Obstructive Upper Airway Disorders

Chapter 161 Obstructive Upper Airway Disorders



Roger B. Fingland


Obstructive upper airway diseases typically are insidious in onset and result in progressively worsening respiratory stridor and dyspnea. The dimensions of the upper airway play a fundamental role in the efficiency of breathing and progression of disease. In narrowed regions of the upper airway, air velocity is higher and pressure is lower than elsewhere (Bernoulli effect), which tends to narrow susceptible regions of the upper airway still more.



ETIOLOGY


Congenital obstructive upper airway diseases are diagnosed so commonly in brachycephalic dogs that they are referred to collectively as the brachycephalic syndrome. Most other obstructive upper airway diseases are acquired and are diagnosed in middle-aged and older dogs. Obstructive upper airway diseases are diagnosed less frequently in cats.



Brachycephalic Syndrome


The brachycephalic syndrome consists of stenotic nares, elongated soft palate, and everted laryngeal saccules.


• Tracheal hypoplasia is a generalized narrowing of the tracheal lumen diameter diagnosed commonly in English bulldogs and, less commonly, in other brachycephalic breeds.

• Stenotic nares and elongated soft palate are congenital conditions diagnosed quite frequently in brachycephalic dogs.

• Laryngeal saccule eversion is a consequence of chronic upper airway obstruction.


Laryngeal Collapse


Laryngeal collapse is recognized most commonly in brachycephalic dogs with chronic obstructive upper respiratory disease (brachycephalic syndrome). Loss of the supporting function of the laryngeal cartilages results from pressure changes within the larynx induced by obstruction rostral to the rima glottidis. Laryngeal collapse is considered a progressive, end-stage disease. However, some dogs have a mild to moderate form of the condition and can do reasonably well with medical management.



Laryngeal Paralysis


This condition is seen primarily in old, large-breed, and giant-breed dogs. Interruption of the innervation to the intrinsic muscles of the larynx, particularly the cricoarytenoideus dorsalis muscle, results in failure of the arytenoid cartilages and vocal folds to abduct during inspiration. The condition is a congenital anomaly in some breeds, such as the Bouvier des Flandres, Siberian husky, and dalmatians. Laryngeal paralysis also has been associated with hypothyroidism (see Chapter 31) and diffuse polyneuropathies in dogs (see Chapter 129). In many cases laryngeal paralysis is idiopathic.



Nasopharyngeal Polyps


These inflammatory masses arise from the epithelium of the nasopharynx, auditory canal, or tympanic cavity (see Chapters 59 and 61).


• Polyps commonly occur in cats and may be congenital in young cats.

• Masses that arise from or involve the nasopharynx result in upper airway obstruction. Although nasopharyngeal polyps are rare in dogs, upper airway obstruction related to soft tissue proliferation can develop in dogs with hyperprogesteronism secondary to drug administration or excessive hormone production in the bitch.


Tracheal Collapse


This condition is seen primarily in old toy-breed dogs. Occasionally it is diagnosed in young dogs and may be congenital.


• The etiology of tracheal collapse is not known, but most likely it is multifactorial and related to changes in airflow dynamics due to primary small airway or upper airway disease. Potential etiologic factors include the following:
• Predisposition in small-breed dogs

• Obesity

• Degeneration of tracheal cartilages

• Chronic bronchitis


Tracheal Stenosis


Tracheal stenosis is usually a sequela of traumatic tracheal disruption. Animal bite wounds, traumatic intubation or extubation, and cervical gunshot wounds are common causes of tracheal injury.



Intraluminal Foreign Bodies


Tracheal foreign bodies rarely cause complete obstruction; large items usually are retained at the carina, whereas small ones often pass into the bronchi, leading to bronchial obstruction and pneumonia.



Primary Tracheal Neoplasia


These tumors are uncommon in dogs and rare in cats.


