Canine Brachycephalic Airway Syndrome: Pathophysiology, Diagnosis, and Nonsurgical Management Canine brachycephalic airway syndrome (BAS), also known as brachycephalic syndrome and brachycephalic airway obstructive

Canine brachycephalic airway syndrome is a progressive disease that affects many brachycephalic dogs. This article describes the components of this syndrome and focuses on acute emergency management and long-term conservative management of these patients. Surgical management is described in a companion article. Canine Brachycephalic Airway Syndrome: Pathophysiology, Diagnosis, and Nonsurgical Management Canine brachycephalic airway syndrome (BAS), also known as brachycephalic syndrome and brachycephalic airway obstructive syndrome, has been reported in many brachycephalic breeds, including the shih tzu, boxer, English and French bulldogs, Lhasa apso, Pekingese, pug, shar-pei, and Boston terrier.1–4 In these breeds, a congenital malformation results in skull bones of normal width but shortened length.3–5 These inherited bony changes lead to the secondary soft tissue abnormalities that characterize BAS. Stenotic nares and elongation of the soft palate are the primary anatomic features of BAS. Secondary changes include eversion of the laryngeal saccules (stage I laryngeal collapse), laryngeal collapse (stages II and III), and enlargement of the tonsils.3,5–8 Hypoplastic trachea is seen concurrently in some brachycephalic breeds (particularly English bulldogs) but is considered independent of BAS.6,9 TABLE 1 lists the frequency of each BAS component identified in four studies. Differences in incidence may be explained by the variation in canine populations in different countries. An Australian study10 noted a high incidence of elongated soft palate alone in Cavalier King Charles spaniels (6 of 15 dogs), a breed not commonly associated with BAS in the United States. Pathophysiology Pathology in BAS results from the changes in air pressure and flow in the upper airway.3,4,11 The relationship between the radius of a tube, pressure, and flow can be modeled using Poiseuille’s law,12 which shows that a 50% reduction in tube radius leads to a 16-fold increase in resistance to flow. To maintain airflow as the radius decreases, pressures in the airway must become more negative. In dogs with BAS, stenosis of the nares and distortion of the pharyngeal region lead to an increase in negative pressure during inspiration.5,11 This results in stretching of the soft palate, which may already be elongated; swelling of the airway; eversion of the laryngeal saccules; edema and inflammation of tonsillar tissue; and, ultimately, inward collapse of the weakened laryngeal cartilages. A vicious cycle develops: collapse of the laryngeal cartilage further decreases the radius of the airway, which increases the velocity of airflow and the negative pressure in the airway, leading to further collapse. This cyclic pathology is why severe cases of BAS can demonstrate advanced laryngeal collapse and why early surgical intervention is recommended to correct identified BAS components in affected dogs. Clinical Presentation Stenotic nares and elongated soft palate are often present at birth, with clinical signs being progressive from young adulthood. Study Stenotic Nares Elongated Soft Palate Everted Sacculesa Laryngeal Collapseb Poncet et al18 84.9% (62/73) 95.9% (70/73) 54.8% (40/73) 69.9% (51/73) Poncet et al8 85.2% (52/61) 100% (61/61) 54.1% (33/61) 63.9% (39/61) Torrez and Hunt10 42.5% (31/73) 86.3% (63/73) 58.9% (43/73) 53.1% (34/64) Riecks et al17 58.1% (36/62) 87.1% (54/62) 58.1% (36/62) 8.1% (5/62) aStage I laryngeal collapse bStages II and III laryngeal collapse Table 1. Incidence of Brachycephalic Airway Syndrome Components For more information, please see the companion article, “Canine Brachycephalic Airway Syndrome: Surgical Management”