Acute Respiratory Distress Syndrome (ARDS)

ARDS is characterized by pulmonary inflammation leading to increased vascular permeability and loss of aerating lung tissues. ARDS is common in many critically ill patients, affecting nearly 175 000 patients/year in Europe alone. This brings with it a substantial fiscal burden for our health care system but also a burden of mortality: some 35-40% fail to survive. Meanwhile, survivors face a substantial and sustained morbidity, with evidence of impaired functional capacity and increased healthcare costs extending up to 5 years or more after hospital discharge. Current ARDS treatments, however, are mostly supportive and no specific pharmacotherapies have been shown to impact to the outcome of the ARDS patients.

The Conceptual Model of ARDS

  • ARDS is a type of acute diffuse lung injury associated with recognized risk factors, characterized by inflammation leading to increased pulmonary vascular permeability and loss of aerated lung tissue.
  • The hallmarks of the clinical syndrome are hypoxemia and bilateral radiographic opacities (standard chest x-ray or CT scan).
  • Physiological derangements include increased pulmonary venous admixture, increased physiological dead-space, decreased respiratory system compliance.
  • morphological hallmarks are lung edema, inflammation, hyaline membrane, and alveolar hemorrhage (i.e., diffuse alveolar damage).

ARDS Risk Factors

The common risk factors for ARDS can be divided into direct and indirect causes.

Direct risk factors:

  • Pneumonia
  • Aspiration of gastric contents
  • Inhalation injury
  • Pulmonary contusion
  • Near drowning

Indirect risk factors:

  • Non-pulmonary sepsis
  • Major trauma
  • Multiple transfusions
  • Severe burns
  • Pancreatitis
  • Non-cardiogenic shock
  • Drug overdose

ARDS: The “Berlin Definition”

Recently, the ARDS definition has been revised with a special focus on feasibility, reliability, validity and objective evaluation of its performance resulting in The “Berlin Definition”. The Berlin Definition was published in 2012 by The ARDS Definition Task Force (JAMA, 2012;307(23):2526-2533. The ARDS severity is defined by PaO2/FiO2 ratio (P:F ratio: the partial pressure of arterial oxygen, in kPa, divided by the inspired fraction of oxygen,  as a measure of impaired oxygenation): a P/F 300-201 mmHg defines mild ARDS, 200-101 mmHg moderate ARDS and ≤100 mmHg severe ARDS. The ARDS “Berlin Definition” is summarized in a Figure below.