Ultrasound evaluation of subglottic diameter and endotracheal tube in children

Abstract

Choosing the proper sized endotracheal tube (ETT) is an important task for airway management under general anesthesia in children. Earlier publications presented several methods for selection of ETT using patients’ demographic data, such as age, weight, and height, but it has a limitation in accuracy and overlooks the individual differences.1-5 Recently, Shibasaki et al., have reported the high correlation between the ultrasound-measured subglottic diameter and the outer diameter of ETT according to the age-based formulas.6 The purpose of this study is to see whether ultrasound-measured transverse diameter of subglottis can give precise information for selecting proper ETT size prior to tracheal intubation. After loss of consciousness with anesthetic induction, axial images of ultrasound on area of vocal cords and subglottis were obtained 3 times on expiratory phase during mask ventilation. After tracheal intubation with cuffed-ETT according to the age-based recommended size, an axial image was obtained from the thyroid level to measure the outer diameter (OD) of the inserted ETT. To assess the reliability of ultrasound-measured distance, the agreement of the ultrasound-measured OD of ETT in trachea and actual OD of the ETT were analyzed. The relationship between subglottic diameter and biographic data (age, height, weight, 5th fingernail width, and body-surface area) were analyzed. Ultrasound-measured outer diameter of ETT following the tracheal intubation, and the actual outer diameter of ETT showed good agreement, suggesting that ultrasound-measurement of subglottic diameter prior to intubation can be valuable information for proper ETT size selection. The biographic data and the ultrasound-measured subglottic diameter showed little correlation among the patients less than 12 months old, but showed good correlation with age, height in the patients older than 12 months. Subglottic diameter measurement using ultrasound can be a convenient and precise method in predicting the proper ETT size in pediatric patients. Our study reveals the statistical relationship between the subglottic diameter and the biographical data of each patients, which enables health care providers to apply the adequate and fit ETT size in children without the inconvenience of using ultrasound every time to measure the subglottic diameter.