Brachycephalic Airway Syndrome

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Also known as: Brachycephalic Upper Airway Syndrome — Brachycephalic Obstructive Airway Syndrome — BOAS

Introduction

Brachycephalic Airway Syndrome is a consequence of the pharyngeal and nasal anatomy in brachycephalic or short-headed dog breeds such as Bulldogs, Pekingese, Pugs and Boxers. The syndrome arises due to increased airway resistance that results from airway narrowing at the nares, nasal turbinates and nasopharynx at the caudal edges of the soft palate and hyoid apparatus. The narrowing means that greater inspiratory effort is exerted by the diaphragm and chest wall muscles. This creates increased negative pressure which has the greatest impact on the soft tissues of the pharynx, especially the caudal soft palate and the hyoid apparatus.

The primary components of the syndrome are:

elongated soft palate
stenotic nares

Secondary problems due to the negative pressure generated at inspiration are:

eversion of the laryngeal saccules
laryngeal collapse

Hypoplastic trachea is usually a common finding in brachycephalic breeds, and this may contribute to the syndrome, although its impact is still unclear.

Hiatal hernia is a condition which brachycephalic dogs are predisposed to, and this might complicate treatment.

Clinical Signs

Animals are presented for excessively noisy breathing and inspiratory dyspnoea. This dyspnoea is made worse by exercise and increased temperature.

There may have been episodes of cyanosis and collapse.

If only the nares are involved in the syndrome: inspiratory dyspnoea is corrected by open-mouthed breathing.

If there is also soft palate elongation and eversion of the laryngeal saccules: the dyspnoea is inspiratory and expiratory.

The pattern of breathing is usually a slow inspiratory phase followed by a rapid expiratory phase.

Diagnosis

Physical examination: stenotic nares may be evident on examination. Thoracic auscultation may be difficult due to the upper respiratory noise.

Radiography: this may reveal an elongated soft palate. A hypoplastic trachea can be diagnosed by comparing the diameters of the thoracic inlet and the trachea. Evaluation of the heart and lungs is possible to check for oedema and right-sided dilation.

Haematology is usually unremarkable, though there may be an increase in PCV due to mild hypoxia.

Laryngeal examination: this should be performed under light general anaesthesia, in order to visualise the defects. The soft palate is considered elongated if it extends past the tip of the epiglottis. Laryngeal saccules appear as white dome-shaped structures cranial to the vocal cords on either side of the larynx.

Laryngeal collapse appears as a medial tipping of both corniculate processes and a medial flattening of the cuneiform processes of the arytenoid cartilage.

The tonsils should also be evaluated.

Treatment

Abnormalities should be corrected if they cause distress to the dog, become more severe with time, or cause life-threatening obstruction.

Stenotic nares: a nasal wedge resection is performed to enlarge the nostrils. The tissue is highly vascular and bleeds profusely, therefore pressure and suction should be used. Electrocautery is not used as the cosmetic result is not optimal.

Elongated soft palate: soft palate resection (staphylectomy) is performed using a scalpel blade or a CO2 laser. The laser reduces bleeding and surgery time.

Everted laryngeal saccules: the everted saccule can be grasped and excised. The procedure is rapid and effective.

Laryngeal collapse: this is an emergency, and a temporary or permanent tracheostomy may have to be performed.

Post-operative complications: these patients are high-risk for surgery and recovery, as inflammation of the airways may cause obstruction and death. A temporary tracheostomy tube may be placed at surgery and kept during the recovery period until tissue inflammation has subsided.

Prognosis

The prognosis is good for young animals and respiratory distress and exercise tolerance may be markedly improved.

Older animals with secondary problems such as laryngeal collapse have a less favourable prognosis.


Brachycephalic Airway Syndrome Learning Resources
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Small Animal Soft Tissue Surgery Q&A 07


References

King, L. (2004) Textbook of respiratory disease in dogs and cats Elsevier Health Sciences

Slatter, D. (2002) Textbook of small animal surgery Elsevier Health Sciences




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