Atelectasis

Epidemiology

  • Definition: collapse of aerated lung
    • Etymology: Greek roots ateles and ektasis = incomplete expansion

Etiology

Obstructive Atelectasis (Due to Airway Obstruction) (see Obstructive Lung Disease, [[Obstructive Lung Disease]])

Tracheobronchial Infection

Tracheobronchial Neoplasm

  • Primary Endobronchial Benign or Malignant Tumor
    • Example: Bronchial Adenoma (see Bronchial Adenoma, [[Bronchial Adenoma]]): obstruction by endotracheal or endobronchial adenoma
    • Example: Bronchial Carcinoid (see Bronchial Carcinoid, [[Bronchial Carcinoid]]): obstruction by endotracheal or endobronchial carcinoid
    • Example: Lung Cancer (see Lung Cancer, [[Lung Cancer]]): obstruction by endotracheal or endobronchial disease
  • Endobronchial Metastases (see Lung Metastases-Endobronchial, [[Lung Metastases-Endobronchial]]): obstruction by endotracheal or endobronchial mets

Extrinsic Tracheobronchial Compression

  • Enlarged Pulmonary Artery: extrinsic compression of tracheobronchial airways
    • Transposition of Great Vessles with Ventricular Septal Defect: in infants and children
    • Tetralogy of Fallot (see Tetralogy of Fallot, [[Tetralogy of Fallot]]): in infants and children
  • Granulomatous Mediastinitis and Fibrosing Mediastinitis (see Granulomatous Mediastinitis and Fibrosing Mediastinitis, [[Granulomatous Mediastinitis and Fibrosing Mediastinitis]]): extrinsic compression of tracheobronchial airways
  • Mediastinal Mass (see Mediastinal Mass, [[Mediastinal Mass]]): extrinsic compression of tracheobronchial airways
    • Bulky Mediastinal or Peribronchial Lymphadenopathy
      • Example: Cancer
      • Example: Hodgkin’s Disease (see Hodgkin’s Disease, [[Hodgkins Disease]])
      • Example: Lymphoma (see Lymphoma, [[Lymphoma]])
      • Example: Tuberculosis (see Tuberculosis, [[Tuberculosis]])
      • Example: Sarcoidosis (see Sarcoidosis, [[Sarcoidosis]])
    • Mediastinal Tumor
      • Example: Schwannoma (see Schwannoma, [[Schwannoma]])
  • Thoracic Aortic Aneurysm (see Thoracic Aortic Aneurysm, [[Thoracic Aortic Aneurysm]]): extrinsic compression of tracheobronchial airways
  • Thyroid Cancer/Thyromegaly/Goiter (see Goiter, [[Goiter]] and Thyroid Cancer, [[Thyroid Cancer]]): extrinsic compression of tracheobronchial airways

Other Tracheobronchial Obstructive Process

  • Bronchial Stenosis (see Bronchial Stenosis, [[Bronchial Stenosis]])
  • Bronchocentric Granulomatosis (see Bronchocentric Granulomatosis, [[Bronchocentric Granulomatosis]])
  • Broncholithiasis (see Broncholithiasis, [[Broncholithiasis]]): endotracheal or endobronchial obstruction by broncholith
  • Bronchopulmonary Amyloidosis (see Amyloidosis, [[Amyloidosis]])
  • Mucoid Impaction (see Mucoid Impaction, [[Mucoid Impaction]]): tracheobronchial obstruction
  • Mucous Plugging of Airway: endotracheal or endobronchial obstruction by mucous plug
  • Post-Pneumonectomy Syndrome (see Post-Pneumonectomy Syndrome, [[Post-Pneumonectomy Syndrome]])
  • Post-Radiation Therapy (see Radiation Therapy, [[Radiation Therapy]]): bronchial granulation tissue (or stricture)
  • Relapsing Polychondritis (see Relapsing Polychondritis, [[Relapsing Polychondritis]]): endotracheal or endobronchial obstruction by loss of supporting cartilage in airways
  • Smoke Inhalation (see Smoke Inhalation, [[Smoke Inhalation]]): tracheobronchial mucosal injury with sloughing and airway obstruction
  • Toxic Fume Airway Injury: tracheobronchial mucosal injury with sloughing and airway obstruction
  • Tracheobronchial Foreign Body (see Airway Foreign Body, [[Airway Foreign Body]]): endotracheal or endobronchial obstruction by foreign body
  • Tracheobronchial Fracture (see Tracheobronchial Fracture, [[Tracheobronchial Fracture]])
  • Tracheobronchomalacia (see Tracheobronchomalacia, [[Tracheobronchomalacia]])
  • Tracheoesophageal Fistula (TEF) (see Tracheoesophageal Fistula, [[Tracheoesophageal Fistula]])
  • Tracheopathia Osteochondroplastica (see Tracheopathia Osteochondroplastica, [[Tracheopathia Osteochondroplastica]])
  • Wegener’s Granulomatosis (see Wegener’s Granulomatosis, [[Wegeners Granulomatosis]]): endotracheal or endobronchial obstruction by granulomatous tissue

