**Core Concept**
In cases of trauma leading to a contusion on the precordium, the clinical presentation of decreased breath sounds on one side, tracheal deviation to the opposite side, and normal heart sounds suggests the presence of a hemopneumothorax or a hemothorax. The first line of management involves stabilizing the patient and draining the air or fluid from the affected hemithorax.

**Why the Correct Answer is Right**
The correct answer is needle thoracocentesis, which involves inserting a needle into the pleural space to drain the fluid or air. This is often performed as an emergency procedure to relieve pressure on the lung and restore adequate ventilation. The choice of needle thoracocentesis as the first line of management is based on the principle of minimizing the risk of further injury while still providing immediate relief to the patient.

**Why Each Wrong Option is Incorrect**
**Option B:** Chest tube thoracocentesis is a more definitive procedure that involves inserting a chest tube to drain the pleural space. While it may be necessary in cases of severe trauma or persistent bleeding, it is not the first line of management due to the increased risk of complications and the need for more extensive surgical intervention.

**Option C:** Pericardiocentesis is a procedure used to drain fluid from the pericardial sac. While it may be necessary in cases of cardiac tamponade, the clinical presentation in this scenario suggests a hemopneumothorax or a hemothorax rather than cardiac tamponade.

**Option D:** Open surgery is a more invasive procedure that may be necessary in cases of severe trauma or persistent bleeding. However, it is not the first line of management due to the increased risk of complications and the need for more extensive surgical intervention.

**Clinical Pearl / High-Yield Fact**
In cases of trauma leading to a contusion on the precordium, the presence of decreased breath sounds on one side, tracheal deviation to the opposite side, and normal heart sounds suggests the presence of a hemopneumothorax or a hemothorax. Needle thoracocentesis is often the first line of management to relieve pressure on the lung and restore adequate ventilation.

**✓ Correct Answer: A. Needle thoracocentesis**