Objective: To predict the proper depth of placement of endotracheal tubes, oral and nasal.
Material and Method: This was a prospective study of 100 patients who underwent general anesthesia with oral endotracheal intubation. The cuff of the endotracheal tube was placed 2 cm below the vocal cords. The positions of the endotracheal tube tip and the airway distances of the patients were measured by fiberoptic bronchoscope; OC = the distance from the right upper canine to the vocal cords, NC = the distance from the right external naris to the vocal cords and T = the distance from the vocal cords to the carina. The correlation between the airway distances and patient’s factors were analyzed. The proper depth of placement of the endotracheal tube was calculated with the formula OTT = OC+T-2, nasal endotracheal tube NTT = NC+T-2.
Results: The mean distance from the endotracheal tube tip to the carina was 3.0 + 1.48 cm (ranged 0.7-7.5 cm). The distance from the endotracheal tube tip to the carina of 86 from 100 patients was more than 2 cm. The mean OC was 9.79 + 1.27 cm. The mean NC was 15.00 + 0.84 cm. The mean T were 13.03 + 1.48 cm in males and 11.63 + 1.25 cm in females and it also related to the height of the person (Pearson correlation =
0.557, p value < 0.05). These distances did not relate to gender.
Conclusion: The predicted formula of the depth of the endotracheal tube as “Chula formula”; OTT = 4 + (Ht/10) cm (The distance from the right upper canine to the point which is 2 cm above the carina) NTT = 9 + (Ht/10) cm (The distance from the right external naris to the point which is 2 cm above the carina)

Keywords: Depth, Endotracheal tube, Thai patient