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Basics ⬇

Basics

Definition

Dyspnea-a subjective term that in human medicine means “an uncomfortable sensation in breathing” or a sensation of air hunger; in veterinary medicine, it is used to indicate difficulty breathing or respiratory distress.

Pathophysiology

Dyspnea and respiratory distress are believed to occur when the central nervous system notes a difference between the afferent feedback from a given efferent motor drive signal (ventilation demanded) and what the brain had anticipated would be the appropriate afferent response (ventilation achieved).

Systems Affected

Respiratory

Signalment

Dogs and cats; age, breed, and sex predisposition vary with inciting cause.

Signs

Historical Findings

  • Acute or chronic onset.
  • Often associated with coughing, tachypnea, exercise intolerance.

Physical Examination Findings

  • General signs of respiratory distress-increased abdominal effort, nasal flaring, open-mouth breathing, cyanosis, orthopnea (neck extension, elbow abduction); other signs depend on underlying cause.
  • Nasal disease-stertor, nasal discharge, lack of airflow through nostrils; dyspnea improves with open-mouth breathing.
  • Upper airway disease-stridor, cough, hyperthermia, respiratory effort and noise on inspiration.
  • Tracheal collapse-honking cough, tracheal sensitivity.
  • Lower airway disease-cough, expiratory wheezes on auscultation,
  • Pulmonary parenchymal disease-may have crackles, harsh or moist lung sounds on auscultation; may be normal.
  • Pneumonia-fever, may have tracheal sensitivity.
  • Cardiogenic pulmonary edema-heart murmur, arrhythmia, hypothermia, pale mucous membranes, prolonged capillary refill time.
  • Pleural space disease-diminished breath sounds: ventrally-fluid; dorsally-air; unilaterally-space-occupying lesions or pyothorax/chylothorax. Often paradoxical respiratory pattern (inward movement of the abdominal wall during inspiration).
  • Thoracic wall disease-can have paradoxical respiratory pattern, visible or palpable trauma.
  • PTE-may have clinical signs of the underlying disease predisposing to thrombosis, e.g., hyperadrenocorticism, IMHA, neoplasia.
  • Other signs will pertain to the underlying disease, e.g., shock, trauma.

Causes & Risk Factors

Upper Airway Disease

  • Nasal obstruction-stenotic nares, nasopharyngeal polyp or stenosis, infection, inflammation, neoplasia, trauma, foreign body, coagulopathy.
  • Pharynx-elongated soft palate, foreign body, neoplasia, granuloma.
  • Larynx-laryngeal paralysis, everted laryngeal saccules, edema, collapse, foreign body, neoplasia, trauma, webbing.
  • Trachea-collapse, stenosis, trauma, foreign body, neoplasia, parasites, extraluminal compression (lymphadenopathy, enlarged left atrium, heart-base tumors).

Lower Airway Disease

Inflammatory, infectious (Mycoplasma), parasitic, neoplastic (bronchogenic carcinoma).

Pulmonary Parenchymal Disease

  • Edema-cardiogenic or non-cardiogenic.
  • Pneumonia-infectious; parasitic; aspiration; eosinophilic; interstitial.
  • Neoplasia (primary or metastatic).
  • Inflammatory-ARDS; uremic pneumonitis; smoke inhalation.
  • Hemorrhage-trauma; coagulopathy.
  • PTE-IMHA; PLN or PLE; heartworm disease; hyperadrenocorticism; neoplasia.
  • Others-lung lobe torsion, atelectasis.

Pleural Space Disease

  • Pneumothorax-traumatic; iatrogenic; secondary to pulmonary parenchymal disease; ruptured bulla; migrating foreign body; primary spontaneous (no underlying cause).
  • Pleural effusion-transudates, exudates; hemothorax; chylothorax.
  • Soft tissue-neoplasia; diaphragmatic hernia.
  • Fibrosing pleuritis.

Thoracic Wall Disease

  • Open pneumothorax-trauma; flail segment-trauma; neoplasia; paralysis due to cervical spinal disease, botulism, polyradiculoneuritis, tick bite paralysis, myasthenia gravis, elapid snake envenomation.

Diaphragmatic Disease

  • Trauma-rupture; hernia
  • Phrenic nerve disease
  • Neoplasia
  • Fibrosis

Abdominal Distention

  • Organomegaly-hyperplasia; neoplasia, pregnancy; obesity; ascites; gastric dilatation, torsion

Diagnosis ⬆ ⬇

Diagnosis

Differential Diagnosis

  • Inspiratory dyspnea-suggests extrathoracic upper airway disease.
  • Expiratory dyspnea-suggests intrathoracic airway disease.
  • Dyspnea on inspiration and expiration can occur with fixed upper airway obstructions and severe intrathoracic disease.
  • Congestive heart failure-murmur, arrhythmia, tachycardia, poor pulse quality, jugular pulses, hypothermia, crackles on auscultation, fluid dripping from nose.

