Atelectasis

Overview
  • Atelectasis refers to a collapse of a section of airspaces within the lung.
Etiology and Pathogenesis
  • Overview
    • A variety of processes can result in atelectasis although etiologies can be divided into several basic pathogenic categories.
  • Resorption Atelectasis
    • Resorption Atelectasis can occur in areas of the lung distal to an airway obstruction. Total gas pressures within venous blood are significantly lower than atmospheric pressure. Consequently, when an area of lung is no longer exposed to atmospheric pressure due to an airway obstruction, the gases within the distal airspaces are progressively resorbed by perfusing blood over a period of hours to days. This appears to be the mechanism by which atelectasis arises in contexts of asthma, bronchiectasis, or chronic bronchitis which are characterized by plugging of airways. Growth of a lung tumor into an airway or aspiration of a foreign body can also cause distal atelectatic disease.
  • Compression Atelectasis
    • Chronic external pressure on sections of the lung can result collapsing of underlying airspaces. This is frequently encountered secondary to pleural effusions, pneumothorax, or hemothorax.
  • Nonobstructive Atelectasis
    • Alveoli lacking surfactant often collapse on themselves due to excessive water tension. Consequently, widespread microscopic areas of atelectasis may be observed in areas of lung deficient in surfactant production as may occur in Neonatal Respiratory Distress Syndrome.
Clinical Consequences
  • Hypoxemia: collapsing of alveoli and small airways within the lung results in a lack of alveolar ventilation to the affected areas. Consequently, atelectasis can result in a profound ventilation-perfusion defect or in some extreme cases right-left shunting of blood, often yielding hypoxemia.
  • Fever: For unknown reasons atelectasis often results in development of early post-surgical fevers, usually 1-2 days post-operatively.
  • Pneumonia: If left uncorrected, atelectasis will increase a patient's risk of developing by pneumonia.