eMedicine Specialties > Pediatrics: General Medicine > Pulmonology

Atelectasis, Pulmonary

Author: Michael R Bye, MD, Professor of Clinical Pediatrics, Division of Pulmonary Medicine, Columbia University College of Physicians and Surgeons; Attending Physician, Pediatric Pulmonary Medicine, Morgan Stanley Children's Hospital of New York Presbyterian, Columbia University Medical Center
Contributor Information and Disclosures

Updated: Sep 8, 2009

Introduction

Background

Atelectasis refers to collapse of part of the lung. It may include a lung subsegment or the entire lung and is almost always a secondary phenomenon, with no sex or race proclivities; however, it may occur more frequently in younger children than in older children and adolescents. The direct morbidity from atelectasis is transient hypoxemia due to blood flowing through the lung, which does not have normal air flow. The blood does not pick up oxygen from the corresponding alveoli. This shunting results in transient hypoxemia.

Pathophysiology

Atelectasis has 4 potential causes, which are as follows:

• Airways may have intrinsic obstruction. 
• Airways may be compressed (extrinsic airway obstruction). 
• Lung tissue may be compressed.
• Alveoli may incompletely expand and eventually collapse.

Because the right middle lobe orifice is the narrowest of the lobar orifices and because it is surrounded by lymphoid tissue, it is the most common lobe to become atelectatic. This is referred to as right middle lobe syndrome.

Intrinsic airway obstruction is the most common cause of atelectasis in children, and asthma is the most common underlying disorder that predisposes patients to atelectasis. Other causes include bronchiolitis, aspiration due to a swallowing disorder, endobronchial tuberculosis, aspiration from gastroesophageal reflux, airway foreign bodies, cystic fibrosis, and increased or abnormal airway secretions for other reasons. Children younger than 10 years are less likely to have developed the interairway canals of Lambert or the interalveolar pores of Kohn. Thus, young children depend more on the feeding airways to move air into the alveoli. When their airways become obstructed, they are more likely to develop atelectasis than older children who have developed those communications.

Extrinsic compression on the airways is most likely to come from enlarged lymph nodes (such as those due to tuberculosis infection), lymphoma and other tumors in the chest, an enlarged heart that compresses the left main or left lower lobe bronchus, and left-to-right intracardiac shunts that increase blood flow through the pulmonary arteries.

In children with hypoventilation for a protracted period, the alveoli may collapse. This may occur in children with neuromuscular disease, those who have had recent thoracic or upper abdominal surgery, those on medications that decrease their minute ventilation (such as narcotics), and those with abnormally small or dysmorphic chest walls, which may be less compliant than the normal chest wall. Such children may also be predisposed to atelectasis because of poor clearance of airway secretions. An ineffective cough allows these secretions to obstruct the airway.

Atelectasis due to compressed lung tissue occurs most commonly when air, blood, pus, or chyle is present in the pleural space. Intrathoracic abdominal contents, chest wall masses, cardiomegaly, and an abnormal chest wall can all compress adjacent lung tissue. If a portion of lung enlarges, such as with congenital emphysema, or if focal overinflation occurs for any other reason, it may compress the adjacent lung, causing atelectasis.

Frequency

United States

No data are available on the frequency of atelectasis.

Mortality/Morbidity

Most of the morbidity and any mortality is due to the underlying disorder. The primary complication of atelectasis is hypoxemia, which is usually transient. Within 24-48 hours, the lung is able to decrease or shut off blood flow to the atelectatic area. This is probably caused by factors such as serotonin that reacts to the local hypoxia in the alveoli and causes an intense vasoconstriction. If the atelectasis is massive enough, it may cause enough hypoxemia acutely to require supplemental oxygen or ventilatory support.

Atelectasis is a suggested cause of fever; however, no known physiologic reason supports this. Recent data dispute this old dogma. A study of adults after open-heart surgery showed no correlation between atelectasis and fever and reported that fever appeared as the incidence of atelectasis was decreasing.¹ Patients with temperatures of more than 38.5°C were less likely to have atelectasis on radiography findings than those patients who were afebrile and undergoing radiography as part of the postoperative routine.

Another concern is the likelihood of infection in the atelectatic portion of the lung. Although the clearance in this portion of the lung is abnormal, the lung is normally a sterile environment. In the otherwise healthy child with atelectasis, infection is unlikely. However, if the child has abnormal secretions or is prone to aspiration, secondary infection of the atelectatic lung may occur. In children with chronically infected lungs, the atelectatic portion is likely to be similarly infected, with decreased ability to clear the infection. This sets up the possibility of bronchiectasis developing in that portion of the lung. Children who remain on assisted ventilation with atelectasis are at risk of developing infection, including infection in the atelectatic portion of the lung. This portion has less intrinsic clearance, which increases the risk of significant infection if organisms enter this portion.

Race

Other than any racial predilections for the underlying disorders, no racial predilection for atelectasis has been reported (see Cystic Fibrosis and Asthma).

Sex

Atelectasis has no sex predilection.

Age

Atelectasis is probably more common in children younger than 10 years because their airways are typically narrower and are more likely to become obstructed by secretions, airway inflammation, or both. In addition, these smaller airways are more easily compressed. These children are also less likely to have collateral ventilation.

Clinical

History

• Most symptoms of pulmonary atelectasis are related to the underlying disorder.
• Atelectasis alone only causes tachypnea as the child attempts to compensate for decreased tidal volume by increasing the frequency of respiration.
• If the atelectasis is large enough, the child may grunt in an attempt to create auto–positive end-expiratory pressure (PEEP), both to improve oxygenation and to attempt to open the atelectatic areas.
• If a child has underlying cardiopulmonary or neuromuscular disease and is on a monitor, sudden decreases in oxygen desaturation may be a sign of atelectasis. Atelectasis is one of the most common causes of sudden decreases in oxygen saturation in children.

Physical

• Most findings upon physical examination are related to the underlying disorder.
• Breath sounds may be decreased in the atelectatic portion of the lung, although the segment involved may be so small that the changes cannot be perceived. Also, the atelectatic portion may be in a segment inaccessible to the stethoscope.
• If the atelectatic portion and chest wall are large enough, dullness to percussion may be detected.
• The atelectasis may also occur in the right middle lobe or lingula in an adolescent girl. Because both are anteriorly located, the physician must listen to the anterior chest of the patient to hear these lobes. If the physician feels awkward about examining this area and fails to do so, the lobes are not correctly evaluated, and any corresponding abnormalities are not heard.

Causes

• Obstruction of an airway or diminished distention of alveoli may cause atelectasis.
• The most common causes involving airway obstruction include the following:
  • Airway obstruction due to a mucous plug or other airway secretions, such as with bronchiolitis
  • Bronchospasm airway secretions and airway inflammation in patients with asthma
  • Abnormal airway secretions in cystic fibrosis
  • Abnormal airway clearance, such as with ciliary dyskinesia syndrome
  • Airway foreign body
  • Extrinsic compression on an airway (eg, compression due to an enlarged or aberrant vessel)
  • Enlarged lymph nodes that compress the airway 
  • Masses in the chest that compress the airway or alveoli
  • Cardiomegaly or enlarged pulmonary vessels that compress adjacent airways
• Causes of diminished alveolar distention include the following:
  • Small or dysmorphic chest wall
  • Severe scoliosis
  • Neuromuscular diseases
  • Anesthesia or sedation
  • Pain from upper abdominal surgery
  • Abdominal distention
  • Chest wall or upper abdominal pain

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