CBC/Biochemistry/Urinalysis

  • Anemia-can cause non-respiratory dyspnea.
  • Polycythemia-chronic hypoxia.
  • Inflammatory leukogram-pneumonia, pyothorax.
  • Eosinophilia-hypersensitivity or parasitic airway disease.
  • Thrombocytosis-hyperadrenocorticism predisposes to PTE.
  • Sodium:potassium ratio <27-can be seen with pleural or abdominal effusions.
  • Azotemia-if severe may lead to uremic pneumonitis.
  • Proteinuria-can predispose to PTE.
  • Multiple organ dysfunction-ARDS.
  • Hypoproteinemia-may suggest protein-losing disease that can predispose to PTE or hydrothorax.

Other Laboratory Tests

  • Pleural fluid analysis.
  • Fecal examination for parasites
  • Serum antigen or antibody titers-heartworm, toxoplasmosis, distemper, FeLV, FIV.
  • Increased urine protein:creatinine ratio with PLN could indicate loss of antithrombin and hypercoagulability resulting in PTE.
  • PaO2-partial pressure of oxygen dissolved in arterial blood; normoxemia: PaO2 80–120 mmHg (room air, sea level); hypoxemia: PaO2 <80 mmHg; FIO2-fraction of inspired oxygen ranges from 0.21 (room air) to 1.0; PaO2/FIO2 ratio-measure of lung efficiency; PaO2/FIO2500-normal lung efficiency; 300–500-mild insufficiency; 200–300-moderate insufficiency; <200-severe insufficiency. Reduction in lung efficiency is most commonly due to pulmonary parenchymal disease.
  • PaCO2 or PvCO2-partial pressure of CO2 dissolved in arterial or venous blood; measure of ventilation; normal 30 mmHg < PCO2 <40 mmHg. Hypercapnia = hypoventilation = decreased alveolar minute ventilation (MV).
  • Coagulation testing-if suspect hemothorax and/or pulmonary hemorrhage.
  • Plasma NT-proANP, BNP, ET-1, and cTNI concentrations may aid in differentiation of cardiac and non-cardiac causes of dyspnea.

Imaging

  • Cervical and thoracic radiography: upper airway disease-soft palate elongation, large airway narrowing, lymphadenopathy, intraluminal abnormalities. Lower airway disease-bronchial thickening, middle lung lobe consolidation (cats), atelectasis, hyperinflation and diaphragmatic flattening (primarily cats). Pneumonia-alveolar infiltrates; lobar sign-lung lobe torsion, foreign body pneumonia,, neoplasia; cardiogenic pulmonary edema-enlarged cardiac silhouette, pulmonary venous distention, enlarged left atrium with perihilar pulmonary infiltrates in dogs; infiltrates can be of any distribution in cats. Non-cardiogenic pulmonary edema-caudodorsal distribution. ARDS-diffuse, symmetrical alveolar infiltrates. Pulmonary vascular abnormalities-PTE, heartworm disease. Pleural space disease-pneumothorax, pleural effusion, mass lesions, diaphragmatic hernias. Thoracic wall disease-rib fractures, neoplasia.
  • Thoracic ultrasonography: evaluation of distribution of pleural effusion, pneumothorax (absence of “glide sign”), and parenchymal disease (presence of “comet tail” artifact). Pulmonary mass identification-guide fine-needle aspiration; mediastinal evaluation.
  • Echocardiography: evaluate cardiac function if cardiogenic pulmonary edema or pleural effusion suspected; elevated pulmonary artery pressure and right ventricular overload can support diagnosis of PTE; visualize heart-based masses.
  • Abdominal radiography or ultrasound: evaluation of abdominal distention.
  • Fluoroscopy: evaluate tracheal and bronchial collapse; evaluate diaphragmatic function.
  • Computed tomography: airway, pulmonary parenchymal, and pleural space disease can be evaluated; can detect lesions not clearly defined on radiographs.
  • Pulmonary vascular angiography: gold standard for diagnosis of PTE.
  • Ventilation perfusion scintigraphy: abnormal perfusion scan is considered supportive of PTE.

Diagnostic Procedures

  • Pulse oximetry-SpO2 of hemoglobin saturated with oxygen. The relationship between PaO2 and SpO2 is defined by the oxygen hemoglobin dissociation curve; PaO2 of 60 mmHg = SpO2 of 90%; PaO2 of 80 mmHg = SpO2 of 95%; PaO2 of >100 mmHg = SpO2 of 100%. Below 95%, small changes in SpO2 signify large changes in PaO2. SpO2 measurements in animals on high inspired oxygen lack sensitivity.
  • Thoracocentesis-fluid analysis and culture.
  • Laryngoscopy/nasopharyngoscopy/tracheoscopy-visualize foreign bodies and masses.
  • Bronchoscopy-evaluate upper and lower airways; perform bronchoalveolar lavage for cytology and culture. Requires anesthesia, perform only when stabilized.

