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Diffuse alveolar damage

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Diffuse alveolar damage
Micrograph showing hyaline membranes, the key histologic feature of diffuse alveolar damage. H&E stain.
SpecialtyRespirology

Diffuse alveolar damage (DAD) is a histologic term used to describe specific changes that occur to the structure of the lungs during injury or disease. Most often DAD is described in association with the early stages of acute respiratory distress syndrome (ARDS).[1] It is important to note that DAD can be seen in situations other than ARDS (such as acute interstitial pneumonia) and that ARDS can occur without DAD[1].

Definitions

  • Diffuse alveolar damage (DAD): an acute lung condition with the presence of hyaline membranes.[2] These hyaline membranes are made up of dead cells, surfactant, and proteins[3]. The hyaline membranes deposit along the walls of the alveoli, where gas exchange typically occurs, thereby making gas exchange difficult.
  • Acute respiratory distress syndrome (ARDS): a potentially life threatening condition where the alveoli are damaged thereby letting fluid leak into the lungs which makes it difficult to exchange gases and oxygenate the blood.[4] It is the general practice of the medical community to use the Berlin criteria to diagnose ARDS. All criteria must be present to make a diagnosis of ARDS.

Berlin Criteria: as stated on UpToDate (2020)[5]

  1. Timing: onset of respiratory symptoms within one week of a injury/insult.
  2. Chest Imaging: can consist of chest x-ray or CT scan and must show bilateral opacities that cannot be fully explained by other conditions such as effusion, lung/lobar collapse, or lung nodules.
  3. Origin of Edema: respiratory failure that cannot be fully explained by cardiac failure or fluid overload, this needs objective assessment such as an echocardiogram.
  4. Impaired Oxygenation: this can be determined by looking at the ratio of arterial oxygen tension to fraction of inspired oxygen (PaO2/FiO2) that can be obtained based on an arterial blood gas test. Note: all PaO2/FiO2 ratios used in the determination of the severity of ARDS require that the patient be on a ventilator at a setting that includes 5 cm H2O or more of positive end-expiratory pressure (PEEP) or continuous positive airway pressure (CPAP).
Level of ARDS PaO2/FiO2 Range PEEP/CPAP
Mild ARDS 201-300 ≥5 cm H2O
Moderate ARDS 101-200
Severe ARDS <100

Diagnosis

Diagnosis of ARDS is based on clinical manifestation and its severity is evaluated with ratio of arterial partial pressure of oxygen to fraction of inspired oxygen (PaO2/FIO2).[6]

Prevalence

It is a common biopsy finding.[7] Through histology, diffuse alveolar damage goes through several stages:

  1. Exudative phase - similar to pulmonary edema. The alveoli become flooded with exudate
  2. Hyaline membrane production. Hyaline membranes are fibrinous structures resulting from organization of the exudate.
  3. Organising phase

References

  1. ^ a b Cardinal-Fernández, Pablo; Lorente, José A.; Ballén-Barragán, Aída; Matute-Bello, Gustavo (2017-06). "Acute Respiratory Distress Syndrome and Diffuse Alveolar Damage. New Insights on a Complex Relationship". Annals of the American Thoracic Society. 14 (6): 844–850. doi:10.1513/AnnalsATS.201609-728PS. ISSN 2329-6933. {{cite journal}}: Check date values in: |date= (help)
  2. ^ Berry, Gerald J; Rouse, Robert V (November 20 2010). "Acute Interstitial Pneumonia - Diffuse Alveolar Damage". surgpathcriteria.stanford.edu. Retrieved 2020-04-03. {{cite web}}: Check date values in: |date= (help)CS1 maint: url-status (link)
  3. ^ O'Morchoe, Patricia J; Thursh, Donald R; Levy, Allan H. "Lung, Hyaline Membrane Disease, Respiratory Distress". Urbana Atlas of Pathology. Retrieved 2020-04-03.{{cite web}}: CS1 maint: url-status (link)
  4. ^ "Acute Respiratory Distress Syndrome (ARDS) | American Lung Association | American Lung Association". www.lung.org. Retrieved 2020-04-03.
  5. ^ Siegel, Mark D (March 2020). "Acute Respiratory Distress Syndrome: Clinical Features, Diagnosis, and Complications in Adults". UpToDate. Retrieved 2020-04-03.{{cite web}}: CS1 maint: url-status (link)
  6. ^ ARDS Definition Task Force; Ranieri, V. M.; Rubenfeld, G. D.; Thompson, B. T.; Ferguson, N. D.; Caldwell, E.; Fan, E.; Camporota, L.; Slutsky, A. S. (20 June 2012). "Acute Respiratory Distress Syndrome". JAMA. 307 (23): 2526–33. doi:10.1001/jama.2012.5669. PMC 3408735. PMID 22797452.
  7. ^ Parambil JG, Myers JL, Ryu JH (August 2006). "Diffuse alveolar damage: uncommon manifestation of pulmonary involvement in patients with connective tissue diseases". Chest. 130 (2): 553–8. doi:10.1378/chest.130.2.553. PMID 16899858.



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