Optimal length of the pre-inserted tracheal tube for excellent view in nasal fiberoptic intubation

Purpose: Inexperienced physicians frequently have difficulty performing nasal fiberoptic intubation. A pre-inserted tracheal tube of the appropriate length allows an excellent view of the laryngeal opening. The purpose of this study was to determine the ideal length of a pre-inserted tracheal tube for nasal fiberoptic intubation and to investigate if it could be predicted from easily measureable patient parameters. Methods: This was an observational study in which data on adult patients (n = 150) requiring nasal intubation were collected and analyzed by stepwise regression. During the pre-anesthesia examination, a right-angled gauge was used to measure the distance from the mid-point of the lateral border of the nares to the tragus of the ear (NT distance) and to the mandibular angle (NM distance). The distance from the tragus to the mandibular angle (TM distance) was also measured. The age, sex, height, and weight of each patient were recorded. After induction of anesthesia, the minimum and maximum lengths of the pre-inserted tracheal tube that provided an excellent view of laryngeal opening during nasal fiberoptic intubation were measured. The optimal length was calculated, and an equation was derived through stepwise regression analysis. Results: The optimal length for each patient could be reliably predicted using the equation (distances in cm, weight in kg): optimal length (cm) = 1.952 + 0.051 × height (cm) + 0.354 × NM distance (cm) − 0.011 × weight (kg) (r² = 0.460, P < 0.001). Conclusion: The optimal length of pre-inserted tracheal tube for nasal fiberoptic intubation can be predicted using a newly developed formula with three patient parameters, namely, height, the NM distance, and weight. Application of this equation in the clinical setting should facilitate nasal fiberoptic intubation.