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Saturday, January 17, 2009

ATELECTASIS

ATELECTASIS - Taylor Sittler, MD; Deborah Heitmann, MD
BASICS
DESCRIPTION
• Atelectasis (lung collapse) is a portion of lung that is nonaerated, but otherwise normal.
• May be an asymptomatic finding on chest radiograph
• Pulmonary blood flow to the area of atelectasis is usually reduced, which limits shunting and arterial hypoxemia.
• Diagnosis and therapy are directed at the etiology.
• Synonym(s): Lung collapse
GENERAL PREVENTION
• Avoid 100% inspired oxygen, which can be rapidly absorbed and cause atelectasis
• Foreign body/aspiration precautions
• Postoperative mobilization and/or rotation several times per hour
• Chest physiotherapy and incentive spirometry as preventive maneuvers in high-risk patients. Shown to be effective and cost-effective preceding pulmonary lobectomy (1)[C] and following myocardial revascularization (2)[C].
EPIDEMIOLOGY
• Predominant age: All ages
• Predominant sex: Male = Female
Incidence
Incidence/prevalence poorly documented: Very common postoperatively, particularly following thoracic/upper abdominal surgery, general anesthesia, and in intensive care with high-inspired oxygen concentrations
RISK FACTORS
• Atelectasis following anesthesia is increased in smokers, obese individuals, and individuals with short, wide thoraces.
• Increased risk in the elderly and in neonates
• Asthmaright middle lobe most common
ALERT
High oxygen content of inspired air increases risk
Genetics
Depends on basic condition (e.g., cystic fibrosis, chronic obstructive pulmonary disease, asthma, congenital heart disease, and congestive heart failure)
ETIOLOGY
• Obstructive (most common)
- Resorptive: Due to airway obstruction from luminal blockage (mucus, tumor, foreign body), airway wall abnormality (edema, tumor, bronchomalacia, deformation), or extrinsic airway compression (cardiac, vascular, tumor, adenopathy)
• Non-obstructive
- Surfactant Impairment: Due to pulmonary edema, infection, primary surfactant deficiency
- Compression: Lobar emphysema, tumor, abscess, cardiomegaly. Right middle lobe atelectasis from chronic inflammation and bronchial compression by lymph nodes
- Relaxation: Loss of contact between parietal and visceral pleura due to fluid or air in the pleural space (pneumothorax, effusion, empyema, hemothorax, chylothorax)
- Chest wall restriction: Due to skeletal deformity and/or muscular weakness (scoliosis, neuromuscular disease, phrenic nerve paralysis, anesthesia)
- Parenchymal scarring: Granulomatous disease, necrotizing pneumonia, asbestosis (more common in elderly), toxic inhalation, drug-induced fibrosis (e.g., amiodarone)
Geriatric Considerations
Increased risk. Primary and secondary lung tumors are sometimes associated.
Pediatric Considerations
• Increased risk. Congenital airway obstruction due to mediastinal cysts, tumor, or vascular rings
• Foreign body aspiration
ASSOCIATED CONDITIONS
• Cystic fibrosis
• Asthma
• Adult respiratory distress syndrome (ARDS)
• Neonatal respiratory distress syndrome
• Pulmonary edema
• Pulmonary embolism
• Neuromuscular disorders
• General anesthesia
• Mechanical ventilation

