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Compendium May 2011 (Vol 33, No 5)

Canine Brachycephalic Airway Syndrome: Pathophysiology, Diagnosis, and Nonsurgical Management

by Michelle Trappler, VMD, Kenneth W. Moore, BVMS, DACVS

    CETEST This course is approved for 3.0 CE credits

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    Abstract

    Canine brachycephalic airway syndrome is a progressive disease that affects many brachycephalic dogs. This article describes the components of this syndrome and focuses on acute emergency management and long-term conservative management of these patients. Surgical management is described in a companion article.

    Canine brachycephalic airway syndrome (BAS), also known as brachycephalic syndrome and brachycephalic airway obstructive syndrome, has been reported in many brachycephalic breeds, including the shih tzu, boxer, English and French bulldogs, Lhasa apso, Pekingese, pug, shar-pei, and Boston terrier.1–4 In these breeds, a congenital malformation results in skull bones of normal width but shortened length.3–5 These inherited bony changes lead to the secondary soft tissue abnormalities that characterize BAS. Stenotic nares and elongation of the soft palate are the primary anatomic features of BAS. Secondary changes include eversion of the laryngeal saccules (stage I laryngeal collapse), laryngeal collapse (stages II and III), and enlargement of the tonsils.3,5–8 Hypoplastic trachea is seen concurrently in some brachycephalic breeds (particularly English bulldogs) but is considered independent of BAS.6,9 TABLE 1 lists the frequency of each BAS component identified in four studies. Differences in incidence may be explained by the variation in canine populations in different countries. An Australian study10 noted a high incidence of elongated soft palate alone in Cavalier King Charles spaniels (6 of 15 dogs), a breed not commonly associated with BAS in the United States.

    Pathophysiology

    Pathology in BAS results from the changes in air pressure and flow in the upper airway.3,4,11 The relationship between the radius of a tube, pressure, and flow can be modeled using Poiseuille’s law,12 which shows that a 50% reduction in tube radius leads to a 16-fold increase in resistance to flow. To maintain airflow as the radius decreases, pressures in the airway must become more negative. In dogs with BAS, stenosis of the nares and distortion of the pharyngeal region lead to an increase in negative pressure during inspiration.5,11 This results in stretching of the soft palate, which may already be elongated; swelling of the airway; eversion of the laryngeal saccules; edema and inflammation of tonsillar tissue; and, ultimately, inward collapse of the weakened laryngeal cartilages. A vicious cycle develops: collapse of the laryngeal cartilage further decreases the radius of the airway, which increases the velocity of airflow and the negative pressure in the airway, leading to further collapse. This cyclic pathology is why severe cases of BAS can demonstrate advanced laryngeal collapse and why early surgical intervention is recommended to correct identified BAS components in affected dogs.

    Clinical Presentation

    Stenotic nares and elongated soft palate are often present at birth, with clinical signs being progressive from young adulthood. Most brachycephalic dogs are evaluated between 2 and 4 years of age due to worsening clinical signs,2,6,13–15 although bulldogs tend to present between 1 and 2 years of age.16,17 The literature shows a higher prevalence of BAS (2:1) in male dogs,6,8,18 although one study10 showed a higher prevalence in females (1.6:1). Clinically affected dogs present for inspiratory stertor/stridor, gagging, productive coughing, difficulty swallowing or sleeping, dyspnea, cyanosis, and hyperthermia.1,3,6,7,12,17 These dogs are often worse after exercise, excitement, or stress or with increased environmental temperature or humidity.2,12 No difference was seen when comparing body weights of dogs presenting for BAS and similar populations presenting for nonrespiratory issues,17 although an association between increased body weight and the severity of respiratory issues is a clinically recognized phenomenon.

    Key Facts

    • Primary components of BAS include stenotic nares and elongated soft palate. Secondary components include everted laryngeal saccules, laryngeal collapse, and enlarged tonsils.
    • BAS is a progressive disease and should be treated early.
    • Animals with BAS often present in respiratory distress and should be treated supportively to decrease dyspnea, cyanosis, and hyperthermia and to minimize stress.
    • Diagnosis of BAS requires an upper airway examination. This examination should be performed during the same anesthetic event as surgical correction, if correction is indicated.
    • Treatment of concurrent GI disease may improve outcomes following BAS surgery.

