SPECIAL SELECTED TOPICS- RESPIRATORY SYSTEM DISORDERS-SSTRSDO-QAA 002
1. 1.
Atelectasis is the incomplete expansion or collapse of
previously inflated lung tissue, resulting in reduced or absent air within the
alveoli. It decreases functional lung volume and impairs gas exchange.
Atelectasis may involve a small segment, an entire lobe, or the whole lung. It
may occur because of airway obstruction, external compression, inadequate
surfactant, or pulmonary fibrosis.
The collapsed alveoli remain perfused but are poorly
ventilated, producing hypoxemia. Persistent collapse predisposes to infection
and fibrosis.
Early treatment usually allows complete re-expansion of the
lung. Severe or prolonged atelectasis may lead to permanent structural damage.
It is a common complication after surgery and prolonged immobilization.
2. What are the main characteristics of
obstruction atelectasis?
Obstructive or resorption atelectasis occurs when an airway
is completely blocked by mucus, tumors, foreign bodies, or inflammatory
secretions. Air trapped distal to the obstruction is gradually absorbed into
the bloodstream. As the air disappears, the alveoli collapse completely.
The affected lung becomes small, airless, and dense.
Mediastinal structures shift toward the collapsed lung because of volume loss.
Ventilation is absent, but blood flow continues, producing
ventilation-perfusion mismatch and hypoxemia. Secondary bacterial infection
commonly develops behind the obstruction.
Removal of the obstruction often allows complete re-expansion
if fibrosis has not occurred. Persistent obstruction may eventually produce
irreversible lung damage.
3. What are the main characteristics of
compression, patchy, and contraction atelectasis?
Compression atelectasis results from external pressure
exerted by pleural effusion, pneumothorax, hemothorax, or tumors that compress
lung tissue. Patchy or microatelectasis occurs due to loss of surfactant,
commonly seen in neonatal respiratory distress syndrome and ARDS. Contraction
atelectasis develops when pulmonary fibrosis prevents normal expansion of lung
tissue.
Compression atelectasis is usually reversible after removal
of the external pressure. Patchy atelectasis affects multiple scattered alveoli
and causes diffuse impairment of oxygenation. Contraction atelectasis is
generally irreversible because of fibrotic scarring. Lung compliance is
markedly reduced in contraction atelectasis.
Gas exchange becomes progressively impaired. The clinical
severity depends on the extent of lung involvement.
DR.C.GANESAN M.D
PROFESSOR OF MEDICINE
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