Non-Obstructive Atelectasis

Abdominal Disorder

  • Abdominal Pain (see Abdominal Pain, [[Abdominal Pain]]): abdominal splinting is common after abdominal surgery
  • Abdominal Compartment Syndrome (see Abdominal Compartment Syndrome, [[Abdominal Compartment Syndrome]]): increased intra-abdominal pressure -> decreased thoracic volume
  • Ascites (see Ascites, [[Ascites]]): increased intra-abdominal pressure -> decreased thoracic volume
  • Obesity (see Obesity, [[Obesity]])
  • Pregnancy (see Pregnancy, [[Pregnancy]]): increased intra-abdominal pressure -> decreased thoracic volume

Space-Occupying Intrathoracic Disorder

  • Bullae (see Bullae, [[Bullae]]): expansion of bulla -> compression of adjacent lung
    • This can especially occur on mechanical ventilation (with positive pressure): due to increased compliance of the bullous lesion, airflow tends to be redirected to the bullous lesion with disproportionate expansion of it (compared the remaining lung)
  • Intrathoracic Tumor (Large): compression of adjacent lung
  • Pleural Effusion (see Pleural Effusion-Transudate, [[Pleural Effusion-Transudate]] and Pleural Effusion-Exudate, [[Pleural Effusion-Exudate]]): loss of contact between the visceral and parietal surfaces with deformation of shape of lung, resulting in atelectasis
    • Even a small pleural effusion can compress adjacent lung
  • Pneumothorax (see Pneumothorax, [[Pneumothorax]])
    • Non-Tension Pneumothorax: introduction of air into pleural space leads to compression of adjacent lung (to some extent) and the loss of contact between the visceral and parietal surfaces with deformation of shape of lung, resulting in atelectasis
    • Tension Pneumothorax: mechanism involves positive pressure in the pleural space with compression of adjacent lung

Neuromuscular Disease (see Acute Hypoventilation, [[Acute Hypoventilation]] and Chronic Hypoventilation, [[Chronic Hypoventilation]])

  • Mechanism: diaphragmatic weakness/paralysis with pressure of abdominal contents on the diaphragm, poor inspiration with low lung volumes, and impaired cough reflex (with decreased mucous clearance)
  • Types of Neuromuscular Disease
    • Chemosensitivity Disorders
    • Brainstem Disease
    • Spinal Cord Disease
    • Upper Motor Neuron Disease
    • Peripheral Neuropathy
    • Neuromuscular Junction Disease
    • Myopathy

