Page 81 - Problem-Based Feline Medicine

6 – THE CAT WITH HYDROTHORAX 73

INFECTIOUS
● Pneumonia (p 84)
Moist, productive cough, fever, halitosis may be seen. Parapneumonic pleural effusions are com-
monly sterile inflammatory exudates, often grossly serous or hemorrhagic rather than purulent.
They often resolve with treatment of the lung disease.
● Feline infectious peritonitis (FIP)* (p 81)
Vasculitis caused by the immune response to feline coronavirus causes exudation of a protein-rich fibri-
nous fluid into various body cavities including the pleura. Systemic illness is common.
● Pyothorax*** (p 75)
There is an accumulation of grossly obvious purulent exudate in the pleural cavity. Turbid, flocculent,
often fetid-smelling fluid with cells that are primarily degenerative neutrophils. Dyspnea, signs of
chronic disease (weight loss, ill-thrift), and fever are common signs.

● oncotic pressure.
INTRODUCTION ● systemic or pulmonary vascular pressure.
● lymphatic hydrostatic pressure, compliance or per-
meability.
MECHANISM?
● vascular permeability.
Pleural space is the cavity between the visceral pleura
Hydrothorax is the accumulation of fluid in the
(covering the lungs and the pericardium) and the pari-
pleural cavity, which may consist of blood, transudate,
etal pleura (covering the internal thoracic wall,
modified transudate, exudate or chylous fluid
diaphragm and mediastinum).
Various fluid types that may accumulate include:
Generally, this space contains a few milliliters of fluid
● Hemorrhage consists of frank blood, and may be
to act as a lubricant for motion of the lungs and the
caused by neoplasia, coagulation defects or trauma.
heart. This fluid is very close to the composition of
The hematocrit of the fluid is often much lower
serum.
than the peripheral blood, and it rarely clots after
Visceral and parietal pleurae have distinctly separate removal.
vascular supplies and lymphatics. The parietal pleural ● Transudates are low protein (< 15 g/L), low cellu-
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lymphatics have stomata – gaps that exist to remove larity (< 1.0 × 10 /L) fluids that leak out of the vas-
particulate matter from the pleural space. Absorption cular space secondary to lymphatic or venous
through these stomata may be facilitated by motion of occlusion from congestive heart failure, mediastinal
the chest wall during breathing. Obstruction of the mass obstruction or infiltration of the pleura.
stomata may decrease absorption of exudative ● Modified transudates or exudates are more cel-
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effusions. lular (1.0–7.0 × 10 /L and 5.0–20 × 10 /L, respec-
tively), and higher protein (25–50 g/L and 30–80 g/L,
Normal fluid dynamics of the pleura balance between
respectively) fluids.
opposing hydrostatic and oncotic pressures across the
– Modified transudates are associated either with
pleurae. There is a delicate balance between the slight
diseases that cause chronic transudates, or
transudation across the parietal pleura and the slight
occur early in diseases that produce exudates.
absorption across the visceral pleura, that maintains a
Over time, chronic transudates produce pleural
steady ratio of production to drainage of fluid through
irritation that results in increased cell numbers
the pleural space.
and slightly increased protein in the fluid, which
Disease conditions that disrupt this balance can lead is then classified as a modified transudate.
to pleural effusion by changing; Modified transudates also occur early in diseases