Brachycephalic obstructive airway syndrome;

more than just a long soft palate.



By Arthur House BSc, BVMS, PhD, Cert SAS, Dip ECVS

Specialist Small Animal Surgeon

Melbourne Veterinary Specialists Centre





 

Brachycephalic obstructive airway syndrome (BOAS) is one of the many terms used to describe obstructive upper airway disease seen in many breeds of brachycephalic (short nosed) dogs such as English Bulldogs, French Bulldogs, Boston Terriers Pekingese and Pugs, though the problem is not restricted to the classically brachycephalic breeds and can affect other breeds such as Cavalier King Charles Spaniels and Staffordshire Bull Terriers. 

 

Causes

BOAS results from a combination of primary structural problems including elongated soft palate, stenotic nares (nostrils), hypoplastic trachea (small wind pipe), redundant pharyngeal folds (excessively fleshy lining of throat), macroglossia (overly large tongue) and protruding ethmoid turbinates (bones within the nose) into the nasal choana (back of the throat). Rarely, enlarged tonsils can contribute to the upper airway obstruction.

 

Secondary problems

Over time, secondary problems can develop which exacerbate the upper airway obstruction. These primarily include laryngeal collapse (collapse of the opening of the wind pipe) and everted laryngeal saccules (fleshy nodules within wind pipe). An additional potential consequence is the development of gastrointestinal disorders predominantly gastrooesophageal reflux and hiatal hernias resulting in chronic gastritis and vomiting.

 

Symptoms

The clinical presentation of dogs with BOAS varies greatly. Dogs present with a combination of snoring, coughing, respiratory stertor/stridor, dysponea, regurgitation / vomiting, exercise intolerance, cyanosis and syncope. The potential for a dramatic deterioration in respiratory function exists for all these dogs as the development of everted laryngeal saccules or laryngeal collapse can result in a dog progressing from snoring and respiratory stertor/stridor to an acute respiratory crisis and syncope. Consequently young dogs with mild clinical presentations should still be considered for surgical intervention to avoid the progression of the secondary problems, which can result in life threatening respiratory distress.

 

Diagnosis and treatment

To maximise outcome, all aspects contributing to the airway obstruction need to be addressed.  Prior to surgery dogs should be evaluated to determine which aspects of the syndrome they suffer. Complete evaluation of each dog facilitates identification of factors that could require additional management or alter prognosis.  Early treatment is advised as this reduces the risk of the development of secondary problems that can result in significant and rapid deterioration in respiratory function in addition to potentially reducing the possibility of a good outcome following surgery. 

 

Nostrils

The nostrils are evaluated during physical examination (Figure 1.). Surgical widening of stenotic nostrils is typically achieved by removing a vertical wedge of tissue from the wing of the nostril and alar fold (cartilage inside nose). It is essential that this wedge extends appropriately deep into the alar fold to achieve opening of the nares in the deep (nasal cavity) aspect as well as at the superficial opening (Figure 2.).

 

Soft Palate

Laryngeal examination under general anaesthesia is used to evaluate palate length, laryngeal function, the presence or absence of everted laryngeal saccules, enlargement of tonsils or oral masses (Figure 3.). Plain lateral skull radiographs are useful for estimating length and thickness of the palate.  An elongated soft palate is managed by standard palatoplasty (surgical shortening of palate) or folded palatoplasty (Figure 4.)

 

Laryngeal Saccules

Everted laryngeal saccules are tissue masses within the region of the vocal folds, protruding into the airway (Figure 5.). Everted laryngeal saccules are managed with simple excision.  

 

Enlarged tonsils

Enlarged tonsils are a rare finding and appear to be predominantly a feature of Cavalier King Charles Spaniels. Enlarged tonsils are easily managed by performing a tonsillectomy.

 

Conditions that cannot be surgically treated

Laryngeal collapse, hypoplastic trachea, macroglossia, redundant pharyngeal folds and protrusion of ethmoid turbinates into the nasal choana all represent aspects of BOAS that cannot be specifically managed with surgery.

 

Laryngeal collapse

It is estimated that approximately 50% of dogs presented for BOAS have a degree of laryngeal collapse. The severity is graded from 1 to 3 with grade 1 the most mild and grade 3 the most severe. Dogs suffering grade 1 and potentially grade 2 respond to correction of the nares, palate and everted saccules. Dogs suffering grade 3 have an extremely poor prognosis.