Cicatrization Atelectasis

Impaired Surfactant Activity

  • Acute Respiratory Distress Syndrome (ARDS) (see Acute Respiratory Distress Syndrome, [[Acute Respiratory Distress Syndrome]]): decreased surfactant synthesis or decreased surfactant activity -> alveolar instability, resulting in collapse
  • Aspiration (see Aspiration Pneumonia, [[Aspiration Pneumonia]]): gastric acid aspiration -> decreased surfactant -> alveolar instability, resulting in collapse
  • Cardiac Bypass Surgery
  • Prolonged Shallow Breathing
  • Pulmonary Contusion (see Pulmonary Contusion, [[Pulmonary Contusion]]): surfactant dysfunction -> alveolar instability, resulting in collapse
  • Radiation Pneumonitis (see Radiation Pneumonitis and Fibrosis, [[Radiation Pneumonitis and Fibrosis]]): inactivation of surfactant -> alveolar instability, resulting in collapse
  • Smoke Inhalation (see Smoke Inhalation, [[Smoke Inhalation]])
  • Uremia (see Chronic Kidney Disease, [[Chronic Kidney Disease]])

Other

  • Acute Pulmonary Embolism (PE) (see Acute Pulmonary Embolism, [[Acute Pulmonary Embolism]])
  • Ankylosing Spondylitis (see Ankylosing Spondylitis, [[Ankylosing Spondylitis]]): atelectasis occurs in a small percentage off cases
  • Bronchioloalveolar Cell Carcinoma: causes “replacement atelectasis”, where the alveoli of an entire lobe of the lung are filled with tumor cells
  • Esophageal Variceal Sclerotherapy (see Esophageal Varices, [[Esophageal Varices]]): atelectasis occurs in 12% of cases
  • General Anesthesia: causes atelectasis, independent of other risk factors

Physiology

  • Mechanism of Obstructive Atelectasis (most common mechanism): endobronchial airway obstruction (at any point between trachea and distal airways) -> reabsorption of alveolar oxygen and nitrogen (with collapse of previously aerated lung)
    • Rate of development of atelectasis depends on the degree of obstruction (complete vs partial), presence of collateral ventilation to the affected alveoli (provided by the pores of Kohn and canals of Lambert), and composition of the inspired gas
    • Stages
      • Early Stage: collapse of aerated lung within hours (volume loss) -> V/Q mismatch (with resulting hypoxemia) and mediastinal shift toward the atelectatic side
      • Later Stage: filling of collapsed alveoli with cells and secretions (which may prevent complete collapse)
      • Late Stage: persistent obstruction -> infection, fibrosis, and/or bronchiectasis
  • Mechanism of Non-Obstructive Atelectasis: may occur due to a space-occupying lesion in the thorax with compression of adjacent lung, due to loss of surfactant (with alveolar collapse), due to the loss of visceral-parietal pleural contact (due to effusion, pneumothorax), or due to replacement of parenchymal lung tissue by scarring or infiltrative disease
    • Middle and lower lobes tend to collapse more readily in the presence of pleural effusion
    • Upper lobes tend to collapse more readily in the presence of pneumothorax
  • Atelectasis Contributing to Development of Pleural Effusion: atelectasis (of any etiology) -> decreased perimicrovascular pressure -> movement of fluid from parietal pleural interstitium into pleural space (until the gradient equalizes)

Diagnosis

  • Physical Exam: see Pulmonary Physical Exam
  • CXR/Chest CT: usual imaging modalities to diagnose atelectasis and assess for potential etiologies
    • Obstructive Atelectasis: volume loss with shifting of mediastinum toward side of atelectasis (except in cases where mediastinum/trachea are fixed)

ATELECTASIS

  • Bronchosocopy: may be required to exclude an endobronchial lesion
    • Bronchoscopic evaluation is particularly indicated in patients with unexplained atelectasis that might represent an undiagnosed endobronchial lesion (delayed diagnosis of such lesions is a common medical-legal issue)