• Primary tracheal tumors reported in dogs include osteosarcoma, osteochondroma, chondrosarcoma, leiomyoma, mast cell tumor, adenocarcinoma, and squamous cell carcinoma.

• Primary tracheal lymphoma and adenocarcinoma have been reported in cats.


Extraluminal Compression of the Trachea


Segmental tracheal stenosis can be caused by compression from extraluminal masses such as parasitic granulomas (Oslerus [Filaroides] osleri), thyroid carcinoma (see Chapter 31), hilar lymphadenopathy (see Chapter 165), left atrial enlargement (see Chapter 149), mediastinal lymphoma (see Chapter 27), and mediastinal lipoma.



CLINICAL SIGNS



Stertor and Stridor


These signs of obstructive upper respiratory disease are so common in brachycephalic dogs that owners frequently do not recognize noisy breathing as abnormal.


• Stridor is a high-pitched inspiratory sound generated from obstruction of laryngeal airflow.

• Dogs with an elongated soft palate often have characteristic stertorous, or snoring, respiratory sounds that result from occlusion of the rima glottidis by the excessively long soft palate.

• Stridor and voice change are common in cats with nasopharyngeal polyps and in dogs with laryngeal paralysis. Dogs with laryngeal collapse can exhibit either stertor or stridor.


Dyspnea


Dyspnea is observed in most animals with obstructive upper respiratory disease.


• Inspiratory dyspnea, expiratory dyspnea, or a combination may be present, depending on the location and severity of obstruction.

• Collapse of the cervical segment of the trachea results in primarily inspiratory dyspnea, whereas collapse of the thoracic segment of the trachea often is associated with expiratory dyspnea.

• Animals with fixed upper respiratory obstruction such as tracheal stenosis and laryngeal collapse usually are continually dyspneic. Dyspnea may be intermittent and exacerbated by exercise, stress, or high ambient temperature in dogs with tracheal collapse or laryngeal paralysis.


Cough


Coughing is common in dogs with tracheal collapse and, less frequently, in dogs with tracheal stenosis or laryngeal paralysis.


• Approximately 50% of dogs with tracheal collapse have a characteristic “goose honk” cough associated with vibration in the collapsing segment. Other dogs with tracheal collapse do not have a characteristic cough, and some do not cough.

• Dogs with tracheal collapse rarely cough continuously. The cough may be intermittent, and paroxysms usually are exacerbated by stress, excitement, and mechanical stimulation of the trachea.


Decreased Exercise Tolerance


Occasionally, decreased exercise tolerance is observed in dogs with laryngeal paralysis, laryngeal collapse, tracheal stenosis, or brachycephalic syndrome.



Voice Change


This may be an early clinical sign in dogs with laryngeal paralysis. It is also common in cats with nasopharyngeal polyps.



Hyperthermia


Symptoms of laryngeal paralysis frequently are not apparent until the animal is exposed to high ambient temperature; some dogs with laryngeal paralysis are presented with profound hyperthermia.




Key Point


Evaluate laryngeal function in large-breed dogs requiring treatment for hyperthermia.



Gagging


Occasionally, gagging is observed early in the course of obstructive upper airway diseases such as laryngeal paralysis and elongated soft palate.



Dysphagia


Dysphagia may occur in cats with nasopharyngeal polyps and, rarely, in dogs with laryngeal paralysis.



Syncope


Fainting associated with exercise (overexertion), excitement, or coughing spells occurs in some dogs with tracheal collapse.



DIAGNOSIS



History



• Animals in the early stages of obstructive upper airway disease typically are asymptomatic at rest.

• Excitement, exercise, or stress leads to varying degrees of coughing, dyspnea, and stridor.

• Clinical signs may progress to constant, severe coughing and dyspnea.

• Some animals with severe obstructive upper respiratory disease are presented with a history of cyanosis or syncope.


Physical Examination


The physical examination often is unremarkable in dogs with obstructive upper respiratory diseases.