Treatment ⬆ ⬇

Treatment

Appropriate Health Care

  • Inpatient care until the cause is identified and treated or determined not to be life-threatening; therapy dependent on underlying cause.
  • ALWAYS administer oxygen and keep patient in sternal recumbency until ability to oxygenate is determined.
  • Lower airway disease-bronchodilators; oxygen therapy until stable; systemic corticosteroids may be required to stabilize cats with acute bronchoconstriction.
  • Pulmonary parenchymal disease-oxygen therapy, antibiotics if pneumonia; treat coagulation disorders; cardiogenic edema requires furosemide ± vasodilators. Non-cardiogenic edema requires oxygen therapy, may require positive-pressure ventilation.
  • Pleural space disease-thoracocentesis for air and fluid. Place a chest tube if repeated thoracocentesis is necessary to keep patient stable.
  • Thoracic wall disease-surgery as indicated, particularly if open chest wound is present; flail chest may require surgery if medical management fails or there is a severe displacement of fractures. Thoracic wall paralysis/muscle fatigue-positive-pressure ventilation if severely hypercapnic.
  • Abdominal distention-drain ascites as needed; relieve gastric distention.

Nursing Care

  • Oxygen therapy via cage, nasal cannula, E-collar covered in plastic wrap, mask, or flow-by. Humidify oxygen source if giving oxygen therapy for more than a few hours.
  • Maintain in sternal recumbency and turn hips every 3–4 hours if patient cannot tolerate lateral recumbency.
  • Monitor temperature regularly, as excess work of breathing results in hyperthermia, which augments respiratory distress.

Diet

Weight-reducing diet if obesity is a contributing cause.

Surgical Considerations

  • Anesthesia must be carefully tailored to the patient. Securing an airway is essential and rapid intravenous induction is important. The ability to positive-pressure ventilate patients is often required.
  • Animals with upper airway obstruction are fragile and can rapidly decompensate. Have multiple-sized endotracheal tubes available.
  • Dyspnea associated with a laryngeal mass can respond to debulking surgery but edema and hemorrhage can lead to worsened obstruction. Warn owners of increased likelihood of aspiration pneumonia complications in animals with laryngeal disease.
  • Avoid positive-pressure ventilation in patients with a closed pneumothorax. Must monitor oxygenation status of anesthetized patients with pulse oximetry and when possible arterial blood gases.

Medications ⬆ ⬇

Medications

Drug(s)

Varies with underlying cause (see “Appropriate Health Care”).

Follow-Up ⬆ ⬇

Follow-Up

Patient Monitoring

  • Patients receiving oxygen therapy can be monitored by assessing the degree of respiratory effort. As the animal stabilizes, perform a room air trial and reevaluate the level of respiratory difficulty. Arterial and venous blood gases can be a useful assessment.
  • Pulse oximetry is an effective and noninvasive tool for monitoring patients on room air.
  • Repeat radiographs are often indicated in assessing pulmonary parenchymal disease and pleural space disease.

Miscellaneous ⬆

Miscellaneous

Abbreviations

  • ARDS = acute respiratory distress syndrome
  • BNP = brain natriuretic peptide
  • cTNI = cardiac troponin-I
  • ET-1 = endothelin-1
  • FeLV = feline leukemia virus
  • FIV = feline immunodeficiency virus
  • IMHA = immune-mediated hemolytic anemia
  • MV = minute ventilation
  • NT-proANP = n-terminal pro-atrial natriuretic peptide
  • PLE = protein-losing enteropathy
  • PLN = protein-losing nephropathy
  • PTE = pulmonary thromboembolism

Authors Yu Ueda and Kate Hopper

Consulting Editor Lynelle R. Johnson

Client Education Handout Available Online

Suggested Reading

Herndon WE, Rishniw M, et al. Assessment of plasma cardiac troponin I concentration as a means to differentiate cardiac and noncardiac causes of dyspnea in cats. J Am Vet Med Assoc 2008, 233:1261–1264.

Mellema MS. The neurophysiology of dsypnea. J Vet Emerg Crit Care 2008, 18:561–571.

Prosek R, Sisson DD, Oyama M, Solter PF. Distinguishing cardiac and noncardiac dypsnea in 48 dogs using plasma atrial natriuretic factor, B-type natriuretic factor, endothelin and cardiac troponin-I. J Vet Intern Med 2007, 21:238–242.