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Cough

Last updated: April 21, 2020

Summary

A cough is a forceful expulsion of air from the lungs that helps to clear secretions, foreign bodies, and irritants from the airway. It may be classified as acute (< 3 weeks), subacute (3–8 weeks), or chronic (> 8 weeks), as well as productive (with sputum/mucus expectoration) or dry. Upper respiratory tract infections (URI) and acute bronchitis are the most common causes of acute cough. Subacute cough is often a sequela of a URI (postinfectious cough) but can also be due to chronic bronchitis or pneumonia. Chronic cough is often caused by rhinitis/sinusitis (upper airway cough syndrome), asthma, GERD, and ACE inhibitors. A thorough medical history and physical examination often suffice to diagnose the etiology of cough. Chronic cough or the presence of associated red flag symptoms (dyspnea, fever, hemoptysis, weight loss) are indications for further investigation. Sputum culture, chest x-ray/CT scan, and pulmonary function tests are useful diagnostic tests in the evaluation of cough, but are not routinely indicated. Treatment of cough depends on the underlying etiology.

Pathophysiology

  • Definition: a forceful expulsion of air from the lungs that helps to clear secretions, foreign bodies, and irritants from the airway
  • May be voluntary or a reflex to airway irritants/triggers
  • Cough reflex arc
    1. Irritation of cough receptors in the nose, sinuses, and upper and lower respiratory tracts (see the triggers above)
    2. Transmission along the afferent pathway via the vagus nerve (CN X) to the cough center in the medulla
    3. Generation of efferent signal in the medulla and initiation of cough via the vagus, phrenic, and spinal motor nerves
  • Mechanism of cough reflex
    • Irritation of cough receptors → initiation of the cough reflex arc, which leads to:
      • Rapid inspiration, closure of the epiglottis and vocal cords (which traps inhaled air in the lungs), and contraction of the diaphragm, expiratory, and abdominal muscles → rapid increase of intrathoracic pressure
      • A sudden opening of the vocal cords and forceful expulsion of air from the lungs

References:[1][2][3][4][5][6][7]

Overview

Conditions

Differential diagnosis of acute cough

(< 3 weeks)

Non-life-threatening causes
Life-threatening causes
In children

Subacute cough

(3–8 weeks)

Differential diagnosis of chronic cough

In adults

(> 8 weeks)

In children

(> 4 weeks)

References:[8][9][10][11][12]

Approach

History

Clinical examination:

References:[6][8][13][14][15][16]

Diagnostics

  • An acute cough is often a clinical diagnosis (diagnostic tests are not routinely indicated in this case).
  • Patients with chronic cough and/or red flag symptoms (see “Approach” above) require further assessment.

Laboratory tests

Imaging

Pulmonary function tests

Miscellaneous

Close history taking and physical examination are sufficient to diagnose the cause of an acute cough without red flag symptoms! In chronic cough and cough with red flag symptoms, thoracic x-ray and pulmonary function testing should be considered at an early stageReferences:[12][17][18][19][20]

Treatment

Acute cough

Subacute cough

Chronic cough

Symptomatic treatment of a cough

Antitussive medications decrease coughing, which is important for the expectoration of mucus! They are not usually indicated if an infection is the cause of cough.

References:[9][12][13][21][22][23][24][25][26][27][28][29][30][31]

References

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  19. Bronchoalveolar Lavage. https://www.thoracic.org/professionals/clinical-resources/critical-care/clinical-education/critical-care-procedures/bronchoalveolar-lavage.php. Updated: May 1, 2004. Accessed: May 22, 2017.
  20. Islam S. Flexible Bronchoscopy in Adults: Indications and Contraindications. In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. https://www.uptodate.com/contents/flexible-bronchoscopy-in-adults-indications-and-contraindications.Last updated: February 1, 2017. Accessed: May 22, 2017.
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