Atelectasis Airlessness Causes Partial Lung Contraction
Atelectasis is a condition in which part of the lungs becomes airless and contracts. The main cause of atelectasis is an obstruction of a bronchus, one of the two main branches of the trachea leading directly to the lungs. Smaller airways can also become blocked.
The obstruction may be caused by a plug of mucous, a tumour, or an inhaled object inside the bronchus. Or the bronchus may be blocked by something pressing from the outside; such as a tumour or enlarged lymphnodes.
When an airway becomes blocked, the air in the alveoli is absorbed into the bloodstream, causing the alveoli to shrink and retract. The collapsed lung tissue commonly fills with blood cells, serum, and mucous and becomes infected.
After surgery - especially chest or abdominal surgery - breathing is often shallow, and the lower parts of the lung does not expand properly. Surgery as well as other causes of shallow breathing can lead to atelectasis.
In middle lobe syndrome, a type of long standing atelectasis, the middle lobe of the right lung contracts, usually because of pressure on the bronchus from a tumour or enlarged lymphglands but sometimes without bronchial compression. The blocked, contracted lung may develop pneumonia that fails to clear up completely and leads to chronic inflammation, scarring, and bronchiectasis.
In acceleration atelectasis, which occurs in jet fighter pilots, the high forces generated by highspeed flying close small airways, leading to the collapse of alveoli.
In patchy or diffuse microatelectasis, the surfactant system of the lung is impaired. Surfactant is the substance that coats the living of the alveoli and reduces surface tension of the alveoli, preventing them from collapsing.
When premature babies have a surfactant deficiency, they develop neonatal respiratory distress syndrome. Adults can also develop microatelectasis from excessive oxygen therapy, a severe generalised infection (sepsis), or many other factors that injure the living of the alveoli.
Essentials of Diagnosis:
- Acute: Sudden marked symptoms of dyspnoea, cyanosis, fever, even if area is small.
- Chronic: almost no symptom even if area is large.
- Homogeneous density on X-ray
- Mediastinal shift towards involved side, diaphragm up, narrowing of intercostal spaces.
Symptoms and signs:
The severity of symptoms depends upon the site of obstruction and the route at which it develops, and the presence or absence of infection in the atelectic area. The more acute the onset (e.g. post operative atelectasis), the more marked the symptoms.
Massive collapse in acute atelectasis causes marked dyspnoea, cyanosis, tachycardia, chest pain and fever. Lesser degrees of collapse produce variable symptoms, but even a small acute atelectasis may produce symptoms. Symptoms, e.g., wheezing and cough are often due to the obstruction itself or to infection distal to the block.
The physical findings in acute atelectasis include tacky cardiac (often out of proportion to the amount of fever), decrease of chest motion on the affected side, with narrowing of inter coastal spaces; displacement of the mediastinum to the involved side, as shown by the shift' of the trachea, cardiac apex, and dullness, percussion dullness; and decreased to absent vocal firemitus, breath sounds, and voice sounds.
Bronchial breath sounds are occasionally present over the atelectatic area and may alternate with diminished breath sounds.
In chronic atelectasis, displacement of the mediastinum is modified by the slowness of the compensatory changes, rigidity of the mediastinum due to the underlying disease, and changes of the elasticity of the surrounding diseased lung.
The collapsed segment is visible as a homogeneous "ground glass" density. The atelectic portion of the lung is denser than a comparable area of consolidation because no air is present with the fluid.
The volume of the collapsed to be immunities markedly. The diaphragm is displaced upward on the side of the collapse. Mediastinal shift to the involved side is a major diagnostic feature. Plural fluid is not infrequently noted on the affected side, but it fails to displace the mediastium back to the midline and the fluid line is seen to run downward and laterally from he midline instead of upward and laterally (as in fluid without atelectasis).
Instrumental Examination :
Bronchoscope is very helpful in diagnosis and treatment.
Pulmonary atelectasis must be distinguished from lober pneumonia, other pulmonary infections, pulmonary interaction, and plural effusion.
The sequelac of unrelieved obstruction with atelectasis are infection, destruction of lung tissue with fibrosis, and bronchiectasis.
Prevention and treatment: People can take steps to avoid atelectasis after surgery. Although people who smoke have a greater risk of developing atelectasis, they can decrease the risk if they, stop smoking 6 to 8 weeks before the operation.
After an operation, people should be encouraged to breath deeply, cough regularly, and move about as soon as possible. Breathing devices and exercises may help.
People with chest deformities or neurologic conditions that cause shallow breathing for long periods may benefit from mechanical devices that assist their breathing. The machine apply continuous pressure to the lungs so that even at the end of a breath, the airway cannot collapse.
The main treatment for sudden massive atelectasis is the removal of the underlying cause. If a blockage cannot be removed by coughing or by suctioning the airways, it often can be removed by bronchoscope.
Antibiotics are given for any infection. Long standing atelectasis often is treated with antibiotics because infection is almost inevitable. In certain cases, the affected part of the lung may be removed when recurrent or persistent infection becomes disabling or bleeding is significant.
If a tumour is blocking the airway, alleviating the obstruction by surgery or other means may prevent atelectasis from progressing and recurrent obstructive pneumonia from developing.
Although the outlook is usually good, unrelieved collapse may result in death (when massive) or in prolonged morbidity (when lober or segmental).
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