ARDS

Question 1

What is ARDS?

Answer 1

Adult Respiratory Distress Syndrome is charcterised by diffuse alveolar capillary damage which leads to:

• severe pulmonary oedema
• respiratory failure
• hypoxaemia refractory to oxygen therapy

It has a mortality of greater than 50%

Question 2

What is the mecahnism of injury in ARDS?

Answer 2

• Basic lesion is diffuse damage to the alveolar wall - initially the capillary endothelium then the epithelium.
• This damage leads to:
  
  • Increased capillary permeability and oedema
  • fibrin exudation
  • formation of hyaline membranes
  • septal inflammation
• Mechanism of injury include:
  
  • Oxygen free radicals
  • Aggregation of activated neutrophils -> damage epithelium by releasing free radicals, proteases and arachidonic acid metabolites
  • Activation of lung macrophages -> release pro-inflam’y cytokines, oxidants and proteases
  • Loss or damage to surfactant -> atelectasis

Question 3

List some some of the common causes of ARDS.

Answer 3

(note similarities to causes of pulmonary oedema)

Infective:

• Sepsis *
• Diffuse pulmonary infections - Viral, mycoplasma, miliary TB *
• Gastric aspiration *

Physical/injury:

• Pulmonary contusions
• Near-drowning
• Mechanical trauma - including head injuries *
• Fat embolism from #s
• Burns
• Ionizing radiation

Inhaled irritants:

• Oxygen toxicity
• Smoke
• irritant gases and chemicals

Chemical injury:

• Heroin or methadone overdose
• Acetylsalicylic acid
• Barbituate overdose
• Paraquat

Haemotological Conditions:

• Multiple or massive transfusion/s
• DIC

Miscellaneous:

• Pancreatitis
• Uremia
• Cardiopulmonary bypass
• Hypersensitivity reactions (drugs, organic solvents)

* > 50% due to these causes