Brachycephalic airway syndrome (BAS) is a combination of one or more anatomical and functional abnormalities of the upper airway of brachycephalic breeds. Brachycephalic breeds are those dogs with very short muzzles and flat faces, including the Boxer, Bulldog, Pug, Boston Terrier, Pekingese and King Charles Spaniel. Dogs with BAS develop elongation and thickening of their soft palate, chronic pharyngitis, tonsillitis and inflammation and diminished diameter of the larynx and trachea, all of which contribute to variable degrees of respiratory distress. The larynx is the structure situated at the top end of the trachea, behind the root of the tongue. It is lined with mucous membrane tissue and contains the dog's vocal cords. Another name for the larynx is the "voice box." The trachea is the tubular passageway between the mouth and the lungs. Brachycephalic airway syndrome is sometimes referred to as brachycephalic upper airway syndrome, brachycephalic obstructive syndrome, upper airway syndrome or brachycephalic syndrome.
BAS is comprised of three main anatomical abnormalities: elongated soft palate, hypoplastic trachea and stenotic nares. The soft palate is the fleshy portion at the back of the mouth (oral cavity) which separates the end of the nasal passages (the nasopharynx) from the back of the mouth (the oropharynx). The soft palate and the hard palate together comprise the "roof of the mouth." The trachea is the air passageway connecting the mouth to the lungs; hypoplasia is the incomplete development or underdevelopment of an organ or tissue. Nares are the openings of the nasal cavity, commonly referred to as nostrils. Stenosis is the narrowing or contraction of a body opening or passageway. Any or all of these physical abnormalities may be present in a dog affected with SAS.
Causes of Brachycephalic Airway Syndrome
Brachcephalic airway syndrome (BAS) is caused by several abnormal physical attributes of affected dogs. First, brachycephalic breeds have structural deformities in their skulls and nasal passageways, caused by generations of selective breeding (by people) to create the exaggerated domed heads, broad foreheads, flat faces and almost nonexistent muzzles characteristic of these breeds. The narrowed nostril openings (stenotic nares) that are so typical of dogs with BAS prevent the normal flow of air into the upper respiratory tract when the dog breathes in (on inspiration). Dogs with BAS also have an elongated soft palate, which is the fleshy structure that separates the back of the mouth from the end of the nasal passages. This redundant soft tissue contributes to increased upper airway resistance and breathing difficulty (dypsnea), because it acts as a physical barrier to the free passage of air. The combination of these anatomical abnormalities leads to inflammation and swelling of the lining of the nasal passages, pharynx (throat), larynx ("voice box") and trachea ("windpipe"), which further exacerbates the dyspnea already associated with this syndrome.
Prevention of Brachycephalic Airway Syndrome
There is no realistic way to prevent a dog from developing brachycephalic airway syndrome. Affected dogs are born with the anatomical abnormalities that cause the respiratory difficulties associated with this condition. Episodes of respiratory distress may be able to be avoided or at least minimized by reducing the stress in the dog's environment, limiting its exercise or exertion, avoiding high temperature enclosed environments and preventing obesity.
Brachycephalic airway syndrome frequently leads to secondary changes to upper respiratory tract tissues because of the increased airway resistance caused by the condition. These commonly include laryngeal collapse and laryngeal saccule eversion. The larynx is the muscular and cartilaginous structure situated at the top end of the trachea, behind the root of the tongue. It is made up of 9 separate cartilages that are held together by ligaments and muscles. The larynx is lined with mucous membrane tissue and contains the dog's vocal cords. Another name for the larynx is the "voice box." The laryngeal saccules are small paired structures lining the laryngeal ventricle, which is simply an outpocketing of the larynx. When the laryngeal saccules evert, or if the larynx itself collapses (several of the cartilages fold inward), the passage of air from the mouth through the larynx and trachea to the lungs is further obstructed, making the dog's breathing much more labored, especially when breathing in. In medical lingo, this is called "increased inspiratory effort."
Hot, humid weather can cause rapid deterioration and severe respiratory distress (difficulty breathing; dyspnea). Confinement in an area with high ambient temperature, such as in a car with poor ventilation, and exercise or exertion, also exacerbate the symptoms of this syndrome.
How Brachycephalic Airway Syndrome Affects Dogs
Brachycephalic airway syndrome (BAS) causes obvious respiratory distress in most affected animals. The narrowed nostrils and trachea, together with the overly long soft palate, make it difficult for a dog to breathe in enough air to provide its tissues and cells with a sufficient supply of oxygen.