DIAGNOSIS
SIGNS AND SYMPTOMS
History
• Small atelectasis
- Commonly asymptomatic
- Produces no change in the overall clinical presentation
• Large atelectasis
- Tachypnea
- Cough
- Pain
Physical Exam
• Hypoxia
• Dullness to percussion
• Absent breath sounds if airway is occluded
• Bronchial breathing if airway is patent
• Diminished chest expansion
• Tracheal or precordial impulse displacement
• Wheezing may be heard with focal obstruction.
TESTS
Lab
Sputum culture if infection is suspected
Imaging
• Chest CT or MRI may be indicated to visualize airway and mediastinal structures and to distinguish cause of atelectasis
• Chest radiograph (posterior-anterior and lateral)
- May demonstrate linear, round, or wedge-shaped densities.
- Right middle lobe and lingular atelectasis will obscure the ipsilateral heart border.
- Lower lobe atelectasis will obscure the diaphragm.
- Raised diaphragm, flattened chest wall, movement of mediastinal structures and diaphragm toward the atelectatic region
- Unaffected lung may show compensatory hyperinflation.
• Obstructive findings
- Air bronchograms usually absent
- Wedge-shaped densities
• Nonobstructive findings
- Evidence of airway compression, pleural fluid, or air should be sought.
- Diffuse microatelectasis in surfactant deficiency may progress to a patchy or diffuse reticular granular pattern, then to a pulmonary edema-like pattern, and finally to bilateral opacification in severe cases.
- Round atelectasis: Pleural-based round density on chest radiograph with a comet tail of vessel and airway; usually indicates asbestosis.
Diagnostic Procedures/Surgery
• Bronchoscopy to assess airway patency in unexplained or refractory cases
• Echocardiography to assess cardiac status in cardiomegaly
• Barium swallow to assess mediastinal vascular compression
Pathological Findings
• Needle biopsy is rarely needed for diagnosis.
• Pathology varies with the cause.
• Obstructive atelectasisnonaerated lung without inflammation or infiltration
DIFFERENTIAL DIAGNOSIS
• Atelectasis is not a specific diagnosis, but rather a result of disease or distorted anatomy. The differential is, therefore, found under Etiology.
• The radiographic differential includes pneumonia, fluid accumulation, lung hypoplasia, tumor, and interstitial lung disease.
TREATMENT
GENERAL MEASURES
• Suction and vigorous coughing to remove obstruction, then physical therapy, and bronchoscopy to remove obstruction if previous measures fail
- Bronchoscopy as therapy is controversial other than for obstruction removal.
• Ensure adequate oxygenation (arterial O2 saturation >90%) and humidification.
• Incentive spirometry
• Initiate intubation and mechanical ventilation with positive end-expiratory pressure (PEEP) in severe respiratory distress or hypoxemia.
- Lower tidal volume (6 mL/kg) and lower end-inspiratory values (30 mm Hg) associated with reduced mortality (3)[B]
- PEEP 15-20 mL may be necessary to maintain arterial O2 saturation in surfactant-impaired states (3)[B]
• CPAP 5-15 cm H2O in recurrent atelectasis or with neuromuscular weakness
• Ensure patient is lying on the unaffected side to promote drainage.
• Maximize patient mobility and encourage frequent coughing and deep breathing every hour. See also "Physical Therapy" section.
Diet
No special diet
Activity
Encourage activity and mobilization as tolerated.
SPECIAL THERAPY
Physical Therapy
Chest physiotherapy with percussion and postural drainage. Deep breathing every hour.
• Consider adding treatments using new airway clearance techniques such as PEEP mask.
MEDICATION (DRUGS)
• Bronchodilator therapy (-agonist aerosol); efficacy controversial
• Empiric, broad-spectrum antibiotics for infection if atelectasis occurs outside the hospital setting see "C ommunity-acquired Pneumonia"
• Analgesia for pain control to permit deep inspiration and coughing
• Other therapies directed at basic cause: Antibiotics, foreign-body removal, tumor therapy, cardiac medication, and steroids in asthma
SURGERY
Only for respectable disease (e.g., tumor)
FOLLOW-UP
PROGNOSIS
• Resolution with medical therapy
• Surgical therapy needed only for resectable causes or if chronic infection and bronchiectasis supervene
COMPLICATIONS
Atelectasis is rarely life threatening and usually resolves spontaneously.
Acute atelectasis
- Hypoxemia and respiratory failure
- Postobstructive drowning of the lung
- Sepsis
Chronic atelectasis
- Acute pneumonia
- Bronchiectasis
- Pleural effusion and empyema
PATIENT MONITORING
• Varies with cause and patient status
• In simple atelectasis associated with asthma or infection, monthly visits are adequate.
REFERENCES
1. Varela G, Ballesteros E, et al. Cost-effectiveness analysis of prophylactic respiratory physiotherapy in pulmonary lobectomy. Eur J Cardiothorac Surg 2006;29(2):216-20. Epub 2006 Jan 11.
2. Leguisamo CP, Kalil RAK, Furlani AP. Effectiveness of a preoperative physiotherapeutic approach in myocardial revascularization. Brazil J Cardiovasc Surg 2005;20(2):134-141.
3. McCunn M, Sutcliffe AJ, et al. Guidelines for management of mechanical ventilation in critically injured patients. TraumaCare 2004;14(4):147-151.


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