What is pneumomediastinum and its pathophysiology?

From the Guidelines

Pneumomediastinum is the presence of air or gas in the mediastinum, which is the central compartment of the thoracic cavity containing the heart, major blood vessels, trachea, esophagus, and other vital structures, and its pathophysiology primarily involves air leakage from the lungs, airways, or digestive tract into the mediastinal space, often due to increased alveolar pressure or trauma. The condition can arise from various causes, including airway perforation, which may occur after difficult intubation, as noted in the Difficult Airway Society guidelines for the management of tracheal extubation 1.

Key Points

• Pneumomediastinum can be characterized by symptoms such as severe sore throat, deep cervical pain, chest pain, dysphagia, and painful swallowing, especially if it progresses to mediastinitis, an infection of the mediastinum 1.
• The pathophysiology involves the dissection of air along bronchovascular sheaths toward the mediastinum, a process that can be facilitated by increased intrathoracic pressure or alveolar rupture.
• Common causes include trauma, excessive coughing, vomiting, asthma exacerbations, mechanical ventilation with high pressures, and strenuous physical activities that increase intrathoracic pressure.
• The air can further dissect into surrounding tissues, potentially causing subcutaneous emphysema in the neck and chest wall.
• Most cases of pneumomediastinum are benign and self-limiting, requiring only conservative management with rest, pain control, and oxygen therapy.
• However, tension pneumomediastinum, though rare, can compress vital structures and requires immediate decompression.

Clinical Considerations

• Patients should be informed about the symptoms of mediastinitis and advised to seek medical advice should they occur, as early detection and treatment are crucial for preventing complications 1.
• A high index of suspicion is necessary, especially in patients with a history of difficult intubation or airway trauma, as pharyngeal and oesophageal injuries can be difficult to diagnose and may present with pneumomediastinum or surgical emphysema in only 50% of cases 1.

From the Research

Definition of Pneumomediastinum

• Pneumomediastinum is a condition in which air is present in the mediastinum, which can result from physical trauma or other situations that lead to air escaping from the lungs, airways, or bowel into the chest cavity 2.
• It is characterized by the accumulation of air within the mediastinum, which can develop spontaneously or as a secondary condition due to trauma or iatrogenic causes 3.
• Pneumomediastinum is a rare situation and occurs when air leaks into the mediastinum, which can be confirmed via chest X-ray or CT scanning of the thorax 2.

Pathophysiology of Pneumomediastinum

• The pathophysiology of pneumomediastinum involves the escape of air from the lungs, airways, or bowel into the chest cavity, which can lead to increased intrapulmonary pressure on venous flow to the heart 2.
• The condition can also be characterized by the shortness of breath that is typical of a respiratory system problem, and it is often recognized on auscultation by a "crunching" sound timed with the cardiac cycle (Hamman's crunch) 2.
• The tissues in the mediastinum will slowly resorb the air in the cavity, so most pneumomediastinums are treated conservatively 2.

Clinical Features and Diagnosis

• The main symptom of pneumomediastinum is usually severe central chest pain, and other symptoms include laboured breathing, voice distortion, and subcutaneous emphysema, specifically affecting the face, neck, and chest 2.
• The diagnosis of pneumomediastinum can be confirmed via chest X-ray or CT scanning of the thorax, and the condition can be evaluated using computed tomography to identify patients at high risk for aerodigestive injury 4.
• The study by 3 found that among symptoms, 50.7% of patients experienced dyspnea, and 49.3% presented with chest pain, while symptoms like cough, fever, nausea, vomiting, and swallowing difficulty were reported in varying proportions.

Treatment and Management

• The treatment of pneumomediastinum usually involves conservative management, as the tissues in the mediastinum will slowly resorb the air in the cavity 2.
• However, in some cases, thoracostomy tube insertion or surgical procedures may be required, especially in patients with a history of trauma or those who develop complications such as mediastinal organ injury 3, 5.
• The study by 5 found that predictors of esophageal injury in patients with pneumomediastinum included instrumentation, pleural effusion, and vomiting, while previous instrumentation was the most significant predictor of airway injury.