    Diagnosis

    The physical examination should include an evaluation of the respiratory pattern. An inspiratory dyspnea that corrects with open-mouth breathing has been reported when only the nares are involved.3,5,14 Involvement of the soft palate and laryngeal saccules often leads to inspiratory and expiratory dyspnea, the severity of which depends on the degree of additional upper airway pathology.14 Brachycephalic dogs with <50% reduction in airway diameter show an obstructive breathing pattern with a slow inspiratory phase and rapid expiratory phase.4,5 In nonbrachycephalic dogs, this pattern is often seen only with >50% reduction in airway diameter. This demonstrates the confounding role that stenotic nares and other BAS components have on respiratory function in affected dogs. Regardless of the respiratory patterns observed, definitive diagnosis can be established only with an upper airway examination.

    The upper airway examination should evaluate the soft palate, tonsils, laryngeal saccules, and laryngeal function. It is best performed under a light plane of IV anesthesia using thiopental (4.5 mg/kg to effect4) or propofol (3 to 6 mg/kg).2 The examination should be planned so that surgical correction, if warranted, may be performed within the same anesthetic episode. Both the owner and veterinarian should be aware that sedation or anesthesia without correction of airway pathology has the potential to precipitate an episode of acute respiratory distress.3,4,12,16,18 Indications for immediate surgical correction versus tracheostomy are discussed in the Emergency Management section.

    Everted laryngeal saccules

    Figure 2A. Everted laryngeal saccules (arrows). No edema is seen, and these saccules were left in place. The dog had a significant improvement in respiratory signs with staphylectomy alone. This dog’s nares were not stenotic.

    The soft palate should be evaluated with the head and tongue in a neutral position and without an endotracheal tube present, as these factors influence the location of the soft palate (FIGURE 1).19 In dogs with a normal airway, the soft palate should not extend past the tip of the epiglottis or the mid to caudal aspect of the tonsillar crypt.2,18,20 If the laryngeal saccules are everted, they will appear as shiny, white, convex structures cranial to the vocal cords along the ventrolateral surface of the laryngeal lumen (FIGURES 2A, 2B, and 2C).3,19 Medial flattening and tipping of the laryngeal cartilage, curling or flattening of the epiglottis, and inability to visualize the vocal cords indicate laryngeal collapse.15,21 This can be difficult to differentiate from laryngeal paralysis. In simple cases of laryngeal paralysis, the laryngeal cartilage is well formed and shows no abduction during inspiration, but paradoxical inward deviation of the laryngeal cartilage and laryngeal collapse can be seen in more complicated cases.21 The degree of swelling of the airway should also be noted during the examination.

    Everted laryngeal saccules

    Figure 2B. Everted, edematous laryngeal saccules are seen between the vocal cords as shiny, white, convex structures (arrows). These have been effectively described to one author of this article (M.T.) as resembling “inside-out pants pockets.”

    Thoracic radiography should be performed to rule out concurrent cardiac and pulmonary pathology that may influence the anesthetic and surgical protocol and prognosis. Dogs that have experienced an acute respiratory crisis should be specifically evaluated for evidence of aspiration pneumonia and noncardiogenic pulmonary edema. Studies9,22 have shown an association between brachycephalic conformation and the presence of congenital cardiac defects, so a complete cardiac examination (electrocardiography, echocardiography) may be indicated in patients with physical or radiographic findings attributable to the cardiovascular system.

    Airway after resection of laryngeal saccules

    Figure 2C. The same dog as in Figure 2B after resection of the saccules.

    Although tracheal hypoplasia is considered independent of BAS, the trachea should be evaluated. Historically, a diagnosis of concurrent tracheal hypoplasia was associated with a worse prognosis after surgery for BAS.15,16 However, more recent studies have found no correlation between degree of tracheal hypoplasia and severity of respiratory signs in preoperative patients8,9 and no significant differences in outcome between dogs surgically treated for BAS with and without tracheal hypoplasia.6,8 To determine the tracheal lumen-to-thoracic inlet (TD/TI) ratio, the diameter of the thoracic inlet (the ventral border of T1 to the inner surface of the manubrium) is compared with the diameter of the tracheal lumen where it crosses the thoracic inlet on a lateral thoracic projection.9,12,23 Median ratios are 0.116 for bulldogs, 0.157 for non-bulldog brachycephalic breeds, and 0.208 for nonbrachycephalic breeds.12,23 A TD/TI ratio below the relevant number establishes the diagnosis of tracheal hypoplasia.

