A previously healthy 20-year-old man is admitted to a hospital with acute onset of left-sided chest pain. The electrocardiographic findings are normal but chest x-ray shows a 40% left pneumothorax. Treatment consists of which of the following procedures?

**Core Concept**
In a patient with a 40% left pneumothorax, the primary goal of treatment is to re-expand the lung and restore normal intrathoracic pressure. This is typically achieved through the insertion of a chest tube to drain air from the pleural space.

**Why the Correct Answer is Right**
A chest tube insertion, also known as thoracocentesis, allows for the evacuation of air from the pleural space, thereby re-expanding the lung and restoring normal intrathoracic pressure. This procedure is typically performed under local anesthesia and is considered the first-line treatment for a tension pneumothorax or large pneumothorax. The chest tube is connected to a suction device to facilitate the removal of air and any potential blood or fluid from the pleural space.

**Why Each Wrong Option is Incorrect**
**Option A:** The patient does not have a tension pneumothorax, which would require immediate decompression with a needle thoracostomy. Needle thoracostomy is a temporary measure and is not a definitive treatment for a large pneumothorax.
**Option B:** While oxygen therapy may be used to support the patient's respiratory status, it does not address the underlying cause of the pneumothorax.
**Option C:** Intercostal nerve blocks may be used for pain management, but they do not treat the pneumothorax itself.

**Clinical Pearl / High-Yield Fact**
In cases of trauma or respiratory distress, a chest x-ray should be performed urgently to rule out a pneumothorax. A pneumothorax can be classified as small (less than 20%), moderate (20-40%), or large (more than 40%).

**Correct Answer:** C. Chest tube insertion

✓ Correct Answer: D. Tube thoracostomy