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Brachycephalic Airway Syndrome

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Brachycephalic Airway Syndrome Brachycephalic airway syndrome Adjunct Professor Philip A Moses BVSc, Cert SAO, FANZCVS Specialist Small Animal Surgeon Founder Veterinary Specialist Services Underwood, Jindalee, Toowoomba and Gold Coast, Queensland Australia www.vss.net.au The popularity of brachycephalic dogs has increased tremendously over the past 10 years – in particular French Bulldogs – now the most popular breed in the UK and among the most popular breeds worldwide. This widespread popularity has highlighted the many problems of these little dogs. From an evolutionary point of view all dogs have descended from the wolf – although looking at a Pug, Frenchie or Bulldog this is difficult to believe. This series of three short presentations looks at the pre-operative assessment, relevant surgical procedures and post-operative management of brachycephalic airway syndrome. PATHOPHYSIOLOGY There is no definitive list of the brachycephalic breeds however I think most are included below: Affenpinscher American Bulldog Australian Bulldog Boston Terrier Boxer Brussels Griffon Bulldog Bullmastiff Cavalier King Charles Spaniel Cane Corso Chow Chow Dogo Argentino Dogue de Bordeaux English Toy Spaniel French Bulldog Japanese Chin Lhasa Apso Neapolitan Mastiff Pekingese Presa Canario Pug Rottweiler Shar-Pei Shih Tzu Tibetan Spaniel Valley Bulldog Proceedings of VetFest 2020 Moses, P - Brachycephalic airway syndrome 249 Brachycephalic airway syndrome is also reported in cats with a brachycephalic conformation - Persian and Himalayan. In brachycephalic animals the skull is shortened rostrally with dorsoventral compression of the nasal passages as well as loss of or dramatic compression of the frontal and maxillary sinuses. There is distortion of pharyngeal and laryngeal soft tissues increasing airway resistance in the upper airway. Selective breeding has worsened this condition significantly over time. The brachycephalic skull – changes over time 1870 2010 Primary components of BAS: - stenotic nares - elongated soft palate - oedematous laryngeal ventricles / laryngeal collapse - choanal hypoplasia - macroglossia - tracheal hypoplasia - obstructive nasal turbinates – recently described Stenotic nares, choanal hypoplasia, elongated soft palate, tracheal hypoplasia and obstructive nasal turbinates are considered primary anatomical components of BAS. Excessive negative pressure during inspiration, through the obstructed nares and pharynx, causes inflammation and mucosal oedema, and results in further stretching of redundant tissue and eventual eversion of laryngeal ventricles and collapse of the larynx. Note – Tracheal hypoplasia is not associated with BAS but will contribute to airway distress in brachycephalic breeds. Tracheal hypoplasia is determined by the ratio of the trachea to the thoracic inlet. The normal ratio is 0.2, less than 0.16 is regarded as tracheal hypoplasia. The breed average in the British Bulldog is 0.106. Proceedings of VetFest 2020 Moses, P - Brachycephalic airway syndrome 250 Brachycephalic airway syndrome is also associated with reflux oesophagitis and hiatal hernia secondary to increased intra-thoracic pressure. Secondary components of BAS: Oedematous laryngeal ventricles Laryngeal collapse Pharyngeal hyperplasia Tracheal collapse Bronchiectasis and bronchial collapse Choanal collapse Hiatal Hernia Gastro-oesophageal reflux Early surgical intervention is essential to help reduce secondary changes. CLINICAL SIGNS Clinical signs are highlighted by inspiratory dyspnoea, usually worsened by exercise and high ambient temperature. Dyspnoea is primarily inspiratory if only the external nares and turbinates are involved, however there is an inspiratory and expiratory pattern with involvement of the choanae, pharynx, soft palate and eventually the larynx. Cyanosis, hyperthermia and collapse may result from increased activity as animals work harder to breathe. These animals often present for noisy breathing, snoring, dyspnoea or hyperthermia. Inspiratory dyspnoea, often with open-mouth breathing. The wings of the nostrils fill the external nares and are sucked inward on inspiration, occluding the nostril. Other signs may include gagging, coughing, difficulty in eating and inspiratory stridor associated with obstructed nasal passages and an elongated soft palate. Approximately 45% of dogs will develop gastrointestinal signs in the first year of life associated with increased abdominal pressure. Reflux oesophagitis and hiatal hernia are commonly seen. Clinical signs worsen with age and exercise. Most brachycephalic dogs require assessment and corrective / reconstructive surgery; ideally this should be undertaken at 12 months of age and before 2 years of age – this helps to prevent the