Clinical Manifestations

General Presentations

  • Asymptomatic: some cases
  • Cough (see Cough, [[Cough]]): particularly common with right middle lobe syndrome
  • Dyspnea (see Dyspnea, [[Dyspnea]])
  • Hypoxemia (see Hypoxemia, [[Hypoxemia]]): due to perfusion of collapsed lung (at least in the early stages of atelectasis) -> V/Q mismatch
  • Small Unilateral Pleural Effusion (see Pleural Effusion-Transudate, [[Pleural Effusion-Transudate]])
    • Epidemiology: atelectasis is a common cause of pleural effusion in the ICU (as well as being a common result of pleural effusion)
    • Diagnosis
      • CXR/Chest CT Pattern: usually small, unilateral effusion, with associated volume loss (and normal heart size)
      • Pleural Fluid: typically transudate in cases with effusion that occurs secondary to atelectasis (however, in cases where the effusion is the primary event, fluid may be either transudative or exudative)
        • Appearance: serous
        • pH: >7.4
        • Glucose: same as serum glucose
        • Cell Count/Diff: <1000 cells (mononuclear-predominant)
  • Acute Respiratory Failure (see Respiratory Failure, [[Respiratory Failure]]): may occur with acute development of large volume atelectasis
  • Plate-Like/Discoid/Subsegmental Atelectasis: plate-like linear densities (typically at the bases) noted on CXR or Chest CT
    • Likely occurs due to small bronchial obstruction (which may with hypoventilation, pulmonary embolism, or lower respiratory tract infection)
  • Post-Operative Atelectasis: common after thoracic or abdominal surgery
    • Likely occurs due to effects of general anesthesia, manipulation of the lung, diaphragmatic dysfunction, hypoventilation (due to pain), and/or surfactant dysfunction
    • Prevention: recruitment maneuver followed by PEEP, may together decrease the development of atelectasis and improved oxygenation in morbidly obese patients undergoing general anesthesia [MEDLINE]
  • Lack of Association Between Atelectasis and Fever: studies do not indicate that there is a correlation between atelectasis and fever [MEDLINE]

Rounded Atelectasis

Right Middle Lobe Syndrome (Brock Syndrome)

Treatment

  • Treat Underlying Etiology of Atelectasis: mainstay of treatment
  • Chest Physiotherapy (Chest PT) (see Chest Physiotherapy, [[Chest Physiotherapy]]): useful
  • Bronchodilators: indicated for patients with airflow obstruction
  • Bronchoscopy (see Bronchoscopy, [[Bronchoscopy]]): indicated for significant mucous plugging with associated atelectasis (particularly in cases with associated hypoxemia and/or respiratory compromise)
  • Incentive Spirometry: useful as preventive strategy (although benefit is greatest when started pre-operatively)
  • Intermittent Positive Pressure Breathing (IPPB) (see xxxx, [[xxxx]]): unclear benefit
  • DNase (see xxxx, [[xxxx]]): may be useful in non-cystic fibrosis childen, but is unproven in adults [MEDLINE]
  • Early Post-Operative Ambulation: indicated for post-operatve prevention of atelectasis
  • RTX Respirator: may be useful in subsets of patients [MEDLINE]
  • Nebulized N-Acetlycysteine (Mucomyst) (see xxxx, [[xxxx]]): not indicated (due to risk of bronchospasm and lack of efficacy)
  • Mechanical Insufflation-Exsufflation Device (Cough Assist Device) (see Mechanical Insufflation-Exsufflation Device, [[Mechanical Insufflation-Exsufflation Device]]): useful in patients with atelectasis associated with spinal cord injury (see Spinal Cord Injury, [[Spinal Cord Injury]])

References

  • DNase and atelectasis in non-cystic fibrosis pediatric patients. Crit Care. Aug 2005;9(4):R351-6 [MEDLINE]
  • Atelectasis as a cause of postoperative fever: where is the clinical evidence?. Chest. Aug 2011;140(2):418-24 [MEDLINE]
  • Prevention of atelectasis in morbidly obese patients during general anesthesia and paralysis: a computerized tomography study. Anesthesiology. Nov 2009;111(5):979-87 [MEDLINE]
  • Marked improvement of extensive atelectasis by unilateral application of the RTX respirator in elderly patients. Intern Med. 2009;48(16):1419-23 [MEDLINE]