Page 339 - Small Animal Internal Medicine, 6th Edition

CHAPTER 20 Diagnostic Tests for the Lower Respiratory Tract 311

aspiration needle into the areas of infiltrate should improve
diagnostic yield and safety. If areas of infiltrate cannot be
VetBooks.ir identified ultrasonographically, BAL should be considered
before lung aspiration in animals that can tolerate the pro­
cedure because it yields a larger specimen for analysis and,
in this author’s opinion, carries less risk than unguided
transthoracic aspiration in patients that are not experiencing
increased respiratory efforts or distress. Tracheal wash and
appropriate ancillary tests are also considered before lung
aspiration in these patients because they carry little risk.
TECHNIQUES
The site of collection in animals with localized disease adja­
cent to the body wall is best identified with ultrasonography.
If ultrasonography is not available, or if the lesion is sur­
rounded by aerated lung, the site is determined on the basis
of two radiographic views. The location of the lesion during
inspiration in all three dimensions is identified by its rela­
tionship to external landmarks: the nearest intercostal space
or rib, the distance from the costochondral junctions, and
the depth into the lungs from the body wall. If available, FIG 20.26
fluoroscopy or CT also can be used to guide the needle or Transthoracic lung aspiration performed with a spinal
biopsy instrument. needle. Note that sterile technique is used. The needle shaft
The site of collection in animals with diffuse disease is a can be pinched with finger and thumb at the maximum
caudal lung lobe. The needle is inserted between the seventh depth to which the needle should be passed. The finger and
and ninth intercostal spaces, approximately two thirds of the thumb thus act as a guard to prevent overinsertion of the
distance from the costochondral junctions to the spine. needle. Although this patient is under general anesthesia,
this is not usually indicated.
The animal must be restrained for the procedure, and
sedation or anesthesia is necessary in some. Anesthesia is
avoided, if possible, because the hemorrhage created by the
procedure is not cleared as readily from the lungs in an hand at the desired maximum depth of insertion. During
anesthetized dog or cat. The skin at the site of collection is insertion, the needle can be twisted along its long axis in an
shaved and surgically prepared. Lidocaine is injected into attempt to obtain a core of tissue. The needle is then imme­
subcutaneous tissues and intercostal muscles to provide local diately withdrawn to the level of the pleura. Several quick
anesthesia. stabs into the lung can be made along different lines to
Lung aspiration can be performed with an injection increase the yield.
needle, a spinal needle, or a variety of thin­walled needles Each stab should take only a second. Prolonging the time
designed specifically for lung aspiration in people. Spinal that the needle is within the lung tissue increases the likeli­
needles are readily available in most practices, are sufficiently hood of complications. The lung tissue will be moving with
long to penetrate through the thoracic wall, and have a stylet. respirations, resulting in laceration of tissue, even if the
A 22­gauge, 1.5­ to 3.5­inch (3.75­ to 8.75­cm) spinal needle needle is held steady.
is usually adequate. The needle is withdrawn from the body wall with a
The clinician wears sterile gloves. The needle with stylet minimal amount of negative pressure maintained by the
is advanced through the skin several rib spaces from the syringe. It is unusual for the specimen to be large enough to
desired biopsy site. The needle and skin are then moved to have entered the syringe. The needle is removed from the
the biopsy site. This is done because air is less likely to enter syringe, the syringe is filled with air and reattached to the
the thorax through the needle tract after the procedure if the needle, and the contents of the needle are then forced onto
openings in the skin and chest wall are not aligned. The one or more slides. Grossly, the material is bloody in most
needle is then advanced through the body wall to the pleura. cases. Squash preparations are made. Slides are stained using
The stylet is removed, and the needle hub is immediately routine procedures and then are evaluated cytologically.
covered by a finger to prevent pneumothorax until a 12­mL Increased numbers of inflammatory cells, infectious agents,
syringe can be placed on the hub. During inspiration the or neoplastic cell populations are potential abnormalities.
needle is thrust into the chest to a depth predetermined from Alveolar macrophages are normal findings in parenchymal
the radiographs, usually about 1 inch (2.5 cm), while suction specimens and should not be interpreted as representing
is applied to the syringe (Fig. 20.26). To keep from inserting chronic inflammation. They should be carefully examined
the needle too deeply, the clinician may pinch the needle for evidence of phagocytosis of bacteria, fungi, or red blood
shaft with the thumb and forefinger of the nondominant cells and for signs of activation. Epithelial hyperplasia can