Читать книгу Canine and Feline Respiratory Medicine - Lynelle Johnson R., Lynelle R. Johnson - Страница 46

Bronchoscopy is one of the most useful techniques for providing a diagnosis in animals with airway or lung disease. It can define the location, grade, and extent of tracheal ring flattening for planning stabilization through surgery or stent implantation, identify protrusion of the dorsal tracheal membrane into the tracheal lumen, document tracheal inflammation or irritation, visualize intrathoracic bronchial or airway collapse, and allow collection of BAL fluid to determine the contribution of small airway disease to respiratory signs. It is also highly useful and successful in managing foreign body inhalation.

Complications that can be encountered after bronchoscopy are worsened cough or increased airway obstruction. These occur most commonly in dogs that have severe tracheal collapse or bronchomalacia, because irritation of the airway potentiates a cough, and suppression of respiratory effort by anesthetic agents allows passive collapse of diseased large and small airways. Excessive stress that induces cough and respiratory distress during recovery is particularly troublesome. Coughing can be partly alleviated by administering dilute lidocaine (approximately 1 ml of 1% lidocaine for a small dog) through the bronchoscope into the trachea at the end of the procedure. Subcutaneous terbutaline (0.01 mg/kg) may improve respirations in dogs with collapsed airways (although it does not act as a bronchodilator in this situation), and recovery in an oxygen‐enriched environment can lessen respiratory distress. Bronchospasm can be a particular problem in the cat with inflammatory airway disease that has severe cough and respiratory distress. Terbutaline should be given subcutaneously immediately prior to the procedure at 0.01 mg/kg to produce airway smooth muscle relaxation and reduce complications. Aerosolized albuterol can be given through the endotracheal tube at the end of the procedure if injectable terbutaline is not available.

General anesthesia is required during bronchoscopy to suppress coughing and laryngospasm, to allow examination of the airways without inducing trauma, and to protect the endoscope. Bronchoscopy can be performed using gas anesthesia if the animal is large enough for a 7–8 mm endotracheal tube. A special T adapter is used to pass the scope through the endotracheal tube while administering anesthetic gas and venting expired gases (Figure 2.18). In small dogs and cats, jet ventilation is typically used to provide oxygenation through bulk flow, because placement of the scope through a small endotracheal tube would lead to airway obstruction and accumulation of CO₂. As an alternative, oxygen can be supplied to the patient using a red rubber catheter attached to the oxygen supply. The catheter should terminate in the distal trachea to avoid the possibility of wedging it into a bronchus and causing airway rupture.

Virtually all animals undergoing bronchoscopy suffer respiratory embarrassment. Prior to bronchoscopy, patients are preoxygenated with a facemask, and an anesthetic protocol is chosen that avoids excessive cardiopulmonary depression. Animals are placed in sternal recumbency and two mouth gags are in place throughout the procedure to protect the bronchoscope. The normal trachea appears round to oval, with minimal laxity in the dorsal tracheal membrane (Figure 2.19). At the carina, bifurcation in the left and right mainstem bronchi provides a reliable landmark for assessing location within the airways (Figure 2.20). Normal airways appear round to oval in shape, demonstrate little change in shape or diameter throughout respiration, have minimal secretions, and are pale pink in color (Figure 2.21). All accessible airways should be evaluated and abnormal regions with mucosal hyperemia or irregularity or areas with mucus accumulation should be identified as possible sites for BAL. If an obviously abnormal site is not visualized, the right middle lobe or caudal portion of the left cranial lobe is often a worthwhile site to lavage, because they are both ventrally oriented and tend to accumulate secretions.

Figure 2.18 A bronchoscopy adapter allows passage of a 5.0 mm endoscope through an endotracheal tube while oxygen and anesthetic gas are administered through the side port.

Figure 2.19 Endoscopic view of the normal canine trachea.

Figure 2.20 Endoscopic view of the carina illustrating the openings into the right principal bronchus (RPB) and left principal bronchus (LPB).

Figure 2.21 Distal airway openings in the dog exhibit relatively sharp bifurcations into round to oval airway openings. The epithelial surface is smooth.

After examining all visible airways, the scope is withdrawn from the airways, the outside is wiped with saline‐soaked gauze pads, and the biopsy channel is flushed with sterile saline. On the second entry to the airway, the scope should be kept in the center of the airways to limit upper airway and mucosal contamination when approaching the site for lavage. Success in achieving a diagnostic BAL will depend on the ability to wedge the bronchoscope gently into a small airway and isolate a segment of alveolar volume (Figure 2.22). The goal is to flood this small wedge of lung with sterile non‐bacteriostatic saline, float the resident inflammatory cells, and gently aspirate back the fluid. Fluid should be fully ejected from the scope into the alveolar space by flushing gently with a small volume of air (3–5 ml) before beginning the aspiration. The volume of fluid used depends on the size of the scope in relation to the size of the animal, experience of the operator, underlying disease process, and degree of respiratory compromise (Table 2.4), although ~1 ml/kg has been also recommended. If the fluid has been in contact with the alveolar space, it will be foamy because of the presence of surfactant. Flocculent material is usually mucus from bronchial contamination. If a sufficient sample is not recovered from the lavage (generally 50–70% of the fluid will be recovered), a second lavage should be performed at the same site. In human medicine, multiple lavages are commonly obtained and the first is not analyzed, because it represents more of the bronchial component rather than alveolar. It is unclear how often this is done in veterinary medicine. It is recommended to lavage at least two distinct lung sites because of inherent differences in the inflammatory cell populations among the lung lobes and with different disease processes.

Figure 2.22Bronchoalveolar lavage (BAL) is performed by gently wedging the bronchoscope into the smallest airway possible. The volume of the region lavaged (represented by red and yellow triangles) will depend on the size of the scope and the size of the animal.

Table 2.4 General guidelines for performing bronchoalveolar lavage (BAL).

Scope size	Animal size	Milliliters per aliquot
2.8–3.8 mm outer diameter	Cats Dogs <6 kg	3–5 ml 5–10 ml
4.9–5.5 mm outer diameter	Dogs	15–20 ml

When using a scope >6 mm outer diameter, consider passing sterile polypropylene tubing through the biopsy channel to wedge for BAL rather than using only the channel. Beware that the tubing can puncture the airway if extended with force.