Causes of Atelectasis
The air sacs (alveoli) present in the lungs, which are the site for the exchange of carbon dioxide with oxygen, are not able to expand because of obstruction at certain level. This causes the collapse of the lung tissue and hampers the oxygen supply to the body. Hence, atelectasis involving major portion of lung tissue is a potentially hazardous situation.
Causes of Atelectasis
The basic reasons behind atelectasis can be grouped into four. They are:
- The cause of hindrance lies inside the airways.
- The obstruction may be due to some external pressure on the airways.
- There may be some external pressure on the lung cells.
- The inflation of air sacs is incomplete resulting in their caving in.
The hindrance inside the airways resulting in reduced expansion of air sacs can be due to:
- Accumulation of various discharges or mucus in the bronchioles in diseases like bronchiolitis, cystic fibrosis, etc.
- Flaring up of the airway lining in patients of asthma causing its contraction.
- Presence of any alien material in the airways, e.g. coin in case of children.
- Hampering of the normal drainage of secretions present in the airways, e.g. in diseases like ciliary dyskinesia syndrome.
The obstruction due to external pressure on airways can be because of:
- enlarged lymph nodes
- enlarged segment of aorta
- compression due to pulmonary blood vessels
- pressure from some anomalous vessel
External pressure on the cells of the lungs may be due to:
- Pneumothorax, i.e., air in between the pleural layers
- Pleural effusion, i.e., fluid in between the two pleurae
- Enlarged heart
- Tumors of the chest wall
- Certain congenital conditions where the abdominal organs are present in the thoracic cavity
- Congenital emphysema, a condition in which a portion of the lung is abnormally big resulting in compression of the other parts
Incomplete expansion of air sacs occurs in conditions like:
- Acute Respiratory Distress Syndrome where the quantity of surfactant is insufficient.
- General anesthesia resulting in temporary paralysis of respiratory muscles.
- Abnormalities of the back bone.
- Incision on chest or abdomen resulting in shallow breathing.
- Laparoscopic surgeries of abdomen which cause undue expansion of abdominal cavity.
- Certain diseases of neuromuscular system resulting in defective expansion of chest wall.
Variations of Atelectasis
Atelectasis has several variations, i.e. it can be classified into various types depending on the causes:
- Obstructive atelectasis
- Non-obstructive atelectasis
Obstructive atelectasis occurs when there is some obstruction between the air sacs and the trachea (wind pipe). It may be due to a foreign body which is common in children, any tumor or due to a mucus plug. Obstructive atelectasis can be further divided into:
- Lobar atelectasis in case of obstruction at the level of lobar bronchus
- Segmental atelectasis when the obstruction is at the level of segmental bronchus
Non-obstructive atelectasis has four further variations:
- Relaxation/Passive atelectasis: in case fluid or air obliterates the contact between the two pleurae.
- Compression atelectasis: when the lung tissue is compressed by some tumor of the thorax
- Adhesion atelectasis: in case of surfactant deficiency, smoking for a prolonged period and shallow breathing, usually as a result of surgery, to avoid pain. Decrease in the amount of surfactant results in the reduction of tension in air sacs causing them to collapse.
- Cicatrization atelectasis: in cases where tumors of lung like bronchoalveolar cell carcinoma or necrotizing pneumonia cause scarring of tissue with resultant reduction in volume of lungs
As the opening of the right middle lobar bronchus is the smallest and lies surrounded by multiple lymph glands, atelectasis of the middle lobe is seen most frequently. It is known as the ‘right middle lobar syndrome’.
Signs and Symptoms of Atelectasis
The most common symptom of atelectasis is breathlessness. The expansion of chest wall during inspiration is also less than normal. Coughing is also seen. If the collapse of lung is sudden, then the most important symptom of atelectasis is the development of cyanosis. The patient experiences an excruciating pain in the chest. The respiratory rate is also increased. There may be sudden fall in blood pressure resulting in shock. If the secretions in the air sacs get infected, then symptoms of atelectasis may also include fever along with an increased pulse rate.
The conclusive signs of atelectasis include reduced or absent breath sounds or evidence of bronchial breathing. On chest examination, one finds the shifting of the wind pipe towards the affected side. A dull note is heard on tapping the chest wall. Confirmatory sign of atelectasis is absence of air in the lungs as seen on a chest X-ray. A bronchoscopic examination or a computerized tomography is useful to find the cause of obstruction.
Treatment and Prognosis of Atelectasis
Treatment of Atelectasis
The main purpose of the treatment is to re-fill the air sacs and re-expand the collapsed lung tissue. If the cause of atelectasis is some obstruction, then the first step is to remove it. A foreign body can be removed by making the patient to cough it out, by suctioning or by removing it by means of bronchoscopy. Mucus plug can be loosened by tapping. After it is loosened, the mucus is allowed to flow out with the help of gravity by keeping the patient’s head lower than his chest. This procedure for treatment of atelectasis is known as ‘postural drainage’. The patient is encouraged to lie on his normal side so that the collapsed lung gets a chance to re-expand. He is encouraged to take deep breaths to inflate the lung tissue. In case of atelectasis due to fluid collection in between the parietal and visceral pleurae, intercostals drainage of pleural fluid is the treatment for atelectasis. If the air sacs are compressed because of some tumor in the thoracic cavity, then removal of the tumor by surgery is to be done. But if the lung tissue is damaged beyond repair and cannot be re-inflated because of some underlying malignancy, then the only recourse for this type of atelectasis is lobectomy.
Prognosis of Atelectasis
The outcome of atelectasis usually depends on the treatment of the underlying cause. When atelectasis affects a small part of the lung, the damage is minimal as the remaining lung takes over its working. But atelectasis affecting a large part of the lung, if not corrected expeditiously, may prove grave. Atelectasis caused as a result of surgeries is transient. Prognosis of atelectasis due to malignancies depends upon the operability of the tumor. Once the cause of obstruction is eliminated, the atelectic lung normally re-expands to its previous size.