Atelectasis may or may not show signs and symptoms depending upon the extent of lung tissue which has collapsed. If a major segment of lung tissue is involved the patient will present the following symptoms:

• Dyspnoea
• Cough
• Low grade fever [5]
• Chest pain
• Pleural effusion transudate
• Hypoxemia
• Cyanosis

In severe cases of atelectasis, acute respiratory failure may occur [6].

Diagnosis is mainly based on plain chest radiography as often the patient may show no signs and symptoms.

A complete physical examination should be done along with a few basic laboratory tests. Physical examination may reveal absence of breath sounds on the affected side of the hemi thorax. On percussion, dullness maybe demonstrated. Chest expansion may be reduced.

Oximetry may reveal low levels of oxygen. Chestradiographs show distinct signs of atelectasis. Usual radiological signs of collapse on chest x-ray result from airlessness of the lung causing opacification [7] and shrinkage.

Each segment or lobe of the lung when collapsed has a particular pattern of blurring normal boundaries (silhouette sign). Middle lobe or lingular lobe collapse causes blurring of the right and left heart border. Upper lobe collapse may obliterate the superior mediastinal border. However, in complete upper lobe collapse, prolapse of the apical segment of the lower lobe can restore the silhouette of the mediastinal boundaries, the luftsichel sign. A collapse of the whole lung [8] results in opacification and shift of mediastinal structures to the same side. Lower lobe collapse does not obliterate cardiac borders and causes a retrocardiac triangular opacity when completely collapsed [9].

CT scan findings are similar to those seen on chest radiographs but in transaxial planes.

The main objective of the treatment is to treat and remove the underlying cause. Small areas of collapse can resolve without treatment.

Treatment mainly includes:

• Chest physiotherapy that aims at improving breathing especially post-surgery to inflate the collapsed lung. Coughing, percussion on affected side will loosen mucus accumulation [10]. Deep breathing exercises are done with spirometry. Postural drainage should be done wherein the head should be positioned lower than the chest allowing mucus to drain out of the lungs.
• Medications mainly antibiotics should be given to treat any chronic infection. Bronchodilators should be administered for easier breathing.
• Bronchoscopy should be done for clearing of airways, by suctioning the mucus or to remove any small obstruction. Bronchoscopy can also be useful for removal of any small tumours of the lung.
• Continuous positive pressure (CPAP) may be useful for low oxygen levels.

The mortality and morbidity of atelectasis mainly depends on the underlying primary pathology.

The collapsed part of the lung usually inflates once obstruction has been resolved or the cause been removed. Some amount of residual scarring or damage may be present [4].

It can be life threatening especially in premature babies, infants and patients with underlying respiratory problems. Thus, the morbidity and complications depends upon the extent of lung tissue collapse.

Certain complications can occur due to atelectasis e.g. pneumonia, hypoxemia and scarring.

The exact etiology is uncertain. Depending upon the type of collapse, atelectasis can be obstructive or non-obstructive. Most common cause of atelectasis is post cardiac surgery.

Obstructive atelectasis is due to an obstruction in the airways. This occurs due to resorption of air distal to the obstruction. The site of obstruction could be central or peripheral. Main causes of blockage are:

• Mucus accumulation post-surgery which results in an inability to cough, resulting in a collection of mucus and secretions. Anaesthesia and other drugs given during surgery can also cause mucus accumulation.
• Foreign body inhalation like small objects, peanuts and small toys, mainly inhaled accidentally by children [1].
• Lung tumours or any space occupying lesion.
• Mucus plugs may also accumulate in cystic fibrosis and asthma [2].

Non obstructive atelectasis can occur due to different reasons as follows:

• Chest injuries or any accidents causing trauma to the chest wall
• Fibrotic collapse occurs due to fibrosis or scarring of the lungs in conditions like ankylosing spondylitis, silicosis and tuberculosis where severe destabilizing forces may be responsible for the collapse.

Compressive collapse occurs from relaxation of the lung due to pleural disease like pleural effusion, pneumothorax and hydropneumothorax.

• Any inflammation of the lungs which can occur from any type of pneumonia can cause temporary atelectasis.
• Adhesive collapse is where there is an abnormality in the surfactant resulting in collapse of the lungs [3].

Atelectasis has no racial predilection, affects men and women equally. The mean age of clinical onset of this condition is around 60 years. It also occurs in premature babies and mainly presents as Acute Respiratory Distress Syndrome (ARDS). There is a high incidence of atelectasis in asbestos workers. Post-surgery atelectasis improves well.

The factors maintaining normal lung expansion are the balance of mechanical and surface forces. The chest wall physio-mechanically coupled by forces through the pleurae is essential for normal lung expansion.The surfactant lining the alveoli aids ventilation via normal and collateral pathways and is essential for maintenance of lung inflation.

Disruption of these properties can lead to lung instability and collapse. It can occur due to resorption of gas distal to an airway obstruction. Relaxation of the lung due to uncoupling of lung and chest wall forces by fluid (pleural effusion) or gas (pneumothorax) and loss of surfactant in ARDS can cause atelectasis.

In an obstructed lobe, the oxygen is consumed raising the partial pressures of other gases above the normal. These gases dissolve in the blood and get absorbed eventually reducing the volume of the affected lobe. During resolution of pneumonia or post-operative conditions, secretions and mucus collect in the central bronchi. Due to a diminished cough reflex and reduced diaphragmatic motion and pain there is absorption of air distal to obstruction.

