Where is a chest tube typically inserted in adults?

• A. 2nd intercostal space at the midclavicular line
• B. 4th-5th intercostal space in the midaxillary line
• C. 7th intercostal space in the posterior axillary line
• D. 9th intercostal space in the anterior axillary line

Answer: (B)

Accessing the pleural space for drainage in adults is best done in the midaxillary line at the 4th–5th intercostal space, inside the safe triangle. This location provides direct entry to the pleural cavity while staying away from the heart, major vessels, and abdominal organs, and it aligns with the highest point where fluid or air tends to collect in the chest. The tube is inserted just above the superior border of the rib to avoid the intercostal vessels and nerves that run along the inferior border.

Other sites are less optimal: the second intercostal space at the midclavicular line is typically used for emergent needle decompression of a tension pneumothorax, not for a formal chest tube. The seventh intercostal space at the posterior axillary line is too low and posterior to be as effective for drainage and carries greater risk of injuring surrounding structures. The ninth intercostal space at the anterior axillary line is even lower and increases the risk of injuring abdominal organs while providing poorer access to the pleural space.