Obstructive airway syndrome in the brachycephalic dog

Transcription

1 Vet Times The website for the veterinary profession Obstructive airway syndrome in the brachycephalic dog Author : RITA FURTADO Categories : Vets Date : May 12, 2014 RITA FURTADO DVM, MRCVS examines upper airway obstruction in certain breeds, their signs and diagnosis, stages of laryngeal collapse and procedures for all the surgical techniques Summary Brachycephalic obstructive airway syndrome (BOAS) is a complex condition that results in varying degrees of upper airway obstruction. The signs most frequently reported by owners include respiratory distress, reduced exercise tolerance, stridor and, in severely affected animals, collapse. The inherent anatomy of the brachycephalic, such as stenotic nares and elongated soft palate, will initiate an increased negative pressure on the upper airway. Increased turbulence on the pharyngolaryngeal region is noted and, as a result, oedema and further obstruction occurs that may lead to potentially life-threatening situations. Treatment of dogs affected with BOAS should involve a combination of medical and surgical management. Medical treatment, including weight loss, sedation, housing in a cool environment and administration of anti-inflammatory drugs, have been described, but surgical correction will give better results. Surgery may include rhinoplasty, staphlectomy and removal of laryngeal and tonsillar saccules. Key words airway, brachycephalic, obstructive, signs, treatment BRACHYCEPHALIC dogs have been gaining popularity all over the world and veterinarians 1 / 15

2 should be aware of the symptoms associated with the upper respiratory malformations that have been greatly exacerbated in recent decades. Brachycephalic obstructive airway syndrome (BOAS) is a combination of abnormalities that results in upper airway obstruction and inspiratory dyspnoea. The most commonly affected breeds are English and French bulldogs, pugs and Boston terriers, although other dogs with similar conformation, such as shih-tzus, bullmastiffs and boxers, have reportedly also been affected. The primary components of BOAS are congenital and, when present, cause upper airway obstruction and consequently increased respiratory effort with chronic increase of negative pressure in the airways. The primary components include: stenotic nares; elongated soft palate; hypoplastic trachea seen particularly in some English bulldogs; and nasopharyngeal turbinates seen more frequently in pugs. Because of the persistent negative pressure, inflammation and stretching of soft tissue may occur, leading to the additional secondary components: everted laryngeal saccules; laryngeal collapse; and everted tonsils. These secondary components will further worsen airway turbulence and oedematous pharyngeal tissue through increased respiratory efforts (Bowlt and Moore, 2009; Fasanella et al, 2010); Ginn et al, 2008; Wykes, Clinical signs Dogs suffering from BOAS show clinical signs including: stertor accompanied with inspiratory dyspnoea; loud snoring; 2 / 15

3 coughing; gagging; stridor if laryngeal collapse is present; syncope and collapse episodes; cyanosis and orthopnoeic posture; and gastrointestinal signs, such as dysphagia, regurgitation and vomiting (not necessarily associated with meals or diarrhoea). Acute signs of respiratory distress may be seen more frequently if the patient is obese or when it is placed in stressful situations, due to overheating, excitement or exercise. Patients with concurrent gastrointestinal signs are at risk of aerophagia and aspiration pneumonia (Bowlt and Moore, 2009; Fasanella et al, 2010; Poncet et al, 2005). Diagnosis Diagnosis of the condition is often straightforward because the stenotic nares can be appreciated on physical examination (Figure 1). The elongated soft palate, everted laryngeal saccules, laryngeal collapse and everted tonsils can be inspected using a laryngoscope on a lightly anaesthetised patient (Monnet, 2002). A radiological examination may also be performed. On a lateral radiographic study, the diameter of the trachea can be appreciated and, in a mesocephalic dog, the ratio of tracheal lumen to thoracic inlet width is around 0:2. In a normal bulldog this ratio is 0:1 and a hypoplastic trachea can be diagnosed in up to 55 per cent of English bulldogs (Monnet, 2002). Despite Coyne and Fingland (1992) finding no significant difference in the trachea and thoracic inlet width between dyspnoeic and non-dyspnoeic bulldogs, due consideration should be given to a severely hypoplastic trachea, especially in a very young, dyspnoeic animal. An alternative assessment is to compare the radiographic diameter of the airway through the cricoid cartilage and the trachea (in an extubated animal): in cases of tracheal hypoplasia, the trachea is obviously narrower than the cricoid. Treatment Treatment should involve a combination of medical and surgical management. Medical treatment, including weight loss, sedation, housing in a cool environment and administration of anti- 3 / 15

