Atelectasis

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Original Editor - Hing Long Yip

Top Contributors = Areeba Raja, Elena Ferrero Vila, Hing Long Yip, Kim Jackson, Lucinda hampton, Jonathan Wong, Wendy Walker and Sujoy Bose

Introduction

Atelectasis is a condition in which small airways of the lung collapse completely or partially, leading to an impaired gaseous exchange between CO2 and O2. It is a reversible condition and usually occurs secondary to an underlying pathology.

Epidemiology

• Atelectasis does not preferentially affect either sex.
• Incidence doesn't increase in patient with increased age, COPD or asthma.
• The incidence of atelectasis in patients who have recently undergone general anesthesia is as high as 90%
• It is commonly observed as a complication in post-operative patients whose breathing mechanism is impacted by the procedure, pain, and prolonged resting.
• Atelectasis is less commonly seen in patients with conditions like COPD, bronchiectasis, and cystic fibrosis.

• Cephalad displacement of the diaphragm in Obese and/or pregnant patients is more likely to cause atelectasis.

Classification

It can be classified as follows

1.    pathophysiologic mechanism (e.g., compressive atelectasis)

2.   the amount of lung involved (e.g., lobar, segmental, or subsegmental atelectasis)

3.   the location (i.e., specific lobe or segment location).

On the basis of pathophysiology

Following table comprises the classification of atelectasis based on pathophysiologic mechanism

Pathophysiologic Mechanism	Pathogenesis	Associated Types of Atelectasis	Cause
Compression of Lung Tissue	This mechanism of atelectasis occurs through compression. This means that the net balance of forces across an alveolar wall shifts toward ensuring its collapse.	Passive Atelectasis Compressive Atelectasis	Airway Stenosis Inflammation and edema caused by aspiration or inhalation injury (smoke, chemical agents) Edema of the airway Bronchial tumor Granuloma Papilloma Cardiomegaly Lobar Emphysema Vascular ring (innominate artery) Lymph node hypertrophy (tuberculosis) Tumors (mediastinum) Chylothorax Hemothorax Pneumothorax General anesthesia
Absorption of Alveolar Air	A second major reason is gas resorption. This may occur in two ways. If airway occlusion is complete, alveolar gas can exit from the alveolar units only through the bloodstream. Thus, atelectasis can develop in the face of obstruction. The second and perhaps more important mechanism of gas resorption may occur in areas that are poorly ventilated and well perfused. If the inspired oxygen concentration increases, the alveolar oxygen, but not nitrogen, uptake will be high; thus, there is less alveolar splinting and a loss of lung volume.	Obstructive Atelectasis Cicatrizion Atelectasis	Foreign Body Aspiration Secretion Plugs Cystic Fibrosis Ciliary Dyskinesia Syndrome Asthma Bronchiolitis Bronchospasm Histoplasmosis General Anesthesia
Impairment of Surfactant Function	Insufficient surfactant function can result from deficiency of acquired dysfunction (e . g ., as for premature neonates), and this occurs in the context of lung injury. Once inactivated, increased local surface tension results in decreased expansion; on a global level, this produces a reduction of resting lung volume.	Adhesive atelectasis	Hyaline Membrane Disease COVID-19 Acute Respiratory Distress Syndrome (ARDS) Pneumonia Pulmonary Edema Almost Drowning General Anesthesia

On the basis of location

Atelectasis can be classified on the basis of location according to radiological patterns of collapse

Complete collapse

The collapse of an entire lung leads to the complete opacification of a hemithorax (a so-called ‘white out’). This is often confused with a large pleural effusion, but can be distinguished by the presence of mediastinal shift towards a collapsed lung compared with movement away from a pleural effusion.

Lobar collapse

Characteristic features associated with individual lobar collapse are as follows:

Right upper lobe (RUL) collapse

• elevation of the right hilum and the minor fissure.
• On the lateral view, the elevation of the minor and major fissures may be visible.
• Golden S sign(The minor fissure is usually convex superiorly but may appear concave because of an underlying mass lesion).

Right middle lobe (RML) collapse

• results in minimal opacity and is often overlooked.
• The loss of silhouette of the right heart border is almost always a feature on a posterior-anterior view.
• The right horizontal and oblique fissures move towards each other leading to a wedge-shaped opacity on the lateral view.

