Atelectasis

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Atelectasis

Background

Greek words ateles and ektasis meaning incomplete expansion One of the most commonly encountered abnormalities in chest radiology Divided physiologically into

Obstructive causes Non obstructive causes

What is atelectasis?

2 schools of thought

Alveolar collapse (volume loss) Fluid accumulation

Types

Obstructive

Compression atelectasis Right middle lobe syndrome Relaxation/passive atelectasis Adhesive atelectasis Cicatrization atelectasis Rounded atelectasis

NonNon-obstructive

Obstructive Atelectasis

Most common Causes: foreign body, tumor and mucus plugging Rate of development and extent depend on:

Extent of collateral ventilation Composition of inspired gas

Pathophysiology

Obstructive atelectasisObstruction of a bronchus Circulating blood absorbs gas in the peripheral alveoli Retraction of the affected lung

PathophysiologyUninvolved surrounding lung tissue distends Displacing the surrounding structures and mediastinal shift toward the atelectatic area Diaphragm is elevated and chest wall flattensObstructive atelectasis

Pathophysiology

Non obstructive atelectasis

Loss of contact between the visceral and parietal pleura Adhesive atelectasis

Due to lack of surfactant Due to filling by a tumor Due to scarring of the lung parenchyma

Replacement atelectasis

Cicatrization atelectasis

Pathophysiology

Platelike atelectasis

Also called discoid or subsegmental atelectasis Most commonly seen in CXR Probably occur because of obstruction of a small bronchus In hypoventilation, pulmonary embolism or LRTI

Pathophysiology

Post operative atelectasis

Due to diaphragmatic dysfunction and diminished surfactant activity Typically basilar and segmental

History

Signs and symptoms are determined by the rapidity with which the occlusion occurs Rapid bronchial occlusion sudden onset of dyspnea and cyanosis Slowly developing atelectasis maybe asymptomatic or with only minor symptoms

Middle lobe syndrome is often asymptomatic Irritation in the middle and right lower lobe bronchi may cause a severe hacking, non productive cough

Physical Examination

Dullness on the affected area Diminished or absent breath sounds

In atelectasis of the upper lobes breath sounds

bronchial

Chest excursion is reduced or absent Trachea and heart are deviated on the affected side

Causes

Primary cause: bronchial obstruction

Plugs of tenacious sputum Foreign bodies Endobronchial tumors Tumors, lymph node or an aneurysm By pleural fluid or air

External pulmonary compression

Causes

Abnormalities of surfactant production

In ARDS

Causes

Resorptive atelectasis

Bronchogenic carcinoma Obstruction from metastatic neoplasm Inflammatory etiology (TB, fungal infection) Aspirated foreign body Mucous plug Malpositioned endotracheal tube Extrinsic compression of an airway

Neoplasm, lymphadenopathy, aortic aneurysm or cardiac enlargement

Causes

Relaxation atelectasis

Pleural effusion Pneumothorax Large emphysematous bullae

Causes

Compression atelectasis

Chest wall, pleural, or intraparenchymal masses Loculated collections of pleural fluid

Causes

Adhesive atelectasis

Hyaline membrane disease ARDS Smoke inhalation Cardiac bypass surgery Prolonged shallow breathing

Causes

Cicatrization atelectasis

Idiopathic pulmonary fibrosis Chronic tuberculosis Fungal infections Alveoli filling of fluid or tumor Asbestos pleural plaques

Replacement atelectasis

Rounded atelectasis

Consequences

Impaired gas exchange Impaired lung mechanics Increased pulmonary vascular resistance Worsening lung injury

Consequences

Impaired gas exchange

Most obvious effect Basis: absence of ventilation with persistent perfusion (VQ mismatch)

Consequences

Impaired lung mechanics

Worsened compliance Larger transpulmonary pressure are required to generate a given tidal volumeWork of breathing is increased In mechanically ventilated children, increased ventilatory pressured are required

Consequences

Increased pulmonary vascular resistance

Due to regional alveolar hypoxia with reduced alveolar and mixed oxygen venous oxygen tension

Local hypoxic pulmonary vasoconstriction

Consequences

Worsening of lung injury

Potentiation of lung injury Ventilator induced lung injury

Imaging Studies

Direct signs

Displacement of fissures Opacification of the collapsed lobe Displacement of the hilum Mediastinal shift towards the side of the collapse Loss of volume on ipsilateral hemithorax Elevation of ipsilateral diaphragm, rib crowding Compensatory hyperlucency of the remaining lobes Silhouetting of the diaphragm or the heart border

Indirect signs

Imaging Studies

Complete atelectasis of an entire lung

Opacification of entire hemithorax Ipsilateral shift of the mediastinum

Imaging Studies

RUL collapse

RUL shifts medially and superiorly, resulting in elevation of the right hilum and minor fissure Tenting of the diaphragmatic pleura juxtaphrenic peak

Imaging Studies

RML collapse

Obscures the right heart border on PA Occasionally, a triangular opacity may be seen because the major fissure shifts upward and minor fissure shifts downward

Imaging Studies

RLL collapse

RLL shifts posteriorly and inferiorly Triangular opacity obscuring the RLL

Imaging Studies

LUL collapse

Shifts anteriorly and superiorly On lat views major fissure displaced anteriorly and the hyperexpanded RUL may herniate across the midline

Imaging Studies

LLL collapse

Increased retrocardiac opacity silhouettes the LLL pulmonary artery and L hemidiaphragm Flat waist sign Superior mediastinum may shift and obliterate

Procedures

Flexible fiberoptic bronchoscopy

Help evaluate the cause of the obstruction Helps clear mucous plugs Limitations: distal endobronchial lesions are not accessible

Treatment

Medical care

NonNon-pharmacologic Pharmacologic

Surgical care

Treatment

NonNon-pharmacologic

Chest physiotherapy

Postural drainage, chest wall percussion and vibration

Positive end-expiratory pressure end-

NonNon-pharmacologic treatment

Post operative atelectasis

Prevention Avoid anesthetic agents associated with postanesthesia narcosis Early ambulation Incentive spirometry If lobar atelectasis, vigorous chest physiotherapy

NonNon-pharmacologic treatment

Post operative atelectasis

Adequate oxygenation Supplemental oxygen If with severe hypoxemia ventilation

mechanical

Positive pressure and larger tidal volumes help to re-expand collapsed lung segments re-

Continuous positive airway pressure Fiberoptic bronchoscopy

Pharmacologic treatment

Bronchodilators Mucolytics

N-acetylcysteine Inhaled recombinant human dNase

Antibiotics Antitussives

Pharmacologic treatment

Bronchodilators

Encourage sputum expectoration Of underlying airflow is present, may also improve ventilation

Pharmacologic treatment

Mucolytics

May promote sputum removal of thick mucous plugs N-acetylcysteine only recommended for direst installation via fiberoptic bronchoscopy or in an intubated patient. Inhaled recombinant human dNase

Decreases viscoelasticity and surface tension of purulent sputum

Pharmacologic treatment

Antibiotics

To treat underlying bronchitis or post obstructive infection Because secondary atelectasis usually becomes infected regardless of the cause of obstruction

Pharmacologic treatment

Antitussives

Reduces the cough reflex Obstruction of a major bronchus may cause severe hacking or coughing

Surgical Care

Segmental resection or lobectomy chronic atelectasis

for

Complications

Acute pneumonia Bronchiectasis Hypoxemia and respiratory failure Postobstructive drowning of the lung Sepsis Pleural effusion and empyema