Collection of bronchoalveolar fluid using a blind technique in cats
Collection of bronchoalveolar lavage fluid using a blind technique in cats
Carol R. Reinero, DVM, DACVIM (Small Animal Internal Medicine), PhD
University of Missouri
Columbia, MO, USA
Disorders of the respiratory tract are a common reason for cats to seek medical attention. There are a wide variety of disorders including those affecting the upper airways, lower airways, pulmonary parenchyma and pleural space. A wide variety of diagnostic tests are available to help discern the underlying reason for the particular type of pathology. One of the earliest and most important diagnostic test for respiratory disease in cats is thoracic radiography. While thoracic radiography provides great value in discriminating cardiac from respiratory causes of clinical signs, and in localizing the site of the affected respiratory tract (airways, parenchyma, or pleural cavity), it does not provide a cellular diagnosis. After initial diagnostic tests, including thoracic radiography are performed and point to disease of the lower airways and pulmonary parenchyma, sampling of these regions may be necessary for a definitive diagnosis. There are a wide variety of clinically important respiratory diseases in the cats affecting these regions including infection, non-infectious inflammatory or fibrotic disorders and neoplasia. Microscopic evaluation and culture of acquired material can be extremely helpful. Cytologic specimens are classically obtained by using trans-thoracic fine needle aspiration, endotracheal lavage, bronchoalveolar lavage or bronchial brushings. This lecture will describe a technique for obtaining bronchoalveolar lavage fluid without the need for a bronchoscope which requires additional expense, expertise and may provide additional risk of airway obstruction. The blind technique for collection of bronchoalveolar lavage fluid can be performed quickly, easily and without the requirement for specialized equipment.
There are several supplies to be gathered prior to performing a blind bronchoalveolar lavage fluid collection. As pre- and post-procedural oxygenation is recommended, an oxygen tank and mask should be hand. The author pre-medicates cats with terbutaline as a bronchodilator, assuming there is no contraindication (e.g., hypertrophic cardiomyopathy, etc). Cats should receive 0.01 mg/kg intramuscularly or subcutaneously 20-30 minutes prior to the procedure. A laryngoscope with an appropriately sized blade, lidocaine (0.2 ml in a tuberculin syringe with the needle removed), sterile endotracheal tube (two sizes based on the size of the cat), an 8 french sterile red rubber catheter, sterile warmed 0.9% saline filling a 20 ml syringe (capped with a needle to ensure sterility until ready), and two to three sterile tubes without additives (one for cytology, one for culture). Depending on prior conversations with the laboratory performing cultures, a sterile tube without additives may be less optimal than using a specialize culturette (swab). Most cats will use an endotracheal tube of 4.0 or above; this is ideal since an 8 french red rubber catheter will easily pass through the lumen of these sized tubes. Saline warmed to body temperature will reduce the degree of bronchoconstriction (compared to cool saline). Monitoring with a pulse oximeter is advised.
ANESTHESIA AND INTUBATION
The cat should have a short intravenous catheter placed (e.g., cephalic catheter). Pre-oxygenation for 3-5 minutes is recommended. A short acting anesthetic agent can be administered using the iv catheter. The author prefers propofol, although other combinations such as ketamine and valium, are also acceptable. The anesthetic protocol should ideally be short lived and given in a low dose titrated to effect. The entire procedure takes well under two minutes. After induction and prior to intubation, a small volume of topical lidocaine can be placed on the arytenoids to prevent laryngospasm. Intubation can then be performed with a sterile endotracheal tube, taking care not to touch the tip of the endotracheal tube to the oral cavity.
POSITIONING AND CATHETER PLACEMENT
After intubation, the cat can be placed in lateral recumbancy. The neck should be outstretched so there is a straight line between the tip of the nose and carina. While the red rubber tube is still within the sterile package, it can be held above the cat to measure/estimate how deep the wedge needs to be. Roughly it should be inserted around the last rib (ie measure the distance from the tip of the endotracheal tube to the last rib). In a sterile fashion, the red rubber catheter should be gently threaded through the lumen of the endotracheal tube, while an assistant helps maintain the straight line of the body position. There should be no resistance to catheter passage until it is close to being wedged. If there is resistance, the catheter can be gently rotated or “spun” while gentle pressure is exerted to move it forward. It should never be forcibly pushed. Once it is firmly wedged and in the correct estimated position, the lavage procedure can be commenced. It is important to remember that the technique of catheter placement must both be done correctly and quickly, as the catheter is occupying the majority of the lumen of the endotracheal tube.
THE LAVAGE PROCEDURE
When the catheter is wedged in place, the 20 ml syringe filled with 20 ml of sterile warmed saline is attached. In a rapid smooth fashion, the entire aliquot of saline should be instilled. Using gentle manual suction, the fluid is aspirated back into the syringe. There should never be extreme suction placed on the syringe as that can create trauma and artificial hemorrhage. If there is negative pressure felt, the pressure should be let off, the catheter backed out very slightly, and pressure can be reapplied again. Aspiration can be continued in this fashion with gentle suction followed by release of the suction if there is no fluid brought into the syringe and backing out of the catheter to try again. If there is any point where fluid is being retrieved into the syringe, the catheter should stay in place at that level until no more fluid is being retrieved. A reasonable volume of retrieval is 50-80% of the volume of the fluid instilled. Within the syringe, a foamy layer which represents surfactant, should be seen. Once there is a reasonable volume of saline within the syringe and no more fluid is aspirated, the red rubber tube should be fully removed. To help remove any residual fluid, the hindquarters are raised and the chest undergoes coupage, with gravity helping drainage of the fluid. Supplemental oxygen can be provide while the cat is intubated, and as needed after extubation using a face mask. In some instances, recovery in an oxygen cage (or other oxygen enriched environment) may be beneficial.
WHAT TO DO WITH THE SAMPLE
As promptly as possible, the samples should be processed. Taking care to keep the aliquots of saline sterile, the culture should be prepared first. If a sterile tube without preservatives is being used for transport, there should be a new needle placed on the 20 ml syringe first. The sterile tube cap can be wiped off with alcohol and a small volume of the bronchoalveolar lavage fluid instilled. The volume in part depends on how much was retrieved, but generally 1 ml should suffice. The remainder of the aliquot is used for cytology. Assuming a large enough volume and the need to send a sample to a clinical pathologist off-site, the remaining sample can be split into two aliquots. One can be placed into the tube without additives and placed on a refrigerated pack for transport (or on ice, or in the fridge if there will be a delay in transport). The other sample can be processed in a similar fashion to a urinalysis. Briefly the bronchoalveolar lavage fluid can be centrifuged to create a pellet and overlying fluid layer. The overlying fluid layer can be decanted leaving the pellet. A drop of sterile saline can be added as needed to resuspend the pellet. The pellet can then be smeared out on several slides. It is recommended to view at least one slide in-house to have a general but rapid determination of the underlying disease process as that may affect the therapeutic plan. The other slides should be left unstained and left to air dry. These slides can be sent to the outside laboratory. in a case along with the other aliquot of bronchoalveolar lavage fluid for cytology; and the culture.
General anesthesia poses a risk to all patients to a certain degree. Those with more severe respiratory compromise or other comorbid conditions have a higher risk. The procedure of bronchoalveolar lavage fluid collection can be associated with transient hypoxemia. Pre-treatment with supplemental oxygen and with a bronchodilator can minimize the severity of the hypoxemia. Pneumothorax is rare and is generally only observed either if there is a risk factor (eg a pulmonary bulla) or if a stiff polypropylene catheter is used in place of a red rubber catheter.