Acute Lung Injury What is it?

      
       

 

          
       

The definition of the syndrome was clarified by a 1992 American-European Consensus Conference (4). The term “Acute Lung Injury” has been used as an umbrella term for hypoxemic respiratory failure, a severe version of which is “Acute Respiratory Distress Syndrome” (ARDS).

The characteristics follow:


• Bilateral pulmonary infiltrates on chest x-ray
• Pulmonary Capillary Wedge Pressure <18mmHg
• PaO2/FiO2* <300 = ALI
• PaO2/FiO2 <200 = ARDS
 

Although not strictly part of the definition, there is widespread airway collapse (low lung volumes), surfactant deficiency and reduced lung compliance.


Classic Chest X Ray of a patient with ARDS, although the lung injury appears diffuse, when you look at the CT scan of the same patient on the right you can see that the lower lobes are densely consolidated and the upper lobes relatively spared. Nevertheless, this patient was severely hypoxic, and responded well to prone positioning.

What causes it?

  • ALI is caused by any stimulus of local or systemic inflammation, principally sepsis

ALI is most often seen as part of a systemic inflammatory process, particularly systemic sepsis, where the lung manifestations parallel those of other tissues – widespread destruction of the capillary endothelium, extravascation of protein rich fluid and interstitial edema. In addition, the alveolar basement membrane is damaged, and fluid seeps into the airspaces, stiffening the lungs and causing ventilation-perfusion mismatch (5).
Other causes of ARDS are listed below, as you can see, this is a mixture of virtually every disorder seen in ICU.

References

(1) Ashbaugh DG, Bigelow DB, Petty TL, Levine BE. Acute respiratory distress in adults. Lancet 1967; 2(7511):319-323.
(2) Petty TL. In the Cards was ARDS. (How we discovered the acute respiratory distress syndrome). Am J Respir Crit Care Med 2001; 163(3):602-603.
(3) Bigelow DB, Petty TL, Ashbaugh DG, Levine BE, Nett LM, Tyler SW. Acute respiratory failure. Experiences of a respiratory care unit. Med Clin North Am 1967; 51(2):323-340.
(4) Bernard GR, Artigas A, Brigham KL, Carlet J, Falke K, Hudson L et al. The American-European Consensus Conference on ARDS. Definitions, mechanisms, relevant outcomes, and clinical trial coordination. Am J Respir Crit Care Med 1994; 149(3 Pt 1):818-824.
(5) Ware LB, Matthay MA. The acute respiratory distress syndrome. N Engl J Med 2000; 342(18):1334-1349.

Copyright Patrick Neligan 2001-2002

          
                   
       

         
     

       
       

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