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Basics ⬇

Basics

Definition

  • Chronic coughing for longer than 2 months that is not attributable to another cause (e.g., neoplasia, congestive heart failure, eosinophilic pneumonia, or infectious bronchitis).
  • Partly non-reversible and often slowly progressive condition owing to accompanying pathologic airway changes.

Pathophysiology

  • Recurrent airway inflammation suspected, but a specific cause is rarely determined.
  • Persistent tracheobronchial irritation-causes chronic coughing; leads to changes in the tracheobronchial epithelium and submucosa.
  • Airway inflammation, epithelial edema, and thickening-prominent.
  • Excess production of a thickened mucus is a hallmark.
  • In severe, very chronic cases-probable increased lung resistance; decreased expiratory airflow, especially in cats. In dogs, possible sequelae such as broncholamacia and bronchiectasis.

Systems Affected

  • Respiratory
  • Cardiovascular-pulmonary hypertension, cor pulmonale
  • Nervous-syncope (infrequent)

Incidence/Prevalence

Common in dogs and cats

Geographic Distribution

Worldwide

Signalment

Species

Dog and cat

Breed Predilections

  • Dogs-small and large breeds.
  • Cocker spaniels-bronchiectasis common after a long history of chronic bronchitis.
  • Siamese cats and domestic shorthairs affected.

Mean Age and Range

Commonly middle-aged and old animals

Predominant Sex

N/A

Signs

Historical Findings

  • Coughing-hallmark of tracheobronchial irritation; usually harsh and dry; post-tussive gagging common (owners often misinterpret this as vomiting).
  • Exercise intolerance, difficult breathing, wheezing (in cats).
  • Cyanosis and syncope can be noted in severe cases.

Physical Examination Findings

  • Patients usually bright, alert, and afebrile.
  • Tracheal palpation-typically results in coughing because of increased tracheal sensitivity.
  • Small airway disease-assumed when an expiratory abdominal push (during quiet breathing) or end-expiratory wheezing is detected.
  • Increased bronchovesicular lung sounds, end-inspiratory crackles, and wheezing can be heard.
  • Loud end-expiratory snap is suggestive of concurrent airway collapse.
  • Cardiac auscultation-murmurs secondary to valvular insufficiency common in dogs but not always associated with congestive heart failure; chronic bronchitis usually results in a normal or slower than normal resting heart rate and pronounced sinus arrhythmia. In cats, tachycardia is possible.
  • Obesity-common; important complicating factor.
  • Severe dental disease may predispose to lower airway colonization and possible infection (dogs).

Causes

Chronic airway inflammation initiated by multiple causes although specific cause rarely identified.

Risk Factors

  • Long-term exposure to inhaled irritants.
  • Obesity.
  • Recurrent bacterial infection.
  • Dental disease and laryngeal disease-result in bacterial showering of the lower airways.

Diagnosis ⬆ ⬇

Diagnosis

Differential Diagnosis

  • Bronchiectasis.
  • Eosinophilic bronchopneumopathy.
  • Foreign bodies.
  • Heartworm disease.
  • Bacterial, pneumonia.
  • Neoplasia-metastatic more common than primary.
  • Pulmonary parasites or parasitic larval migration.
  • Pulmonary fibrosis-cats and dogs.
  • Congestive heart failure-typically associated with a high resting heart rate, left atrial enlargement, pulmonary venous engorgement, and hilar pulmonary edema (dogs).

CBC/Biochemistry/Urinalysis

  • Rarely diagnostic.
  • Neutrophilic leukocytosis common.
  • Absolute eosinophilia-suggests but not diagnostic for parasitic or allergic bronchitis.
  • Polycythemia secondary to chronic hypoxia-can be seen.
  • Liver enzymes and bile acids may be elevated due to passive congestion.

Other Laboratory Tests

  • Fecal and heartworm tests-rule out pulmonary parasites.
  • Pulse oximetry-useful for detecting hemoglobin desaturation.
  • Arterial blood gas analysis-collect, ice, and have analyzed at a local hospital; mild-moderately low PaO2 seen with severe condition; aids in prognosis and monitoring treatment.

