How should you estimate endotracheal tube depth in adults?

• A. Depth should be about 1-2 cm below the carina.
• B. Tip about 2-3 cm above the carina; at the teeth about 21-23 cm in women and 23-25 cm in men; verify with capnography and radiography when available.
• C. Depth at the level of carina.
• D. Depth is not important.

Answer: (B)

The main concept tested is placing the endotracheal tube at the correct depth so the tip sits safely in the trachea and ventilates both lungs. For adults, aim for a depth about 2–3 cm above the carina, with a practical external reference at the teeth: roughly 21–23 cm in women and 23–25 cm in men. Verifying placement with capnography (to confirm tracheal placement by detecting exhaled CO2) and radiography when available confirms the tube isn’t too shallow or too deep.

This depth range minimizes the risk of mainstem bronchus intubation (too deep, which can ventilate only one lung) and reduces the chance of accidental extubation or tube movement causing loss of airway. Placing the tip at or near the carina is unsafe and can cause airway injury or single-lung ventilation. Saying depth isn’t important is incorrect because precise depth is essential for safe, effective ventilation.

So the best approach combines the 2–3 cm above the carina guideline, the teeth-based measurements, and confirmation with capnography and imaging when possible.