Symptoms of Brachycephalic Airway Syndrome
The symptoms of BAS are directly related to the increased airway resistance that is caused by the anatomical abnormalities of an elongated soft palate, stenotic nares and/or a constricted trachea. The noticeable signs of this syndrome usually are apparent at an early age. In some cases, the signs don't become evident until the dog reaches middle-age. Affected dogs typically show one or more of the following symptoms:
Narrowed nostrils (stenotic nares)
Harsh sounds when breathing in (increased inspiratory sounds; snorting-like noise on inspiration; stridor)
Increased inspiratory effort
Bluish discoloration of the skin and mucous membranes (cyanosis)
Temporary cessation of breathing (apnea)
Dogs at Increased Risk
Brachycephalic breeds, which are predisposed to developing BAS, include English and French Bulldogs, Pugs, Boston Terriers, Boxers, Shih Tzus, Pekingese and King Charles Spaniels. Most dogs become affected by the time they reach 3 or 4 years of age. Boston Terriers and Pugs are particularly prone to developing laryngeal collapse secondary to BAS, because their laryngeal cartilages are unusually flexible. Obesity can greatly aggravate the symptoms of brachycephalic airway syndrome.
How Brachycephalic Airway Syndrome is Diagnosed
Brachycephalic airway syndrome (BAS) is not difficult to diagnose. In most cases, a veterinarian can diagnose the condition based on observation of the dog's breathing and a physical examination. Stenotic nares (narrowed nostril openings) are visibly obvious. Those, together with the characteristic inspiratory snorting sounds of predisposed breeds, are highly suggestive of BAS. A urinalysis and routine blood work (a complete blood count and serum biochemistry profile) frequently are also part of the initial data base. Dogs with BAS typically have no abnormalities on the results of these tests, unless they have some other disease or disorder.
To make a definitive diagnosis, the dog must be heavily sedated or placed under general anesthesia so that the attending veterinarian can make a thorough examination of the mouth (oral cavity), soft palate, voice box (larynx) and throat (pharynx). The veterinarian will be able to assess the presence or absence of laryngeal collapse, laryngeal saccule eversion and elongated soft palate during this oropharyngeal/orolaryngeal examination.
Radiographs (X-rays) of the dog's head, neck and chest are also important to confirm the diagnosis of brachycephalic airway syndrome. Radiographs can disclose an overly long soft palate as well as a constricted or narrowed trachea. They also can reveal tracheal collapse, pneumonia and some other secondary medical conditions associated with BAS.
Aspiration pneumonia is a common sequella of BAS. Early surgical intervention is one of the most important factors in having a good outlook and prognosis for dogs that are diagnosed with this disorder.
The immediate goals of treating a dog with severe breathing difficulty as a result of brachycephalic airway syndrome (BAS) are to remove the upper airway obstruction and restore a patent airway. This can be done by intubating the dog and placing it under general anesthesia, with oxygen and anesthetic gas being provided mechanically to the animal through the endotracheal tube. An open airway can also be established through a surgical procedure called a tracheostomy. This involves creating an opening directing into the trachea through the neck and inserting a tube to facilitate the free flow of air. Tracheostomies can be performed on an elective or emergency basis. Another goal of treating a dog in extreme respiratory distress due to BAS is to reduce the animal's stress, anxiety and discomfort, which in turn will help minimize the risk of adverse secondary complications. The long term therapeutic goal is to remove the tissues or structures that are causing the airway obstruction through surgery.
The narrowed nostrils (stenotic nares) associated with BAS can be widened or opened surgically, either using a traditional surgical scalpel or using the more recently developed carbon dioxide laser. Basically, both of these techniques involve surgically sculpting the nasal openings to allow the free flow of air as a dog breathes in and out. An elongated soft palate can be shortened surgically as well, using either a traditional scalpel or a CO2 laser. Everted laryngeal saccules can be removed with a scalpel, a laser or scissors. Unfortunately, there is no reported surgical procedure or technique to correct an underdeveloped trachea or laryngeal collapse, both of which are often present in brachycephalic breeds.
Dogs with BAS should be kept fit and trim. Obese brachycephalic dogs usually suffer much more serious respiratory difficulties than do dogs kept in a good, normal weight. Because hot, humid environments exacerbate this condition, dogs with BAS should be kept out of areas with high ambient temperatures. They also should be kept as stress-free as possible.
Dogs that undergo successful surgical correction of stenotic nares and/or elongated soft palates at an early age typically have a good to excellent long-term prognosis, especially if they do not also have a hypoplastic trachea or secondary complications such as everted laryngeal saccules or laryngeal collapse. If the dog has an underdeveloped trachea, or if it develops secondary complications of BAS, it has a variable prognosis, ranging from poor to good depending upon the nature and extent of those conditions and the amount of upper airway obstruction that they cause. When a brachecephalic dog develops severe and acute breathing difficulties, the situation can rapidly become life-threatening. If that happens, the outlook is guarded. However, the dog may recover fully if medical treatment is sought and administered promptly to reestablish an open airway.