Atelectasis

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Introduction

Atelectasis describes a state of the collapsed and non-aerated regions of the lung parenchyma. It results from the partial or complete, reversible collapse of the small airways leading to an impaired exchange of CO2 and O2 - i.e., intrapulmonary shunt.

Epidemiology

• Atelectasis does not preferentially affect either sex.
• There is also no increased incidence of atelectasis in patients with COPD, asthma, or increased age.
• It is more common in patient's who recently underwent general anesthesia, with the incidence being as high as 90% in this patient population.
• It is most commonly seen in the post-operative patients whose breathing mechanism is impacted by the procedure, pain, and prolonged recumbency.
• Less commonly, atelectasis is seen in people with conditions signify chronic sputum production or airway obstruction, such as COPD, bronchiectasis, and cystic fibrosis.

• Obese and/or pregnant patients are more likely to develop atelectasis due to cephalad displacement of the diaphragm

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 sub segmental 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 blood stream. 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 C 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

Collapse of an entire lung leads to 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
• Right middle lobe (RML) collapse
• Right lower lobe (RLL) collapse
• Left upper lobe (LUL) collapse
• Left Lower Lobe (LLL) collapse

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

Physiotherapy

Most atelectasis that appears during general anesthesia leads to transient lung dysfunction that resolves within 24 hours after surgery.  Nevertheless, some patients develop significant perioperative respiratory complications that can lead to increased morbidity and mortality if not treated.

• Atelectasis is preventable through avoidance of general anesthesia, early mobilization, adequate pain control, and minimizing parenteral opioid administration.
• Changing position from supine to upright increases FRC and decreases atelectasis.
• Encouraging patients to take deep breaths, early ambulation, incentive spirometry, use of Positive Expiratory Pressure (PEP) Device, chest physiotherapy, tracheal suctioning (in intubated patients), and/or positive pressure ventilation has been shown to decrease atelectasis.
• Prophylactic measures, such as incentive spirometry, should be taught and instituted before surgery and continued on an hourly basis following surgery until discharge to obtain the maximal benefit.

Airway clearance techniques

As atelectasis can be caused by blockage of bigger airways, physiotherapy treatment to assist in airway clearance can improve atelectasis. Examples of airway clearance technique include:

• Active cycle breathing techniques
• Supported cough
• Positioning
• Postural drainage

Breathing exercises:

• Incentive spirometry can be useful for treating or preventing atelectasis in post-operative patients, it gives visual feedback to the patient on how he is performing. Consists of a deep and slow maximal inspiration, through the mouth, followed by a post-inspiratory pause and exhalation up to functional residual capacity.
• Sustained maximal inspiration (SMI): is the same as incentive spirometry but it does not require material . SMI is often used to prevent and manage atelectasis in abdominal and thoracic surgery patients. Its effects are often compared with incentive spirometry, and interestingly evidence has shown similar effects in SMI in improving breathing patterns, chest expansion, and thoracoabdominal asynchrony. Hence, it could be an alternative where incentive spirometry is unavailable.

Early mobilization

This fits in the picture of both post-operative patients and populations with acute respiratory conditions, such as acute pneumonia. When a patient is medically stable enough, the physiotherapist should assist with mobilization in accordance with the patient's status. Early mobilization, includes sitting position and ambulation either with/without aids (onset <48h after surgery). It is believed that early mobilization results in increased lung volume, preventing therefore of atelectasis.

Complications

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.