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Today's VeTerinary PracTice | november/december 2015 | tvpjournal.com aPProach To resPiraTory disTress Peer reviewed 56 may involve tracheobronchoscopy with a fexible bronchoscope or endoscope. When evaluating laryngeal function as part of an upper airway examination: • Take care to minimize the level of anesthesia to preserve laryngeal function as best as possible • Consider using the respiratory stimulant doxapram HCl (0.5–1.1 mg/kg IV) to stimulate laryngeal motion • Carefully observe inspiration versus expiration to ensure that the larynx is abducting (increasing the aperture of the rima glottis) on inspiration (rather than on expiration as might occur with paradoxical motion in patients with laryngeal paralysis). Cervical and thoracic radiographs are useful for patients with laryngeal or tracheal disease to detect masses and collapse. Fluoroscopy is useful for detecting dynamic upper airway collapse that may not be visible on standard radiographs. Management Defnitive management for upper respiratory tract obstruction is extremely varied, depending on the defnitive diagnosis, and beyond the scope of this review. LOWER AIRWAY OBSTRUCTION Etiology Lower airway obstruction is associated with a narrowed bronchial lumen, which can be caused by varied pathophysiologic processes, including: • Bronchial infammation with edema and hyperemia of bronchial mucosa • Bronchospasm • Bronchomalacia • Mucus accumulation • Acute anaphylactic reaction (uncommon). In all of these conditions, the bronchial lumen tends to close early during expiration, while it is opened by radial traction from the lungs during inhalation. Therefore, expiratory dyspnea is a hallmark of lower airway obstruction. Specifc Diseases Feline asthma and chronic bronchitis in dogs and cats are associated with accumulation of mucus in the lower airways that contributes to obstruction. Feline asthma. The classic disease in cats that causes lower airway obstruction is feline asthma, the hallmarks of which are eosinophilic airway infammation, reversible bronchoconstriction and, ultimately, airway remodeling. 3 Chronic bronchitis. Lower airway disease in cats may also be associated with neutrophilic infammation (often referred to as chronic bronchitis), or a combination of both eosinophilic and neutrophilic infammation. 3 In dogs, bronchomalacia—seen in severe, end-stage, chronic bronchitis—can also cause lower airway obstruction. Clinical Signs Characteristic signs in an animal with lower airway obstruction usually include expiratory distress and, sometimes, an expiratory grunt or push. These patients may have an expiratory wheeze on thoracic auscultation and, less commonly, an externally audible wheeze. Initial Stabilization Initial stabilization and therapy usually involve: • Oxygen supplementation: See recommendations in the Initial Stabilization section (page 53) • Bronchodilator trial: Options for an acute bronchodilator trial include either: » Inhaled albuterol (1 or 2 puffs from a metered dose inhaler with a spacer) » Single dose of terbutaline (0.01 mg/kg IM or SC). 3 Bronchodilator therapy often results in rapid improvement in these patients (eg, within 5–15 minutes). Diagnostic Approach Once the patient is stable, the diagnostic approach usually involves: 3 • Thoracic radiographs: Lower airway disease is classically associated with a bronchial or bronchointerstitial pattern on thoracic radiographs. Additonally, air trapping in cats with asthma may result in pulmonary hyperinfation and a fattened diaphragm. • Lower airway cytology: Eosinophilic infammation (> 17% eosinophils) is characteristic of feline asthma, while neutrophilic infammation is evident in dogs and cats with chronic bronchitis. • Heartworm testing (ideally both antigen and antibody tests): Determines if heartworm associated respiratory disease is present in cats. • Baermann fecal test: Evaluates for lungworm disease. Management Treatment of lower airway disease may involve bronchodilators, corticosteroids and, potentially, deworming in cats. 4 See Treatment of Feline Lower Airway Disease (March/April 2014), available at tvpjournal.com.