Causes of Atelectasis

There are two main causes of atelectasis. Atelectasis that is caused by a blockage of the airways is known as obstructive atelectasis while that caused by pressure from outside the lung is known as non-obstructive atelectasis.

An understanding of the mechanism of atelectasis is made easier by taking the example of a soap bubble. In a soap bubble, the liquid surface forms and keeps the bubble intact. Similarly, in the case of alveoli, a surface agent or surfactant, coats each of the alveoli in the lungs, ensuring that they do not collapse. Pressure on the lungs can diminish the amount of surfactant, leading to a collapse of the alveoli.

Obstructive atelectasis results from a blockage of the bronchial tubes. Some of the include:

  • Foreign Body: This usually happens in the case of children, who inhale a foreign body like a peanut, into their lungs.
  • Mucus Plug: This is the most common cause of atelectasis. It happens due to an accumulation of mucus in the airways which commonly happens after surgery. Drugs given during surgery suppress the functioning of the lungs, making them inflate less than normal. This results in secretions collecting in the airways. Deep breathing and coughing help to get rid of these accumulated secretions so that they do not form an obstructing plug. Mucus plugs are common in people suffering from cystic fibrosis and asthma.
  • Tumors: A tumor, either benign or malignant, may cause a blockage in an airway.
  • Diseases: Tuberculosis and other diseases involving major airways may cause a narrowing of the airways.
  • Blood Clots: This is caused by bleeding in the lungs.

Non-obstructive atelectasis is usually caused by pressure on the outside of the lungs. The causes include:

  • Chest Injury: An injury that damages and compresses the lungs. This may occur during a fall or a car accident.
  • Pleural Effusion: Fluid buildup between the pleura and the inside of the chest wall.
  • Pneumonia: An inflammation of the lungs, pneumonia can cause both obstructive as well as non-obstructive atelectasis. A lung that remains collapsed for a few weeks can result in bronchiectasis. This is a condition where the airways widen and become scarred and flabby.
  • Tumor: Large tumors can exert pressure on the lungs from without.
  • Scarring of Lung Tissue: The scarring may be due to lung disease like tuberculosis, surgery or injury.
  • Pneumothorax: This occurs when air leaks into the space between the lung and the chest wall.

Factors that increase the risk of atelectasis include:

  • Anesthesia
  • Foreign body blocking the airway
  • Diseases of the lung, such as asthma, cystic fibrosis, bronchiectasis
  • Mucus buildup that blocks the airways
  • Pleural effusion
  • Prolonged bed rest with few changes in position
  • Shallow breathing due to rib fracture or abdominal pain
  • Premature birth where the lungs are under-developed
  • Conditions that interfere with coughing and yawning
  • Abdominal or chest surgery
  • General anesthesia
  • Obesity
  • Muscular dystrophy, spinal cord injury or other neuromuscular conditions that result in weakened respiratory muscles.

  1. Janet Aldrich, Chapter 62 - Atelectasis, In: Lesley G. King, MVB, MRCVS, DACVECC, DACVIM, DECVIM-CA, Editor(s), Textbook of Respiratory Disease in Dogs and Cats, W.B. Saunders, Saint Louis, 2004, Pages 465-472, ISBN 9780721687063, 10.1016/B978-0-7216-8706-3.50066-9.