• Distinct lateral tracheal borders may be identified on cervical palpation in dogs with tracheal collapse. Gentle tracheal palpation may cause paroxysms of coughing.

• An ear discharge occasionally is identified in cats with nasopharyngeal polyps. Otoscopic examination may reveal polypoid masses within the external ear canal.

• Stenosis of the external nares may be evident in brachycephalic dogs.


Oropharyngeal Examination


A thorough oropharyngeal examination under light general anesthesia is diagnostic for most obstructive upper airway diseases.



Brachycephalic Syndrome



• The soft palate overlaps the tip of the epiglottis.

• Everted laryngeal saccules are identified as oval mucosal masses projecting into the ventral rima glottidis, lateral to the vocal folds.

• Enlarged tonsils and edematous pharyngeal mucosa are common.


Laryngeal Paralysis



• Animals with laryngeal paralysis are unable to abduct the arytenoid cartilages and vocal folds during inspiration.



Key Point


Use light anesthesia for evaluation of laryngeal function. A surgical plane of anesthesia will obliterate normal laryngeal reflexes and possibly result in a false-positive diagnosis.


• Slight, asynchronous abduction of the arytenoids may be observed in some cases.

• The majority of dogs with laryngeal paralysis have bilateral dysfunction of the cricoarytenoideus dorsalis muscle. Unilateral laryngeal paralysis (hemiplegia) is identified infrequently, perhaps because animals with unilateral involvement remain asymptomatic.

• Laryngeal edema and inflammation also may be seen.

• Evaluate arytenoid abduction during inspiration. Do not consider passive expiratory opening of the glottis and arytenoids as evidence of normal function.


Laryngeal Collapse



• The corniculate and cuneiform processes of the arytenoid cartilages are apposed or overlap, causing collapse of the airway.

• Abduction of the arytenoids is not observed.


Nasopharyngeal Polyp



• With the animal in dorsal recumbency, expose the polyp by gently retracting the soft palate ventrally and rostrally.


Radiography


Obtain radiographs of the pharyngeal, cervical, and thoracic regions.


• A soft tissue density cranial to the pharynx or an increased radiodensity of one of the osseous bullae may be identified on skull radiographs of cats with nasopharyngeal polyps. Computed tomography (CT) scan is also useful in identifying tympanic bulla changes in cats with polyps.

• The soft palate may appear thickened and lengthened in dogs with an elongated soft palate. Normally, the soft palate does not extend beyond the tip of the epiglottis.

• Narrowing of the tracheal diameter may be evident on lateral cervical and thoracic radiographs in dogs with tracheal collapse. Collapse occurs most commonly at the thoracic inlet. Tracheal collapse is a dynamic disease, especially in the early stages. Obtain full inspiratory and expiratory views because the trachea may not be collapsed during all phases of respiration. A normal or near-normal tracheal diameter on plain film radiographs does not rule out tracheal collapse.

• Tracheal stenosis is identified on a lateral cervical or thoracic radiograph as a focal reduction of the tracheal lumen diameter. Radiographs usually are adequate to establish a diagnosis of tracheal stenosis because of the static nature of the condition.

• Aspiration pneumonia is an infrequent sequela of obstructive upper respiratory disease. Aspiration pneumonia typically is characterized by a mixed alveolar-interstitial density in the dependent portions of the cranial and middle lung lobes (see Chapter 163).


Fluoroscopy


Fluoroscopy allows continual assessment of the tracheal lumen diameter during all phases of the respiratory cycle. In dogs suspected of having tracheal collapse, evaluate the entire trachea and both main stem bronchi during quiet respiration and induced coughing.



Tracheoscopy


Tracheoscopy is beneficial in assessing the location and severity of stenotic tracheal lesions. Perform tracheoscopy under general anesthesia and pay close attention to patient oxygenation.



TREATMENT



Brachycephalic Syndrome



Nasal Wedge Resection



Surgical Anatomy


In the dog, the nasal vestibule is occupied by the end of the ventral nasal concha, called the alar fold.



