Dyspnea

Dyspnea (also called respiratory distress) is an inappropriate degree of breathing effort based on respiratory rate, rhythm, and character. Dyspnea is a common sign associated with a wide variety of respiratory and nonrespiratory disorders. Physical examination is the first step in diagnosis. Patients with obstructive respiratory diseases have a breathing pattern characterized by increased depth, rate, and effort. Dynamic obstruction (e.g., laryngeal paralysis) cranial to the thoracic inlet (i.e., the upper airway) causes increased inspiratory effort. Dynamic obstruction (e.g., collapsing trachea) caudal to the thoracic inlet (i.e., lower airway) causes increased expiratory effort. Fixed obstructions (e.g., tracheal tumor) often are associated with increased inspiratory and expiratory effort. Nasal cavity obstruction only causes an obstructive breathing pattern if the animal does not breathe through the mouth. Auscultation of wheezes suggests obstruction, but wheezes are not always found in obstructed patients. Monophonic wheezes (i.e., single tone) may be noted with an elongated soft palate. Alternatively, wheezes can have multiple tones (i.e., polyphonic wheezes), as heard in asthmatic cats.

Dyspnea due to extra-respiratory causes (e.g., severe anemia, severe metabolic acidosis) can have what appears to be an obstructive breathing pattern with an increased intensity of normal lung sounds (i.e., bronchovesicular sounds) but without wheezes.

Diseases limiting ability of the lungs to expand cause a restrictive breathing pattern characterized by an increased rate but a normal to decreased depth with or without increased inspiratory effort. Auscultation may reveal crackles, particularly inspiratory, or a complete absence of lung sounds with certain restrictive lung diseases (e.g., pneumothorax, hydrothorax). It may be difficult to auscultate pulmonary parenchymal abnormalities, especially in small patients with low tidal volumes. Thoracic radiographs of these patients can reveal substantial pulmonary parenchymal disease despite apparently normal lung sounds. Distinction between obstructive and restrictive breathing patterns is not always clear; the pattern of breathing exhibited depends on the relative amount of pathologic change in affected tissues. For example, a dog with severe pulmonary edema may have obstructive (airway fluid) and restrictive (interstitial fluid) disease.

Patients with disorders such as flail chest occasionally have paradoxical movements (i.e., a section of the chest wall collapsing during inspiration and expanding during expiration). Pulmonary vascular diseases can be associated with either inspiratory or mixed inspiratory and expiratory dyspnea.

Common causes of dyspnea are listed in Box 11-1.

Useful Tests

After the site of an abnormal breathing pattern has been localized by physical examination, tracheal and thoracic radiographs are typically the most useful next diagnostic step (Figure 11-1).

FIGURE 11-1 Approach to respiratory distress and tachypnea in dogs and cats. CBC, Complete blood count; CT, computed tomography; ECG, electrocardiogram.

Note

Although a collapsed trachea can be diagnosed radiographically, it cannot be ruled out by such, even if inspiratory and expiratory films are made. Fluoroscopy or tracheobronchoscopy may be needed to establish the diagnosis.

Transtracheal aspiration (TTA), bronchoalveolar lavage (BAL), or transthoracic fine-needle aspiration (see subsequent sections) may follow if radiography suggests the need for cytologic analysis or culture of the lower airway, especially if coughing is present. Pharyngoscopy, nasopharyngoscopy, and laryngoscopy are useful in patients with upper airway obstruction. Tracheobronchoscopy is useful in tracheal and bronchial disorders, especially for diagnosing obstructive disease such as collapsed trachea, and it is mandatory in most pharyngeal and laryngeal abnormalities (see Figure 11-1). Pleural effusion is always an indication for fluid analysis (see Chapter 10). If dirofilariasis is suspected, a Knott’s test, filter test, or Dirofilaria immitis antigen (or antibody in cats) test is indicated (see Chapter 15). Although they rarely provide a diagnosis, fecal flotation and Baermann’s fecal analysis are inexpensive and noninvasive and can definitively diagnose respiratory parasites. Serologic testing for systemic mycoses (except histoplasmosis) may be useful in dogs (see Chapter 15). Tests for detecting Histoplasma and Blastomyces antigens in the urine are now available (http://www.miravistalabs.com) and might be better than serology.

