Other namesCrepitations, rales
Crackles heard in the lungs of a person with pneumonia using a stethoscope.

Crackles 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, and occasionally during exhalation. They are usually heard only with a stethoscope ("on auscultation"). Pulmonary crackles are abnormal breath sounds that were formerly referred to as rales.[2]

Bilateral crackles refers to the presence of crackles in both lungs. Basal crackles are crackles apparently originating in or near the base of the lung. Bibasal crackles, also called bilateral basal crackles, are crackles heard at the bases of both the left and right lungs.

Crackles are caused by the "popping open" of small airways and alveoli collapsed by fluid, exudate, or lack of aeration during expiration.

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


René Laennec adopted the existing word râles (which has been translated as "rattles", 'groans" and otherwise) to describe the added breath sounds that 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 he soon realized that he was unable to use the term in front of his patients because it conjured the association of le râle de la mort, which translates to "the death rattle", 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 word rhonchus, which originally meant a 'snore'. That was not clearly understood by his translator, John Forbes, and the terminology became very confusing after the publication in the 1830s of Forbes's English translation of Laennec's De L'Auscultation Mediate.[3][4] The difficulty of translating râle itself had been remarked upon in a British review of Laennec's work in 1820.[5]

The terminology of rales and rhonchi in English remained variable until 1977, when a standardization was established by the American Thoracic Society and American College of Chest Physicians.[6] As a result, the term râles was abandoned, and crackles became its recommended substitute.[6][7] The term rales is still[as of?] common in English-language medical literature, but cognizance of the ATS/CHEST guidelines calls for crackles.


Crackles are caused by explosive opening of small airways[7] and are discontinuous,[8] nonmusical, and brief. Crackles are more common during the inspiratory than the expiratory phase of breathing, but they may be heard during the expiratory phase.

They can also be described as unilateral or bilateral,[9] as well as dry or moist/wet.[10]

Associated diagnoses

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.

Interobserver consistency

In 2016, the European Respiratory Society reported on a study of various physicians listening to audiovisual recordings of auscultation findings and interobserver variation was analyzed.[11] The study found that broad descriptions agreed better than detailed descriptions.[11]

See also


  1. ^ Jones D (2003) [1917], Roach P, Hartmann J, Setter J (eds.), English Pronouncing Dictionary, Cambridge: Cambridge University Press, ISBN 978-3-12-539683-8
  2. ^ Cahalin LP, Buck LA. Physical Therapy Associated With Cardiovascular Pump Dysfunction and Failure. In: DeTurk WE, Cahalin LP. eds. 'Cardiovascular and Pulmonary Physical Therapy: An Evidence-Based Approach, 3e'. McGraw-Hill; Accessed August 16, 2020
  3. ^ Laennec RT (1819). De l'Auscultation Médiate, ou Traité du Diagnostic des Maladies des Poumons et du Coeur [On Mediate Auscultation or Treatise on the Diagnosis of the Diseases of the Lungs and Heart] (in French). Paris: Brosson & Chaudé.
  4. ^ Laennec RT (1835). A Treatise on the Diseases of the Chest and on Mediate Auscultation. Translated by Forbes J. New York & Philadelphia: Samuel Wood & Sons; Desilver, Thomas & Co.
  5. ^ "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
  6. ^ a b "Report of the ATS-ACCP Ad Hoc Subcommittee on pulmonary nomenclature". ATS News. 3: 5–6. 1977.
  7. ^ a b Forgacs P (March 1978). "The functional basis of pulmonary sounds". Chest. 73 (3): 399–405. doi:10.1378/chest.73.3.399. PMID 630938.
  8. ^ "Rale".
  9. ^ "Unilateral crackles".
  10. ^ Paz JC, West MP (2009). "Chapter 2; Respiratory System". Acute care handbook for physical therapists (3rd ed.). St. Louis, Mo.: Saunders/Elsevier. p. 56. ISBN 978-1-4160-6948-5.
  11. ^ a b Melbye H, Garcia-Marcos L, Brand P, Everard M, Priftis K, Pasterkamp H (2016). "Wheezes, crackles and rhonchi: simplifying description of lung sounds increases the agreement on their classification: a study of 12 physicians' classification of lung sounds from video recordings". BMJ Open Respiratory Research. 3 (1): e000136. doi:10.1136/bmjresp-2016-000136. PMC 4854017. PMID 27158515.