Page 28 - Feline Cardiology

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Pleural Effusion

Key Points

• Pleural effusion can occur with right or left heart disease in cats, but other causes are also common. If an echocardiogram
reveals normal left and right atrial size, heart disease is unlikely to be causing the effusion.
• Pleural effusion responds very slowly to diuretic therapy. If the effusion is sufficient to cause dyspnea, therapeutic
thoracocentesis should be performed rather than relying on medical diuresis.

Pleural effusion is the abnormal accumulation of fluid The type of fluid that accumulates depends on the
in the pleural space. It can result from conditions that underlying etiology. Chylous effusion is common in cats
increase systemic and pleural capillary hydrostatic pres- and can be idiopathic or secondary to poor lymphatic
sure (e.g., congestive heart failure), decrease plasma drainage. Hemorrhagic effusion can occur secondary to
oncotic pressure (i.e., hypoproteinemia), increase capil- trauma, coagulopathies, or vascular erosion by a neo-
lary permeability (e.g., vasculitis), or cause lymphatic plastic process. Transudates and modified transudates
obstruction (e.g., neoplasia). Pleural effusion has tradi- occur secondary to processes that lead to increased
tionally been thought to occur secondary to right heart hydrostatic pressure, decreased oncotic pressure, and/or
failure and elevated right atrial pressure because pleural increased vascular permeability. See Box 3.1 for descrip-
fluid is primarily cleared by the parietal pleural lym- tion of various fluid characteristics. In a series of 82
phatics, which empty into the systemic veins. However, feline cases of pleural effusion, underlying disease was
a retrospective study of human cardiac patients demon- diagnosed in 63 of the cats. In these 63 cats, 17% were
strated that cardiogenic pleural effusion is most often found to have cardiac disease and the pleural effusions
associated with left heart disease and elevated left atrial associated with the represented heart diseases (hypertro-
pressures (Weiner-Kronish et al. 1967). Cats also develop phic cardiomyopathy, unclassified cardiomyopathy and
pleural effusion as a consequence of left heart disease. pericardial-peritoneal diaphragmatic hernia in this
The most often proposed hypothesis for this develop- series) were modified transudates, exudates, or chylous
ment is that the visceral pleural veins drain into the left effusions (Davies and Forrester 1996). In a large series
atrium and the parietal pleural veins empty into the of cats with hypertrophic cardiomyopathy (n = 260),
cranial vena cava. When left atrial pressure increases, pulmonary edema was the more common cause of
visceral pleural venous drainage is inhibited, allowing dyspnea when congestive heart failure was present. In
transudation through the vein walls and into the pleural this series, only 15% of the cats with congestive heart
space. Therefore, either left or right heart disease can failure had pleural effusion of sufficient quantity felt to
lead to pleural effusion in the cat, although diseases be responsible for dyspnea. However, pleural effusion
affecting the left heart are more common in the species was present in 34% of the cats that underwent thoracic
than are right heart diseases. radiography (Rush et al. 2002). Echocardiography is the

Feline Cardiology, First Edition. Etienne Côté, Kristin A. MacDonald, Kathryn M. Meurs, Meg M. Sleeper.
© 2011 John Wiley & Sons, Inc. Published 2011 by John Wiley & Sons, Inc.

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