Brachycephalic airway obstructive syndrome

The English bulldog, a typically brachycephalic dog breed, may suffer from brachycephalic syndrome.

Brachycephalic syndrome is a pathological condition affecting short nosed dogs and cats which can lead to severe respiratory distress. There are four different anatomical abnormalities that contribute to the disease, all of which occur more commonly in brachycephalic breeds: an elongated soft palate, stenotic nares, a hypoplastic trachea, and everted laryngeal saccules (a condition which occurs secondarily to the other abnormalities). Because all of these components make it more difficult to breathe, in situations of exercise, stress, or heat, an animal with these abnormalities may be unable to take deep or fast enough breaths to blow off carbon dioxide. This leads to distress and further increases respiratory rate and heart rate, creating a vicious circle that can quickly lead to a life-threatening situation.

Dogs experiencing a crisis situation due to brachycephalic syndrome typically benefit from oxygen, cool temperatures, sedatives, and in some cases more advanced medical intervention including intubation.

Causes and risk factors

This diagram illustrates what the airway structure looks like in a brachycephalic dog; in this case, a Boxer.

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1. Nasal cavity 2. Oral cavity 3. Soft palate 4. Pharynx 5. Larynx 6. Trachea 7. Esophagus 8. Nasopharynx 9. Hard palate

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The brachycephalic dog has a shorter snout which causes the airway to be shorter, that means all the parts that make up the airway get pushed closer together. Due to this phenomenon, a brachycephalic dog has an elongated soft palate which can cause most of the problems with the dogs breathing. They can also have problems getting enough air in because of their elongated soft palate and shorter airway.

• Stenotic nares (narrowed nostril)
• Elongated soft palate
• Hypoplastic trachea (reduced trachea size)
• Short/irregular nasal turbinate

Muzzle length scales with the risks of brachycephalic syndrome. Other risk factors identified include neck girth and body condition score.^[1]

Signs and symptoms

• dyspnea (breathing difficulty)
  • noisy/labored breathing
  • stridor (high pitched wheezing)
  • continued open-mouth breathing
  • extending of head and neck to keep airway open,
  • sitting up or keeping chin in an elevated position when sleeping
  • sleeping with toy between teeth to keep mouth open to compensate for nasal obstruction^[2]
  • cyanosis (blue/purple discoloration of the skin, due to poor blood oxygenation in the lungs )
  • sleep apnea
• exercise, stress and heat intolerance.
• snoring/gagging/choking/regurgitation/vomiting
• collapse

Symptoms progress with age and typically become severe by 12 months.^[2]

Despite observing clinical signs of airway obstructions, some owners of brachycephalic breeds may perceive them as normal for the breed, and may not seek veterinary intervention until a particularly severe attack happens.^[3][4]

After awaking from surgery, most dogs that are intubated will try to claw out their tracheal tube. But brachycephalic dogs often seem quite happy to leave it in place as it gives them an open/bigger airway.^[5]

Diagnosis

x-ray on neck and bronchscopy

Treatment

Stenotic nares in a Boxer before(left) and after (right) surgery.

Surgery for widening nostrils, removing excess tissue for elongated soft palate, removing everted laryngael saccules. Early treatment prevents secondary conditions.

Potential complications including hemorrhages, pain, and inflammation, during and after surgery make some veterinarians hesitant to perform soft palate correction surgery. With CO₂ surgical lasers, these complications are greatly diminished.^[6]

Prevention

To prevent or limit exacerbation of symptoms, avoid stress and high heated climates. Maintain ideal body weight (14 to 18 pounds), avoid overfeeding. Use harnesses instead of collars to avoid pressure on trachea.

Brachycephalic dogs are more likely to die during air travel^[7] and have been banned by many airlines.^[8]

The risk of brachycephalic syndrome increases as the muzzle becomes shorter.^[1] To avoid producing affected dogs, breeders may choose to breed for more moderate features rather than for extremely short or flat faces. Dogs with breathing difficulties, or at least those serious enough to require surgery, should not be used for breeding.^[9] Removing all affected animals from the breeding pool may cause some breeds to be unsustainable and outcrossing to non-brachycephalic breeds might be necessary.^[10]

Other health problems

Non-airway problems associated with brachycephalia may include

• Inflammation in skin folds
• Mating and birthing problems
• Malocclusion - misalignment of the teeth.
• Dental crowding

Exophthalmos in a pug

• Brachycephalic ocular syndrome^[10]
  • Ectropion/entropion - inward/outward rolling of eyelid
  • Macropalpebral fissure
  • Lagophthalmia - inability to close eyelids fully
  • Exophthalmos/eye proptosis - abnormal protrusion of the eye
  • Nasal fold trichiasis - fur around the nose fold rubs against the eye.
  • Distichiasis - abnormally placed eyelashes rubs against the eye.
  • Poor tear production.
  • Gastrointestinal problems^[11]

List of brachycephalic dog breeds

Breeds with less extreme brachycephalia, such as the Boxer, have less compromised thermoregulation and thus are more tolerant of vigorous exercise and heat.

• Affenpinscher
• Boston Terrier^[12]
• Boxer
• Brussels Griffon
• Bulldog^[12]
• Bullmastiff
• Cane Corso
• Chihuahua (apple-headed)
• Dogue de Bordeaux
• English Mastiff
• French Bulldog^[12]
• Griffon Bruxellois^[12]
• Japanese Chin^[12]
• King Charles Spaniel
• Neapolitan Mastiff
• Pekingese^[12]
• Pug^[12]
• Rottweiler
• Shih Tzu^[12]
• Valley Bulldog

References