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ARDS-Acute Respiratory Distress Syndrome-Causes-Signs-Symptoms


ARDS (Acute Respiratory Distress Syndrome) follows lung injury And Characterized by an inadequate expansion of lungs and hypoxemia ( inadequate oxygenation of Blood).


1. Diffused alveolar capillary damage
2. Alveolar epithelial damage.

Signs and Symptoms:

  • Respiratory insufficiency 
  • Cyanosis
  • Arterial hypoxemia which is refractory to oxygen therapy
  • Multi-organ failure ( eg. liver, kidney, heart etc )

  1. Damage to either
  • alveolar epithelium 
  • or Vascular endothelium
     2.  Imbalance between pro-inflammatory and anti-inflammatory factors 

Vascular injury causes
  1. An increase in vascular permeability 
  2. Alveolar flooding
  3. loss of diffusion capacity ( gases fail to diffuse across the alveolar membrane )
  4. Surfactants abnormality.  ( due to damage of type II pneumocytes )
IL 8 ( Interleukine 8 ) is synthesized at the site of vascular endothelial or alveolar epithelial injury which causes chemotaxis of leukocytes (neutrophils). 
IL 1 and TNF alpha activate neutrophils 

Function Of Activated Neutrophills:

Activated neutrophils release
  • oxidants 
  • proteases
  • Platelets activating factor
  • leukotrienes 
These cause damage to the alveolar membrane.
But these destructive factors are counteracted by protective factors (eg. IL 10 ) 
Therefore, in the end, the balance between protective and destructive factors determine the degree and extent of the injury.

Clinical Features: 

The mortality rate with ARDS was virtually 100 %. But proper treatment and cure decrease the mortality rate to 60 %. 
ARDS develops within 72 hours after the initial injury.
Advanced age, sepsis, cardiac and renal failure are predisposing factors. 
If a patient survives intra-alveolar and interstitial fibrosis will continue to compromise respiratory function and eventually patient develops respiratory insufficiency.
If a patient escapes chronic sequel Respiratory function takes 6 - 12 months to become normal. 


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