A No. 6 endotracheal tube indicates which size?

A No. 6 endotracheal tube indicates which size?

• A. 6 mm internal diameter
• B. 6 mm external diameter
• C. 6 mm external circumference
• D. 6 mm internal circumference

Answer: (A)

Sizing of endotracheal tubes comes from the inner diameter of the airway lumen. The number printed on the tube denotes that internal lumen size in millimeters, not the outer diameter or the circumference. The outer diameter is larger because of wall thickness and the cuff, and it varies by manufacturer. Understanding this helps you predict ventilation: a larger lumen reduces resistance and makes ventilation easier, while a smaller lumen increases resistance and the work of breathing. So the label specifically reflects the internal diameter of the tube’s airway passage.

Sizing of endotracheal tubes comes from the inner diameter of the airway lumen. The number printed on the tube denotes that internal lumen size in millimeters, not the outer diameter or the circumference. The outer diameter is larger because of wall thickness and the cuff, and it varies by manufacturer. Understanding this helps you predict ventilation: a larger lumen reduces resistance and makes ventilation easier, while a smaller lumen increases resistance and the work of breathing. So the label specifically reflects the internal diameter of the tube’s airway passage.