Imaging

Thoracic Radiography

Common features (in descending order of frequency)-bronchial thickening; interstitial pattern; middle lung lobe consolidation (cats); atelectasis; hyperinflation and diaphragmatic flattening (primarily cats).

Echocardiography

  • Helps rule out cardiac disease as a cause of coughing.
  • Can reveal right heart enlargement with pulmonary hypertension. Doppler echocardiography to evaluate.

Diagnostic Procedures

Electrocardiography (Dog)

Wandering atrial pacemaker, marked sinus arrhythmia, P pulmonale, occasionally evidence of right ventricular enlargement.

Evaluation of Airway Secretions

  • Must collect from lower airways-helps to establish underlying cause if present or to determine the severity of inflammation.
  • Throat swab cultures are not representative of lower airway flora.
  • Tracheal aspiration or bronchoalveolar lavage-collect specimens for cytologic examination and bacterial/mycoplasmal culture.
  • Quantitated aerobic BAL cultures help differentiate infection versus airway colonization; reported cutoff is >1.7 × 103 CFU for infection in dogs. Anaerobic and Mycoplasma cultures recommended as well.
  • Cytology-inflammation primary finding; most cells are neutrophils, eosinophils, or macrophages; evaluate for bacteria, parasites, neoplastic cells, and contamination with foreign material.

Bronchoscopy

  • Preferred test for assessing the lower airways.
  • Allows direct visualization of structural as well as functional (dynamic) changes; allows selected airway sampling (e.g., biopsy and lavage).
  • Gross changes-excess mucoid to mucopurulent secretions; epithelial edema or thickening with blunting of bronchial bifurcations; irregular or granular mucosa; mucosal polypoid proliferations can indicate chronic bronchitis or chronic eosinophilic pneumonia.
  • Large airway caliber changes (e.g., static or dynamic airway collapse and bronchiectasis)-can be detected as complicating problems.

Pathologic Findings

Histopathology of bronchial nodules reveals neutrophilic inflammation and fibrotic changes; markers of irreversible damage.

Treatment ⬆ ⬇

Treatment

Appropriate Health Care

  • Usually outpatient-oxygen can be given at home in chronic cases.
  • Inpatient-if requires oxygen therapy, parenteral medication, or aerosol therapy; patients that owners cannot keep calm at home during initial stages of therapy.

Nursing Care

Consider saline nebulization followed by coupage and/or gentle exercise to encourage removal of airway secretions.

Activity

  • Exercise-moderate (not forced) useful in clearing secretions; assists with weight loss.
  • Limit if exertion causes excessive coughing.
  • Use a harness instead of a collar.

Diet

Weight loss critical-improves PaO2, attitude, and exercise tolerance in obese patients; reduces cough frequency.

Client Education

  • Warn client that chronic bronchitis is an incurable disease and complete suppression of all coughing is an unattainable goal.
  • Stress that aggressive treatment-including weight control, avoiding risk factors, and medical treatment-minimizes the severity of the coughing and slows disease progression in most patients.

Surgical Considerations

Treat severe dental disease to minimize secondary bacterial complications.

Medications ⬆ ⬇

Medications

Drug(s) Of Choice

Corticosteroids

  • Diminish airway inflammation and coughing regardless of the underlying cause.
  • Indicated for non-infectious conditions.
  • Require long-term administration; attempt to wean off steroids or determine lowest effective dosage.
  • Prednisolone preferred in cats.
  • Prednisone or prednisolone usually initiated at 0.5–1 mg/kg PO q12h for a variable time, with tapering of the dosage based on clinical signs.
  • Inhaled agents (e.g., budenoside or fluticasone 1–3 puffs a day; variable concentrations exist) are often effective and can be used to reduce systemic side effects of corticosteroids. These drugs are delivered via spacer chamber and face mask (e.g., AeroDawg); however, the most appropriate dose is not clearly established.

Bronchodilators

  • Commonly prescribed, although limited evidence of efficacy.
  • Beneficial effects: (Theophylline-bronchodilation; increased mucociliary clearance; improvement in diaphragmatic contractility; lowered pulmonary artery pressure.
  • Sustained-release theophylline-oral administration; only generic sustained release products currently available. Consider dosing dog, 10 mg/kg PO q12h; cat, 15–20 mg/kg/day in the evening.
  • Aminophylline-immediate-release tablets or injectable formulations are not recommended.
  • -agonists-terbutaline (1.25–5 mg/dog PO q8–12h; 0.625 mg/cat PO q12h) and albuterol (0.02–0.05 mg/kg PO q8–12h in dogs). Can also be administered by inhalation via a spacer and face mask (salbutamol), immediate but transient effect, dose is unclear, can be used for acute relief but not for prolonged treatment.