    Results of blood tests (complete blood cell count, serum chemistry panel) and urinalysis are usually normal in dogs with BAS without any concurrent medical conditions. If respiratory signs are severe, acid–base and blood gas abnormalities may be observed.4,15

    Emergency Management

    Emergency medical therapy of dogs in crisis focuses on relief of dyspnea or cyanosis and reduction of stress and hyperthermia.3 Establishment of IV access is recommended as soon as possible without causing additional stress. A rectal temperature should be taken at presentation, and active cooling should be instituted in dogs with temperatures above 103°F (39.44°C). Animals in acute distress should be placed in a cool, dry environment with supplemental oxygen. To prevent overheating, a cool environment is indicated even if the patient is normothermic. Oxygen supplementation should be provided with minimal stress; options include the use of flow-by oxygen, an intranasal catheter, an oxygen cage, or endotracheal intubation. Sedation with acepromazine can be beneficial; we recommend an initial dose of 0.005 mg/kg IV (or SC)3 to decrease the risk of acepromazine-induced vasodilatory hypotension, with incremental increases in dose up to 0.02 mg/kg IV or SC3 as needed. The onset of effect should be approximately 15 minutes, and doses should not be repeated in the acute crisis more often than every 15 minutes, up to a total dose of 0.02 mg/kg. Antiinflammatory doses of short-acting corticosteroids (e.g., dexamethasone: 0.05 to 0.1 mg/kg IV)3 can be used; higher doses and repeat doses of dexamethasone should be avoided due to the high risk of gastrointestinal (GI) ulceration.2 Aerophagia, esophageal dilation, sliding hiatal hernia, or gastric dilatation with or without volvulus may also occur in patients during acute crisis.4,18

    Placement of a tracheostomy tube may be necessary to bypass upper airway swelling in severe cases.3,12 Patients that are in severe distress, are unable to be intubated, have severe laryngeal or airway swelling, or are in distress with suspected pulmonary pathology as a result of their disease (aspiration pneumonia, pulmonary edema) would likely benefit from temporary tracheostomy and a short period (1 to 3 days) of conservative management before surgical correction. Surgical correction of the identified BAS components can be pursued once the acute crisis has resolved.

    Medical Management

    Long-term conservative medical therapy comprises a weight management program and management of the dog’s lifestyle.18 Although one study was not able to correlate increased body weight and the severity of respiratory signs,17 this is a clinically recognized problem, and weight loss should be recommended in BAS patients that are overweight or obese. Dogs with BAS should avoid activity in warm or humid weather. Walks should be kept short and taken at a cool time of day, and dogs should be walked on a harness to take pressure off the upper respiratory system. In the hospital setting, patients should be handled in a manner that minimizes stress and keeps them cool and calm.18

    Brachycephalic dogs have been identified as having a high incidence of GI issues, including hiatal hernias, pyloric stenosis, and esophageal deviation.18 A 2005 study showed that 74% of dogs presenting with respiratory signs had moderate to severe GI signs (ptyalism, regurgitation, vomiting).18 There was a strong correlation between the severity of respiratory signs and the severity of GI signs that was statistically significant in overweight brachycephalic dogs, males, and French bulldogs.18

    In 2006, the same researchers found that dogs with upper respiratory and GI disorders had improved clinical outcomes when treatment was instituted for both conditions concurrently compared with correction of airway pathology alone.8 Corrective surgery was performed on the identified components of BAS, and dogs were treated with various GI medications based on histopathologic findings for 2 to 3 months. The researchers found that in more than 80% of cases, digestive tract signs resolved on a short- and long-term basis, even when medical therapy was discontinued. It should be noted that many BAS patients demonstrate an improvement in GI signs after surgery for BAS alone.8 This is most likely attributable to the improvement in airway pressures following surgery and the indirect effects on the GI tract (decreased aerophagia, decrease or resolution of sliding hiatal hernias). However, the above studies found that 89% of owners of dogs treated concurrently for GI signs reported good or excellent resolution of BAS signs compared with 68% of owners of dogs that received surgical treatment of BAS alone.8,18 This suggests that concurrent treatment of primary GI tract disease further improves the outcomes in patients with BAS and GI disease. This significant improvement in positive outcomes after surgery supports the notion that all surgical BAS candidates should be evaluated and treated for concurrent primary GI disease.18

    Conclusion

    Dogs with BAS often present at a young age with typical clinical signs associated with the upper respiratory tract. Emergency treatment is aimed at alleviation of dyspnea or cyanosis and reduction of stress and hyperthermia. Long-term conservative therapy for BAS consists mainly of weight management and environmental modifications. Because of the progressive nature of the disease, early surgical intervention is recommended to halt or delay secondary changes. Treatment of concurrent GI disease may improve outcomes following corrective BAS surgery. Surgical treatment options are discussed in a companion article.

