Ideal endotracheal intubation depth at the vocal-cord level to avoid single-lung intubation using the percentage ratio of the tracheal length to body height

Introduction:
Our previous study revealed racial differences in the tracheal length of cardiac paediatric patients between Germany and Japan. The current study was conducted in two stages, aiming to determine whether the tracheal length differs between cardiac and non-cardiac paediatric patients and whether the results could also be generalised to adults.

Material and methods:
The first stage was a retrospective observational evaluation of 335 cardiac and 275 non-cardiac paediatric patients in Japan. The tracheal length, the distance between the vocal cords and carina tracheae, was measured on preoperative chest radiographs taken in the supine position. The second stage was a validation process including 308 Japanese patients. Endotracheal intubation was performed based on the results of the first-stage investigation.

Results:
It was revealed that the tracheal length ranged from 7 to 11% of the body height in both the cardiac and non-cardiac Japanese paediatric patients. None of 308 Japanese paediatric and adult patients underwent single-lung intubation after the endotracheal tube was inserted at a depth of 7% of the body height at the vocal-cord level, corresponding to the minimum tracheal length for Japanese patients. The distance between the endotracheal tube tip and carina tracheae on postoperative chest radiographs was generally less than 4% of the body height across all paediatric and adult Japanese patients.

Conclusions:
The current study demonstrated that endotracheal intubation avoiding single-lung intubation can be achieved by inserting endotracheal tubes to the minimum tracheal length for a specific ethnic group at the vocal-cord level in paediatric patients, including neonates and premature infants, as well as adults.