Page 390 - Small Animal Internal Medicine, 6th Edition

362 PART II Respiratory System Disorders

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A B C

D E F

FIG 23.1
Characteristic gross appearance of the various types of pleural effusions. Note that
cytologic analysis should always be performed to ensure accurate classification of fluid
and to avoid missing diagnostic organisms or neoplastic cells. (A) Transudate. Fluid is
nearly clear. (B) Modified transudate. Fluid is slightly opaque and, in this example,
red-tinged. (C) Nonseptic exudate. Fluid is more opaque. The fluid shown is from a cat
with feline infectious peritonitis (FIP). FIP fluid is characteristically straw-colored with
grossly visible fibrin clots. (D) Septic exudate. Fluid has a purulent appearance, with
cellular debris gravitating toward the bottom of the tube. (E) Chylous effusion. Fluid is
milky white. (F) Hemorrhagic effusion. Hemorrhagic effusions are bright to dark red. In
this case, cytologic examination revealed filamentous organisms, demonstrating the
importance of cytologic analysis.

Decreased plasma oncotic pressure is a result of hypo- 1 g/dL before transudation caused only by hypoalbumin-
albuminemia. Effusions secondary to hypoalbuminemia emia occurs. However, a combination of factors may con-
alone are pure transudates that have very low protein con- tribute to effusions (e.g., vasculitis, hypoalbuminemia, and
centrations. Subcutaneous edema may be detected in depen- fluid overload).
dent areas of the body. Decreased production of albumin Neoplasia and diaphragmatic hernias can cause lymphatic
causes hypoalbuminemia in patients with liver disease, and obstruction. Diaphragmatic hernias should be suspected in
increased loss of albumin causes it in patients with glomer- any animal with a history of trauma. The trauma may have
ulopathy or protein-losing enteropathy. The total plasma been recent or may have occurred years ago. Although a
protein concentration shown by refractometry during initial modified transudate usually forms as a result of chronic dia-
evaluation of the dog or cat can serve as a rapid screen- phragmatic hernia, an exudative fluid can also be found.
ing test for hypoalbuminemia. Serum biochemical analysis Diaphragmatic hernias are identified by radiography or
provides an exact measurement of the albumin concentra- ultrasonography. Occasionally, it is necessary to administer
tion. In general, albumin concentrations must be lower than barium orally and perform an upper gastrointestinal series,