    Downloadable PDF

    References

    1. Helund CS. Brachycephalic syndrome. In: Bojrab MJ, ed. Current Techniques in Small Animal Surgery. 4th ed. Philadelphia: Williams & Wilkins; 1998:357-362.

    2. Helund CS. Stenotic nares. In: Fossum TW, ed. Small Animal Surgery. 2nd ed. St Louis: Mosby; 2002:727-730.

    3. Hendricks JC. Brachycephalic airway syndrome. Vet Clin North Am Small Anim Pract 1992;22(5):1145-1153.

    4. Hobson HP. Brachycephalic syndrome. Semin Vet Med Surg (Small Anim) 1995;10(2):109-114.

    5. Aron DN, Crowe DT. Upper airway obstruction. General principles and selected conditions in the dog and cat. Vet Clin North Am Small Anim Pract 1985;15(5):891-917.

    6. Huck JL, Stanley BJ, Hauptman JG. Technique and outcome of nares amputation (Trader’s technique) in immature shih tzus. JAAHA 2008;44(2):82-85.

    7. Pink JJ, Doyle RS, Hughes JM, et al. Laryngeal collapse in seven brachycephalic puppies. J Small Anim Pract 2006;47(3):131-135.

    8. Poncet CM, Dupre GP, Freiche VG, Bouvy BM. Long-term results of upper respiratory syndrome surgery and gastrointestinal tract medical treatment in 51 brachycephalic dogs. J Small Anim Pract 2006;47(3):137-142.

    9. Coyne BE, Fingland RB. Hypoplasia of the trachea in dogs: 103 cases (1974-1990). JAVMA 1992;201(5):768-772.

    10. Torrez CV, Hunt GB. Results of surgical correction of abnormalities associated with brachycephalic airway obstruction syndrome in dogs in Australia. J Small Anim Pract 2006;47(3):150-154.

    11. Robinson NE. Airway physiology. Vet Clin North Am Small Anim Pract 1992;22(5):1043-1064.

    12. Holt D. Surgery of the upper airway in the brachycephalic dog. Proc ACVS Symp 1998;1:25-31.

    13. Harvey CE. Upper airway obstruction surgery. I. Stenotic nares surgery in brachycephalic dogs. JAAHA 1982;18:535-537.

    14. Harvey CE. Upper airway obstruction surgery. II. Soft palate resection surgery in brachycephalic dogs. JAAHA 1982;18:538-544.

    15. Monnet E. Brachycephalic airway syndrome. In: Slatter D, ed. Textbook of Small Animal Surgery. 3rd ed. Philadelphia: WB Saunders; 2003:808-813.

    16. Lorison D, Bright RM, White RAS. Brachycephalic airway obstructions syndrome: a review of 118 cases. Canine Pract 1997;22:18-21.

    17. Riecks TW, Birchard SJ, Stephens JA. Surgical correction of brachycephalic syndrome in dogs: 62 cases (1991-2004). JAVMA 2007;230(9):1324-1328.

    18. Poncet CM, Dupre GP, Freiche VG, et al. Prevalence of gastrointestinal tract lesions in 73 brachycephalic dogs with upper respiratory syndrome. J Small Anim Pract 2005;46(6):273-279.

    19. Harvey CE. Upper airway obstruction surgery. III. Everted laryngeal saccule surgery in brachycephalic dogs. JAAHA 1982;18:545-547.

    20. Davidson EB, Davis MS, Campbell GA, et al. Evaluation of carbon dioxide laser and conventional incisional techniques for resection of soft palates in brachycephalic dogs. JAVMA 2001;219(6):776-781.

    21. Bjorling D, McAnulty J, Swainson S. Surgically treatable upper respiratory disorders. Vet Clin North Am Small Anim Pract 2000;30(6):1227-1251.

    22. Harvey CE. Upper airway obstruction surgery. VIII. Overview of results. JAAHA 1982;18:567-569.

    23. Harvey CE, Fink EA. Tracheal diameter: analysis of radiographic measurements in brachycephalic and non-brachycephalic dogs. JAAHA 1982;18:570-576.

    References »

    NEXT: Canine Brachycephalic Airway Syndrome: Surgical Management [CE]

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