Airway sampling may seem like a daunting procedure to perform in a private practice setting. However, it can be an invaluable tool to aid in the diagnosis and treatment of certain airway diseases.
The main methods for airway sampling include transtracheal wash, endotracheal wash and bronchoalveolar lavage. Transtracheal wash is performed by instilling fluid into the upper airway through a catheter that is passed in between cartilage rings of the trachea, bypassing the oropharynx, decreasing the risk of oropharyngeal contamination. It is performed in a lightly sedated patient and uses a special through-the-needle catheter and generally works best in medium to large breed dogs. An endotracheal wash is performed by passing a tube or suction catheter through a sterile endotracheal tube. Bronchoscopy is a procedure by which a sterile endoscope can be used to travel to specific portions of the respiratory tree. A focal wash performed via bronchoscopy is referred to as a bronchoalveolar lavage. There are the added benefits of using a bronchoscope including visualization of pathology in the airway and the ability to biopsy lesions.
Both the transtracheal and endotracheal washes are limited in their ability to truly reach the smaller branches of the respiratory tree and the catheter cannot be guided into a specific part of the lung. Generally, the samples obtained via transtracheal and endotracheal washes are representative of pathology present in the larger airways. By contrast bronchoscopy enables the clinician to reach a specific portion of the airway and there is a higher level of confidence that the lavage sample will be representative of the area of interest.
Knowing the differences between the airway sampling procedures gives us some general guidance as to which technique to recommend. In general, transtracheal and endotracheal washes are indicated in working up disease with diffuse lesions whereas bronchoscopy is more useful when working up focal lesions. Per cutaneous sampling may also be considered for lesions that are accessible, e.g. close to the thoracic wall. Of the three sampling methods described above, the endotracheal wash is likely the least intimidating to perform and requires the least amount of specialized equipment. Therefore, the focus of the remainder of this article will be on endotracheal wash.
Diseases with diffuse lesions such as asthma, bronchitis, eosinophilic bronchopneumopathy, hematogenous pneumonia, diffuse neoplasia. The anatomy of the respiratory tree influences where aspirated material ends up, primarily the middle lobes. Thus, any fluid used to instill into the airway may also end up in this location making endotracheal wash useful for middle lobe focal disease such as aspiration pneumonia.
Set up with the red rubber catheter.
- Sterile gloves
- Sterile endotracheal tube
- Red rubber catheter (5Fr or 8Fr)
- Two to three 10 ml (cat or small dog) or 20 ml (medium/large dog) syringes of saline
- 20 ml empty syringe for aspirating
- EDTA tube and plain tube (or culturette)
- Alternatively, if your hospital has central suction or portable suction, you may use a closed collection system such as a Lukens specimen trap (Figure 1)
Figure 1: Set up with the closed suction trap.
Step One: Preparing
Make sure you have the materials you will need to perform the procedure including sterile gloves, sterile endotracheal tube, any pre-loaded syringes with sterile wash solution, suction tubing and collection tubes/swabs. Don’t forget monitoring equipment such as pulseoximeter and EKG. Even though you may not utilize gas inhalant, it is best to prepare for this procedure like you would any other patient undergoing general anesthesia, including an emergency drug sheet and obtaining a CPR code status from the client. Begin by preoxygenating the patient using flow by oxygen. Administer the premedication drugs followed by induction drug titrated to allow sterile intubation. Take time to attach monitoring equipment while delivering oxygen to the intubated patient.
Step Two: Instilling the Saline
Once you have determined it is safe to proceed, detach the oxygen from the endotracheal tube and using sterile gloves, place the catheter down the endotracheal tube. A good guideline is to measure the catheter to the level of the carina. Instill one aliquot of saline down the catheter. You may get a cough response from the patient. This is okay as long as they continue to tolerate being intubated.
Step Three: Aspirating
If you are manually aspirating the fluid, use the 20 ml syringe to suction the airway. Once the plunger is fully aspirated, you can detach, push the air out careful to avoid pushing out any sample, reattach the syringe to the catheter and aspirate again. You will only get a few milliliters of fluid out of the original amount. Reattach the patient to the oxygen line. If the patient is stable to continue, repeat the procedure with one or two more additional aliquots of saline, using a fresh empty syringe to suction with each aliquot. If your hospital has central suction, you will use the same sample trap to aspirate after each aliquot is instilled. You will need sterile suction tubing to connect the closed collection system to the suction unit. Guide your assistant on keeping the suction at a safe level so as not to damage any fragile alveoli. Keeping the suction on medium (80-100 mmHg) level is reasonable.
- Avoid using lubricant at the end of the endotracheal tube as this can adversely affect the cytologic interpretation.
- Consider choosing an endotracheal tube one size smaller than needed to more easily facilitate intubation while decreasing contact with the pharyngeal tissues.
- Remember the amount of fluid recovered from the airway will only be a fraction of what was instilled.
- Some patients may experience a temporary worsening of their respiratory signs as a result of the wash, thus keeping them intubated as long as they will tolerate it and recovering them with oxygen supplementation via cage or nasal canula is recommended.
Airway sampling is unlikely to be painful, thus mild sedative premedications such as butorphanol or midazolam either used alone or in combination is reasonable. Titratable induction agents such as propofol or alfaxalone are good options to facilitate intubation and maintain anesthesia for the duration of the procedure. The procedure itself is very quick, lasting less than 10 minutes. But be prepared to keep the patient intubated for as long as it takes for them to make a reasonable recovery.
EDTA samples are used for cytology. Aerobic and anaerobic cultures can be submitted in a plain top tube (no additives) or a culturette swab in transport medium. Respiratory PCR can also be performed on airway wash samples. Viral cultures are usually submitted on a dry synthetic fiber tipped swab with a plastic handle. Wooden handled swabs are NOT recommended because they are porous and can harbor contaminants. Mycoplasma culture can be requested with the bacterial culture sample. This may be a particularly useful culture to request for cats with diffuse lower airway disease.
Keep a sample for yourself! You may not be a clinical pathologist, but you should feel confident evaluating for obvious cytologic abnormalities such as intracellular bacteria, eosinophils, and degenerative neutrophils. Characterizing the bacteria (rods v. cocci) may help you better choose an empirical antibiotic while waiting for cytology and culture results to return.
Managing client expectations is always important. The following discussion points are good to communicate with a client:
- There is risk involved with performing this procedure and sometimes the patient’s respiratory status can worsen after the procedure.
- The turn around time for cytology can be 1-3 days and culture can be 7 days for a positive culture, and up to 2 weeks for Mycoplasma culture.
- The cytology and culture may not provide the complete picture regarding the patient’s condition. There are times when we recommend a bronchoalveolar lavage as a follow up to a non-diagnostic endotracheal wash.
Endotracheal wash is a great diagnostic tool that can be used in private practice to work up a variety of lower airway diseases. It does not require specialized equipment and it should be considered for your patients that have radiographic evidence of diffuse lower airway disease.