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

Definition 


ARDS (Acute Respiratory Distress Syndrome) follows lung injury And Characterized by an 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. 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.