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
- 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.
- 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.
- 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
- 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
- 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.
- 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
- Left and right alternating recovery position
- Prone or semi-prone positioning