Page 91 - BSAVA Manual of Canine and Feline Head, Neck and Thoracic Surgery, 2nd Edition

Chapter 6
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Brachycephalic airway disease

Gert ter Haar and Gerhard U. Oechtering

Introduction in brachycephalic breeds. Nearly all brachycephalic dogs
are affected by upper airway obstruction to some degree,
Brachycephalic dogs such as English and French but the clinical signs depend on the severity of functional
Bulldogs, Pugs, Pekingese, Shih Tzus, Shar-Peis and stenosis of the airway. The upper airway obstruction is
Boston Terriers, and Persian and Himalayan cats, fre- usually associated with some combination of abnormal-
quently present with signs of upper airway obstruction as ities and the clinical signs vary from mild respiratory
a result of an anatomical distortion of their faces caused noise to severe signs of airway occlusion, including rough
by selective breeding. Breeding for exaggerated, short- ster torous respiratory sounds, abducted forelimbs, slow
ened skull features has deformed the heads of brachy- forceful inspiratory effort and rapid forceful expiratory
cephalic animals in such a way that health and welfare effort, and pale or cyanotic mucus membranes.
are compromised in an increasing number of individuals Besides these obvious effects on breathing, the small
(Roedler et al., 2013; Oechtering et al., 2016b; ter Haar, nasal cavity is no longer capable of performing other
2016a). Termed brachycephalic airway disease (BAD), but natural functions, all of which depend upon air being able
also referred to as brachycephalic airway obstruction to flow through the nose in well defined patterns over the
syndrome (BAOS), brachycephalic obstructive airway turbinates. For a dog, drastic reduction of nasal breathing
syndrome (BOAS) and brachycephalic airway syndrome means that it loses its principal organ of thermoregulation
(BAS), the condition develops as a result of an inherited and is no longer capable of evacuating body heat effi-
defect in the development of the bones of the base of the ciently in the event of physical effort, excitement or even
skull (Harvey, 1989), whereby the head is of normal width warm ambient temperatures (Oechtering, 2010, 2017).
but significantly reduced length. Because the soft tissues This causes the internal body temperature to rise and can
of the head are not reduced proportionally, redundant lead to collapse and death. This is why brachycephalic
tissue increases the resistance to the flow of air through animals are particularly heat-sensitive, why many pant to
the upper airway. Problems go beyond the usually quoted no avail even at room temperature and without physical
triad of stenotic nares, overlong soft palate and everted effort, and why they may need several hours to recover
laryngeal saccules. The syndrome entails narrowing of even after brief exercise (Roedler et al., 2013). To date, it
the entire nasal passageways as a result of relative is unclear how much the last function of the nose, olfac-
i
conchal hypertrophy, with increased mucosal contact tion, is affected by the nasal abnormal ties seen.
points and obstructive and protruding aberrant conchae Furthermore, the abnormal morphology of the tym-
(Roedler et al., 2013; Oechtering, 2010; Schuenemann panic bulla (Mielke et al., 2017) seen in these breeds may
and Oechtering, 2014b; Oechtering et al., 2016b). The predispose to auditory tube dysfunction and subsequent
nasopharyngeal passage is a narrow bony cage further middle ear effusion, leading to conductive hearing loss
compromised by excessive redundant tissue, and the and further decreasing the quality of life of these animals.
aforementioned protrusion of nasal conchae and is prone As a result of the chronic high negative intrathoracic
to collapse (Rubin et al., 2015). The pharyngeal and laryn- pressure generated upon inspiration, secondary gastro-
geal airway passages are narrow as well, with dorso- intestinal abnormalities such as hiatal hernia, oeso -
ventral flattening of the pharynx, a thickened base of the pha gitis, gastritis and pyloric mucosal hyperplasia,
tongue, tonsillar hypertrophy and protrusion, and diffuse evidenced by gagging, vomiting and regurgitation, can
pharyngeal mucosal oedema all contributing to the develop (Poncet et al., 2005), especially in the French
obstruction caused by the relatively or absolutely over- Bulldog. Relative or absolute tracheal hypoplasia is
long soft palate. Whereas, classically, laryngeal collapse commonly seen in the English Bulldog and is likely to be
has been described as the limiting factor in laryngeal air- an important predisposing factor for development of
flow, narrowing of the larynx as a result of narrow and aspiration pneumonia at an early age in this breed.
oval-shaped cricoid dimensions appears to be equally Excessive facial and nasal skin folds make the animal
important (Rutherford et al., 2017). prone to skin fold dermatitis. Corneal ulceration, as a
The set of airway signs characterized by stertor result of large corneal exposure, reduced tear production,
(excessive noise during breathing), reduced tolerance to reduced sensitivity of the cornea and distichiasis or
exercise and stress, respiratory distress and, in severe medial canthal entropion, is commonly seen, especially
cases, cyanosis and collapse, is frequently encountered in the Pug.

82 BSAVA Manual of Canine and Feline Head, Neck and Thoracic Surgery, second edition. Edited by Daniel J. Brockman, David E. Holt and Gert ter Haar. ©BSAVA 2018

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