Right lower lobe (RLL) collapse

• triangular opacity adjacent to the right heart border.
• There is the obliteration of the right hemidiaphragm and it may appear elevated.
• right heart border is clearly seen.
• On lateral projection, the right hemidiaphragm outline is lost posteriorly and the lower thoracic vertebrae appear denser

Left upper lobe (LUL) collapse

• Owing to the lack of a minor fissure, LUL collapse appears as a veil-like opacity extending from the hilum and fading inferiorly.
• On the lateral view, the major fissure displaces anteriorly and the lower lobe is hyper-expanded.
• Luftsichel sign (hyper-expanded superior segment of the left lower lobe (LLL), which is positioned between the atelectatic upper lobe and the aortic arch in half of the cases).

Left Lower Lobe (LLL) collapse

• increased retrocardiac opacity, which silhouettes the left hemidiaphragm.
• On the lateral view, the left hemidiaphragm outline is lost posteriorly and the lower thoracic vertebrae appear denser than normal.

The video below demonstrates thelobar classification of atelectasis on a radiograph:

Clinical Implications

Following are the clinical implications of atelectasis

• Decreased lung compliance
• Hypoxemia
• Increased pulmonary vascular resistance (PVR)
• Inflammation as a local tissue biologic response
• Local immune dysfunction
• Damage of the alveolar-capillary barrier
• Potential loss of lung fluid clearance
• Increased lung protein permeability
• Susceptibility to infection
• Impaired penetration of antibiotics into lung tissue
• Factors that can initiate or exaggerate lung injury
• Acute respiratory failure.

Clinical Presentation

The signs and symptoms of atelectasis are often non-specific:

• Chest pain

• Shortness of breath

• Shallow breathing pattern

• Reduced chest expansion

• Increased respiratory rate

• Increased work of breathing

• Reduced breath sound on the ipsilateral side of auscultation. In cases of the upper lobe atelectasis, bronchial sounds may be heard, because of the proximity to the major airways.

• Hypoxia/hypoxemia

Diagnosis

• Chest X-ray
• Bronchoscopy
• CT Scan
• Ultrasound

Prevention

• It can be prevented by avoiding general anesthesia.
• The use of continuous positive airway pressure (CPAP), low tidal volumes, lowest possible FiO2 during induction and maintenance, Positive end-expiratory pressure (PEEP), and lung recruitment maneuvers will help in preventing atelectasis at the point when the use of general anesthesia is unavoidable.
• Early mobilization.
• adequate pain control.
• minimizing parenteral opioid administration.

Management

Management of atelectasis depends upon the duration and severity of the condition, from non-invasive intervention ( chest physiotherapy and pharmacological agents) to invasive treatment (bronchoscopy) can be opted according to the individual's state of health.

Physiotherapy Management

Different physical therapy interventions have shown to be beneficial in the resolution of atelectasis. Physical therapy treatment can also be used as a preventative or prophylactic measure before surgery.

The table below contains the different physical therapy treatment options in patients with atelectasis.

Physical Therapy Treatment
Airway clearance techniques	Suctioning of respiratory secretions. Percussion and vibration therapy. Positive end-expiratory pressure. Active cycle of breathing technique. Postural drainage. Chest high-frequency oscillations (CHFO) can be delivered via The Metaneb System. Mechanical insufflation and exsufflation. Manual lung hyperinflation.
Breathing exercises	Incentive spirometry Sustained maximal inspiration Intermittent positive pressure breathing
Positioning	Kinetic Therapy Turning side to side Prone positioning
Early mobilization	Sitting out of bed Standing on the first postoperative day, Walking a short distance in the room or corridor on the second postoperative day

The Video below demonstrates on the use incentive spirometer:

The Video below demonstrates on different chest physiotherapy treatment options in pediatric population:

Non-conservative Management

Flexible bronchoscopy can be used for both diagnosing and treating a patient with atelectasis. It is a safe mode of treatment for lung collapse. It can be used under the following circumstances:

1. lobar atelectasis from retained secretions with an air bronchogram pattern that is visible only to the level of the segmental bronchi; (2)
2. when standard chest physiotherapy has been administered properly for retained secretions without positive results;
3. (3) life-threatening near- or whole-lung atelectasis;
4. (4) when a symptomatic patient is unable to undergo vigorous respiratory therapy treatments from chest trauma, unstable vertebral fractures, extensive burns, smoke inhalation, neuromuscular diseases, etc.; and
5. (5) when an important diagnostic question exists.

Clinical Bottom Line

Atelectasis is one of the most common respiratory complications in the perioperative period, and it may contribute to significant morbidity and mortality, including the development of pneumonia and acute respiratory failure. Prevention of atelectasis is vital to improving patient outcomes in the postoperative period. Despite employing these strategies, atelectasis is not always preventable and, therefore, early recognition and treatment are equally important.