During thoracentesis, a catheter is inserted into the pleural space to drain the air or fluid collected inside. Before performing thoracentesis, the provider must determine which side of the chest is affected. The insertion site for aspirating air from a pneumothorax is higher on the thorax than the insertion site for aspirating the fluid from a pleural effusion. 

When performing thoracentesis for a pneumothorax, the clinician marks either the fourth intercostal space at the anterior axillary line or the second intercostal space at the mid-clavicular line. The baby is positioned with the affected side up. Since air rises, the trapped air is displaced superiorly. 

When draining a pleural effusion, the clinician marks the fifth or sixth intercostal space at the posterior axillary line. The baby is positioned supine to allow gravity to displace the pleural fluid posteriorly.

Once the appropriate insertion site is marked, the site is cleaned with an antiseptic solution, and sterile towels are placed around the site.

Thoracentesis is performed with an 18- or 20-gauge percutaneous catheter. The catheter is inserted perpendicularly to the skin and on top of the rib. Since vessels and nerves run below the rib, inserting the catheter in the rib’s superior aspect protects the blood vessels and nerves from iatrogenic trauma. 

• To evacuate air: the catheter is directed superiorly relative to the patient. 
• To evacuate fluid: the catheter is directed inferiorly relative to the patient. 

After entering the pleural space, the provider:

• Removes the needle.
• Connects a large syringe (preferably 20–60 mL) to the catheter via a 3-way stopcock. 
• Opens the stopcock between the catheter and syringe.
• Drains air or fluid.
• Closes the stopcock once adequate air or fluid has been drained.
• Empties the syringe.

Air or fluid should continue to be removed until the baby’s situation has improved. The fluid sample can be sent to the lab for pathologic study and documentation. An X-ray should be ordered to ensure that the pleural space is empty of air or fluid.