4 inflammatory drugs have been described, but surgical correction will give better results (Riecks et al, 2007). Dogs undergoing surgery should be monitored carefully for decompensation and progressive respiratory distress and, in critical cases, transtracheal intubation may rarely be required. Investigation and surgery should be performed under the same anaesthetic. It is recommended to preoxygenate the patient for at least five minutes, premedicate with a sedative in combination with an opioid and perform a rapid induction with thiopental, alfaxalone or propofol. Anaesthesia should be maintained with inhalation agent and oxygen. Some surgeons use steroids (prednisolone 0.5mg/kg to 1mg/kg or dexamethasone 1mg/kg IV) in the presurgical period to decrease oedema, but others prefer to avoid their use. The dog s age at surgery is still very controversial. While some authors (Pink et al, 2006; Wykes, 1991) believe early surgical correction from three to four months old in dogs with clinical signs will minimise the cycle of mucosal irritation, others (Bowlt and Moore, 2009) suggest early correction may result in a severe degree of inflammation and so, where possible, surgery should be delayed until five months of age. For all the surgical procedures, the dog should be positioned in sternal recumbency with the endotracheal tube secured to the lower jaw to ensure free access to the soft palate (Figure 2). Rotation should be minimised by taping the head to the table. The nose should be aseptically prepared (Fossum, 2002). Stenotic nares The aim of the surgical treatment for stenotic nares is to increase the diameter of the nostril by removing a triangle of the nostril wings and apposing the wound edges. The most popular techniques with better cosmetic results are vertical, horizontal or lateral wedge resections (Monnet, 2002). Bleeding is normally moderate and the use of electrocoagulation techniques should be avoided. In the experience of most surgeons, manual pressure is helpful to reduce haemorrhage while suturing the defect. Once the defect is closed, the haemorrhage will discontinue. Elongated soft palate The soft palate is considered elongated when it extends more than 1mm to 3mm caudal to the tip of the epiglottis or tonsils (Figure 3; Fossum, 2002). The soft palate can be shortened by cutting the excess tissue and suturing it with a rapidly absorbable material (for example, Monocryl) or by using an electro or laser technique. When 4 / 15

5 performing these techniques correctly, haemorrhage should be absent or extremely mild and, in every case, the pharynx and oral cavity should be completely clear of haemorrhage before extubation. If in doubt about the amount of soft palate that needs to be resected, the clinician should always choose a more conservative approach (Figure 4). A second surgery is always preferable to excessive resection, as the latter may result in severe complications, such as aspiration pneumonia. Everted laryngeal saccules Everted laryngeal saccules is considered to be the first stage of laryngeal collapse (Table 1) and it is a consequence of the constant negative pressure that pulls the saccules from the crypts. Some surgeons believe not all the saccules will need surgical treatment (Riecks et al, 2007), but others do. Once inverted, they may cause significant obstruction of the glottis and oedema due to the chronic turbulent airflow. Before removal of the saccules the patient should be extubated and the saccules grasped with Allis tissue forceps before sharply transecting the base with Metzenbaum scissors. Avoiding electrosurgery will reduce inflammation and, consequently, the risk of postoperative obstructive oedema (Monnet, 2002). Everted tonsils Protrusion of the tonsils occurs as a result of irritation or negative pressure in the air passages (Figure 5). Some surgeons advocate they should be left intact because they rarely interfere with breathing; others hypothesise that if hypertrophic tonsils are protruding from the tonsilar fossae, they should be removed to create a little more space within the nasopharynx. The tonsils can be removed with techniques such as bipolar scissors or sharp dissection and suturing. Laryngeal collapse Dogs with persistent stage two or higher of laryngeal collapse as part of a BOAS syndrome are less common (White, 2012). The management of laryngeal collapse is controversial and it will depend on the stage of collapse. The role of surgery in the management of stage two and three laryngeal collapse is also controversial. Some authors (Monnet 2002; Pink et al, 2006) consider dogs suffering from stage two and three laryngeal collapse carry a guarded prognosis. Nevertheless, the life-threatening respiratory signs either may cease or greatly be reduced if the patient undergoes rhinoplasty, staphylectomy and laryngeal saccule resection surgery (Torrez and Hunt, 2006). If no improvement is seen, arytenoid laryngoplasty, laryngectomy or lateralisation procedures might 5 / 15

