Atelectasis

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 there is collapse of lung tissue (parenchyma) with loss of volume. The word "parenchyma" signifies the functional units, the alveoli, of the lungs. Atelectasis describes involvement of relatively smaller units (of alveoli). When larger units of lung parenchyma is involved it is called "collapse" (or collapsed lung), which is essentially just a larger atelectasis. Atelectasis does not involve the airways.

The loss of volume leads 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%, with up to 20 - 25% of normal lung noted to be either poorly aerated or atelectatic on CT during anesthesia
• 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.Atelectasis was found to increase with an increase in BMI for both normal and overweight patients.

Classification

It can be classified as follows

1. pathophysiological mechanism (e.g., compressive atelectasis, absorption atelectasis, surfactant impairment atelectasis)
2. the amount of lung involved (e.g., lobar, segmental, or subsegmental atelectasis)
3. the location (i.e., specific lobe or segment location).

Pathophysiology

Following table comprises the classification of atelectasis based on pathophysiologic mechanism

Pathophysiologic Mechanism	Pathogenesis	Associated Types of Atelectasis	Cause
Compression of Lung Tissue	When there is an imbalance of net forces across an alveolar wall, it causes the alveoli to collapse. this mechanism of atelectasis causes the lung tissue to compress.	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 there is a complete occlusion of the airway, the alveolar gas can only exit via the bloodstream and not the alveolar unit, this obstruction can cause atelectasis. The second and perhaps more important mechanism of gas resorption may occur due to the ventilation/perfusion mismatch in certain areas of the lung. If the alveolar oxygen increases because of the increased inspired oxygen concentration and the nitrogen does not, uptake will be high resulting in less alveolar splinting and decreased 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	Deficiency of acquired dysfunction(e . g ., for premature neonates) can result in lacking surfactant capacity. Surfactant reduces alveolar surface tension, stabilising the alveoli and preventing collapse. When inactivated, decreased expansion of the alveoli can occur as a result of increased local surface tension causing a reduction in resting lung volume globally.	Adhesive atelectasis	Hyaline Membrane Disease COVID-19 Acute Respiratory Distress Syndrome (ARDS) Pneumonia Pulmonary Edema Almost Drowning General Anesthesia

Patterns of Collapse

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

Complete Collapse

The white out (complete opacification of a hemithorax) can be seen in complete lung collapse. This appearance can be confused with a large pleural effusion, but the mediastinal shift towards a collapsed lung can distinguish it from pleural effusion where the shift is in the opposite direction of the pathology.

Lobar Collapse

Characteristic features associated with individual lobar collapse are as follows:

Right upper lobe (RUL) collapse

• Elevation of the right hilum
• Elevation of the minor fissure.
• Minor and major fissures may be visible on the lateral view.
• Golden S sign is present (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.
• In a posterior -anterior view, the loss of silhouette of the right heart border can be seen.
• A wedge-shaped opacity can be seen on the lateral view as the result of right horizontal and oblique fissures moving towards each other.

Right lower lobe (RLL) collapse

• Triangular opacity can be seen alongside the right heart border.
• The right hemidiaphragm may appear elevated because of the obliteration.
• The right heart border is clearly seen.
• Loss of the right hemidiaphragm outline posteriorly and denser lower thoracic vertebrae can be observed on the lateral view.

Left upper lobe (LUL) collapse

• It appears as a veil-like opacity because of the absence of minor fissure, stretching out from the hilum and disappearing inferiorly.
• The major fissure is seen displaced anteriorly and the lower lobe is hyper-expanded on the lateral view.
• Luftsichel sign is present (hyper-expanded superior segment of the left lower lobe).

Left Lower Lobe (LLL) collapse

• Increased retrocardiac opacity is seen which shadows the left hemidiaphragm.
• Loss of the Left hemidiaphragm outline posteriorly and denser lower thoracic vertebrae can be observed on the lateral view.

The video below demonstrates the lobar 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

Following video explains the interpretation of the chest x-ray:

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 (to limit absorption atelectasis) 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 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: It is defined as the continuous turning of a patient slowly along the longitudinal axis to ≥ 40° onto each side, using a specialized bed. 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. When the retained secretions with an air bronchogram pattern are present only to the extent of segmental bronchi causing lobar atelectasis.
2. when standard chest physiotherapy has been failed to produce a positive outcome.
3. Life-threatening partial- or complete-lung atelectasis
4. When vigorous chest therapy is not favorable for the patient or contraindicated for example individuals with chest trauma, unstable vertebral fractures, extensive burns, smoke inhalation, neuromuscular diseases, etc.
5. when there is a question in diagnosing the patient.

Following video shows how bronchoscopy is performed to remove an inhaled foreign body:

Clinical Bottom Line

Atelectasis is a pathology that often occurs secondary to an underlying condition or as a postoperative complication and can be significantly morbid or mortal. There is consensus in the literature whether or not it is always preventable but there are different conservative and non-conservative approaches that have shown to be effective in preventing and treating atelectasis.