Antibiotics

  • Select on the basis of quantitated culture and sensitivity test results.
  • Bacterial culture results unavailable-choose an agent with a good Gram-negative spectrum, with good tissue and secretion penetration that is bactericidal with minimal toxicity (e.g., potentiated sulfa/trimethoprim, amoxicillin/clavulanic acid, or enrofloxacin). Consider drugs suitable for management of Mycoplasma, e.g., doxycycline or chloramphenicol.
  • Associated chronic aspiration or dental disease-prefer antibiotic with anaerobic and Gram-positive spectrum.

Antitussives

  • Indicated for non-productive, paroxysmal, continuous, or debilitating cough associated with airway collapse. Use when inflammation is controlled.
  • Dogs-butorphanol (0.55 mg/kg PO q6–12h; 0.055–0.11 mg/kg SC); hydrocodone (2.5–5 mg/dog q6–24h PO); codeine (0.1–0.3 mg/kg q6–8h PO). Over-the-counter cough suppressants are rarely effective.

Contraindications

Lasix and atropine-do not use because of drying effects on tracheobronchial secretions.

Precautions

  • -agonists (e.g., terbutaline and albuterol)-can cause tachycardia, nervousness, and muscle tremors; typically transient.
  • Theophylline-can cause tachycardia, restlessness, excitability, vomiting, and diarrhea; evaluate EDTA plasma sample for peak plasma concentration (ideally 5–20 µg/mL). Toxicity may be more common with generic formulations (unpredictable metabolism).

Possible Interactions

Fluoroquinolones decrease theophylline clearance in dogs and can result in theophylline toxicity.

Alternative Drug(s)

  • Metered dose inhalers (poorly metabolized steroids-fluticasone or budesonide) can be used. These should be administered via face mask and spacing chamber.
  • Cyclosporine-induced immune suppression-insufficient evidence to advise this medication in practice.

Follow-Up ⬆ ⬇

Follow-Up

Patient Monitoring

  • Follow abnormalities revealed by physical examination and selected diagnostic tests-determine response to treatment.
  • Monitor weight; arterial blood gases usually improve after significant weight loss.

Prevention/Avoidance

Avoid and address risk factors (see “Risk Factors”).

Possible Complications

  • Syncope-frequent complication of chronic coughing, particularly in toy-breed dogs.
  • Pulmonary hypertension and cor pulmonale-most serious complications.
  • Bronchectasis and airway remodeling.

Expected Course and Prognosis

  • Progressive airway changes-syncopal episodes, chronic hypoxia, right ventricular hypertrophy, and pulmonary hypertension.
  • Acute exacerbations-common with seasonal changes, air quality changes, worsened inflammation, and potentially the development of secondary infection.

Miscellaneous ⬆

Miscellaneous

Associated Conditions

  • Syncope-secondary to chronic coughing or development of pulmonary hypertension.
  • Increased susceptibility to airway infection, chronic hypoxia, pulmonary hypertension, and cor pulmonale.

Pregnancy/Fertility/Breeding

Safety in pregnant animals not established for most of the recommended drugs.

Synonyms

  • Chronic bronchitis
  • Chronic obstructive lung disease (COLD)
  • Chronic obstructive pulmonary disease (COPD)

Abbreviations

  • BAL = bronchoalveolar lavage
  • CNS = central nervous system
  • EDTA = ethylene diamine tetra-acetate
  • SRT = sustained-release theophylline

Suggested Reading

Trzil JE, Reinero, CR. Update on feline asthma. In: Vet Clin North Am Small Anim Pr. 2014, pp. 91–105.

Rozanski E. Chronic bronchitis. Vet Clin North Am Small Anim Pract 2014, 44:107–116.

Authors Cécile Clercx and Brendan C. McKiernan

Consulting Editor Lynelle R. Johnson

Client Education Handout Available Online