The most appropriate endotracheal tube size for a 6-year-old child is:

• A. 5.5 mm, uncuffed.
• B. 6.0 mm, cuffed.
• C. 4.5 mm, uncuffed.
• D. 5.0 mm, cuffed.

Answer: (A)

The size is determined using a simple age-based rule for uncuffed endotracheal tubes: internal diameter in millimeters equals (age in years divided by 4) plus 4. For a 6-year-old, that’s 6/4 + 4 = 5.5 mm. This size gives a good balance between a secure airway and minimizing trauma to the delicate pediatric airway, and it typically allows a small leak around the tube when the cuff is not inflated or is minimally inflated.

If a cuffed tube were chosen, many clinicians would select about 0.5 mm smaller, but the traditional uncuffed size for this age is 5.5 mm. An oversized tube risks airway injury and subglottic stenosis, while too small a tube can lead to increased airway resistance and poor ventilation. In any case, tube placement should be confirmed with clinical assessment and capnography, and cuff pressures (if a cuffed tube is used) should be monitored.