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.

Depth of endotracheal tubes in Thai adult patients.

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).