Using the standard formula for uncuffed endotracheal tube (ETT) sizing in children, the appropriate ETT internal diameter for a 6-year-old child is:

• A 4.0 mm
• B 4.5 mm
• C 6.0 mm
• D 5.5 mm ✓

Explanation

For uncuffed ETT in children: internal diameter (mm) = (age in years / 4) + 4. For a 6-year-old: (6/4) + 4 = 1.5 + 4 = 5.5 mm. For cuffed ETT, one size smaller is used: (age/4) + 3.5 = 5.0 mm for a 6-year-old. The uncuffed formula yields 5.5 mm. Always have a tube 0.5 mm larger and smaller available. The chosen uncuffed tube should allow an audible leak at 20–25 cmH2O, confirming that subglottic pressure is not excessive at the cricoid ring, which is the narrowest point in the paediatric airway.

Reference: Morgan & Mikhail's Clinical Anesthesiology, 6th ed.

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Written and medically reviewed by the StethoPrep medical team.