Shrinkage due to lung collapse results in compensatory hyperinflation. In a collapsed lung unit there is no ventilation, but perfusion continues producing a shunt effect. This results in hypoxemia which cannot be corrected by oxygen therapy. Refractory hypoxemia is therefore the basic pathophysiological abnormality.

Expansion of collapsed lobe can occur after the obstruction is removed as ventilation is restored.

Atelectasis can be prevented by certain modifications in posture and habits. Smoking should be stopped. Small objects and toys should not be given to children to prevent obstruction.

Post-surgery deep breathing exercises should be done along with posture changes for easy drainage of mucus. Coughing should be encouraged post-surgery. In case of pain in chest, pain medication should be given. Position of lying down should not remain constant and frequently altered. Ambulation should be encouraged.

Atelectasis is the total or incomplete collapse of a part of the lung or the entire lung. This results in failure of expansion of the lungs due to deflated alveoli. It is a condition which results in airlessness with shrinkage of the lungs.

It can be congenital (atelectasis neonatorum) due to an inborn failure of lungs to expand and usually presents in premature babies. It can be acquired anytime during the lifetime wherein there is absorption of air secondary to obstruction, compression, contraction or surfactant loss.

Atelectasis occurs mainly secondary to other respiratory problems like cystic fibrosis, lung tumours, foreign body inhalation, pneumothorax and chest injuries. Atelectasis is frequently known as lung collapse and is the commonest complications post-surgery.

If only a small segment of the lung has collapsed, there may be no signs and symptoms. If not treated timely, it can cause severe complications as the oxygen supply to the body reduces.

Atelectasis is a medical condition where a part of or the entire lung tissue collapses resulting in reduced gaseous exchange. This leads to reduced oxygen levels in the body. Atelectasis results from either an obstruction in the airways or after a surgical operation. It can also occur if there is some external pressure from other tissues on the lungs.

It usually occurs secondary to some respiratory problem .In premature babies too, atelectasis can occur. The main cause for atelectasis is mucus accumulation in the lung thus resulting in no air in the air sacs which lead to reduced gaseous exchange. Most common conditions which cause atelectasis are any obstruction like tumours, or any foreign objects, any chronic infections in the lungs and trauma to the chest. Post surgery there is a high chance of developing atelectasis due to reduced coughing reflex.
Majority of the cases show no signs and symptoms unless a large segment of lung tissue is involved. There may be difficulty in breathing, chest pain and low fever.

A medical care provider will be able to confirm the condition by a physical examination as well as may advice to do a chest X-ray. Chest X-ray will confirm the diagnosis as atelectasis is very prominent on a radiograph. CT scan may be needed.

Treatment mainly involves removal of the cause of atelectasis, thus enabling the inflation of the lung. Chest physiotherapy should be done regularly for removal of the mucus. Deep breathing techniques are advised. Post-surgery posture should be frequently changed for easy drainage of any secretions. Coughing should be encouraged. Medications may be given for an infection.
Bronchoscopy is done to clear the air passages and remove any obstruction if present. If treatment not administered on time it can lead to severe complications which can ultimately lead to respiratory failure. Post any operation, proper care should be taken to avoid accumulation of secretions and postural modifications should be done. Patient should be encouraged to walk as much as possible.

The outlook depends on the primary cause, but with prompt treatment and removal of any obstruction atelectasis has a good recovery.

1. Priftis KN, Mermiri D, Papadopoulou A, Anthracopoulos MB, et al. The role of timely intervention in middle lobe syndrome in children. Chest. 2005 Oct;128(4):2504-10.
2. Hendriks T, de Hoog M, Lequin MH, Devos AS, Merkus PJ. DNase and atelectasis in non-cystic fibrosis pediatric patients. Crit Care. 2005 Aug;9(4):R351-6.
3. Franken EA Jr, Klatte EC. Atypical (peripheral) upper lobe collapse. Ann Radiol (Paris). 1977 Jan-Feb;20(1):87-93.
4. Reinius H, Jonsson L, Gustafsson S, et al. Prevention of atelectasis in morbidly obese patients during general anesthesia and paralysis: a computerized tomography study. Anesthesiology. 2009 Nov;111(5):979-87.
5. Mavros MN, Velmahos GC, Falagas ME. Atelectasis as a cause of postoperative fever: where is the clinical evidence? Chest. 2011 Aug;140(2):418-24.
6. Chen HA, Lai SL, Kwang WK, Liu JC, et al. Middle lobe syndrome as the pulmonary manifestation of primary Sjogren's syndrome. Med J Aust. 2006 Mar 20;184(6):294-5.
7. Herold CJ, Kuhlman JE, Zerhouni EA. Pulmonary atelectasis: signal patterns with MR imaging. Radiology. 1991 Mar;178(3):715-20.
8. Proto AV. Lobar collapse: basic concepts. Eur J Radiol. 1996 Aug;23(1):9-22.
9. Woodring JH, Reed JC. Radiographic manifestations of lobar atelectasis. J Thorac Imaging. Spring 1996;11(2):109-44.
10. Pryor JA. Physiotherapy for airway clearance in adults. Eur Respir J. 1999 Dec;14(6):1418-24.