Page 368 - Clinical Small Animal Internal Medicine

336 Section 4 Respiratory Disease

Table 34.3 Classification of effusions in dogs and cats
VetBooks.ir Total protein Cells per Cell types Special features

(g/dL)
microliter
Transudate <2.5 <1500 Mononuclear Low cellularity
Modified 2.5–7.5 1000–7000 Mononuclear Cell type varies with etiology
transudate
Exudate >3.0 >3000 Neutrophils or specific to Subcategories: hemorrhage, bile,
underlying disease chyle, septic, aseptic

Diagnostics diaphragmatico‐hepatic site is the most sensitive and
specific area to diagnose pleural effusion because it has
Patient presentation, stability, and available resources less air interface than the pericardial sites; however, with
will often guide the diagnostic approach in patients with breed conformation and size variation of veterinary
pleural effusion. The cyanotic cat with open mouth patients, this has yet to be prospectively evaluated.
breathing will have a different initial diagnostic and Thoracic ultrasound is useful for the detection, charac-
treatment plan from a dog presenting for vomiting or terization, and subjective quantification (by depth) of
diarrhea with scant pleural effusion found during rou- pleural fluid, in addition to guiding therapeutic interven-
tine testing for underlying gastrointestinal disease. tion. Abdominal ultrasound and echocardiogram may
Regardless of the underlying pathology, the goal should also help determine the cause of pleural effusion.
be patient stabilization first followed by a thorough Thoracic radiographs are useful to evaluate for the
investigation into the inciting cause of pleural effusion presence of pleural effusion and survey the thoracic cav-
using imaging techniques, pleural fluid tests, and, if nec- ity for an underlying etiology. Radiographic signs of
essary, histopathology. pleural effusion include retraction of the lung margins
from the thoracic wall and sternum with increased
opacity in the pleural space, widened interlobar fissures,
Imaging
rounding of lung margins, pleural thickening, and
Ultrasonography, radiography, and computed tomogra- obscuring of the diaphragm and cardiac silhouette by
phy (CT) are currently available imaging techniques in radiopaque fluid. Pleural fluid will often obscure struc-
dogs and cats with pleural effusion. In general, the tures in the thoracic cavity, including the heart, medi-
patient requiring emergent treatment for respiratory dis- astinum, and diaphragm; therefore, in patients with
tress due to pleural effusion is likely to have an ultra- significant pleural effusion it is advantageous to perform
sound in the emergency department initially followed by thoracocentesis, ideally ultrasound guided, prior to radi-
thoracocentesis prior to the pursuit of additional imag- ographs to allow better evaluation of intrathoracic struc-
ing techniques whereas a stable patient will likely have tures. Since the pleura cannot normally be seen on
thoracic radiographs with or without a thoracic ultra- radiographs, if pleural lines are seen, horizontal beam
sound followed by advanced imaging if necessary. radiographs, in addition to the standard three‐view
Although the name implies a single subset of patients, series, may help differentiate pleural thickening from
which benefit from the test, the thoracic focused assess- pleural effusion because vertical beam projections are
ment with sonography for trauma (TFAST) is the most limited by superimposition of fluid and soft tissue struc-
common initial test in an emergency situation due to tures. In addition, more pleural effusion is present than
pleural space disease because it allows for rapid assess- predicted based on vertical beam (standard‐view) radio-
ment of the thoracic cavity with a therapeutic goal. graphs because large fluid pockets are not struck head‐
TFAST is performed with the patient in sternal or right on by the X‐ray beam; however, a horizontal beam allows
lateral recumbency and assessing five areas of the tho- fluid to collect ventrally such that the X‐ray beam strikes
racic cavity: the right and left chest tube site (dorsolat- the fluid–lung interface tangentially. However, ultra-
eral 7th–9th intercostal spaces), right and left pericardial sound remains the most sensitive test for detection of
site (ventrolateral 5th–6th intercostal space), and the small amounts of fluid.
diaphragmatico‐hepatic (subxiphoid) site. Pleural Thoracic CT has become increasingly available in
effusion is recognized as anechoic or echogenic fluid in veterinary practice; CT allows better lesion delineation
the pleural space and its presence may allow better and characterization than conventional radiography
visualization of some mediastinal masses. In people, the for many thoracic disorders. Prior to thoracic CT,