RESUMO
INTRODUCTION: The age-based formula is commonly used to predict tracheal tube (TT) sizes although its inaccuracy has been reported to reach as high as 60%. We aim to determine a practical formula using age in months and weight in kilograms to predict uncuffed tracheal tube (TT) size in children and infants. METHODS: A retrospective cross-sectional study was conducted on data obtained from a prospective study on children aged less than 9 years who came for elective surgery and received general anesthesia with oroendotracheal tube intubation at Songklanagarind Hospital between September 2008 and December 2012. The uncuffed TT sizes were based on the age-based formulae and the discretion of the attending anesthesiologist. The age (in months), weight (in kg), and final TT size were measured. Univariate and multivariate linear regression analyses were used to find potential predictors of final uncuffed TT size and therefore the best formula. The correlation coefficient (r) for each model was calculated. The kappa statistic was used to measure the agreement between predicted and actual TT size. RESULTS: A total of 668 patients were recruited. The age/weight formulae for infants aged ≤12 months and children aged >12 months were 3.15 + (age [months] × 0.05) + (weight [kg] × 0.05) with r value of 0.75 (n = 216) and 3.83 + (age [months] × 0.017) + (weight [kg] × 0.017) with r value of 0.85 (n = 452), respectively. The formulae correctly predicted 69.0% and 65.0% of actual TT sizes for infants and children, respectively (both p < 0.001). The formulae for malnourished infants and children whose weights were less than the 3rd percentile for age were 2.70 + (weight [kg] × 0.21) (n = 43) and 3.59 + (age [months] × 0.012) + (weight [kg] × 0.056) (n = 105) with r values of 0.81 and 0.87, respectively. CONCLUSION: The age/weight formula can be used to estimate TT size in infants and children. In failure to thrive children, our formula for malnourished children and infants provided high correlation with final TT sizes.