6 be an option (White, 2012). If the collapse does not improve, an alternative to these surgeries is a permanent tracheostomy (Monnet, 2002). BOAS-associated gastrointestinal disease Gastrointestinal problems such as dysphagia, regurgitation and vomiting may occur, especially when dogs with BOAS get excited or are in respiratory distress (Poncet et al, 2005). In the oesophagus, the most common non-inflammatory anomalies include cardial atony, oesophageal deviation, hiatal hernia and gastro-oesophageal reflux. In the stomach, the most common are gastric stasis, pyloric mucosal hyperplasia, pyloric stenosis and pyloric atony (Poncet et al, 2005; Poncet et al, 2006). Gastric inflammatory disease was found in 98 per cent of dogs with BOAS and it is thought to be associated with the aforementioned functional and anatomic anomalies (Poncet et al, 2005). In French bulldogs (particularly male or heavy dogs), the severity of the gastrointestinal signs is associated with the severity of the respiratory clinical signs (Poncet et al, 2006). It is recommended to start dogs with BOAS on medical treatment for upper gastrointestinal diseases, since this will dramatically improve the prognosis following surgical treatment. Medical treatment may include a combination of the antacid and prokinetic drugs, such as omeprazole (1mg/kg every 24 hours) and metoclopramide (0.25mg/ kg to 0.5mg/kg every 12 hours). If distal oesophagitis is noted, an antacid, such as sucralfate, may be given PO every eight hours. After discontinuing the course of medication, improvement has been maintained in most cases (Poncet et al, 2005; Poncet et al, 2006). Postoperative considerations The surgical site should be kept clean and protected from potential rubbing with an Elizabethan collar depending on the patient s temperament. Blood clots should be removed from the throat and nares before extubation to minimise further obstruction. Monitoring for signs of respiratory distress is mandatory during recovery from anaesthesia and for at least 24 hours after surgery. Light sedation should be administered if the animal is stressed. Barking should be discouraged and animals should be kept cool. 6 / 15

7 Analgesia with opioids should be provided. NSAIDs may also be appropriate, depending on the case and surgeon s preference. Postoperative antibiotics are usually not required. Metoclopramide (0.5mg/ kg) and omeprazole (1mg/ kg) may be administered pre and postsurgically to prevent or treat gastrointestinal signs. Fasting should be maintained until the animal is completely recovered from surgery. Some surgeons prefer to withhold food for at least 24 hours postsurgery, whereas others offer tinned food as soon as the animal is awake. Short walks with a harness for at least four weeks is recommended. Note some drugs mentioned in this article are not licensed for use in dogs. Acknowledgement The author is grateful to Kelly Bowlt for her assistance with this article and accompanying photographs. References Bowlt K and Moore A H (2009). Surgery of the upper respiratory tract part 2: brachycephalic obstructive airway syndrome (BOAS), Companion Animal 14(8): Coyne B E and Fingland R B (1992). Hypoplasia of the trachea in dogs: 103 cases ( ), Journal of the American Veterinary Medical Association 201(5): Fasanella F J et al (2010). Brachycephalic airway obstructive syndrome in dogs: 90 cases ( ), Journal of the American Veterinary Medical Association, 237(9): 1,048-1,051. Fossum T (2002). Surgery of the upper respiratory system, Small Animal Surgery: Ginn J A et al (2008). Nasopharyngeal turbinates in brachycephalic dogs and cats, Journal of the American Animal Hospital Association 44(5): Monnet E (2002). Brachycephalic airway syndrome. In Slatter D (ed), Textbook of Small Animal Surgery: Pink J J et al (2006). Laryngeal collapse in seven brachycephalic puppies, The Journal of Small Animal Practice 47(3): Poncet C M et al (2005). Prevalence of gastrointestinal tract lesions in 73 brachycephalic dogs with upper respiratory syndrome, Journal of Small Animal Practice 46(6): Poncet C M et al (2006). Long-term results of upper respiratory syndrome surgery and gastrointestinal tract medical treatment in 51 brachycephalic dogs, The Journal of Small Animal Practice 47(3): Riecks T W, Birchard S J and Stephens J A (2007). Surgical correction of brachycephalic 7 / 15

8 syndrome in dogs: 62 cases ( ), Journal of the American Veterinary Medical Association 230(9): 1,324-1,328. Torrez C V and Hunt G B (2006). Results of surgical correction of abnormalities associated with brachycephalic airway obstruction syndrome in dogs in Australia, The Journal of Small Animal Practice 47(3): White R N (2012). Surgical management of laryngeal collapse associated with brachycephalic airway obstruction syndrome in dogs, The Journal of Small Animal Practice 53(1): Wykes P M (1991). Brachycephalic airway obstructive syndrome, Problems in veterinary medicine 3(2): / 15

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10 Figure 1. A four-year-old pug with stenotic nares. 10 / 15

11 Figure 2. A two-year-old pug being positioned for BOAS surgery. 11 / 15

12 Figure 3. An intraoral view of a pug demonstrating an overlong soft palate. 12 / 15

13 Figure 4. An intraoral view of an eight-year-old cairn terrier referred for investigation of aspiration pneumonia four weeks after BOAS surgery at a different practice. The soft palate has been shortened too much. 13 / 15

14 Figure 5. An intraoral view of a two-year-old pug with everted tonsils. 14 / 15

15 Table 1. Laryngeal collapse classification 15 / 15 Powered by TCPDF (