/min and increased until the systolic pressure has decreased by at least 10 to 15 mm Hg. ()

General Supportive Measures

Although dogs commonly start to drink water and eat once they are no longer in respiratory distress, cats may not. Dehydration is a common side effect of aggressive diuretic therapy, and some cats are dehydrated at presentation. Generally cats do better if they are sent home as soon as possible. However, if hospitalization is required after the edema and effusion are controlled, judicious use of fluid therapy may be needed. Electrolyte disturbances, most commonly hyponatremia, hypokalemia, and hypochloremia, are also more frequent in cats than in dogs in this acute setting. Consequendy, serum electrolyte concentrations should be monitored.