From the Guidelines
The correct answer is c. Mediastinal shift. In a tension pneumothorax, air enters the pleural space but cannot escape, creating a one-way valve effect that causes increasing pressure within the affected hemithorax. This pressure pushes the mediastinum (heart and major vessels) away from the affected side toward the unaffected lung. On a chest x-ray taken in the emergency department before treatment, this mediastinal shift would be visible as a deviation of the trachea, heart, and other mediastinal structures away from the side of the pneumothorax. Other findings might include a completely collapsed lung on the affected side and hyperexpansion of the hemithorax, but the mediastinal shift is the most characteristic radiographic finding of tension pneumothorax. This shift occurs because the increasing pressure in the pleural space not only collapses the lung but also compresses the mediastinal structures, potentially compromising venous return to the heart and causing hemodynamic instability, which makes tension pneumothorax a life-threatening emergency requiring immediate decompression, as described in the management guidelines for tension pneumothorax 1. The use of chest radiographs in trauma patients, as discussed in the ACR Appropriateness Criteria for major blunt trauma 1, supports the importance of identifying mediastinal shift as a key finding in tension pneumothorax, despite the limitations of chest radiographs in detecting all types of thoracic injuries. While ultrasound can also be used to identify pneumothorax, as recommended by the European Society of Intensive Care Medicine 1, the characteristic mediastinal shift on a chest x-ray remains a critical diagnostic feature of tension pneumothorax. Key points to consider in the diagnosis of tension pneumothorax include:
- Clinical presentation with rapid deterioration, distress, and signs of compromised cardiopulmonary status
- Radiographic findings of mediastinal shift, lung collapse, and hyperexpansion of the hemithorax
- The need for immediate decompression to relieve the life-threatening pressure in the pleural space.
From the Research
Expected Features in Chest X-ray
- The expected feature in the chest x-ray of a patient with tension pneumothorax, such as Ms Everett, would be a mediastinal shift 2.
Rationale
- Tension pneumothorax is characterized by the accumulation of air in the pleural space, which can cause the mediastinum to shift away from the affected side 3, 4.
- A mediastinal shift is a classic sign of tension pneumothorax and can be seen on a chest x-ray 5, 6.
Other Options
- Symmetrical lung fields would not be expected in a patient with tension pneumothorax, as the condition typically causes uneven lung expansion 2.
- Dense cloudy opacities may be seen in cases of hemothorax or other conditions, but are not a characteristic feature of tension pneumothorax 4, 5.
- Blunting of the costophrenic angle may be seen in cases of pleural effusion, but is not a typical feature of tension pneumothorax 3, 6.