Atelectasis is the collapse or closure of all or part of a lung that results in reduced or no gas exchange. A pneumothorax or "collapsed lung" is a type of atelectasis, but so is normal exhalation of breath. It is a common finding during a radiological study of the lungs and it's features can be useful for diagnosing many different conditions. It is a very common post-operative condition, and its appearance in a newborn can lead to infant respiratory distress syndrome.
Surgery of the abdomen is the most common cause of the condition as it often restricts the ability of a patient to take a full breath from the diaphragm. Suction is contraindicated as it can remove both fluid and air from the lungs.
The condition must be treated by addressing the underlying cause. Physiotherapy is common after surgery and this is why patients are asked to engage in light exercise directly after surgery to speed recovery.