Page 331 - Small Animal Internal Medicine, 6th Edition

CHAPTER 20 Diagnostic Tests for the Lower Respiratory Tract 303

is used, and, in cats, sterile topical lidocaine is applied to the
laryngeal cartilages to ease passage of the tube with minimal
VetBooks.ir contamination. The tip of the endotracheal tube should be
positioned beyond the larynx but sufficiently in front of the
carina to allow the flushing catheter to rest against the floor
of the trachea.
The catheter is passed through the endotracheal tube to
just proximal to the level of the carina (approximately the
fourth intercostal space), while sterile technique is main­
tained. The wash procedure is performed as described for the
transtracheal technique. Slightly larger boluses of saline may
be required, however, because of the larger volume of the
catheter. Use of a catheter larger than 5F seems to reduce the
yield of the wash, except when secretions are extremely
viscous. FIG 20.15
Photomicrograph of a Blastomyces organism from the lungs
SPECIMEN HANDLING of a dog with blastomycosis. The organisms stain deeply
The cells collected in the wash fluid are fragile. The fluid is basophilic, are 5 to 15 µm in diameter, and have a thick
ideally processed within 30 minutes of collection, with refractile cell wall. Often, as in this figure, broad-based
minimal manipulation. Bacterial culture is performed on at budding forms are seen. The cells present are alveolar
macrophages and neutrophils. (Bronchoalveolar lavage
least 0.5 to 1 mL of fluid. Fungal cultures can be performed fluid, Wright stain.)
if mycotic disease is a differential diagnosis, and Mycoplasma
culture or polymerase chain reaction (PCR) testing is con­
sidered for cats and dogs with signs of bronchitis. Cytologic
preparations are made both from the fluid and from any
mucus within the fluid. Both fluid and mucus are examined
because infectious agents and inflammatory cells can be con­
centrated in the mucus, but the proteinaceous material
causes cells to clump and interferes with evaluation of the
cell morphology. Mucus is retrieved with a needle, and
squash preparations are made. Direct smears of the fluid
itself can be made, but such specimens are usually hypocel­
lular. Sediment or cytocentrifuge preparations are generally
necessary to make adequate interpretation possible. Strain­
ing the fluid through gauze to remove the mucus is discour­
aged because infectious agents may be lost in the process.
Routine cytologic stains are used.
Microscopic examination of slides includes identification FIG 20.16
of cell types, qualitative evaluation of cells, and examination Photomicrograph of Histoplasma organisms from the lungs
for infectious agents. Cells are evaluated qualitatively for of a dog with histoplasmosis. The organisms are small
evidence of macrophage activation, neutrophil degeneration, (2-4 µm) and round, with a deeply staining center and a
lymphocyte reactivity, and characteristics of malignancy. lighter-staining halo. They are often found within phagocytic
cells—in this figure, an alveolar macrophage.
Epithelial hyperplasia secondary to inflammation should not (Bronchoalveolar lavage fluid, Wright stain.)
be overinterpreted as neoplasia, however. Infectious agents
such as bacteria, protozoa (Toxoplasma gondii), fungi (His-
toplasma, Blastomyces, and Cryptococcus organisms), and relatively large volumes of saline were used. Most macro­
parasitic larvae or eggs may be present (see Fig. 20.12, and phages are not activated. In these instances the presence of
Figs. 20.15 through 20.17). Because only one or two organ­ macrophages does not indicate disease but rather reflects the
isms may be present on an entire slide, a thorough evaluation acquisition of material from the deep lung (see the section
of each slide is indicated. on nonbronchoscopic bronchoalveolar lavage).
Slides are examined for evidence of overt oral contamina­
INTERPRETATION OF RESULTS tion, which can occur during transtracheal washing if the
Normal tracheal wash fluid contains primarily respiratory catheter needle was inadvertently inserted proximal to the
epithelial cells. Few other inflammatory cells are present cricothyroid ligament. Rarely, dogs can cough up the cath­
(Fig. 20.18). Occasionally, macrophages are retrieved from eter into the oropharynx. Oral contamination can also result
the small airways and alveoli because the catheter was from drainage of saliva into the trachea, which usually occurs
extended into the lungs beyond the carina, or because in cats that hypersalivate or dogs that are heavily sedated,