BOAS in flat-faced dogs: breathing signs and veterinary assessment

Brachycephalic obstructive airway syndrome (BOAS) is a breathing disorder in some flat-faced dogs, caused by narrowing and blockage in the upper airway.

The shortened head leaves less room for structures such as the soft palate, nostrils and tissues around the larynx. Different dogs can have obstruction at different sites, so BOAS is a syndrome rather than one identical airway problem in every dog. [1]

BOAS is most closely associated with flat-faced breeds, including Bulldogs, French Bulldogs, Pugs, Pekingese and Boston Terriers.

Head shape is only part of the picture, and dogs within the same breed can differ greatly. A breed label cannot show whether one dog is affected or how severe its obstruction is; that requires an assessment of the individual dog. [1]

No. A flat-faced head shape raises concern for BOAS, but dogs vary in whether they are affected and how severe their breathing problems are.

A dog can also appear comfortable while resting yet develop abnormal noise or effort during activity. Veterinary respiratory function grading separates dogs without clinically important signs from those whose breathing is affected. [2]

Snoring, snorting or other noisy breathing should not be dismissed as normal for a flat-faced dog, because these sounds can indicate upper-airway obstruction.

The noise may be present while the dog is awake or may become obvious only during excitement, play, exercise, eating, drinking or stress. Its sound can also offer clues about where the airway is narrowed. [2]

Stertor is a low-pitched snoring or snorting sound that can come from obstruction and vibration in a dog's throat.

In BOAS, an elongated or thickened soft palate can extend towards the airway opening. The extra suction created during breathing may then make the palate and other loose throat tissues vibrate, including while the dog is awake. [2]

A high-pitched breathing sound, called stridor, can indicate that a dog's larynx is narrowed or collapsing.

Stridor sounds different from lower-pitched snoring or snorting. Laryngeal collapse can develop as a secondary change when the dog repeatedly works against obstruction elsewhere in the upper airway, making this sound clinically important. [2]

Very narrow nostrils can pull inward during inhalation and make it harder for a dog with BOAS to breathe through the nose.

The narrowing may involve both the visible nostril opening and tissue further inside the nose. Affected dogs may use more effort to breathe, flare the muscles around the nose or switch to open-mouth breathing. [2]

Open-mouth breathing at rest can mean that a flat-faced dog is struggling to move enough air through the nose.

Narrow outer nostrils are only one possible blockage. Crowded nasal turbinates, narrowing further inside the nostrils and collapse behind the nasal cavity can also restrict airflow, including problems that are not visible from the outside. [2]

Reverse sneezing is not the same as a BOAS diagnosis, although it is common in flat-faced dogs and may be linked to throat irritation from an elongated soft palate.

An episode often ends with the dog breathing normally again. Repeated reverse sneezing still needs to be considered alongside the dog's other signs, such as airway noise, effort, exercise tolerance, sleep and heat tolerance. [2]

BOAS can become more serious over time because repeated effort to breathe may draw soft tissue and cartilage further into the airway.

The larynx may first collapse only during inhalation, exercise or excitement. If this continues, its supporting cartilage can lose rigidity and the collapse may become permanent, adding another obstruction to the original airway problems. [2]

Laryngeal collapse means that tissue and supporting cartilage around a dog's voice box are being drawn into the airway, narrowing the opening.

The increased suction created by chronic upper-airway obstruction can pull the laryngeal saccules and cartilage inward. Early collapse may happen mainly during inhalation or activity, while more advanced changes can become fixed and harder to relieve. [2]

During activity, a dog with BOAS may develop noisy breathing, reduced stamina, blue or grey gums, or collapse.

Signs can be more obvious after over-activity, excitement or heat. Blue or grey gums, severe breathing difficulty or collapse are emergencies, not expected consequences of exercise, and need immediate veterinary care. [1]

BOAS makes it harder for a dog to lose heat through panting because restricted nasal airflow reduces the nose's cooling function.

An affected dog may be unable to cool down effectively as body temperature rises. Rapidly worsening breathing, blue or grey gums, weakness or collapse in warm conditions are emergencies and need immediate veterinary care. [2]

Excitement and stress can make BOAS signs more obvious because the dog needs to move more air through passages that are already narrowed.

A dog that sounds quiet at rest may snore, snort, pant heavily or show greater breathing effort while excited, playing or under stress. This change is useful clinical information rather than simply a feature of the dog's personality. [2]

Blue or grey gums or tongue, collapse or unconsciousness are emergency signs in a dog with suspected BOAS and require immediate veterinary care.

These changes can mean that the dog is not getting enough oxygen. Severe airway obstruction can deteriorate rapidly, particularly during exercise, excitement, sleep or overheating, so they are not signs to watch casually at home. [2]

BOAS can disturb sleep and can cause periods when a dog stops breathing, known as sleep apnoea.

