Pre-operative nares in eight-month-old female American bully (left), and post-operative stenotic nares correction using CO2 laser. Images courtesy Kendra Freeman It’s a warm, summer day and you are just about to wrap up a busy shift in your emergency department when a STAT page is called overhead. A four-year-old female spayed pug in respiratory distress is brought to you for evaluation by your triage technician. The patient was out on a late afternoon walk, began making more noise than normal before finally collapsing. You perform a brief exam and find cyanotic mucus membranes, tachypnea, hyperthermia, and inspiratory stertor. You make the diagnosis of upper airway obstruction and implement stabilization measures. Pathophysiology Brachycephalic obstructive airway syndrome (BOAS) is a complex combination of anatomic anomalies leading to restricted air movement in brachycephalic breeds. This syndrome generally includes varying degrees of stenotic nares, everted laryngeal saccules, redundant laryngeal tissue, presence of abnormal concha, elongated soft palate, and tracheal hypoplasia. Primary anatomic anomalies (i.e. stenotic nares, elongated soft palate) can restrict airway movement and increase the work needed to move air leading to secondary changes (i.e. everted saccules, laryngeal collapse, thickening of the soft palate). Management of this syndrome involves surgical correction of several components of the abnormal anatomy along with lifestyle changes to prevent/limit secondary changes Emergency stabilization For patients presented on an emergent basis, treatment consists of oxygen support and sedatives, such as butorphanol or acepromazine, to help the patient relax. Cooling measures may be needed in hyperthermic patients. Anti-inflammatories can be helpful to decrease soft tissue swelling, but should be used with caution as hyperthermia can lead to gastrointestinal disturbances. In severe cases, swelling of the upper airway, especially the soft palate, may occur leading to an obstruction. Temporary tracheostomy may be needed in a small subset of these patients. These can be challenging to create given the presence of a hypoplastic trachea and abundant skin folds in these breeds. Surgical treatment The components of BOAS most commonly addressed surgically are stenotic nares and elongated soft palates. Many techniques are available to widen the nares, including sharp lateral, vertical, or horizontal wedge resection of the dorsolateral cartilage, mobilization of the dorsal lateral cartilage, and carbon dioxide laser. The advantages of the carbon dioxide laser are reduced surgical time, no need to place sutures and minimal bleeding. Keep in mind that a small increase in diameter can have a significant decrease in airway resistance (Poiseuille’s law). This is a relatively straight forward procedure and should be considered in at-risk breeds or affected dogs and cats at the time of spay or neuter. The second most common component of this syndrome corrected with surgery is the elongated soft palate. In BOAS patients, the soft palate is often too long and thickened due to chronic inflammation. Ideally, the soft palate should not extend past the caudal margin of the tonsils. Trimming the soft palate can be completed with sharp dissection and primary closure with absorbable suture or with a surgical laser. A carbon dioxide laser makes this surgery efficient and nearly bloodless. A potential complication following soft palate surgery is swelling, possibly leading to upper airway obstruction. This tissue should be handled delicately to minimize iatrogenic trauma. Everted laryngeal saccules can be present in up to half of brachycephalic obstructive airway cases at the ventral aspect of the larynx. Increased airway pressures lead to eversion of this tissue, which causes further obstruction of the larynx. If present, the everted tissue can be removed at the time of correction of the stenotic nares and soft palate. Recent studies (Oechtering et al Veterinary Surgery 2016; Heidenreich et al Veterinary Surgery 2016) found many brachycephalic patients, especially pugs, had abnormal turbinates present in the nasal passage that were identified on computed tomographic and endoscopic imaging. Based on these findings, a novel technique for laser ablation of the turbinates was developed. Due to the specialized equipment needed for both identification and treatment of these turbinates, surgical correction via ablation of the abnormal tissue is not widely performed at this time. Components of BOAS, such as laryngeal collapse and redundant laryngeal folds, are not easily corrected with surgery. Additionally, overweight patients tend to store adipose tissue around the airway, further complicating their situation. It is preferred that surgical correction of stenotic nares and removal of overly long soft palate tissue is performed prior to development of laryngeal collapse. Maintenance of lean body weight