Estimation of the proper length of nasotracheal intubation by Chula formula.

OBJECTIVES To assess whether Chula formula can predict the proper length of nasotracheal intubation. MATERIAL AND METHOD This was a prospective study of 100 patients (50 males and 50 females) who underwent general anesthesia with nasotracheal intubation (number 8.0 for male and 7.0 for female) between December 2005 and March 2007. The Chula formula was used to calculate the length of endotracheal tube (ETT) at the right external naris = 9 + (body height/10) cm. After intubation, a fiberoptic bronchoscope was inserted into the ETT to measure the distance from the tip of ETT to the carina and the distance from the upper border of the cuff of ETT to the vocal cords. RESULTS The mean length of nasotracheal tube at the right external naris calculated by Chula formula was 25.4 cm in males and 24.4 cm in females. The mean distance from the tip of ETT to the carina was 3.9 cm in males and 3.1 cm in females. The mean distance from the upper border of the cuff of ETT to the vocal cords was 2.6 cm in males and 3.0 cm in females. Ninety-three patients with upper border of the cuff of ETT had it placed at least 2 cm below the vocal cords, and in seven patients, the distance from the tip of ETT to the carina was found to be 1 to 1.9 cm. In every patient, it was found that the tip of ETT was placed at least 2 cm cephalad to the carina. CONCLUSION In the present study, the Chula formula could be used to predict the proper length of nasotracheal intubation in 93 of 100 patients.