Endoscopy allows the unique opportunity to visualize the internal anatomy of the nasal cavity and airways, to document alterations in the space and structure of the airways, and to collect specific airway samples from areas of disease. It also provides the opportunity for minimally invasive cure of benign, obstructive lesions of the upper or lower airway, such as nasopharyngeal stenosis and tracheal collapse. In addition, palliation of clinical signs can be achieved when malignant obstructions are identified in the nose, nasopharynx, or airway. In most animals, endoscopy is a safe and effective procedure that provides complementary information to that gained from imaging studies. Careful patient selection and an understanding of potential complications that can be encountered are essential for performing a successful procedure.
Rhinoscopy is indicated for evaluation of acute or chronic nasal discharge, epistaxis, or obstructed nasal airflow. Examination of the choanae with a flexible endoscope (> 5 mm outer diameter) is generally performed first. The animal is fully anesthetized and has 2 large mouth gags in place. Local anesthesia of the oropharynx with lidocaine gel can facilitate placement of the scope around the soft palate. Extending the neck and pulling the tongue forward will also help place the endoscope in the proper position. The non-flexed scope is placed in the oral cavity and then flexed until the light can be seen above the soft palate. The scope is then pulled forward (with the flex in place) until the choanae are visualized. Note that the image is upside down and backwards. After the caudal nasopharynx is examined and samples are obtained, the scope is un-flexed and withdrawn. A moistened lap pad is used to pack the throat and prevent aspiration during rostral rhinoscopy.
Equipment available for rostral rhinoscopy includes flexible and rigid endoscopes. Rigid scopes have better optics, are easier to maneuver, and come in smaller sizes, while flexible scopes allow greater access to the nasal cavity and can permit examination of the frontal sinuses when there is marked turbinate destruction (as in aspergillosis). Rhinoscopy can be performed using the telescope portion of the rigid scope alone (~ 2.7 mm outer diameter), or by using the sheathed scope (~ 5 mm outer diameter), which has flush and suction ports, and a biopsy port that accepts standard endoscopic biopsy or foreign body retrieval instruments. Continuous saline infusion and intermittent suction can be valuable for clearing the visual field when excessive mucus or blood is present.
When performing antegrade rhinoscopy, evaluate the less affected side first. Before entering the nasal cavity, place the scope against the skull and measure to the level of the medial canthus of the eye. Place a piece of tape on the scope and biopsy instrument to avoid penetrating the brain via the dorsal nasal meatus. The primary changes to look for and record are mucosal hyperemia, mucus accumulation, epithelial irregularities, turbinate destruction (visualized as increased space between turbinates), and mass lesions (these usually reduce space in the nasal cavity, either by growing between the turbinates or causing swelling of the turbinates into the meati). In dogs with turbinate destruction or loss, close evaluation for fungal plaques is indicated, and if sinus involvement is evident on CT or skull radiographs, trephination and sinuscopy are recommended.
Indications for tracheoscopy or bronchoscopy include chronic cough, hemoptysis, obstructed breathing, or unexplained pulmonary infiltrates (focal, diffuse, lobar, bronchial, alveolar, or consolidation). Bronchoscopy allows collection of deep respiratory samples for culture and cytology and allows characterization of disease by visualization of the airways. A more accurate prognosis can be provided for animals with chronic bronchitis or bronchiectasis. Bronchoscopy also allows evaluation of dynamic airway changes in tracheal collapse and bronchomalacia, and helps determine whether a tracheal stent is indicated for therapy. Foreign body removal can be performed, and with bronchoscopy, causes for treatment failure or relapsing disease can often be detected.
A bronchoscope ≤ 5.0 mm outer diameter is most versatile for evaluating the airways of various sizes of dogs, and 2.5–3.8 mm is best for cats. Most of these scopes have small (2 mm) channels that accept instruments of 1.8 mm or less. At least bidirectional flexion of the endoscope tip is required to provide maneuverability while evaluating the airways, and 4-way flexion is of value for use in foreign body retrieval.
Bronchoscopy is most commonly performed in sternal recumbency although some practitioners prefer lateral positioning. General anesthesia is a necessity for bronchoscopy in order to suppress coughing and laryngospasm, to allow examination of the airways without inducing trauma, and to protect the endoscope. Two large mouth gags should be in place throughout the procedure to protect the bronchoscope. The anatomy of the bronchi has been defined, and the roadmap of the airways should be consulted frequently. A standard procedure should be developed to evaluate all accessible airways, record abnormal findings, and obtain respiratory samples. Evaluate the larynx, trachea, entire left side, then entire right side in a standard order. Use the carina for orientation. During the first pass through the airways, describe abnormalities including airway hyperemia, mucus accumulation, airway collapse or dilatation, and decide on sites for BAL. After a complete examination, remove the scope, flush the channel and wipe down the exterior to limit contamination. When returning to the airways for BAL, limit contact with the airways and wedge the scope gently in the chosen airway. Instill ~1 ml/kg lavage fluid (depending on the size of the animal and the size of the scope used), inject air to clear the channel, and then retrieve as much fluid as possible. If the patient is stable, lavage a second site and submit both for cytology. A pooled sample can be submitted for cultures.
Performing interventional techniques in the nasal or tracheobronchial tree can require various wires, cutting or expanding balloons, endoscopic equipment including biopsy forceps, grabbers and snares, and different sizes and types of intraluminal stents. At least two clinicians are generally required to accomplish respiratory tract procedures, and patience is a virtue!
What are some lessons learned in respiratory endoscopy?
Know the anatomy. Recognition of normal is essential to detect abnormal anatomy, stenoses, dilatation, or mass lesions.
Practice techniques in models. This is particularly important for bronchoscopy, where knowledge of the anatomy is essential.
Review protocols frequently. Discuss what did and didn't work, record all details immediately after the procedure.
Anticipate the diagnosis and be prepared for disasters - brachycephalic dogs often develop airway obstruction and gastroesophageal reflux when anesthetized; animals with airway obstruction can require sedation or tracheostomy; dogs with nasal tumors and aspergillosis can bleed out from biopsy procedures; cats tend to bronchoconstrict and desaturate during bronchoalveolar lavage.
Have the right equipment and be prepared to improvise. A variety of tracheal stent sizes should be readily available in practices that see cases suitable for stenting (larger sizes are generally needed); rigid and flexible endoscopes should be on hand for foreign body retrieval in the nose, nasopharynx, and trachea; always have suction available.
Be flexible and innovative. One technique cannot work in all cases. Don't be afraid to be aggressive, but ensure that the scopes are not damaged and that the procedure is in the best interests of the patient. This is particularly true with attempts at foreign body retrieval or debulking or with sinus trephination.
Collaborate on challenging cases and review the human and veterinary literature. Sharing ideas with others who are more experienced in endoscopic techniques is extremely valuable, and seeking advice from novel sources can open up new opportunities.
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