should also be encouraged. Risks Upper airway surgery, especially in brachycephalic breeds, is not without risk. This is often what makes some veterinarians reluctant to perform these procedures. There are technical challenges of the surgical procedure itself (i.e. knowing appropriate landmarks for soft palate resection) as well as perioperative considerations. Management of a BOAS patient in the perioperative/anesthetic period is critical for a successful outcome. Brachycephalic breeds have been reported to have a perianesthetic complication rate of 49 percent (Darcy et al JAVMA 2018). Two major concerns for these patients are upper airway obstruction and aspiration. Chronic airway changes, recent respiratory crisis leading to swelling and aggressive soft tissue manipulation can lead to swelling of the upper airway. Following surgery, these patients should be allowed to recovery from general anesthesia is a calm environment and remain intubated as long as possible. Veterinarians and technical staff should be prepared for sedation and rapid re-intubation, as well as the possibility for emergent placement of a temporary tracheostomy. Aspiration is another major concern for BOAS patients, occurring in about four percent of patients (Gruenheid et al JAVMA 2018). Breeds such as pugs, French bulldogs, and bulldogs have a 3.8 time increase in relative risk for aspiration pneumonia (Darcy et al JAVMA 2018). This risk is highest in patients with a history of gastrointestinal signs prior to anesthesia. Administering anti-emetics (maropitant, ondansetron) and prokinetic agents (metoclopramide) in combination with pre-anesthetic medications and induction agents that are least likely to cause nausea are helpful. Concurrent issues The more we learn about brachycephalic breeds, the more we learn they have a multitude of anomalies. Issues related to the gastrointestinal tract may include gastroesophageal reflux and hiatal hernias (Type I). The hiatal hernia is thought to be due to sub-atmospheric airway pressures created by the upper airway anomalies. This causes the gastroesophageal junction to cross the diaphragm. Gastroesophageal reflux is common in these breeds, especially French bulldogs. A significant reduction in reflux has been noted after surgical correction of stenotic nares and elongated soft palate in in this breed (Kaye et al JSAP 2018). Expected outcome The goal of surgery for BOAS patients is to reduce the work of breathing, minimize development of chronic airway changes (i.e. laryngeal collapse) and avoid respiratory distress. Clients should be counseled their pets will likely always make some noise and is unlikely to be a top athlete. Patients have a better outcome when surgery is performed prior to four years of age and before permanent secondary airway changes occur. Conclusion Surgical correction of stenotic nares and an elongated soft palate in a brachycephalic breed can greatly improve the patient’s comfort, decrease the work of breathing and hopefully avoid a future respiratory crisis. These procedures may have the added benefit of improvement or resolution of gastrointestinal symptoms. Performing these procedures prior to the presence of permanent, chronic changes, using appropriate surgical technique and careful attention to peri-anesthetic management will maximize patient outcomes. Thankfully, for your pug patient responded quickly to emergency stabilization with sedation and oxygen support. She spends the night with oxygen support and is successfully transferred to your hospital’s surgery department. Kendra Freeman DVM, MS, DACVS, is a graduate of Colorado State University and maintains dual certification with the American College of Veterinary Surgeons. She is an associate surgeon in Albuquerque, N.M. Her case load consists of orthopedics, general soft tissue, and sports medicine cases with the occasional return to her roots in large animal lameness and surgery. References Oechtering, Gerhard U., et al. “A novel approach to brachycephalic syndrome. 1. Evaluation of anatomical intranasal airway obstruction.” Veterinary Surgery 45.2 (2016): 165-172. Heidenreich, Dorothee, et al. “Nasopharyngeal dimensions from computed tomography of pugs and French bulldogs with brachycephalic airway syndrome.” Veterinary Surgery 45.1 (2016): 83-90. Darcy, Hannah P., Karen Humm, and Gert Ter Haar. “Retrospective analysis of incidence, clinical features, potential risk factors, and prognostic indicators for aspiration pneumonia in three brachycephalic dog breeds.” Journal of the American Veterinary Medical Association 253.7 (2018): 869-876. Gruenheid, Michaela, et al. “Risk of anesthesia-related complications in brachycephalic dogs.” Journal of the American Veterinary Medical Association 253.3 (2018): 301-306. Kaye, B. M., et al. “Relationship between brachycephalic airway syndrome and gastrointestinal signs in three breeds of dog.” Journal of Small Animal Practice 59.11 (2018): 670-673.
