Using a too big or a too small size of an endotracheal tube in pediatric patients would result in tracheal injury or insufficient ventilation. Determining the appropriate endotracheal tube size is important because using an inappropriate size can cause complications. This study was performed to predict the appropriate endotracheal tube size by measuring the transverse diameter of the epiphysis of the distal radius under the assumption that the growth rates of cartilages in the entire body are close to each other.

Fifty-eight children aged 3 to 10 years who required general anesthesia were intubated with an uncuffed endotracheal tube. The tube size was considered to be appropriate when leaks occurred at inspiratory peak pressures between 10 to 25 mmHg. The transverse diameters of the epiphysis were measured with an ultra-sonogram at the distal radius and the proximal phalanx of the third finger and the fifth finger. Correlations and prediction probabilities of measurements were evaluated. The number needed to harm (NNH), which indicates the number of patients who need to be intubated for one patient who needs tube exchange, was investigated.

The Spearman's correlation coefficient between the endotracheal tube size and the epiphysis of the distal radius was 0.814, which was the biggest coefficient. For epiphysis of the proximal phalanx of the third finger and the fifth finger, the correlation coefficient was 0.704 and 0.701, respectively. If the Cole's formula was applied for selection of the tube size, the NNH would be 7.

The appropriate endotracheal tube size could be predicted by means of the epiphyseal transverse diameter of the distal radius rather than the circumference measurements of the phalanx.