The word atelectasis is of Greek origin and refers to an inability to stretch, or lack of elasticity. The lungs must stretch in order to take in oxygen from the environment and to release carbon dioxide from the body's cells. Atelectasis is a partial or a complete collapse of a lung caused by complications arising out of respiratory illnesses. It develops when the alveoli, the tiny air sacs within the lungs, get deflated. Severe asthma, chest injuries, cystic fibrosis and congestion due to mucus in the airways are some of the common causes of atelectasis.

The severity of atelectasis depends on the amount of lung tissue affected which in turn depends on the underlying cause. In severe cases it can impair the exchange of oxygen and carbon dioxide in the lungs. Treatment depends on both the severity and the underlying cause. It can involve a small area the lung or the entire lung.

Atelectasis is also linked to a condition called Pleural Effusion where a patient's lungs fill up with dangerous levels of fluid. The rise in fluid levels is often caused by a weak heart that cannot pump adequately. This fluid "build up" can also be caused by other inflation in the body. When this condition occurs the patient is at risk for developing Atelectasis, or in simple terms a collapsed lung. These conditions are linked by a common thread, the mechanical ventilator. Patients using this device must be well monitored to prevent this debilitating situation. Ventilated patients are at special risk of developing a collapsed lung when exposed to the right conditions.

Obstructive Atelectasis is another type of related condition. In this situation a foreign body or a mucus plug becomes lodged in a lung. When undergoing this type of medical crisis, a patient can easily experience a collapsed lung. Only a chest x-ray can visually reveal the cause of the obstruction

Types of Atelectasis

There are two types of atelectasis, acute and chronic.

Acute atelectasis usually occurs after surgery involving the chest or abdomen. It may also occur after an injury to the chest. This type of atelectasis involves most of the alveoli in one or more regions of the lung, with the alveoli collapsing completely. Tight bandages, immobility, chest or abdominal pain or swelling and large doses of opioids or sedatives, increase the risk of acute atelectasis after surgery or injury. Premature babies may also develop acute atelectasis owing to a deficiency in the amount of surfactant in their lungs. For patients with or at risk for atelectasis, fiberoptic bronchoscopy can be performed. This is a procedure in which the tracheobronchial tree is inspected and aspiration can be performed to assist with bronchial hygiene and remove secretions. It is also necessary to carefully measure airway pressure especially in patients who have just had major surgery.

There are two types of chronic atelectasis, middle lobe syndrome or rounded atelectasis. Right middle lobe syndrome, also known as Andy Wilson’s Disease, involves the middle lobe of the right lung. This collapses and contracts due to pressure exerted on the bronchus by enlarged lymph glands. Pneumonia may set in leading to chronic inflammation, scarring and bronchiectasis.

Rounded atelectasis or folded lung syndrome involves the slow collapse of an outer portion of the lung. This is usually caused by scarring and shrinking of the pleura, the membranes covering the lung. The resulting rounded appearance on an x-ray image is sometimes mistaken for a tumor. Rounded atelectasis is commonly caused by asbestos related respiratory diseases.

  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.