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]])
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
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
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
Example: Lung Cancer (see Lung Cancer, [[Lung Cancer]])
Example: Pleural Mesothelioma (see Pleural Mesothelioma, [[Pleural Mesothelioma]])
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
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
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)
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
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)
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)
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
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)
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]
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]