 

Hypoplastic Trachea

Hypoplastic trachea is most commonly seen in Bulldog and Boston terrier breeds. These breeds have a relative hypoplasia of the trachea which is considered normal. Tracheal hypoplasia can not be managed surgically but as with laryngeal collapse dogs will still respond to correction of the nares, palate and everted saccules.  The tracheal width is assessed on a lateral thoracic radiograph.

 

Macroglossia

As with hypoplastic tracheas, Bulldog breeds have a relative macroglossia.  The degree of macroglossia is difficult to evaluate and is often overlooked as a component of the BOAS. It is extremely rare for macroglossia to be the primary cause of upper airway obstruction. It is suggested that in dogs with marked macroglossia that a folded palatoplasty is more appropriate than simple excision of an overlying long palate. Macroglossia can be associated with muscular dystrophy diseases and hence represent a different disease process. This should be suspected if it is observed in a non Bulldog breed.

 

Redundant pharyngeal folds

Redundant pharyngeal folds cannot be managed surgically.  Some surgeons advocate excision of the subglottic fold if this is considered to be excessively large however this does not address the redundancy in the pharyngeal mucosa.

 

Ethmoid turbinates into the nasal choana

The presence of ethmoid turbinates into the nasal choana is not at present routinely evaluated as surgical methods to address this aspect have not yet been refined or evaluated for efficacy.

 

Anaesthesia

Brachycephalic breeds have an increased risk of anaesthesia associated death and consequently equal focus should be placed on confirming the diagnosis / surgery and anaesthesia regime. Despite this increased risk good anaesthetic preparation, monitoring, and strategies for recovery from anaesthetic can overcome the risks encountered. In general, anaesthetic induction (going under anaesthesia) is not associated with increased risk of death. Appropriate premedication (sedative and pain relief drugs given before anaesthetic) to reduce anxiety facilitates smooth and low risk induction. Premedication resulting in profound sedation should be avoided as rapid recovery following discontinuation of anaesthesia is required.

Recovery from anaesthesia presents the biggest anaesthetic challenge. The period between extubation (removal of the anaesthetic tube from the wind pipe) and return of laryngeal function (opening of wind pipe function) requires close supervision (Figure 6 and 7). A low stress environment is critical.

 

Post operative prognosis

Improvement in breathing function is considered good to excellent in approximately 85 to 95% of dogs following surgery (approximately 50 � 55% excellent). It is not uncommon for owners to comment on how much of a change in their dog�s life style has occurred following surgery. Many dogs experience a dramatic increase in exercise ability and an increased ability to recover from heat or excitement. In addition to good to excellent improvements in respiratory function, approximately 90% of dogs with concurrent gastrointestinal complaints have resolution of these complaints following the airway surgery.  


Figure 1. An example of stenotic nares (left nostril) in which the nostril opening is small and the lateral wings of the nostril displaced medially. The right nostril has had a vertical wedge rhinoplasty (surgical opening of nostril) performed to open the nostril opening.




 

Figure 2. Appearance of nostrils following a vertical wedge rhinoplasty. It is essential that this wedge extends appropriately deep into the alar fold to achieve opening of the nares in the deep (nasal cavity) aspect as well as at the superficial opening.


 

Figure 3. Overly long soft palate which extends into the glottis and covers the ventral surface of the glottis and epiglottis. Soft palate white arrow, glottis is obscured, epiglottis red arrow.


 

Figure 4. Appearance of oropharynx (oral cavity) following excision of the caudal aspect of the overly long soft palate.  Compare with Figure 3 how the glottis (white arrow) is now visible and the palate no longer extends into the glottis.

 

Figure 5. Everted laryngeal saccules protruding into the rima glottis (black arrow). These are easily excised with sharp dissection.


 

Figure 6. A nasopharyngeal tube in place for the recovery of a French Bulldog from anaesthesia. The tube is connected directly to an oxygen source and allows delivery of oxygen to the oropharynx (oral cavity) during recovery. A simple and effective way to oxygenate a patient in a stress free manner during the critical stage of recovery from anaesthesia.


 

Figure 7. Intravenous anaesthesia induction agent, laryngoscope, a range of endotracheal tubes (anaesthetic tubes placed in wind pipe) and tracheosotomy tubes ready by the patient cage in event of acute respiratory obstruction during recovery from anaesthesia. A nurse directly monitors the patient until laryngeal (opening of wind pipe) function has returned. This preparation and level of anaesthesia monitoring should be considered routine for all brachycepahlic anaesthesia events.




Many thanks to Arthur for sharing this wonderful article