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Airway lavage (Proceedings)
There are several ways to obtain samples from the airways and lower respiratory tract for cytologic evaluation and microbiologic culture. In general, samples should be handled quickly since respiratory epithelial cells degrade with some rapidity after retrieval, and samples should be handled gently to avoid damaging cell membranes.
There are several ways to obtain samples from the airways and lower respiratory tract for cytologic evaluation and microbiologic culture. In general, samples should be handled quickly since respiratory epithelial cells degrade with some rapidity after retrieval, and samples should be handled gently to avoid damaging cell membranes. Ideally, samples are placed on ice if there will be a delay in preparation for cytologic exam. Preferably, samples may be prepared by cytospin. Alternatively, lavage samples can be sedimented in a manner similar to urine specimens and a gentle line smear prepared and allowed to air dry. Samples can be evaluated cytologically for quantification of cell types, identification of neoplastic or reactive cells, and identification of infectious organisms or foreign material.
Cultures should be performed quantitatively since normal airways are not necessarily sterile. It is also important to interpret culture in light of cytologic findings, because bacterial growth in the absence of inflammation may not be meaningful but may instead represent contamination or normal flora. Since up to 25% of bacterial pneumonia is caused by anaerobic pathogens, anaerobic culture assumes an importance that may not be intuitive in lung disease. When samples are sent out, transport tubes to support anaerobic growth should be used as well as routine transport media. Liquid samples can be placed in transport media directly, or swabs of the liquid may be used for culture. Special cultures or PCR procedures are needed to identify Mycoplasma sp. or fungal organisms.
Tracheal lavage is indicated for diagnosis of large airway disease, and is particularly useful to obtain microbiologic and cytologic samples in animals with productive pneumonia. These samples can sometimes provide useful diagnostic material for diffuse alveolar disease, but tracheal lavage is rarely useful in the diagnosis of interstitial lung disease. Tracheal lavage is a simple, inexpensive technique that requires no special equipment and is relatively safe and minimally invasive. The two techniques are endotracheal lavage and transtracheal lavage.
Endotracheal lavage is useful for cats and small dogs. It does require a brief general anesthesia but is extremely simple to perform and complications are very rare. Supplies needed include laryngoscope, sterile endotracheal tube, sterile red rubber catheter, several syringes of sterile saline, and sterile collection tubes. Syringes should be pre-filled with from 5-8 ml of sterile saline. The animal is administered injectable anesthetic to a depth that allows endotracheal intubation. Intubation is facilitated by topical application of lidocaine to the laryngeal cartilages of cats, and by the use of a laryngoscope. In either species, the tongue should be grasped with a gauze sponge and pulled forward to improve visualization of the larynx. The animal is intubated as cleanly as possible, trying to avoid allowing the tip of the endotracheal tube to contact the oral surfaces. From 2-10 breaths of 100% oxygen should be administered prior to completion of the wash procedure, usually by attaching the endotracheal tube to an anesthetic machine. The endotracheal tube is disconnected from oxygen, and the sterile catheter is advanced through the endotracheal tube until its tip is at approximately the level of the carina. The first fluid filled syringe is attached and the fluid injected as a bolus. The syringe is then used to rapidly aspirate back in an attempt to recover injected fluid. This procedure is repeated 2-3 times. Because the anesthetized animal does not actively cough, fluid recovery may be poorer than for TTW and only a small volume of fluid is recovered (the rest is reabsorbed). The lumen size of a red rubber catheter may mean that more suction needs to be applied to recover fluid all the way into the syringe; this may be better accomplished with a larger syringe (20 cc) as opposed to repeatedly emptying the air from the smaller injection syringe. As soon as adequate diagnostic samples (1-2 ml of turbid fluid) are recovered, anesthesia may be discontinued. Tipping the animal with head down and abdomen elevated may allow drainage of excess fluid through the endotracheal tube, and this fluid can be used for cytologic exam (but not for culture because of oral contamination). The animal should be administered oxygen via the endotracheal tube until a laryngeal reflex (swallow) has returned, and then extubated. The animal should be observed for cyanosis or dyspnea for 15-30 minutes after completion of the procedure.
