Question 3.3 from the first  paper of 2010  presented the candidates with a scenario where a post-operative patient suddenly develops decreased air entry on the left side, as well as complete white-out on the chest Xray. Question 1b from the second paper of 2000 presents a scenario where a recently intubated obese patient develops left lower lobe collapse, and asks for management options.

Causes of atelectasis

Resorptive atelectasis

  • Something has blocked an airway and the distal lung collapses as all gas in the blocked alveoli is sucked up into the capillaries.
  • Causes of this could include:
    • Intraluminal pathology:  sputum plug, foreign body, aspiration
    • Mural pathology: eg. carcinoma
    • Extramural pathology: eg. peribronchial lymphadenopathy,  an enlarged left atrium, etc.

Passive atelectasis

  • Something has interrupted the negative pressure between the visceral and parietal pleura. The lung collapses passively as a result.
  • Causes of this include pleural effusion and pneumothorax.

Compressive atelectasis

  • Something has put direct pressure on the lung, collapsing the alveoli.
  • Causes of this include masses (eg. cancer and abscess) or enlarged mediastinal structures (eg. thoracic aneurysms or cardiomegaly

Cicatrisation atelectasis

  • Something has caused parenchymal scarring, and the extent of the scar tissue limits the expansion of surrounding parenchyma.
  • Causes of this include pulmonary fibrosis, recovery from necrotising pneumonia, and radiation pneumonitis

Adhesive atelectasis

  • Something has caused surfactant to fail. Usually, because it is not being produced (eg. the hyaline membrane disease of the newborn). The alveoli collapse in the absence of surfactant.

Dependent atelectasis

  • Gravity is responsible for the collapse of lung bases in a chronically supine or recumbent person, in the absence of regular vigorous deep breathing exercises. The weight of the lung above pushes on the lung below, producing compression. Under real-world condition, the weight of the massive obese chest wall and distended post-operative abdomen are also contributing to this.

Radiological features of atelectasis

  • Increased opacity of the atelectatic lung
    • "plate-like" atelectasis appears as thin linear densities parallel to the diaphragm. They are otherwise known as Fleischner's lines.
  • displacement of the fissures toward the area of atelectasis
  • upward displacement of the ipsilateral diaphragm
  • crowding of pulmonary vessels and bronchi in region of atelectasis
  • compensatory overinflation of unaffected lung
  • displacement of thoracic structures toward the affected lung (if much of that lung has collapsed)

Clinical features of atelectasis

  • Decreased air entry
  • Dyspnoea, tachypnoea
  • Crackles on auscultation, which clear with cough

Management of atelectasis in the intubated patient

  • Higher levels of PEEP
  • Larger tidal volumes
  • Use of volume support ventilation
  • Intermittent "sigh" breaths
  • Improved analgesia (especially in the context of abdominal surgery and chest trauma)
  • Chest physiotherapy
  • Regular suctioning
  • Humidification of the circuit
  • Posture:
    • Left and right alternating recovery position
    • Prone or semi-prone positioning

References

Woodring, John H., and James C. Reed. "Types and mechanisms of pulmonary atelectasis." Journal of thoracic imaging 11.2 (1996): 92-108.

Ashizawa, K., et al. "Lobar atelectasis: diagnostic pitfalls on chest radiography." The British journal of radiology 74.877 (2001): 89-97.