BackgroundThis study aims to validate our previously reported prediction technique for uncuffed tracheal tube (TT) sizes in children younger than 2 years of age based on a calculated outer diameter (ODCal, mm) in each patient according to the regression equation ODCal = 0.00223 × age (day) + 4.88 and to investigate a better method to select initial TT sizes to decrease re-intubation frequency, especially since large tubes can damage the trachea.MethodsWe included patients younger than 2 years of age who underwent oral surgery under general anesthesia with tracheal intubation between July 2011 and December 2016 at the Osaka University Dental Hospital. The OD of the actual TT and the age in days were extracted from anesthesia records. Agreement rates, estimated numbers of required tubes, and size reduction frequencies were compared to obtain recommended OD (ODRec) values in 2 selection groups: “average selection” in the range “nearest to the ODCal value (ODCal - 0.35 < ODRec ≤ ODCal + 0.35)” and “safe selection” in the range “nearest to the value below ODCal (ODCal - 0.7 < ODRec ≤ ODCal)”.ResultsThe agreement rates for an ODRec in the average selection and safe selection groups were 60.8 and 55.1%, respectively (P = 0.001). The estimated number of required tubes per patient were 1.40 ± 0.51 and 1.47 ± 0.55 (P < 0.001), respectively. The estimated frequencies of size reductions were 13.3 and 4.0% (P < 0.001), respectively.ConclusionsBecause the size reduction frequency is lower despite a slightly higher number of required TTs, selecting an ODRec based on “safe selection” parameters is desirable to avoid complications due to intubation with larger TTs.