Transtracheal lavage is used instead of endotracheal lavage in medium to large dogs, and has the advantage of not requiring general anesthesia. In depressed animals, only a SQ injection of lidocaine is required. For more active dogs, a mild sedative may be needed (ideally, avoid opioid sedatives as they suppress cough). Complications, though rare, include lacerations, SQ emphysema, pneumomediastinum, and possible tracheal foreign body if the catheter tip is sliced off. Supplies needed include lidocaine, sterile gloves and prep solution, several 10-12 ml syringes, sterile saline solution, sterile collection tube, "through-the-needle" jugular catheter (e.g., Intercath; 16-22 ga), gauze sponge, antibacterial ointment, and bandage wrapping material. A 14 ga "over-the-needle" catheter and 3.5 Fr. polypropylene catheter can be used as an alternative to the "through-the-needle" catheter. An endotracheal tube and oxygen source should be available as a precaution.
Four to five syringes should be pre-filled with 5-8 ml of sterile saline. The dog should be restrained in either sternal recumbence or in a sitting position with the nose tilted towards the ceiling at about a 45° angle. The ventral surface of the neck is clipped and cleaned, and a small bleb of lidocaine placed at the site of needle insertion. Insertion may occur through the cricothyroid ligament, but in larger dogs entry may be between any two tracheal rings. In choosing the point of entry, catheter length must be considered. The catheter should be able to reach from the point of insertion to approximately the level of the carina (at about the fourth intercostal space). This length of catheter should be noted ahead of time. The skin is tented over the point of entry, and the needle inserted with the bevel facing downward. This is important to guide the catheter down toward the lungs rather than up toward the mouth. Grasping the trachea to stabilize it, insert the needle through the lidocaine bleb and the cricothyroid ligament (or between the cartilage rings) with a rapid, firm, stabbing motion. The needle is threaded slightly downward into the tracheal lumen. The catheter may now be advanced through the needle. The dog will often be stimulated to cough during this movement. If instead they gag, it may mean that the catheter has gone up toward the mouth rather than down toward the lungs. The catheter should NEVER be backed up through the needle as it may be sheared off by the needle bevel thus creating an airway foreign body. If there is minor resistance to catheter advancement, the entire needle and catheter can be adjusted and moved AS A UNIT. Once the catheter has been advanced to just past the level of the carina, the needle can be backed out of the trachea while leaving the catheter in place. Remember to move the needle and catheter as a unit. Place the needle guard over the needle, or pinch it with your fingers so that it can not slice the catheter off. At this point, your grasp on the trachea can be released. The first of the fluid-filled syringes is attached to the catheter. The fluid is rapidly injected as a bolus. Ideally, the dog begins to cough when the fluid is administered. If not, an assistant can coupage the chest to stimulate cough. Nearly as soon as fluid injection is complete, the syringe should be used to aspirate back quickly in an attempt to draw the fluid back up into the catheter and syringe. Unlike aspirating a lump or mass, the syringe will rapidly fill with air as well as fluid. Because multiple aspirations must be completed in rapid succession, you will need to quickly disconnect the syringe, expel the air (but not fluid), reattach, and aspirate again. Alternatively, the syringe can be exchanged for an empty one that is used for the next aspiration. After a number of attempts to aspirate fail to produce more fluid, a new fluid filled syringe is attached and the procedure is repeated. This sequence can be repeated several times. The goal is to recover only a small fraction of the injected fluid. If one to two ml of turbid fluid containing flecks of mucus is recovered, that is a very adequate diagnostic yield. When the procedure is complete, the samples may be aseptically transferred to a sterile tube such as a serum vacutainer tube for transport, or may be processed for cytologic examination and culture immediately. Samples degrade rapidly, and should therefore be processed within one hour. If they will be sent to an outside laboratory, some dry cytologic slides should be prepared as well as submitting the cooled fluid. The needle and catheter unit may be removed as soon as adequate samples are obtained. A small gauze sponge with antibacterial ointment should be placed over the entry site and held in place for several hours with a loose wrap. The dog should be observed for signs of dyspnea or cyanosis for 15-30 minutes after completion of the procedure.