development of secondary changes. Warning – it is our preference to undertake definitive corrective procedures at the same time as assessment and examination under anaesthesia. Otherwise anaesthetic recovery in a dog with compromised airways may be problematic. PRE-OPERATIVE ASSESSMENT It is not possible to assess the airways – other than the nares, in a conscious dog. A complete assessment of brachycephalic dogs prior to surgery is essential for attaining the best possible outcome and to give the animal’s owners the most accurate prognosis. Prior to surgery we recommend the following assessment be undertaken: Pedigree – record of the dog’s pedigree is essential for information gathering purposes. History – a thorough clinical history including diet, previous and current illness and medications. Physical examination – include auscultation of the sinuses, larynx, pharynx as well as the thorax. Proceedings of VetFest 2020 Moses, P - Brachycephalic airway syndrome 251 Neurological examination – essential due to the high incidence of hemivertebrae and encephalopathies. Haematology / biochemistry / blood gasses – biochemical and haematological analysis prior to anaesthesia is essential prior to any anaesthetic induction. Ophthalmological examination – brachycephalic dogs have many eye issues Musculoskeletal examination – many orthopaedic conditions are commonly seen in brachycephalic dogs – in particular medial patella luxation and hip dysplasia. Imaging minimum database is thoracic radiology however assessment by whole body CT is our preferred imaging modality Once all data is available a veterinarian can develop an assessment of the risk of brachycephalic surgery and have a discussion with the owner of the dog about these risks so that informed consent may be obtained. DIAGNOSIS Clinical signs of obstructive breathing are common, auscultation especially over the larynx as thoracic auscultation is complicated by referred upper airway sounds. In the UK some centers advocate Exercise Tolerance Testing however in the heat and humidity of Brisbane running a Pug up and down the carpark would not end well. For me the most telling diagnostic test is the presence of Grade 1 laryngeal collapse – if a dog has oedematous laryngeal ventricles – it has significantly increased inspiratory pressures – enough to lead to laryngeal collapse. This is my diagnostic test for the requirement for surgery. RADIOLOGY Cervical area: elongated soft palate extending into the rima glottides. It is essential to evaluate the tracheal diameter as a hypoplastic trachea significantly worsens prognosis. The normal tracheal diameter-to-thoracic inlet ratio is 0.2 The tracheal diameter-to-thoracic inlet ratio in normal British Bulldogs is 0.106 Presence of hemivertebrae – these are common in many of the brachycephalic breeds. The incidence in French Bulldogs is around 80%. Any dog with ANY hemivertebrae (including caudal vertebrae) must NOT be used for breeding. Tracheal hypoplasia is the ratio of the width of the trachea at the thoracic inlet to the thoracic inlet = X/Y above YY X Proceedings of VetFest 2020 Moses, P - Brachycephalic airway syndrome 252 British Bulldogs have the highest incidence of hypoplastic trachea (55%) of all the brachycephalic breeds. Thorax radiography: Hiatal hernia, aspiration pneumonia and pulmonary oedema are very common. If there is evidence of right-sided heart failure an echocardiogram is recommended, particularly if there are radiographic signs of cardiac enlargement, to help assess myocardial function and arrhythmias. ENDOSCOPY Given the high incidence of oesophagitis, hiatal hernia and other upper GI disorders consideration should be given to routine upper GI assessment in all brachycephalic dogs. BRONCHOSCOPY Assessment of the trachea to the level of the tracheal bifurcation is important to rule out tracheal collapse. The trachea should be observed along its entirety during both inspiration and expiration. We use a 4mm flexible endoscope and find this instrument adequate for all animals. The same instrument can be retroflexed to examine the choanae. CHOANAL EXAMINAITON Using a small flexible endoscope retroflexed it is important to examine the choanal region. Abnormalities seen include foreign bodies, aberrant turbinates, infection – fungal and bacterial and the presence of hyperplastic lymphoid tissue. OROPHARYNGEAL EXAMINATION Examination of the caudal pharynx and larynx requires light general anaesthesia. Neither the depth of anaesthesia nor the anaesthetic agent should depress normal abduction and adduction of the arytenoid cartilages and vocal cords. Acepromazine and barbiturates are best avoided; we use medetomidine and methadone premed and an Alfaxan induction to anaesthetise these animals for oropharyngeal assessment. The first thing to assess is laryngeal function.
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