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respiratory diseases

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





Definition 


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

Causes:

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 )

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

Vascular injury causes
  1. 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 pnemocytes )
IL 8 ( Interleukine 8 ) is synthesized at the site of vascular endothelial or alveolar epithelial injury which causes chemotaxis of leukocytes (neutrophills). 
IL 1 and TNF alpha activate neutrophills 

Function Of Activated Neutrophills:

Activated neutrophills release
  • oxidants 
  • proteases
  • Platelets activating factor
  • leukotriens 
These cause damage to alveolar membrane.
But these destructive factors are counteracted by protective factors (eg. IL 10 ) 
Therefore, in the end balance between protective and destructive factors determine the degree and extent of 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 initial injury.
Advanced age, sepsis, cardiac and renal failure are predisposing factors. 
If patient survives intra-alveolar and interstitial fibrosis will continue to compromise respiratory function and eventually patient develops respiratory insufficiency.
If patient escapes chronic sequel Respiratory function takes 6 - 12 months to become normal. 
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