Respiratory Diagnostics

Radiographic patterns are used both to establish lists of differential diagnoses and to decide on the type of airway sampling that will be most helpful in making a final diagnosis. In general, bronchial or alveolar patterns are best evaluated with a tracheal wash or bronchoscopy. Mass lesions can be evaluated with a fine needle aspirate or needle biopsy, and ultrasound guidance is helpful in achieving accurate positioning for sample collection. Definitive diagnosis of diffuse interstitial diseases often requires lung biopsy.

Transoral Tracheal Wash

To perform a transoral tracheal wash, a sterile endotracheal tube and a sterile long catheter are needed. This technique is appropriate for use in large and small dogs or in cats. The animal is anesthetized with a shortacting anesthetic agent. A sterile endotracheal tube is passed into the trachea, taking care to avoid touching the oral mucosa or larynx with the end of the tube in order to limit contamination with oropharyngeal bacteria. The cuff of the endotracheal tube does not need to be inflated for this short procedure, but an assistant should hold the tube in place to prevent the animal from aspirating it into the lower airway.
With the endotracheal tube held in place, a polypropylene or red rubber catheter is passed sterilely to the level of the carina. An aliquot of saline (4-6 mls) is instilled into the airway, and gentle suction is used to retrieve the fluid and cells from the lower airway. Removal of fluid can be enhanced by having the assistant compress the chest or by stimulating a cough during suction. Instillation and aspiration of fluid can be repeated several times until an adequate sample has been retrieved (0.5-1.0 mls is usually sufficient for culture and cytology). Fluid is submitted for bacterial culture and susceptibi-lity testing and for cytologic examination.

Transtracheal Wash

For larger dogs, or those in which anesthesia is contraindicated, a transtracheal wash is often preferred. The easiest way to perform a transtracheal wash is with a through-the-needle jugular catheter. The trachea can be entered at the cricothyroid notch but is preferable to enter the trachea between the tracheal rings at the lowest spot on the neck in order to avoid potential damage to laryngeal structures. This also facilitates collection of a sample from the lower airway since the jugular catheter is relatively short in length. The ventral portion of the neck is clipped and lightly scrubbed with antiseptic solution followed by alcohol wipes. A more complete surgical preparation is performed after local anesthesia is instilled.
Local anesthesia with lidocaine (0.25-0.5 mls) is used at two sites that will be penetrated by the needle: at the skin and between the tracheal rings. The needle of the jugular catheter will penetrate the skin low on the neck, and the skin will then be drawn upward prior to entering the airway lumen. This creates a subcutaneous seal that limits air leakage from the skin entry into the airway.
When the needle is placed into the trachea, the bevel of the needle should face downward, away from the neck, so that the catheter passes directly through the center of the needle and down the trachea. When orientated in this fashion, the catheter does not ride over the sharp edge of needle as it is advanced through the lumen, and it is less likely that the sharp edge of the needle will cut off the catheter during passage. To penetrate the skin, the left hand stabilizes the trachea to prevent it from moving away from needle, and the needle is initially oriented perpendicular to the trachea. [...]