CHAPTER 45 Bronchoscopy
Bronchoscopy is a valuable tool for investigation of lower respiratory tract disease. Direct visualization of the airways and bronchoalveolar lavage (BAL) of a specific airway segment can provide a definitive diagnosis of infectious, inflammatory, or neoplastic causes of cough and respiratory distress. Additionally, bronchoscopy allows therapeutic intervention and cure in cats with respiratory disease related to foreign body aspiration. Several factors make this procedure technically challenging in cats. Bronchoscopy requires general anesthesia, and this often is a concern in a patient with respiratory disease. The small size of the feline trachea does not allow intubation for ventilation and oxygenation throughout the procedure as is usually possible in dogs. In addition, small-diameter flexible endoscopes are preferred because of the small airways in cats, and these can be difficult to manipulate. Specific training and experience is needed to ensure proficiency and efficiency in completion of the endoscopic evaluation. Finally, cats are believed to develop bronchospasm during BAL, resulting in an increase in airway resistance1 that could impact anesthetic recovery adversely. Nevertheless, bronchoscopy can be performed safely in most cats and can provide invaluable information on the etiology of disease and the need for specific therapy.
Careful case selection and prior planning maximizes the likelihood of successful completion of a bronchoscopic procedure in the cat. Feline bronchial disease is the most common cause of acute or chronic cough, tachypnea, or respiratory distress, and these cats are all potential candidates for bronchoscopy. Bronchoscopy with BAL for cytological examination and culture can confirm inflammatory airway disease in the absence of Mycoplasma infection, airway parasites, or foreign body pneumonia that can cause clinical signs similar to bronchial disease. However, bronchoscopy should not be performed in any animal unstable for anesthesia. Obese patients with increased respiratory effort may have difficulty recovering from anesthesia, although this is less common in cats than in dogs.
Surgical intervention may be required in a cat with an intraluminal airway mass, obstruction, or foreign body in a large airway. If a mass is present in the tracheal region, preparations should be made before anesthesia for a possible tracheotomy. Alternately, a foreign body or mass in the lower airways could require a thoracotomy. These procedures usually should be performed immediately because of the difficulty in recovering a cat with an airway obstruction. Cats with bullous or emphysematous lung disease evident on radiographs or computed tomography (CT) are at risk for pneumothorax during ventilation or during bronchoscopy, if the endoscope is wedged in a fragile airway.
Complications from bronchoscopy with BAL in the cat are relatively common and should be anticipated. In a recent report, over one-third of cats experienced some form of complication; however, the majority were minor and consisted of hemoglobin desaturation, abrupt termination of the procedure, or prolonged recovery from anesthesia.2 These complications may not be a specific feature of bronchoscopy because nonbronchoscopic BAL via endotracheal tube collection in healthy cats also can result in dramatic reduction in arterial oxygenation.3 In most situations, administration of supplemental oxygen results in rapid resolution of hypoxemia. Some cats may require recovery in an intensive care unit. Careful monitoring of respiratory rate, effort, and lung sounds always is advised in the immediate postoperative period. Although rare, pneumothorax has been reported as a complication of bronchoscopy in both cats and human beings.2 Owners should be aware that bronchoscopy can result in mortality caused by worsened respiratory distress postprocedure or from an inability to restore ventilation and oxygenation after anesthesia.
A number of companies supply fiberoptic or video endoscopes that can be used in feline airways. A key component in the flexible endoscope is the presence of a channel through which to perform BAL. Although a rigid telescope can be used for laryngeal and tracheal investigation, it can not be maneuvered throughout the airways and does not have a channel for lavage. In addition to the flexible endoscope, a light source (xenon or halogen) is required. An imaging system is valuable for archiving the visual appearance of the airways. The following discussion details the author’s experience with endoscopes used in feline bronchoscopy.
Feline bronchoscopy ideally should be performed with a flexible endoscope less than 5.0 mm in outer diameter that contains a channel for lavage and instrumentation. A pediatric bronchoscope commonly available in specialty veterinary hospitals or universities (Olympus P20D, Melville, NY) can be used in cats, although it is slightly larger in diameter than ideal at 5.0 mm × 55 cm in length. This endoscope provides good visualization of the carina and mainstem bronchi but is too large in most cats to pass into lobar bronchi other than the left and right caudal bronchi. When performing BAL with this endoscope, the relatively large diameter of the channel (2.0 mm) results in sampling of a larger bronchus rather than a bronchoalveolar segment. This endoscope is valuable for foreign body retrieval and biopsy of proximal lesions because of the relatively large channel and the availability of multiple instruments that can pass through this channel.
A specialized fiberoptic endoscope (Karl Storz 60003VB, Goleta, CA) designed for urethroscopy provides access to many of the segmental bronchi of the cat and therefore allows thorough examination of the airways. This 2.5 mm × 70 cm endoscope has a 1.2 mm channel that can be used for lavage or for obtaining small biopsy samples. The small diameter of the endoscope results in less light transmission down the airways, which can compromise image quality. Additional practice is required to maneuver this endoscope through the airways because of its small diameter and relatively long length. Recovering lavage fluid requires patience because of the small channel size, and gentle intermittent suction generally is most successful in recovering lavage fluid. A hybrid fiberoptic videoscope of similar diameter is now available from Olympus Medical.
Olympus also makes a number of smaller (3 to 3.8 mm diameter) fiberoptic or video endoscopes. The 3.8 mm × 55 cm video endoscope (Olympus BF3C160, Melville, NY) has a 1.2 mm channel and can access lobar bronchi and some segmental bronchi in most cats. The main advantage of this endoscope is improved maneuverability in the airways and better image quality, which allows superior assessment of epithelial changes associated with disease.