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Summary
The abnormal accumulation of fluid in the tissues between blood vessels is generally referred to as edema. When this accumulation of fluid happens to the tissues of the lungs, however, it’s known as pulmonary edema.
The fluid that accumulates in the tissues of the lungs do so in the tiny, air-filled bubbles of the lung tissue known as alveoli. These structures are those designed to allow the oxygen in the air to enter the bloodstream. As such, they’re critical not only to normal respiration but to the oxygenation of all tissues of the body. The fluid that enters these alveoli comes from the disease-affected blood vessels and tissues surrounding them.
Pulmonary edema is associated with a variety of causes. These are generally classified as cardiogenic (originating in the heart) and non-cardiogenic.
Cardiogenic causes include any of the diseases of the heart that allow the accumulation of fluid in the lungs. These are typically those that affect the workings of the left side of the heart, as it’s this side’s failure that’s inextricably intertwined with the accumulation of fluid in the lungs. Consider these, several of its more common causes:
Chronic valve disease (especially of the left atrioventricular or mitral valve)
Hypertrophic cardiomyopathy in cats
Dilated cardiomyopathy in dogs
The following comprise the most common of pulmonary edema’s non-cardiogenic causes:
Cancer of the lungs
Electrocution
Head trauma
Seizures
Acute lung injury
ARDS (acute respiratory distress syndrome)
Symptoms and Identification
Pets with pulmonary edema typically present with signs consistent with lung disease, including the following:
Coughing
Difficulty breathing (increased respiratory rate or effort)
Blue tongue and/or mucous membranes
Weakness
Collapse
Physical examination, including listening to the chest with a stethoscope (auscultation), is a necessary first step. Abnormal lung sounds consistent with pulmonary edema (wet, crackly sounds) are typically observed, though these can sometimes be obscured by the loudness of a heart murmur or other abnormal cardiac sound. If a cardiogenic cause is suspected, careful attention to heart sounds is crucial, though these may not always be present.
To confirm and definitively diagnose pulmonary edema, chest X-rays are typically undertaken. These will elucidate any areas of fluid accumulation within the lungs.
Abnormalities in the heart that may be related to the pulmonary edema’s underlying causes may or may not be visible on chest X-rays. For this reason, an echocardiogram (ultrasound of the heart) is strongly recommended for pets suspected of suffering from a cardiogenic cause.
Standard tests for all pulmonary edema patients also includes a CBC, blood chemistry screen and urinalysis.
Affected Breeds
Any breed of dog or cat is equally subject to the effects of pulmonary edema. Cats and dogs of breeds predisposed to specific, heritable cardiac diseases, however, are doubtless at higher risk.
Treatment
Treatment of pets with pulmonary edema depends to a large extent on its cause, as treatment of any underlying disease is the primary approach in all cases. Nonetheless, there is a set approach to treatment that involves a three-pronged strategy:
Patient stabilization: Most pulmonary patients arrive in distress. They are typically treated with oxygen therapy and drugs to help them relax so they can properly oxygenate their tissues.
Resolution of the edema: Treatment with diuretics and other drugs can help remove the fluid from the lungs (temporarily, at least).
Treat the underlying cause: This three-pronged approach always culminates in treating the causative disease. Without this step there can be no expectation of long-term survival.
When the cause of pulmonary edema cannot be isolated, or when it’s deemed untreatable, there are nonetheless some well-established methods to help control the accumulation of fluid in the lung tissue. Diuretics are the mainstay of treatment in these cases, as are other drugs to help control other issues associated with the underlying disease.
For example, most cardiac diseases in pets are considered manageable but not curable. These chronic illnesses may require long-term therapy with diuretic drugs along with any additional drugs to control the heart disease itself.
Veterinary Cost
The veterinary cost of pulmonary edema varies depending on the cost of the underlying disease’s treatment. In general, however, treatment of an acute event (such as trauma) is less expensive than the long-term treatment of cardiac diseases, which may cost hundreds of dollars a month in medications alone.
Prevention
As many of its underlying causes are either inherited or traumatic, pulmonary edema is generally not considered a preventable condition. Nonetheless, many patients with underlying heart diseases can be successfully managed so that their conditions never progress to pulmonary edema (except, perhaps, in their very last stages).
References
Goodwin JK, Strickland KN. The emergency management of dogs and cats with congestive heart failure. Vet Med 1998;93:818-822.
Hansen B, DeFrancesco T. Relationship between hydration estimate and body weight change after fluid therapy in critically ill dogs and cats. J Vet Emerg Crit Care 2002;12(4):235-43.
Muir WW, DiBartola SP. Fluid therapy. In: Kirk RW, ed. Current veterinary therapy VIII. Philadelphia, Pa.: WB Saunders Co, 1983;33.
Sisson D, Kittleson MD. Management of heart failure: principles of treatment, therapeutic strategies, and pharmacology. In: Fox PR, Sisson D, Moise NS, eds. Textbook of canine and feline cardiology. Philadelphia, Pa: WB Saunders Co, 1999.
Ware WA, Bonagura JD. Pulmonary edema. In: Fox PR, Sisson D, Moise NS, eds. Textbook of canine and feline cardiology. Philadelphia, Pa: WB Saunders Co, 1999.