Evaluation of ultrasonographic thyrohyoid distance measurement for prediction of difficult intubation and prediction of pediatric endotracheal tube size by ultrasonography
Author(s):	Hamamcioglu E.A., Altindas F., Kendigelen P., Erbabacan S.E., Ekici B., Tutuncu C.
Institute(s):	Cerrahpasa Medical Faculty, Dept of Anaesthesiology & Intensive Care, Istanbul, Turkey
Goal: Our aim was to evaluate ultrasonographic (USG) measurement of thyrohyoid distance to predict difficult intubation and compare ultrasonographically measured subglottic and glottic diameters with age-relying formulas for correct ETT size in pediatric patients. 
Metod: After ethics committee approval, 119 patients planned to be intubated for surgery, were included in study. Patients were divided into three groups; Group I(1-2 years,n=38), Group II(3-5 years,n=46) and Group III(6-8 years,n=35). Age, gender, height, weight, Mallampati scores were recorded. We performed USG measurements following midazolam administration in children older than five years and during sevoflurane induction in children younger than five years old. ETT (cuffed/uncuffed) was selected using age-relying formulas. We considered ETT size optimal when a leak was detected at 20-30cmH₂O inflation pressures. If a resistance was felt in the subglottic region, the tube was exchanged with a smaller and was exchanged with a larger(0.5 mm) size if a leak occurred at inflation pressures lower than 20cmH₂O. Patients were evaluated with Intubation Difficulty Scale. We compared age-relaying formulas with USG subglottic measurements for the prediction of correct tube size. 
Results and discussion: No significant difference was found between groups regarding gender, age, weight and height distributions. 5% of patients were below the 3rd percentile. Mallampati scores were recorded as I in 106(89,1%) patients and II in 13(10,9%) patients. Cormack-Lehane scores were I, II and III in 101(84,8%), 17(14,2%) and III 1(0,008%) patients respectively. Based on the IDS; in group I, 23(60,5%) cases were easy, 14(36,8%) cases were slight difficult, 1(0,02) case was moderate/major difficult; in group II 38(82,6%) cases were easy, 8(17,4%) cases were slight difficult; in group III 26(74,3%) cases were easy, 9(25,7%) cases were slight difficult. No significant difference was observed in terms of thyrohyoid distances in Group I and II between the easy and slightly difficult cases in contrast to Group III where a significant difference was observed with a Cut-off value for thyroid distance of 17,45 mm. ETT size was predicted correct with USG in 52.5% and with age relying formulas in 19.7% of cases.
Conclusion: Thyrohyoid distance measured by USG can be used to predict difficult intubation in children between 6-8 years and USG measurement of subglottic diameter predicted correct tube size better than age relying formulas.

Evaluation of ultrasonographic thyrohyoid distance measurement for prediction of difficult intubation and prediction of pediatric endotracheal tube size by ultrasonography