Recent data estimates the incidence at 190,000 cases per year in USA. True incidence is unknown due to difficulty in defining the disease and making the diagnosis.

Represents 10.4% of all ICU admissions and 23.4% of pts requiring mechanical ventilation per a recent 2016 publication.

Mortality rates vary from 25% to 40%. Mortality rate is strongly influenced by associated conditions (e.g., higher when associated with sepsis, liver disease, and advanced age; lower with trauma, transfusion-related lung injury, drug overdose, or other reversible conditions).

Increased risk of sudden and profound hypoxia secondary to loss of alveolar recruitment

Worsening resp status due to effects of anesthesia and surgery

Difficult balance between maintaining adequate intravascular volume and avoiding pulm edema and right heart strain leading to decreased oxygenation and ventilation

Increased risk of sudden and profound hypoxia secondary to loss of alveolar recruitment

Worsening resp status due to effects of anesthesia and surgery

Difficult balance between maintaining adequate intravascular volume and avoiding pulm edema and right heart strain leading to decreased oxygenation and ventilation

Maintaining required PEEP during pt transport with Ambu bag or Mapleson circuit. Transport with ICU ventilator may be necessary.

Inability of standard OR ventilators to deliver required minute ventilation, high inspiratory pressures, and inverse ratio ventilation.

Berlin definition of ARDS (published in 2012) requires each of the following criteria:

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  Timing—onset within 1 week of a known clinical insult or new or worsening resp symptoms.

  
  
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  Chest imaging (CXR or CT)—bilateral opacities; not fully explained by effusions, lobar/lung collapse, or nodules.

  
  
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  Origin of edema—resp failure not fully explained by cardiac failure or fluid overload, need objective assessment (ECHO) to exclude cardiogenic pulm edema.

  
  
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  Oxygenation:

  
  
  
  
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    Mild—PaO ₂ /FiO ₂ 200 to 300 mm Hg with PEEP or CPAP ≥ 5 cm H ₂ O.

    
    
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    Mod—PaO ₂ /FiO ₂ 100 to 200 mm Hg with PEEP ≥ 5 cm H ₂ O.

    
    
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    Severe PaO ₂ /FiO ₂ ≤ 100 mm Hg with PEEP ≥ 5 cm H ₂ O.

  
  

Though classically defined by severe hypoxia, also can be associated with profound hypercarbia due to elevated alveolar dead space.

Associated with low pulm compliance and lung volumes (due to alveolar edema and atelectasis) and, in certain pts, with abnormally low chest wall compliance.

Most deaths are from sepsis or multisystem organ failure (more rarely from refractory hypoxemia or hypercarbia).

Direct or indirect lung injury leading to acute inflammatory alveolar damage characterized by increased microvascular permeability with interstitial and alveolar edema and often progressing to fibrosis.

Precipitants include aspiration, pneumonia, sepsis, massive transfusion, pancreatitis, trauma, ischemia-reperfusion, drugs and alcohol, CNS injury, air embolism, cardiopulmonary bypass, genetic predisposition.

Mechanical ventilation may worsen lung injury through alveolar overdistention and shear forces from cyclic opening and closing of collapsed alveoli (ventilator-associated lung injury).