A complete blood count (CBC) is useful but rarely diagnostic. Allergic or parasitic disease occasionally causes eosinophilia in a dog, but this is inconsistent in cats. Dyspnea due to severe anemia may also be found. Serum chemistry profile and arterial blood gas analysis are less cost-effective in most of these patients unless the abnormal breathing pattern is nonrespiratory in origin (e.g., severe metabolic acidosis). Percutaneous fine-needle pulmonary aspiration biopsy is occasionally diagnostic in infiltrative disease (e.g., blastomycosis, histoplasmosis, carcinoma, lymphoma), especially if BAL and aspiration of more superficial structures (e.g., lymph nodes) are nondiagnostic. Guiding the needle with radiography, ultrasonography, or fluoroscopy may increase the chance of diagnosis with aspiration of mass lesions. Fine-needle aspiration carries some risk of pneumothorax or hemothorax, however.

Coughing, Including Hemoptysis

Common causes of coughing in dogs and cats are listed in Box 11-2. History is used first to eliminate self-limiting, contagious, infectious diseases. The owner should be carefully questioned to differentiate cough from gagging, because many owners confuse gagging with coughing. Gagging (not that after a coughing stint) would suggest nasopharyngeal or nonrespiratory disorders (i.e., oropharyngeal, esophageal, or gastrointestinal disease). Differentiation of a productive cough (e.g., bronchopneumonia) from a nonproductive cough (e.g., viral tracheobronchitis) and identification of abnormal breathing patterns (see Box 11-1 and Figure 11-1) are also helpful. Tracheal and thoracic radiographs are essential in patients with chronic cough, hemoptysis, or cardiovascular disease but are less useful in acute infectious tracheobronchial diseases unless secondary pneumonia is suspected. Radiographs can be used to diagnose but not reliably rule out a collapsed trachea. Fluoroscopy may be required to rule in or out tracheal collapse and is often needed for evaluation of extent of tracheal collapse if present. TTA or BAL (especially if combined with bronchoscopy) is often diagnostic of allergic disease, parasitic infections, or bacterial infections and supports a clinical diagnosis of certain chronic bronchial diseases (e.g., chronic bronchitis). Bronchoscopy is often needed to diagnose foreign body or obstructive disease. A CBC is seldom helpful unless marked eosinophilia (e.g., allergic or parasitic disease) is present. Fecal flotation and Baermann’s fecal analysis are rarely revealing but are indicated because they are easy and cost-effective. Arterial blood gas analysis is rarely diagnostic or cost-effective in coughing patients without dyspnea.

Nasal Discharge, Sneezing, and Epistaxis

Nasal discharge and sneezing may be the result of primary nasal cavity disease or secondary to bronchopulmonary disease (e.g., pneumonia). Epistaxis may be the result of a primary nasal problem (e.g., neoplasia) or a systemic problem (e.g., coagulopathy). Common causes of these problems are listed in Box 11-3.

When epistaxis occurs, evaluation for coagulopathy should be the initial diagnostic step (see Chapter 5). Radiography, but preferably computed tomography (CT) or magnetic resonance imaging (MRI) of the nasal cavity, is usually performed next (Figure 11-2); however, these studies may not be diagnostic in acute disease. If a mass lesion or bone lysis is identified, biopsy via the naris is indicated. Rhinoscopy to look for foreign objects is done following diagnostic imaging studies and can be performed while a patient is anesthetized for imaging. Direct examination may reveal adult Pneumonyssoides caninum. Serologic testing for nasal aspergillosis can be falsely negative and should not be relied on for a diagnosis (see Chapter 15). Direct examination of the nasal cavity (dorsal and ventral meatus) can be performed with rigid or flexible scopes (see under Rhinoscopy). The nasopharynx and posterior portion of the nasal cavity can be visualized with a dental mirror and penlight or more efficiently with a flexible endoscope. Endoscopy of the anterior portion of the nasal cavity in small dogs and cats is limited by the endoscope’s diameter. Nasal lavage is rarely diagnostic. Bacterial culture is not routinely recommended; interpretation is difficult because of the large normal bacterial population of the nasal cavity (see Chapter 15). Fungal culture for aspergillosis can have both false-positive and false-negative results (see Chapter 15). Cultures for fungi are generally more reliable if performed on nasal biopsy specimens rather than nasal cavity swabs. Nasal biopsy samples can be obtained with alligator-type clamshell instruments, with uterine or colonic biopsy forceps, or bone curettes (described later). If these procedures are not diagnostic and the condition persists, exploratory rhinotomy should be considered providing nasal CT or MRI has also been performed.

FIGURE 11-2 Approach to nasal discharge and epistaxis in dogs and cats. CBC, Complete blood count; CT, computed tomography; MRI, magnetic resonance imaging.