Atelectasis J98.1

In 1963, Bendixen et al. were the first to show that general anesthesia with mechanical ventilation can lead to a deterioration in intraoperative oxygen saturation (Zeng 2022).

Atelectasis is defined as partially airless lung tissue that shows no inflammatory changes (Herold 2023).

Atelectasis is divided etiologically into primary and secondary atelectasis (Herold 2023). For more details, see "Etiology".

Atelectasis can be complete or only partial, as so-called dystelectasis. It can be permanent or temporary, congenital or acquired (Mathis 2007).

Atelectasis is very common in intensive care patients. After upper abdominal surgery, for example, they occur in up to 30 % of patients and in over 90 % of thoracic operations (Schaefer-Prokop 2009).

• Primary atelectasis:

These are found exclusively in premature or newborn infants (Herold 2023).

• Secondary atelectasis:

Secondary atelectases are those that occur in an already ventilated area of the lung. A distinction is made between:

• Obturation atelectasis: These are also known as resorption atelectasis and are the result of bronchial obstruction, e.g. due to bronchial carcinoma, a mucus plug or foreign bodies (Herold 2023).
• Compression atelectasis: They are caused by
  • compression of the lung tissue from the outside, predominantly in the form of basal squamous atelectasis. They are found, for example, with reduced or abolished diaphragmatic breathing, pleural effusions or diaphragmatic elevation (Herold 2023).
  • postoperative after abdominal surgery: risk factors include obesity, smoking, patient age, diaphragmatic dysfunction, lung disease, intra-abdominal hypertension, general anesthetic drugs such as opioids, sedatives, hypnotics, regional anesthesia, neuromuscular blockers and antagonists, blood transfusions, positioning during surgery (Lagier 2022)
  • after a pulmonary embolism
  • Middle lobe syndrome: Middle lobe syndrome can occur with atelectasis of the middle lobe due to e.g. enlarged lymph nodes, tuberculosis (Herold 2023)
• Relaxation atelectasis: This can be caused by a pneumothorax (Herold 2023).

Pathomorphologically, a distinction is made between compression atelectasis and resorption atelectasis, the latter also referred to as obstructive atelectasis (Mathis 2007).

• Compression atelectasis:

This can occur if, for example, the intrapleural pressure exceeds the pressure of the outside air due to an accumulation of fluid. The limit is usually at an effusion of more than 2 liters (Mathis 2007). For more details see compression atelectasis.

• Resorption atelectasis:

Resorption atelectasis, on the other hand, can occur when a bronchus is displaced from its supply area due to external compression or endobronchial obliteration. A distinction is made here between a central and a peripheral form.

• Central form:

Central bronchial obstruction can be caused by endobronchial obstruction, e.g. bronchial carcinoma or inhalation of foreign bodies, or by extrabronchial changes such as enlarged lymph nodes (Mathis 2007).

• Peripheral form:

In peripheral bronchial obstruction, the focus is more on inflammatory mucus plugs, which lead to smaller bronchial branches being displaced (Mathis 2007).

The formation of an atelectasis leads to

• impaired blood flow to the lung parenchyma, resulting in a lack of oxygen (Mathis 2007)
• This leads to non-oxygenated blood being passed into the pulmonary veins. Depending on the extent of the non-ventilated part, this leads to hypoxia (Schaefer-Prokop 2009)

Due to gravity and reduced respiratory excursions after surgery, atelectasis is found particularly in the dorso-basal lung sections, and is significantly more common on the left than on the right (Schaefer-Prokop 2009).

• Dyspnea (Krombach 2015)
• Hypoxemia
• tachypnea
• Cyanosis
• Possibly pain in the thorax (Kahl- Scholz 2018)

• Medical history
• Physical examination: Atelectasis is characterized by
  • weakened vocal fremitus
  • weakened breath sound
  • Bronchophony positive
  • Tapping sound attenuation (Herold 2023)

• Sonography of the lungs:

This may show evidence of resorption atelectasis in the case of airway obstruction or compression atelectasis in the case of e.g. relevant pleural effusion (Herold 2023).

In the case of resorption atelectasis, sonography shows a low-echo image similar to liver tissue. They are smoothly bordered towards the ventilated lung. The bronchi are recognizable as echogenic, ribbed reflex bands. The atelectatic tissue is not re-aerated during inspiration. If there is post-stenotic pneumonia in the context of resorption atelectasis, complex structures such as small abscesses or melting zones may form (Seitz 2000).

In compression atelectasis , there is usually a blurred boundary to the air-containing lung tissue. The atelectatic part of the lung is almost always surrounded by fluid (Mathis 2007). The atelectasis floats concavely in the effusion in a breath-dependent manner and is partially ventilated again during inspiration (Seitz 2000). If the effusion continues to increase, the atelectasis only appears as a narrow, echo-like crescent, also referred to as "squamous atelectasis" (Michels 2014).

• Computer tomography

CT is a recognized method for the diagnosis and quantification of atelectasis. Attenuation values of - 100 to + 100 Hounsfield units correspond to an aerated lung. Further signs are: displacement of the interlobar fissures, mediastinum, heart and pulmonary hilus towards the collapsed area, ipsilateral diaphragmatic elevation, overinflation of the remaining aerated lung and narrowing of the intercostal space (Lagier 2022).

• Magnetic resonance imaging

MRI is also used to diagnose and quantify atelectasis. T2-weighted MRI can be used to identify tissue containing water in particular (Reimer 2003).

• Chest X-ray

A chest X-ray in 2 planes shows signs of volume reduction (Herold 2023). In supine radiographs, atelectasis can be recognized less by the reduction in transparency and more by a displacement of the lung fissures (Schaefer-Prokop 2009).

Direct signs of atelectasis are:

• Displacement of the interlobar septum
• Basal strip or plate atelectasis
• Local reduction in transparency with biconcave borders (Herold 2023)

Indirect signs of atelectasis are:

• Displacement of hilar or mediastinum
• Absence of bronchopneumogram
• Diaphragmatic protrusion (Herold 2023)

In the early phase of atelectasis, a protein-rich fluid can be detected intra-alveolar. As the disease progresses, macrophages migrate and lymphocytic infiltration occurs. Prolonged atelectasis eventually leads to shrinkage of the parenchyma with fibrous induration of the tissue (Mathis 2007).

A pneumonia in particular must be differentiated in the differential diagnosis (Herold 2023), as well as a pulmonary embolism if necessary (Kahl-Scholz 2018).

Atelectasis can lead to the following complications:

• Abscess
• infection
• Respiratory insufficiency (Herold 2023)
• Development of bronchiectasis in approx. 40 % of cases
• Evidence of hemorrhagic or necrotic foci (Mathis 2007)

Causal therapy by e.g.:

• Aspiration of a mucous plug
• Removal of any tumor stenosis that may be present
• Removal of any foreign body that may be present (Herold 2023)

Non-invasive positive pressure ventilation can also be used for regional atelectasis (Kasper 2015).

If there are indications of additional inflammatory changes such as pneumonia or abscess, initiate antibiotic treatment quickly (Herold 2023).

A segment or flap resection is required in the case of a chronic form (Herold 2023).

Atelectasis can be acute or chronic (Herold 2023). It is not known exactly when atelectasis becomes irreversible. From a period of 6 - 8 weeks, it is referred to as chronic atelectasis (Hoffmann-Lentze 2014).

The prognosis of atelectasis depends on the cause or underlying disease (Galanski 2010).

Rapid p. o. mobilization, respiratory therapy and respiratory gymnastics are recommended for the prophylaxis of postoperative compression atelectasis (Herold 2023).

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