Bronchoalveolar lavage (BAL) is indicated for the diagnostic evaluation of small airway disease and alveolar disease, and can sometimes prove useful in the diagnosis of interstitial lung disease. The samples produced by BAL are quite different from samples produced by tracheal lavage, coming from the deeper areas of lung and distal airways. While BAL samples are excellent for cytologic evaluation of the airways and for culture, there are disadvantages to its use. It requires general anesthesia, results in transient hypoxemia due to ventilation perfusion mismatching, and can produce bronchospasm. Because of the induced hypoxemia, respiratory distress is a relative contraindication to BAL.
There are two methods for BAL, a blinded method and a bronchoscopically guided method. The blinded method requires no special equipment, and is simple and inexpensive. The bronchoscopically guided method allows lavage of specific areas of the lung, a useful feature when disease is localized to only some lung lobes. Of course, use of the bronchoscope also allows direct observation of the airways but requires appropriate bronchoscopic equipment and a degree of expertise.
Blinded BAL is perhaps most useful in the evaluation of cats with suspected asthma. The cat is administered injectable anesthesia to a depth to allow intubation. As for endotracheal wash, efforts should be made to keep intubation as clean as possible. After several minutes of breathing 100% oxygen, a catheter is passed through the endotracheal tube. Instead of stopping at the level of the carina, the tube is advanced until it is firmly wedged; at this point is should be in a bronchus but there is no way of guiding it to a specific bronchus or even a specific lung lobe. A syringe filled with warm or room temp sterile saline is attached to the catheter, the saline rapidly administered, and suction applied to the syringe. The cat's hindquarters can be elevated to promote fluid recovery. This procedure can be repeated twice more. Usually, from half to 3/4 of the volume instilled is removed, although even smaller recovery of fluid can be adequate and safe. Recovery of a foamy liquid indicates the presence of surfactant, and is evidence of a good wash. The cat is allowed to recover with 100% oxygen, and may benefit from bronchodilator administration during recovery.
For bronchoscopically guided BAL, the scope is guided into one or more specific lobes; airways are observed prior to lavage. The lavage is accomplished through the scope itself after the scope is lodged into a distal airway. Aliquots from different lobes can be kept separate or combined. Complete discussion of bronchoscopy is beyond the scope of this talk, but requires some expertise.
Sterile bronchial brush samples can be used for both culture and cytology of the airways and can be obtained in a blinded or bronchoscopically guided fashion. The samples are only useful for airway or productive alveolar disease, and the samples are vastly smaller than samples produced by BAL. The brush itself is expensive, making this procedure more costly than BAL. The single advantage over BAL is that the quick procedure does not cause hypoxemia.
Blind BAL, the specifics
Obtain samples for culture and cytology for animals with diffuse pulmonary alveolar infiltrates, bronchial disease or a cough of unknown cause. The blinded BAL cannot be obtained from any specific region of lung and is therefore best for diffuse disease. Bronchoalveolar lavage is used to obtain diagnostic specimens from the lower airways and alveolar space, in contrast with tracheal wash procedures which obtain samples from the trachea. While tracheal wash may yield a diagnostic sample, a greater degree of diagnostic information can be obtained from the bronchoalveolar lavage procedure. Prior antibiotic or corticosteroid therapy may affect test results
Since the indication for BAL is pulmonary disease, animals are at risk for respiratory compromise and potential respiratory arrest during or following the procedure. Hypoxemia and bronchoconstriction (cats) are frequently encountered and plans to deal with these complications should be in place (ie, supplemental oxygen and premedicating with bronchodilators in cats). Specifically, pleural space disease can develop after the procedure (eg, pneumothorax, pyothorax). The procedure is contraindicated in animals with coagulopathy that may be associated with intrapulmonary hemorrhage.