A thick tongue base, long or thick soft palate and crowded nasal tissues can obstruct the airway when the dog's mouth is closed during sleep. Repeated breathing difficulty at night can affect both safety and quality of life. [2]

Some flat-faced dogs may sleep on their backs because that position can let soft-palate tissue fall away from the larynx and ease airflow.

A preferred sleeping position does not show how healthy the airway is. Restlessness, repeated waking, loud breathing or pauses in breathing can still point to sleep-disordered breathing associated with upper-airway obstruction. [1]

BOAS can make eating and swallowing harder because excess throat folds and an elongated soft palate may crowd the area shared by the airway and oesophagus.

A dog may need to coordinate breathing around an already narrowed throat while taking food or water. Eating difficulty, gagging or repeated interruption of meals can therefore be part of the wider BOAS picture rather than a separate habit. [2]

BOAS can affect everyday breathing, activity, sleep and eating, so its effects can substantially compromise a dog's welfare and quality of life.

The condition is more than a breathing noise. Difficulty coping with heat, sleep apnoea and regurgitation can sit alongside reduced exercise tolerance, while severe obstruction can lead to oxygen shortage and collapse. [3]

BOAS can be missed when noisy breathing, poor stamina or disturbed sleep are mistaken for normal features of a flat-faced breed.

Signs may also be absent during quiet rest and emerge only with activity, eating, excitement, stress or warm conditions. A familiar sound or long-standing limitation can still represent a health problem even when the dog has behaved that way for years. [3]

A vet assesses BOAS by combining the dog's history and physical examination with an evaluation of breathing before and after controlled exercise.

The assessment can include the sound and effort of breathing, exercise tolerance, nostril shape and body condition. Imaging or an examination of the deeper airway may be added when the visible examination cannot explain the signs or treatment is being planned. [2]

Exercise assessment can reveal BOAS that is not obvious while a dog is resting.

Comparing breathing before and after a short, controlled exercise test helps show whether noise, effort or recovery changes when the airway is asked to do more work. This makes the assessment more representative of the dog's daily function. [2]

A respiratory function grade describes how much breathing difficulty is found during a standardised BOAS assessment, with the higher grades representing clinically important disease.

The grade gives the veterinary team a shared way to discuss severity and whether monitoring, weight management or further investigation may be appropriate. It reflects the dog's function at that assessment rather than replacing a full clinical evaluation. [2]

A vet can see whether a dog's outer nostrils are open or narrowed and whether they collapse inward during breathing.

The visible opening does not tell the whole story. Narrowing can also occur behind the nostril wings, and crowded turbinates or a deviated septum further inside the nose may restrict airflow without being obvious from the outside. [2]

A deeper airway examination under general anaesthesia is needed to confirm an elongated soft palate or everted laryngeal saccules.

Flat-faced dogs often have a thick tongue that makes the larynx difficult to see while they are awake. Examining the airway under anaesthesia lets the veterinary team assess obstruction that cannot be judged from external appearance alone. [1]

X-rays or CT scans can help a vet look beyond the visible nostrils and assess other parts of a dog's airway, chest and digestive tract.

Imaging may identify a narrow or collapsing windpipe, lung changes such as aspiration pneumonia, an oesophageal pouch or a hiatal hernia. Head and neck CT can also show hidden nasal obstruction and help plan airway surgery. [2]

Excess body fat can worsen BOAS by adding tissue around an airway that is already narrow.

A body condition score is more useful than comparing a dog with an average breed weight, because it assesses the individual dog's fat cover. Veterinary weight planning can form part of BOAS management, especially when excess weight is adding to breathing effort. [4]

Surgery does not cure BOAS, but suitable upper-airway surgery can improve breathing and quality of life for some dogs.

Results vary with the severity and location of obstruction and with secondary damage such as laryngeal collapse. A dog may still need long-term attention to body condition, heat tolerance, exercise response and any returning respiratory or digestive signs. [4]

Swelling or bleeding around the airway can make breathing difficult after BOAS surgery, so close hospital monitoring is an important part of recovery.

Some dogs may temporarily need a breathing tube placed through the neck if swelling obstructs the airway. Regurgitation can also allow material into the lungs and cause aspiration pneumonia, another recognised complication after surgery. [4]

A dog's outlook after BOAS surgery depends partly on how advanced the airway damage is, with established laryngeal collapse linked to a poorer prognosis.

Dogs treated before long-standing obstruction has made the laryngeal cartilage inflexible may have more room for improvement. The procedures performed, other airway or digestive problems and the dog's recovery from anaesthesia also shape the individual outcome. [1]

Veterinary follow-up remains important after BOAS surgery because improvement varies and some severely affected dogs may need further assessment or revision surgery.

BOAS is not cured by an operation, and the airway can still be affected by body condition, heat, exertion or secondary changes. Rechecks allow breathing, recovery and any continuing respiratory, sleep or digestive signs to be assessed over time. [4]