Preoperative Considerations



• Administer oxygen through a face mask for 3 to 5 minutes prior to induction (preoxygenation). Minimize stress to the patient.

• Consider temporary tracheostomy in brachycephalic dogs undergoing upper respiratory tract surgery.

• Rapid induction of anesthesia and control of the airway is essential. Mask induction is discouraged.

• Thoroughly evaluate the upper airway in animals with stenotic nares. Staphylectomy (soft palate excision) and laryngeal sacculectomy probably will be necessary.


Surgical Procedure



Objective

To increase the cross-sectional area of the nasal vestibule



Equipment


• #15 or #11 blade

• 4-0 or 5-0 monofilament nylon or polypropylene suture material

• Standard minor surgery pack


Technique


1. Excise a vertical triangular or elliptical wedge of tissue extending from the wing of the nostril caudally to include part of the alar cartilage. The base of the wedge should include one-third to one-half of the free edge of the nostril (Fig. 161-1).

2. Close the incision with 4–0 or 5–0 nylon or polypropylene suture material in a simple interrupted pattern.

3. If the cross-sectional area of the nasal vestibule has not been increased adequately, remove the sutures and excise more tissue. Remove the same amount of tissue on each side to ensure symmetrical nostrils.

image

Figure 161-1 Wedge resection of the alar fold for stenotic nares.



Postoperative Care and Complications



• Carefully monitor the dog during recovery and for several hours after surgery.

• Incisional hemorrhage may occur but resolves with direct pressure.

• Signs of respiratory obstruction persist following nasal wedge resection if concurrent obstructive upper respiratory diseases have not been managed properly.


Staphylectomy (Correction of Elongated Soft Palate)



Surgical Anatomy



• The soft palate is a valve-like partition composed of mucosal and muscular layers.

• The free edge of the soft palate should appose or slightly overlap the epiglottis.


Preoperative Considerations



• See preceding discussion under “Nasal Wedge Resection.”

• Just prior to beginning the procedure, administer dexamethasone sodium phosphate (0.2 mg/kg IV) to reduce tissue edema and inflammation associated with the surgery.


Surgical Procedure



Objectives


• To shorten the soft palate so that the free edge apposes or barely overlaps the epiglottis

• To minimize pharyngeal and laryngeal edema by using an atraumatic technique


Equipment


• Standard instrument pack and suture

• Babcock forceps


Technique


1. Position the dog in ventral recumbency with the mouth held open with an oral speculum or adhesive tape sling.

2. Determine the portion of the soft palate that is excessive (Fig. 161-2) by placing it adjacent to the epiglottis. Alternatively, excise that portion of the soft palate that extends beyond an imaginary line across the caudal pole of the tonsils.

3. Place traction sutures of 4-0 absorbable suture material in the lateral aspect of the soft palate adjacent to the point at which the epiglottis touches the soft palate.

4. Grasp the center of the free border of the soft palate with Babcock forceps and retract it rostrally.

5. Incise approximately one-half the width of the soft palate with curved Metzenbaum scissors. Suture the incised mucosal edges with 4-0 absorbable suture material in a simple continuous pattern. The nasal mucosa tends to retract caudally.

6. Continue the “cut-and-sew” technique (Fig. 161-3) until the palate is resected and closure is complete.

7. Avoid using crushing clamps and electrocautery.

image

Figure 161-2 Staphylectomy for elongated soft palate. The area of soft palate to be resected is in red.


image

Figure 161-3 “Cut-and-sew” procedure for soft palate resection.



Postoperative Care and Complications



• Laryngeal edema is a common postoperative complication in brachycephalic dogs that have had surgery on the upper respiratory tract.



Key Point


Excessive resection of the soft palate may allow aspiration of food postoperatively because the shortened palate is unable to close the nasopharynx during swallowing.

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Aug 27, 2016 | Posted by in SMALL ANIMAL | Comments Off on Obstructive Upper Airway Disorders

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