Age-based formulae have been widely used to predict appropriate size of the endotracheal tube (ETT) in children. The objective of this study was to evaluate the effectiveness of formula (internal diameter (ID) (mm) = [age in years + 16]/4) in Korean children.

Ninety children under 8 years who required intubation with the regular uncuffed ETT were included in the study. Appropriate sizes were to permit a gas leak at 10-25 cmH₂O with positive pressure ventilation. Initial intubation was tried with predetermined size and ETT was adjusted to meet this guideline.

A range of three tubes around the predicted tube size covered 79 cases (88%), whereas one size predicted by the formula applied to only 29 cases (32%). The selection of ETT which is 0.5 mm larger than the predicted size could allow appropriate intubation in 41 (45.6%) patients.

The age-based formula (ID (mm) = [age in years + 16]/4) could predict the appropriate tube size in less than one third our patients. Therefore, we recommend three sizes be available before endotracheal intubation.