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Brachycephalic airway syndrome (Proceedings)
Brachycephalic airway syndrome refers to the condition of airway distress attributable to anatomical abnormalities.
Brachycephalic airway syndrome refers to the condition of airway distress attributable to anatomical abnormalities. Commonly affected breeds include English bulldog, Boston terrier, pug, Pekingese, French bulldog, Cavalier King Charles spaniels, and Persian and Himalayan cats. There are main four components of brachycephalic syndrome; two primary and two secondary. The primary components are stenotic nares and elongated soft palate. Secondary components, everted laryngeal saccules and laryngeal collapse, arise as a result of chronic obstructive breathing against the primary components. Technically, everted laryngeal saccules are considered the first stage of laryngeal collapse. Hypoplastic trachea is not considered part of brachycephalic syndrome, but it occurs in high incidence in brachycephalic dogs and may contribute to clinical signs and affect prognosis following treatment.
Dogs with brachycephalic airway syndrome typically present for loud stridorous breathing. More severely affected dogs may have exercise intolerance, cyanosis, and syncope. Affected cats usually present for severe inspiratory stertor and open-mouth breathing. The primary components are present at birth, but often animals do not present until they are 2 or 3 years old. In general, the older the animal is when it presents, the more likely it is to have secondary problems, such as everted laryngeal saccules or laryngeal collapse.
Diagnosis of brachycephalic airway syndrome is made from physical examination and laryngeal examination. Thoracic radiographs are essential in order to rule out other possible underlying conditions that may affect the animal's overall prognosis. Such conditions include, but are not limited to, aspiration pneumonia, hiatal hernia, cardiomegaly, stress rib fractures, and hypoplastic trachea.
Hypoplastic trachea is the most common concurrent condition. It is a congenital tracheal stenosis that uniformly affects the entire length of the trachea. Parameters used to define hypoplastic trachea are:
Tracheal diameter at the thoracic inlet (TD) < 0.16
Thoracic inlet diameter (TI)
Tracheal diameter at midpoint between thoracic inlet and carina <3
Width of third rib
The TD:TI ratio is the most reliable parameter, however results may still be difficult to interpret, especially in English Bulldogs. English Bulldogs without clinical respiratory signs do not have significantly different TD:TI ratios than English Bulldogs that are clinical. There is no definitive treatment for hypoplastic trachea, only symptomatic therapy and correction of other anatomical defects may alleviate clinical signs. The extent to which hypoplastic trachea contributes to the severity of clinical signs in dogs with brachycephalic airway syndrome is unknown.
Brachycephalic breeds may have a congenital malformation of the nasal cartilages resulting in medial collapse and restriction of airflow into the nasal cavity. Stenotic nares are easily correctable. Various surgical techniques are used and all have the same end result, permanent enlargement of the external nares. A #11 scalpel blade is preferred in order to make deep and even cuts in the wing of the nostril. There is no difference in outcome between a horizontal or vertical wedge resection. Expect a fair degree of hemorrhage as this tissue is extremely vascular. Bleeding is managed by digital pressure and then controlled once sutures are in place. Absorbable 3-0 to 4-0 multifilament or monofilament suture in a simple interrupted pattern is used to appose cut surfaces. Absorbable sutures to avoid suture removal in 2 to 3 weeks from a fairly sensitive area. Early correction of stenotic nares has recently been advocated.
Elongated soft palate
Heavy sedation or a light plane of general anesthesia is required to adequately assess the palate and larynx. A normal soft palate should just touch the tip of the epiglottis. To appropriately assess soft palate length, the tongue should be in a normal position. An elongated soft palate typically extends past the tip of the epiglottis by at least several millimeters.
Soft palate resection is a relatively simple procedure. The most important aspect of the surgery is to make sure that the palate is not made too short. The consequences of a short soft palate are nasal regurgitation and rhinitis. The procedure is typically performed by placing stay sutures on either side of the palate at the level of planned resection. Metzenbaum scissors are used to transect approximately one-third to one-half the width of the palate. A simple continuous pattern with 4-0 absorbable suture is used to oppose the nasal and oral mucosa over the exposed palatine muscle. Removal of the rest of the palate is performed and the suture line is continued to the opposite side. Hemorrhage and swelling are usually minimal, but premedication with dexamethasone (0.5mg/kg, IV) is often routine.
Soft palate resection may also be performed using surgical laser. In a prospective study of 20 brachycephalic dogs undergoing soft palate resection, surgical time for laser resection was significantly shorter than traditional resection. However, clinical outcomes were similar between the two groups.
Everted laryngeal saccules and laryngeal collapse
Chronic upper airway obstruction causes increased airway resistance and increased negative intraglottic luminal pressure. Over time this results in laryngeal collapse due to cartilage fatigue and degeneration. There are three stages of laryngeal collapse:
Stage 1 – everted laryngeal saccules
Stage 2 – aryepiglottic collapse
Stage 3 – corniculate collapse
In a retrospective study of dogs with brachycephalic airway syndrome, everted laryngeal saccules were present in almost 50% of dogs. The saccules are pulled from their crypts due to the high negative pressure within the glottis. Once the saccules are everted, the tissue is exposed to highly turbulent airflow resulting in swelling which further obstructs the airway.
Resection of the everted laryngeal saccules is relatively simple. Each saccule is grasped with Allis tissue forceps and then sharply transected with Metzenbaum scissors. Suturing is not necessary. The difficulty of this technique lies is getting good visualization of the larynx and glottis. Often these dogs have redundant pharyngeal tissue that swells rapidly with minimal handling. The presence of an endotracheal tube can also make visualization difficult. It is for these reasons that some surgeons advocate using a temporary tracheostomy tube when performing this surgery.
Laryngeal collapse is the end-stage component of brachycephalic airway syndrome. Weakened laryngeal cartilages become displaced medially, severely obstructing the airway. Options for treatment at this stage are limited. First, all other underlying conditions (stenotic nares, elongated soft palate, everted laryngeal saccules) are addressed. Unilateral arytenoid lateralization techniques are rarely successful as the opposite cartilage will continue to collapse medially. Bilateral arytenoid lateralization techniques are considered unacceptable due to the high risk for aspiration pneumonia. Partial arytenoidectomy procedures have also been associated with a high rate of complications and perioperative mortality. Permanent tracheostomy is the recommended treatment for stage 3 laryngeal collapse, although many owners consider this an unacceptable option.
Surgical correction of brachycephalic airway syndrome will alleviate signs of respiratory distress and improve quality of life in most dogs. The degree of improvement is usually dependent on how severely the dog is affected preoperatively. One study reported an overall prognosis following any surgery for brachycephalic airway syndrome was good to excellent in 59% of cases and poor in 41%. Dogs corrected for stenotic nares and elongated soft palate had a better postoperative response than dogs with elongated soft palate alone. A more recent study describes a good to excellent long-term outcome in 94%. English bulldogs have been found to have a worse response to surgery when compared to all other breed combined and are far more likely to develop aspiration pneumonia postoperatively. An association with gastrointestinal disease has been investigated in Europe. It is believed that brachycephalic dogs surgically treated for upper airway disease and concurrently medically managed for gastrointestinal disease have an overall better outcome.
Without surgery, prognosis for dogs with elongated soft palate and everted laryngeal saccules is guarded, as respiratory signs and laryngeal collapse will progress over time.
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