Radiographic Evaluation of Lobar Atelectasis

Image: “Atelectasia1” by Pabloes. License: CC BY-SA 3.0

Overview of Lobar Atelectasis

Atelectasis is more common in preterm infants with hyaline membrane disease, patients with acute respiratory distress syndrome, and in the postoperative period. The common features among these three conditions is either the absence of lung surfactant or surfactant dysfunction, both of which are hypothesized to play a crucial role in the pathogenesis of atelectasis.

The postoperative period puts the patient at an increased risk of atelectasis owing to the inability to inhale deeply due to chest pain from an incision, prolonged faulty ventilation, or poor chest physiotherapy.

Epidemiology of Atelectasis

Children are at an increased risk of atelectasis because of the smaller diameter of their airways, which are more likely to collapse. The chest wall is more compliant in children, which also predisposes them to atelectasis. As stated earlier, the absence or dysfunction of pulmonary surfactants is also a risk factor for atelectasis in children.

Atelectasis is common in both sexes and can occur in individuals of any ethnic origin.

Etiologies of Atelectasis in Children

The primary reasons for atelectasis in children are as follows:

1. Bronchial obstruction is known to cause resorption atelectasis. The lumen of the bronchus can be obstructed by abnormal thick secretions in response to a foreign body or in conditions such as asthma.
2. Changes in the bronchial-wall thickness can lead to an obstruction of the bronchioles and subsequent atelectasis.
3. Bronchial abnormalities that can lead to atelectasis include mucosal edema, inflammation, and smooth muscle tumors. Extrinsic bronchial compression by a tumor can also lead to atelectasis.
4. Direct compression of the lung parenchyma can also cause atelectasis. This can result from cardiomegaly, massive pleural effusion, or diaphragmatic hernia.

Prematurity can alter the lung-surfactant coating of alveoli. The absence of the lung surfactant is associated with abnormal surface tension; consequently, the alveoli can collapse during expiration.

The other causes of atelectasis in children could result from the following conditions:

1. Decreased compliance of the pulmonary parenchyma due to depressed respiration in the post-operative period
2. Decreased inspiration due to chest pain or weakness of chest muscles
3. Guillain-Barré, spina bifida, and Duchenne syndrome leading to paralysis of the diaphragmatic muscles

Pathophysiology of Atelectasis

The main pathologic change that can lead to atelectasis is an alteration in the surface tension of the alveoli. This can occur due to an absolute deficit of lung surfactant, which is common in hyaline membrane disease, or an alteration in the composition of the lung surfactant, which is induced by anesthetics. The latter is responsible for most cases of postoperative atelectasis.

Obesity, a history of lung disease, duration of surgery, and pulmonary compression are also implicated in the pathogenesis of perioperative atelectasis. If a small bronchiole is obstructed in the lungs, intra-alveolar pores (pores of Kohn) and broncho-alveolar communications (Lambert channels) can ensure adequate ventilation of the affected alveoli and limit the extent of atelectasis.

During atelectasis, blood oxygenation is altered. The collapsed lung parenchyma is usually not as compliant as that on the contralateral side. Pulmonary vascular resistance tends to increase in the collapsed lung and pulmonary edema can occur. The consequences of these functional changes are hypoxemia and hyperventilation of the adjacent alveoli. In case of a complete collapse of an entire lung, hyperinflation of the contralateral lung is usually seen.

Clinical Presentation of Atelectasis in Children

If atelectasis occurs during an exacerbation of asthma, bronchitis, or bronchiolitis, the diagnosis can be missed. If atelectasis is extensive and involves multiple lung segments, the patient’s condition may worsen.

The main symptoms of atelectasis in the post-operative period are early fever, tachypnea, cough, and dyspnea. Auscultation of the chest can reveal decreased breath sounds on the affected side. If atelectasis involves a large segment of the lung, a dull or percussion note might be elicited. Wheezing is also a common finding during auscultation of the chest in the case of a collapsed lung segment.

Diagnostic Evaluation of Atelectasis in Children

Chest X-ray

When a patient presents with the previously mentioned symptoms, a chest X-ray is usually the first imaging modality to be ordered. Atelectasis results in a loss of lung volume and increases in density; thus, the following features may be seen on a chest X-ray:

• Sharply defined opacification of the lung lobe or segment that obscures vessels; air bronchograms are absent
• Interlobar fissure (usually displaced)
• A mediastinal shift towards the affected side (if a large segment of the lung is involved)
• Compensatory hyperinflation on the contralateral side
• Foreign bodies, if they are the cause of atelectasis

While a chest X-ray is useful in the identification of atelectasis, it is of limited help in differentiating between the different causes of atelectasis. In fact, some physicians do not consider atelectasis as a diagnosis; therefore, if atelectasis is suspected, the most likely etiology should be identified instead. Treatment of atelectasis is tailored towards the etiology, as discussed in the subsequent sections.

Computed tomography (CT)

A CT scan is useful in the evaluation of atelectasis in children, as this technique helps in better visualization and accurate localization of pulmonary lesions. Atelectasis is seen as volume loss in a lung CT scan and presents the following characteristics:

• Bronchial narrowing
• Change in the shape of the lung lobe
• V-shaped structure of lesions

If contrast agents are used, hyper-attenuation of the affected segment of the lung may be seen. This presentation is useful to differentiate between atelectasis and lung consolidation due to pneumonia, which does not enhance after the administration of intravenous contrast.

Laboratory investigations

Laboratory investigations, including a complete blood count, are used to evaluate febrile patients. Unfortunately, these tests do not add more certainty to the diagnosis of atelectasis. Magnetic resonance imaging provides excellent three-dimensional images of the lungs and might be helpful in the diagnosis of atelectasis.

Treatment of Atelectasis in Children

Positive end-expiratory pressure (PEEP)

Atelectasis caused by prolonged ventilation can be relieved by the application of PEEP, which stops alveolar collapse by preventing zero-pressure conditions during expiration. PEEP can also re-open collapsed alveoli.

Chest physiotherapy

Chest physiotherapy, early ambulation, and bronchodilators can be used postoperatively to prevent or treat atelectasis. In infants, bronchodilators and chest physiotherapy have been proven to be useful in treating atelectasis.

Use of DNase

Complications due to atelectasis include respiratory syncytial virus infection, which results in viscous secretions plugging the bronchioles. The use of DNase has been shown to be effective in the treatment of atelectasis. Bronchiolitis-related atelectasis has been previously shown to improve two hours after the introduction of DNase using a tracheal cannula. This condition completely resolves within 24 hours after commencing treatment.

Bronchoscopy

Patients with massive lung atelectasis can have a mucus plug or foreign body obstructing the lumen of a major bronchus. Bronchoscopy with or without bronchoalveolar lavage might be helpful in these situations.

Exercises

Frequent percussion that constitutes conventional respiratory physiotherapy is not useful in children. Instead, the patient should be encouraged to cough and inhale deeply. These two exercises, which can be considered as part of respiratory physiotherapy, are proven to be effective in the management of postoperative atelectasis in children.

Other modalities

Treatment of the etiology of atelectasis should be initiated as soon as possible to prevent re-collapse of the lung parenchyma. For example, appropriate antibiotics should be used if the patient has an acute exacerbation of asthma due to a bacterial infection in the lung. Bronchodilators or steroids may be needed in a patient with asthma to prevent atelectasis. Plasma electrophoresis and immunoglobulin antibody therapy might be a reasonable option for a child with Guillain-Barré syndrome.