The purpose of this study was to assess whether ultrasonography is useful for determining uncuffed tracheal tube sizes for paediatric patients. The equation for selecting the correctly sized tracheal tube was developed using data on the subglottic diameter measured by ultrasonography and air leak test. The efficacy of the new equation was evaluated by comparing it with the conventional age-based formula (4 + age/4) in another 100 patients. Tracheal tube sizes were selected using two methods, and air leakage pressure was measured after each intubation. The ultrasonographic method allowed the correct tube size to be selected in 60% of cases, whereas the age-based method enabled this in 31% of cases (p < 0.001). Ultrasound can offer a useful means of selecting correct tracheal tube size compared with the age-based formula in paediatric patients. However, even using ultrasound, the success rate of correct tube size selection is still not very high.
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