Predicting the appropriate uncuffed endotracheal tube size for children: a radiograph-based formula versus two age-based formulas.

STUDY OBJECTIVES: To determine whether a radiograph-based formula using the tracheal diameter from a chest radiograph predicted the appropriate endotracheal tube (ETT) size in children, and to compare these results with those produced using age-based formulas.

DESIGN: Retrospective, observational study.

SETTING: Medical record review.

MEASUREMENTS: Data from 537 pediatric patients, aged 3 to 6 years, who underwent orotracheal intubation with an uncuffed ETT, were randomly divided into two datasets: one was used to derive a formula and the other was for validation. A radiograph-based formula was obtained by linear regression modeling between the tracheal diameter at the seventh cervical vertebra (C7) on chest radiography and the appropriate ETT size from the estimation dataset (n=268). The appropriate size was defined as the ETT size when air leak pressure was 10 to 30 cmH2O. The predictive ability of this equation was evaluated using the validation dataset (n=269). The primary outcome was the success rate of the prediction.

MAIN RESULTS: The following radiograph-based formula was obtained: ID = 3 + 0.3 × (tracheal diameter at C7). The success rate of the radiograph-based formula was 57%, which is higher than the 32% (P < 0.001) of the standard age-based formula (ID = 4 + age/4) or 43% (P = 0.002) of Penlington's formula (ID = 4.5 + age/4). An underestimation of the actual tracheal size occurred in 65% of cases using the age-based formulas, but in only 19% with the radiograph-based formula (P < 0.001).

CONCLUSIONS: The radiograph-based formula may be useful for predicting the appropriate ETT size in children aged 3 to 6 years.