Definition, Causes and Differential Diagnosis of ARDS

Many past paper questions ask about the causes and differential diagnosis of " a diffuse bilateral infiltrate on CXR." There are many scenarios available.  It is important to be able to generate a lot of differentials in this sort of question.

  • Question 4 from the second paper of 2015 puts the infiltrate into an APML patient receiving ATRA
  • Question 20 from the first  paper of 2014 talks about some non specific "diffuse bilateral infiltrate."
  • Question 17 from the second paper of 2011 puts the infiltrates into a patient recovering from a bone marrow transplant. 
  • Question 10 from the second paper of 2010 puts this radiological finding in the context of a recent cardiac arrest.

ARDS: The Berlin definition

  • Acute onset of hypoxemia with PaO2 / FiO2 ratio < 300
  • Bilateral infiltrates on chest X-ray
  • Not completely explained by heart failure or fluid overload
 ARDS Severity   PaO2/FiO2 on PEEP of 5   Mortality 
Mild 200 – 300 27%
Moderate 100 – 200 32%
Severe < 100 45%

In 2012, learned scholars came together and revised the old ARDS definition, making some changes to the inclusion and exclusion criteria.

  • There is no longer such a thing as "acute lung injury" when you have a PaO2/FiO2 ratio of 200-300.
    We call it "mild ARDS" instead.
  • Onset must be acute: within 7 days of whatever pathology is thought to be the cause
  • There is no need to exclude heart failure - you can have as much heart failure as you like, so long as its severity is insufficient to by itself explain the bilateral pulmonary infiltrates.

Differential diagnosis of pulmonary infiltrate in ICU patients

An excellent article from Silvia Blanco and Antoni Torres (antimicrobe.org) actually contains a brilliant table of differentials, which is incorporated into the table below.

Differential Diagnosis for Diffuse Bilateral Pulmonary Infiltrates

Vascular:

  • Pulmonary haemorrhage
  • Cardiogenic pulonary oedema

Infectious

  • Bacterial
  • Viral
  • Fungal
  • PJP

Neoplastic

  • Lymphangitis
  • Infiltrative neoplasm

Idiopathic

  • ARDS
  • Idiopathic pneumonia syndrome

Drug-induced

  • Eosinophilic pneumonitis
  • BOOP
  • Alveolar haemorrhage
  • Methotrexate-induced

Autoimmune

  • Goodpastures (haemorrhagic)
  • Rheumatoid pneumonitis
  • TRALI
  • Graft vs host disease in BMT
  • Engraftment syndrome
  • ATRA syndrome

Traumatic

  • Bilateral atelectasis
  • Pulmonary contusions
  • Chemical pneumonitis

Idiopathic pneumonia syndrome and ATRA syndrome have been added since Question 4 from the second paper of 2015 introduced them into the list of differentials.

 

References

Blanco, Silvia, and Antoni Torres. "Differential Diagnosis of Pulmonary Infiltrates in ICU Patients." www.antimicrobe.org

ARDS Definition Task Force. "Acute Respiratory Distress Syndrome." Jama307.23 (2012): 2526-2533.

Esteban, Andrés, et al. "Prospective randomized trial comparing pressure-controlled ventilation and volume-controlled ventilation in ARDS." CHEST Journal 117.6 (2000): 1690-1696.
 
Gainnier, Marc, et al. "Effect of neuromuscular blocking agents on gas exchange in patients presenting with acute respiratory distress syndrome*."Critical care medicine 32.1 (2004): 113-119.

Watling, Sharon M., and Joseph F. Dasta. "Prolonged paralysis in intensive care unit patients after the use of neuromuscular blocking agents: a review of the literature." Critical care medicine 22.5 (1994): 884-893.

Armstrong Jr, Bruce W., and Neil R. MacIntyre. "Pressure-controlled, inverse ratio ventilation that avoids air trapping in the adult respiratory distress syndrome." Critical care medicine 23.2 (1995): 279-285.

Hodgson, Carol, et al. "Recruitment manoeuvres for adults with acute lung injury receiving mechanical ventilation." Cochrane Database Syst Rev 2.2 (2009).

Zavala, Elizabeth et al.Effect of Inverse I: E Ratio Ventilation on Pulmonary Gas Exchange in Acute Respiratory Distress Syndrome Anesthesiology: January 1998 - Volume 88 - Issue 1 - p 35–42

Brower RG, Lanken PN, MacIntyre N, et al; National Heart, Lung, and Blood Institute ARDS Clinical Trials Network. Higher versus lower positive endexpiratory pressures in patients with the acute respiratory distress syndrome. N Engl J Med. 2004;351(4):327-336.

Meade MO, Cook DJ, Guyatt GH, et al; Lung Open Ventilation Study Investigators. Ventilation strategy using low tidal volumes, recruitment maneuvers, and high positive end-expiratory pressure for acute lung injury and acute respiratory distress syndrome: a randomized controlled trial. JAMA. 2008;299(6):637-645.

Mercat A, Richard JC, Vielle B, et al; Expiratory Pressure (Express) Study Group. Positive end-expiratory pressure setting in adults with acute lung injury and acute respiratory distress syndrome: a randomized controlled trial. JAMA. 2008;299(6):646- 655.

Briel, Matthias, et al. "Higher vs lower positive end-expiratory pressure in patients with acute lung injury and acute respiratory distress syndrome." JAMA: the journal of the American Medical Association 303.9 (2010): 865-873.

De Campos, T. "Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and the acute respiratory distress syndrome. The Acute Respiratory Distress Syndrome Network." N Engl J Med342.18 (2000): 1302-130g.

Putensen, Christian, et al. "Meta-analysis: ventilation strategies and outcomes of the acute respiratory distress syndrome and acute lung injury." Annals of internal medicine 151.8 (2009): 566-576.

de Durante, Gabriella, et al. "ARDSNet lower tidal volume ventilatory strategy may generate intrinsic positive end-expiratory pressure in patients with acute respiratory distress syndrome." American journal of respiratory and critical care medicine 165.9 (2002): 1271-1274.

Kahn, Jeremy M., et al. "Low tidal volume ventilation does not increase sedation use in patients with acute lung injury*." Critical care medicine 33.4 (2005): 766-771.

Hodgson, Carol L., et al. "A randomised controlled trial of an open lung strategy with staircase recruitment, titrated PEEP and targeted low airway pressures in patients with acute respiratory distress syndrome." Crit Care 15.3 (2011): R133.

MANCINI, MARCO, et al. "Mechanisms of pulmonary gas exchange improvement during a protective ventilatory strategy in acute respiratory distress syndrome." American journal of respiratory and critical care medicine 164.8 (2012).

Amato, Marcelo Britto Passos, et al. "Effect of a protective-ventilation strategy on mortality in the acute respiratory distress syndrome." New England Journal of Medicine 338.6 (1998): 347-354.

Chu, Eric K., Tom Whitehead, and Arthur S. Slutsky. "Effects of cyclic opening and closing at low-and high-volume ventilation on bronchoalveolar lavage cytokines*." Critical care medicine 32.1 (2004): 168-174.