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:
- Damage to either
- alveolar epithelium
- or Vascular endothelium
2. Imbalance between pro-inflammatory and anti-inflammatory factors
Vascular injury causes
- increase in vascular permeability
- Alveolar flooding
- loss of diffusion capacity ( gases fail to diffuse across the alveolar membrane )
- 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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