Classification and external resources
Specialty Pulmonology
ICD-10 R09.8
ICD-9-CM 786.7
Crackles heard in the lungs of a person with pneumonia using a stethoscope.

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Crackles, crepitations, or rales (i/ˈrɑːlz/ RAHLZ or /ˈrælz/ RALZ[1]) are the clicking, rattling, or crackling noises that may be made by one or both lungs of a human with a respiratory disease during inhalation. They are often heard only with a stethoscope ("on auscultation"). Bilateral crackles refers to the presence of crackles in both lungs.

Basal or basilar crackles (not to be confused with the basilar artery of the brain) are crackles apparently originating in or near the base of the lung. Bibasal or bibasilar crackles refer to crackles at the bases of both the left and right lungs. Bilateral basal crackles also refers to the presence of basal crackles in both lungs.

Crackles are caused by the "popping open" of small airways and alveoli collapsed by fluid, exudate, or lack of aeration during expiration. The word "rales" derives from the French word râle meaning "rattle".

Crackles can be heard in patients with pneumonia, atelectasis, pulmonary fibrosis, acute bronchitis, bronchiectasis, interstitial lung disease or post thoracotomy or metastasis ablation. Pulmonary edema secondary to left-sided congestive heart failure can also cause rales.


René Laennec developed the term râles ('rattles' in French) to describe the added breath sounds which are now referred to as 'crackles'. He described them using unusual daily examples, such as 'whistling of little birds', 'crackling of salt on a heated dish', 'cooing of the woodpidgeon' etc. but soon realised that he was unable to use this term in front of his patients because it conjured the association of 'le râle de la mort', which translates to 'death rattle' i.e. the noise that people who are about to die make when they can no longer clear secretions. Therefore, at the bedside, he used the Latin equivalent, 'rhonchus'. This was not clearly understood by his translator, John Forbes, and the terminology became very confusing after the publication of De L'Auscultation Mediate. The difficulty of translating râle itself was remarked upon in a British review of Laennec's work in 1820.[2] The terminology in English remained variable until 1977, when a standardization was established by the American Thoracic Society and American College of Chest Physicians.[3] As a result of this, the term 'râles' was abandoned, and 'crackles' became its recommended substitute. Therefore, these sounds should be correctly described as 'crackles'.[3][4] The term 'rales' is still common in English-language medical literature, but cognizance of the ATS/ACCP guidelines calls for 'crackles'.

The sound of crackles

Crackles are caused by explosive opening of small airways[4] and are discontinuous,[5] nonmusical, and brief. Crackles are much more common during the inspiratory than the expiratory phase of breathing, but they may be heard during the expiratory phase. Crackles are often associated with inflammation or infection of the small bronchi, bronchioles, and alveoli. Crackles that do not clear after a cough may indicate pulmonary edema or fluid in the alveoli due to heart failure, pulmonary fibrosis, or acute respiratory distress syndrome. Crackles that partially clear or change after coughing may indicate bronchiectasis.

They can also be described as unilateral or bilateral, as well as dry or moist/wet.[6]

See also


  1. Jones, Daniel (2003) [1917], Peter Roach, James Hartmann and Jane Setter, eds., English Pronouncing Dictionary, Cambridge: Cambridge University Press, ISBN 3-12-539683-2
  2. "Laennec's new system of diagnosis", The Quarterly Journal of Foreign Medicine and Surgery and of the Sciences Connected with Them, 2: 51–68, 1820.
  3. 1 2 "Report of the ATS-ACCP Ad Hoc Subcommittee on pulmonary nomenclature". ATS News. 3: 56. 1977.
  4. 1 2 Forgacs P (1978). "The functional basis of pulmonary sounds" (PDF). Chest. 73 (3): 399–405. doi:10.1378/chest.73.3.399. PMID 630938.
  5. "rale" at Dorland's Medical Dictionary
  6. > Crackles Book Source Details: * Book Title: Alarming Signs and Symptoms: Lippincott Manual of Nursing Practice Series * Author(s): Springhouse * Year of Publication: 2007
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