Sedation/ anesthesia/analgesia protocols
This procedure requires brief general anesthesia. This can be performed with Propofol, and Propofol or ketamine-diazepam combinations. The plane of anesthesia should be of sufficient depth to allow for endotracheal tube placement, but not to such depth that voluntary respiration ceases. The animal should be allowed to breathe 100% oxygen before and immediately following the procedure since oxygen desaturation is common when the animal has significant pulmonary disease. Pain is not generated by BAL and analgesics are not specifically indicated. Cats benefit from premedication with a bronchodilator such as terbutaline, providing there are no other contraindications (eg, cardiac disease).
• Sterile endotracheal tube of a size sufficient for the animal
• Sterile 8 French Brunswick red rubber catheter with the tip cut off and the edges smoothed
• There is no one agreed upon amount of saline to use in the literature. Our "standard" amounts are as follows:
o Cats 15-20 ml aliquot. Can be repeated ONCE in a patient that is doing well under anesthesia. Oxygen support may be given between aliquots if appropriate
o Dogs 20 ml aliquot. Should be repeated at least once and multiple times (3-4) in larger dog breeds
• Lidocaine (few drops topically placed on arytenoid cartilages to prevent laryngospasm in cats)
•Warmed (37o C) sterile saline in 20ml syringes
• Sterile scissors or scalpel blade to adjust the syringe-attachment end of the catheter to form a tight seal (specifically for Brunswick Red Rubber Catheters)
• Sterile sample tube or culture media for culture sample
• Glass slides for cytology
• Ambu-bag or anesthetic circuit to provide manual ventilation if voluntary respiration stops
• Terbutaline or albuterol for cats
• Emergency drugs in case of sudden cardiopulmonary arrest
Prepare all materials prior to induction of anesthesia in order to minimize duration of anesthesia.
Place indwelling intravenous catheter to deliver injectable anesthesia and emergency drugs if needed. Typically, cats are given 0.01 mg/kg Terbutaline SQ or IM 15 minutes just prior to the procedure. Albuterol can also be given after the procedure (1-2puffs of a 90mcg metered dose inhalant, or 1.25mg (0.25ml) as a 0.5% solution for nebulization in 2ml of normal saline using a face mask.
Pre-oxygenate for 5 minutes with mask oxygen
Induce anesthesia. Place sterile endotracheal tube as rapidly and cleanly as possible (idea is to keep the inside sterile, the outside does not need to stay sterile). Lidocaine can be used for cats and does not affect sample collection. Using sterile technique, introduce the sterile catheter into the endotracheal tube and advance it through the trachea into the lower airways until the catheter will no longer advance. Do not force the catheter or use excessive pressure. Once the catheter has "seated" into a bronchus (the point at which the catheter stops), attach a saline-filled syringe, rapidly instill the aliquot of saline, and gently aspirate using manual suction. If no saline is retrieved, gradually withdraw the catheter by a few millimeters while aspirating. If the animal does not show excessive respiratory distress, repeat this step one to two more times until a diagnostic sample is retrieved. Alveolar fluid should demonstrate some foam which represents surfactant. Following the procedure, anesthetic monitoring and recovery should proceed as normal. The patient will typically have crackles for a short period of time following the procedure, but should resolve in 10-20 minutes. Once the animal is extubated, careful attention is warranted to assess for respiratory difficulty and need for supplemental oxygen.
An aliquot should be placed sterilely into an appropriate container for bacterial culture and cytology. Ideally the remainder should be properly processed by a lab (Cytospin, automated cell counts) within 20 minutes of collection. However, if this is unfeasible then an aliquot can be spun on the urine setting with a centrifuge. The supernatant is removed and the pellet is stained and evaluated for quality of sample (a small amount of saline can be added to resuspend the pellet so it can be smeared on a slide). If the cellularity is too dense, the additional saline should be added to the pellet and another slide prepared. Unstained slides can also be made from the pellet and let to air dry to ideally be evaluated later by a clinical pathologist.
The animal should be extubated when spontaneous respiration is present and the swallowing reflex returns. 100% oxygen can be delivered until pulse oximetry readings indicate > 96% hemoglobin saturation. Continued supplemental oxygen should be prescribed on an "as-needed" basis pending diagnosis and response to therapy.