How bad a complication is atelectasis to a post op patient?

Very common but...: Atelectasis, a collapse of a portion of the lung, is very frequently seen in greater or lesser extent in post-op patients. Patients who have had surgery on their chest or abdomen frequently find it painful to take a deep breath or cough. As a result, lung secretions accumulate in the lungs and result in atelectasis. The atelectatic lung becomes a setup for development of pneumonia (bad!).