Page 328 - Small Animal Internal Medicine, 6th Edition

300 PART II Respiratory System Disorders

Tracheal wash is less likely to provide representative The cricothyroid ligament is identified by palpating the
material from interstitial and focal disease processes. trachea in the ventral cervical region and following it dor­
VetBooks.ir However, the procedure is inexpensive and minimally inva­ sally toward the larynx to the raised, smooth, narrow band
of the cricoid cartilage. Immediately above the cricoid carti­
sive, and this makes it reasonable to perform in most animals
with lower respiratory tract disease if the risks of other
lage is a depression, where the cricothyroid ligament is
methods of specimen collection are deemed too great. located (see Fig. 20.13, B). If the trachea is entered above the
Potential complications are rare and include tracheal lac­ cricothyroid ligament, the catheter is passed dorsally into the
eration, subcutaneous emphysema, and pneumomediasti­ pharynx and a nondiagnostic specimen is obtained. Such
num. Bronchospasm may be induced by the procedure in dorsal passage of the catheter often results in excessive
patients with hyperreactive airways, particularly cats with gagging and retching but may go unrecognized in sedate
bronchitis. patients.
Lidocaine is always injected subcutaneously at the site of
TECHNIQUES entry. The skin over the cricothyroid ligament is prepared
Tracheal wash is performed with the use of transtracheal or surgically, and sterile gloves are worn to pass the catheter.
endotracheal techniques. Transtracheal wash is performed The over­the­needle catheter is held with the bevel of the
by passing a catheter into the trachea to the level of the carina needle facing ventrally. The skin over the ligament is then
through the cricothyroid ligament or between the tracheal tented, and the needle is passed through the skin. The larynx
rings in an awake or sedated animal. Endotracheal wash is is stabilized with the nondominant hand. To properly stabi­
performed by passing a catheter through an endotracheal lize it, the clinician should grasp at least 180 degrees of the
tube in an anesthetized animal. The endotracheal technique circumference of the airway between the fingers and the
is preferred in cats and very small dogs, although either thumb. Failure to hold the airway firmly is the most common
technique can be used in any animal. Patients with airways technical mistake. Next, the tip of the needle is rested against
that may be hyperreactive, particularly cats, are treated the cricothyroid ligament and inserted through the ligament
with bronchodilators (see the section on endotracheal with a quick, short motion. The syringe end of the catheter
technique). is raised without withdrawing the needle, and the catheter is
threaded down the trachea. The hand stabilizing the trachea
Transtracheal Technique is then used to pinch the hub at the skin, with the hand kept
Transtracheal wash fluid is collected by inserting a short, firmly in contact with the neck, while the needle is removed.
large bore over­the­needle catheter through the cricothyroid By keeping the hand holding the hub of the catheter against
ligament or between tracheal rings; removing the needle; the neck of the animal so that the hand, needle, and neck can
passing a long, smaller bore, flushing catheter through the move as one, the clinician prevents laceration of the larynx
catheter into the trachea to reach just cranial to the carina; or trachea and inadvertent removal of the catheter from the
then performing the saline wash. Options for catheters trachea.
include a prepackaged kit containing a 14­gauge introduc­ The flushing catheter is then threaded through the over­
tion catheter and a 10­ to 28­inch flushing catheter (Mila the­needle catheter. Threading the catheter provokes cough­
International, Inc., Florence, Kentucky) or a 14­gauge over­ ing. Little or no resistance to passage of the catheter should
the­needle catheter and a 3.5F polypropylene male dog be noted. Elevating the hub of the over­the­needle catheter
urinary catheter. For the latter, the ability to pass a specific slightly so that the tip points more ventrally facilitates passage
brand of urinary catheter through a specific over­the­needle of the flushing catheter if it is abutting the opposite tracheal
catheter should be tested before use, as the fit may be too wall. Once the catheter has been completely threaded into
tight in some instances. Alternatively, a 12­inch­long, 18­ to the airway, the head can be restrained in a natural position
22­gauge through­the­needle intravenous catheter can be Note that if the flushing catheter will not pass despite
used, but in our area, these catheters are no longer commer­ adjustments in position of the over­the­needle catheter, the
cially available. The flushing catheter should be long enough over­the­needle catheter must be completely removed and
to reach the carina, which is located at approximately the the procedure repeated from the beginning. Attempting to
level of the fourth intercostal space. reinsert the needle into the over­the­needle catheter while it
The dog can sit or lie down, depending on what position is within the patient is dangerous as it can result in a piece
is more comfortable for the animal and the clinician. The of the catheter being sheared off and lost deep within the
dog is restrained with its nose pointing toward the ceiling airways.
at about 45 degrees from horizontal (Fig. 20.13, A). Overex­ It is convenient to have six to eight 12­mL syringes ready,
tension of the neck causes the animal to be more resistant. each filled with 3 to 5 mL of 0.9% sterile preservative­free
Dogs that cannot be restrained should be tranquilized. If sodium chloride solution. The entire bolus of saline in one
tranquilization is needed, premedication with atropine or syringe is injected into the flushing catheter. Immediately
glycopyrrolate is considered to minimize contamination of after this, many aspiration attempts are made. After each
the trachea with oral secretions. Narcotics are avoided to aspiration, the syringe must be disconnected from the cath­
preserve the cough reflex, which can facilitate the retrieval eter and the air evacuated without loss of any of the retrieved
of fluid. fluid. Attachment of a three­way stopcock between the