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Ann Card Anaesth. 2018 Oct-Dec;21(4):382-387. doi: 10.4103/aca.ACA_220_17.

Usefulness of ultrasound-guided measurement of minimal transverse diameter of subglottic airway in determining the endotracheal tube size in children with congenital heart disease: A prospective observational study.

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Department of Anesthesia, Christian Medical College, Vellore, Tamil Nadu, India.



The search for an accurate and predictable method to estimate the endotracheal tube (ETT) size in pediatric population had led to derivation of many formulae. Of this, age-based formulae are the most commonly used. Studies have shown that minimal transverse diameter of subglottic airway (MTDSA) measurements using a high-frequency probe improves the success rate of predicting the airway diameter to about 90%. We did a prospective observational study using MTDSA as the criteria to select the size of ETT in children with congenital heart disease.


In this prospective observational study, 51 children aged from 1 day to 5 years, scheduled for cardiac surgery, were enrolled for this study. The ETT size was guided solely based on the MTDSA. Leak test was used to determine the best-fit ETT size.


Data from 49 patients were analyzed. Agreement between the ETT determined by MTDSA and that predicted by Cole's age-based formulas with the best-fit ETT size was analyzed using a Bland-Altman plot.


Age-based formula showed poor correlation (27.5%) compared to MTDSA (87.8%) in predicting the best-fit ETT. We observed that pediatric patients with congenital heart disease need a larger sized ETT as compared to what was predicted by age-based formula. Using ultrasound MTDSA measurements to guide selection of ETT size is a safe and accurate method in pediatric cardiac population.


Endotracheal tube; minimal transverse diameter of subglottic airway; ultrasound

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