Atelectasis

Atelectasis:  Is an incomplete expansion
of lobules (clusters of alveoli) or lung segments may result in partial
or complete lung collapse.  The collapsed tissue, unable to perform
gas exchange, allows unoxygenated blood to pass through it unchanged, producing
hypoxemia (deficient oxygenation of the blood).  Atelectasis can be
present at birth (incomplete expansion of the lungs), or during adulthood
(from a  collapsed lung).  It may be chronic or acute. 
It occurs to some degree in many patients undergoing upper abdominal or
thoracic surgery.  Prognosis depends on prompt removal of any airway
obstruction, relief of hypoxia, and reexpansion of the collapsed lobule(s)
or lung(s).

Cause:  Atelectasis may be the result from:

Bronchial occlusion by mucus plugs (common problem  with 
-Chronic obstructive pulmonary disease patient)

Bronchiectasis

Cystic fibrosis

Heavy smoking

Occlusion by foreign bodies 

Bronchogenic carcinoma

Inflammatory lung disease

Idiopathic respiratory distress syndrome of the newborn (hyaline membrane
disease)

Oxygen toxicity

Pulmonary edema

Prolong immobility

CNS depression such as ; drug overdose

Any condition that inhibits full lung expansion or makes deep breathing
painful, such as; rib fractures, obesity, an abdominal surgical incisions

Symptoms:

Symptoms varies with the degree of hypoxia

Dyspnea (labored or difficulty breathing), may be mild and subside without
treatment if atelectasis involves only a small area of the lung. Severe if massive collapse occurs

Anxiety

Cyanosis

Diaphoresis

Decreased breath sounds

Dull sound on percussion if a large portion of the lung is collapsed

Peripheral circulatory collapse

Tachycardia

Substernal or intercostal retraction

Compensatory hyperinflation of unaffected areas of the lung

Mediastinal shift to the affected side

Treatment:

Incentive spirometry

Chest percussion

Postural drainage

Frequent coughing and deep-breathing exercise

If these measures fail, bronchoscopy may help remove secretions

Humidity and bronchodilators can improve mucociliary clearance and dilate
airways and are sometimes used with a nebulizer

Atelectasis secondary to an obstructing neoplasm may require surgery
or radiation therapy.

Postoperative thoracic or abdominal surgery patients require analgesics
to facilitate deep breathing, which minimizes the risk of atelectasis