Table 3.

Formulae of subglottic diameter, mid-glottic and glottic transverse diameter to predict outer diameter of endotracheal tube size and the correlations among them (N = 95).

Formula to predict outer diameter	R (95% CI)	p-value*
5.7 + (subglotticmm/3)	0.45 (0.28, 0.60)	< 0.001
5.5 + (mid-glotticmm/2)	0.47 (0.29, 0.61)	< 0.001
5.7 + (glotticmm/4)	0.46 (0.28, 0.60)	< 0.001

Correlations	R (95% CI)	Difference (mm)**
Subglottic and mid-glottic diameter	0.50 (0.34, 0.64)	1.09 [0.72, 1.60]
Glottic and subglottic diameter	0.46 (0.28, 0.60)	1.82 [0.86, 2.34]
Glottic and mid-glottic diameter	0.89 (0.84, 0.93)	2.93 [2.45, 3.39]

CI confidence interval.

*Pearson's correlation.

**Median [interquartile range].