In atelectasis, the alveoli in the lung collapse in on themselves and can no longer perform their function. Atelectasis can affect a portion of the lung or the whole lung. Treatment varies, with respiratory physiotherapy and endoscopic treatment being the most commonly used treatments. Atelectasis can be scarring, obstructive (the most common), rolling, adhesive or passive.

1. What is atelectasis?

In the respiratory system, air follows a specific path. The air passes through the nose or mouth, the pharynx, the larynx, the trachea, the bronchi, the bronchioles and then the pulmonary alveoli. The pulmonary alveoli are small air-filled pockets at the end of the bronchioles, of which there are several million in an adult. The alveolus is richly vascularised: all around it there is an important blood network allowing gas exchanges.

The blood is loaded with carbon dioxide in the vicinity of the tissues and supplies them with oxygen. This so-called "non-haematosed" (i.e. non-oxygenated) blood will then return to the lungs where the carbon dioxide will be exhaled and the blood will be charged with oxygen, becoming haematosed again. The blood capillaries and the alveoli are separated by a very thin barrier, called the alveolar-capillary barrier, which is made up of a film called surfactant. Surfactant is a liquid composed of phospholipids and phosphoproteins and is secreted by specific alveolar cells called pneumocytes II. Surfactant acts as a surfactant (decreasing the surface tension of the alveoli) and helps to keep the alveoli open by preventing collapse. In addition to surfactant, deep breathing and coughing prevent the alveoli from collapsing. When alveoli collapse due to lack of ventilation while blood flow is normal, it is called atelectasis. Airflow blockage occurs when the bronchi and bronchioles become blocked and there is an imbalance in the ventilation/perfusion ratio. Atelectasis may involve a lobe, a lung segment or the entire lung.

2. What are the symptoms of atelectasis?

Atelectasis is usually an asymptomatic condition if it is not extensive unless there is pneumonia or hypoxaemia (low oxygen levels in the blood). Pneumonia may trigger breathing difficulties or pleural pain. Pneumonia may also be accompanied by a dry cough, fever, or a change in general health. In the case of severe atelectasis, signs such as dyspnoea (breathing difficulties), chest pain or respiratory failure may occur. Breathing may also become rapid and shallow, and the heart rate may also increase. Sometimes the skin may turn blue due to a lack of oxygen.

Atelectasis in newborns can be particularly severe, as the alveoli in the lungs only unfold at the last moment. Surfactant in the foetus does not really develop until the 32nd week of pregnancy (but there are variations between children) according to the French National Institute for Health and Medical Research (Inserm). If a surfactant is insufficient and ventilation is impaired, then the lungs collapse and this causes inflammation and pulmonary oedema, leading to hypoxia in the newborn (and respiratory distress syndrome). Premature newborns are more likely to suffer from atelectasis, as they have not had time to make enough surfactant.

3. What causes atelectasis?

There are different types of atelectasis: cicatricial atelectasis, which is related to scarring of the parenchyma caused by interstitial disease or necrotizing pneumonia, obstructive atelectasis, which is the most common, coiling atelectasis, in which there are comet-shaped blood vessels, adhesive atelectasis and passive atelectasis. Thus, there are several factors that can trigger atelectasis. The vast majority of atelectasis is triggered by obstruction of the pulmonary alveoli. Stenosis (narrowing) of inflammatory or tumour origin, a foreign body or broncholithiasis may be the cause of the cessation of ventilation in certain pulmonary territories. Some atelectasis may be non-obstructive and related to extrinsic bronchial compression, such as adenopathy or lymphadenopathy (e.g. a lymph node may swell to a very large volume), or compression by an effusion (pleural effusion is an accumulation of fluid in the pleural cavity).

Surfactant damage can also cause atelectasis, as some conditions can reduce surfactant, such as hyaline membrane disease in children. Atelectasis can also occur after surgery, especially if an endotracheal tube was used. During surgery, the patient is immobilised and anaesthetised, so the chest cavity tends to collapse, and sedation and anaesthesia reduce breathing and coughing, so they are risk factors for atelectasis. It is estimated that 90% of anaesthetised patients will develop atelectasis of varying degrees (5 to 20% of total lung volume) according to the Bordeaux University Hospital. Overweight or obese people are also at greater risk of atelectasis (because of the volume of the abdomen which can press on the diaphragm).

4. When to seek help for atelectasis?

Atelectasis is usually asymptomatic, but when signs of respiratory distress occur, it is very important to seek medical attention. In case of major surgery or surgery that required intubation, respiratory signs should be monitored. Continued atelectasis can become complicated and increase the risk of developing a lung tissue infection.

5. What tests should be done to diagnose atelectasis?

Atelectasis, when large enough, may give visible signs on clinical examination, such as asymmetric ventilation. When the doctor performs percussion, a dull sound called dullness is heard. The vesicular murmur (breathing sound) is also diminished. X-rays can detect direct signs of atelectasis, such as homogeneous opacification, or indirect signs, such as tracheal and mediastinal traction, costal pinching or homolateral ascension of the diaphragmatic dome. Magnetic Resonance Imaging (MRI) may also be of interest to study more precisely the respiratory structures involved.

6. What are the treatments for atelectasis?

Treatment of the cause of atelectasis is essential. Respiratory obstruction can be treated by endoscopic fibroscopy for example or bronchoscopy. These techniques allow the mucous plugs to be aspirated. Respiratory physiotherapy exercises can be used to treat congestion, hypersecretion of mucus retention. Aerosol therapy may be useful for thick sputum or difficult expectoration. Incentive spirometry is also useful. The physiotherapist may also perform manual de-cluttering techniques. In all cases, coughing and deep breathing should be maximised to combat atelectasis. In the event of complications or pneumonia, oxygen therapy and antibiotic treatment may be prescribed. Pneumonia requires rest in a semi-seated position and very good hydration. Respiratory physiotherapy may also be prescribed for pneumonia. Usually, the lung tissue returns to normal without further complications.

7. How can atelectasis be prevented?

Some atelectasis can be prevented by following some simple rules:

Stopping smoking is important in case of surgery, this should be done at least 6-8 weeks before surgery, according to the MSD Manual.
After each operation, it is necessary for patients to be able to walk around quickly, patients should avoid lying down for more than two hours and should sit up as soon as possible.
Patients with respiratory problems should be given special care before surgery. For example, people with chronic respiratory diseases such as COPD (Chronic Obstructive Pulmonary Disease) should have their treatment optimised for the upcoming operation.
During surgery of the chest or abdomen, it is important to warm and humidify the insufflated gases in order to reduce the risk of the patient suffering from mucus plug formation. This is a real bronchial cleansing that must be performed.
After surgery, it is important to take time to take deep breaths.
During surgery, the use of sedatives should be kept to a minimum.
Pre-oxygenation (breathing pure oxygen by the patient before intubation) before surgery seems to protect the airway from atelectasis in an interesting way.
If preterm delivery is planned, then corticosteroids can be given (especially between 24 and 34 weeks of amenorrhoea) according to the Merck Manual, which will stimulate surfactant production and avoid or reduce the severity of the respiratory distress syndrome associated with atelectasis.

Sources:

Inserm, Bordeaux University Hospital, Le Manuel MSD, Le Manuel Merck, Delplanque formation, Ferhat Abbas University of Medicine, CHU Vaudois, Radeos