Felis ISSN 2398-2950

Lung: atelectasis

Contributor(s): Lesley G King

Introduction

  • Cause: reduction in lung volume due to collapse of alveoli.
  • Signs: may be asymptomatic, cough, hypoxemia.
  • Diagnosis: radiography.
  • Treatment: resolve underlying cause, provide oxygen. 
  • Prognosis: good to guarded depending on underlying cause.

Pathogenesis

Etiology

  • Ateclectasis is collapse of empty alveoli. Because the alveoli are collapsed there is a decrease in size of the affected lung lobe(s).
  • It differs from consolidation, which is filling of alveoli by cells or fluid. Consolidated lung lobes are normal or increased in size.
  • Lung lobe atelectasis is caused by:
    • Compression of alveoli: seen in obese cats or those with abdominal effusions Peritoneal: effusion or hepatomegaly Hepatomegaly.
    • Loss of negative intrapleural pressure.
    • Concurrent lung disease, usually inflammatory, which leads to loss of surfactant.
    • Absorption atelectasis due to complete obstruction of a bronchus: occurs commonly in the right middle lung lobe of cats with bronchial disease Chronic bronchitis.

Predisposing factors

General

  • Obesity.
  • Bronchial disease.
  • Anesthesia.

Pathophysiology

  • Compression atelectasis:
    • Collapse of normal alveoli.
    • Most severe in ventral airspaces, which normally have smaller alveoli.
    • Often caused by pressure on the chest wall from obesity or tight bandages; or pressure forward on the diaphragm from an enlarged liver, abdominal effusion or mass.
    • Predictable following initiation of anesthesia with spontaneous breathing.
  • Loss of negative intrapleural pressure:
    • Pleural space disease such as pneumothorax Pneumothorax or pleural effusion Pleural effusion results in loss of negative intrapleural pressure, which normally helps keep alveoli open. Atelectasis is then caused by passive recoil of the lungs.
    • Smaller and more ventral lung lobes, eg right middle and caudal part of the left cranial, are most severely affected.
    • Large volumes of fluid or air can result in positive intrapleural pressure (eg tension pneumothorax Tension pneumothorax) which then causes compression atelectasis.
    • Thoracocentesis Drainage: thorax usually allows re-expansion of the collapsed lung lobes.
  • Concurrent lung disease:
    • Because of lack of effective surfactant, atelectasis is often a component of inflammatory lung diseases such as pneumonia or acute respiratory distress syndrome Acute Respiratory Distress Syndrome (ARDS).
    • During lung inflammation, surfactant is often defective or produced in decreased amounts due to injury to Type 2 alveolar epithelial cells.
    • Consolidation is usually more obvious than atelectasis in these patients (ie there is usually no decrease in size of the affected lung lobes).
    • Management should focus on treatment of the inflammatory disease.
  • Obstruction of bronchus (absorption atelectasis):
    • Airway obstruction must be complete and this is common due to mucus occluding the bronchus of the right middle lung lobe of cats with feline asthma Allergic bronchitis; it can also occur due to an inhaled foreign body Foreign body migration (particularly pebbles or seeds); mucus or inflammatory debris secondary to pneumonia; external compression of the bronchus by an extraluminal mass; or an intraluminal mass (neoplasm Lung: pulmonary neoplasia) completely obstructing the bronchus.
    • If the bronchus is completed obstructed, air in the alveoli distal to the obstruction is gradually absorbed by diffusion into the blood, resulting in collapse of the alveoli.
    • Nitrogen (room air is about 80% nitrogen) is the slowest gas to be absorbed from the alveoli. Because of its slow diffusion into tissues compared with oxygen and carbon dioxide, it is said to create a "nitrogen scaffold" that holds alveoli open.
    • If a bronchus is obstructed while the animal is breathing 100% oxygen (eg under anesthesia), atelectasis occurs very quickly because oxygen is musch nore diffusible into blood compare with nitrogen.

Timecourse

  • Minutes to weeks.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Winegardner K, Scrivani P V, Gleed R D (2008) Lung expansion in the diagnosis of lung disease. Compend Contin Educ Vet 30 (9), 479-489 PubMed.
  • Henninger W (2003) Use of computed tomography in the disease feline thorax. JSAP 44 (2), 56-64 PubMed.


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