Foot length, an accurate predictor of nasotracheal tube length in neonates

Background-Existing guidelines for optimal positioning of endotracheal tube s in neonates are based on scanty data and relate to measurements that are either non-linear or poorly reproducible in sick infants. Foot length can b e measured simply and rapidly and is related to a number of external body m easurements. Objectives-To evaluate the relation of foot length to nasotracheal length i n direct measurements at post mortem examinations, and then compare its cli nical relevance with traditional weight based estimates in a randomised con trolled trial. Methods-The dimensions of the upper airway were measured at autopsy in 39 i nfants with median (range) postmenstrual age and birth weight of 32 (24-43) weeks and 1630 (640-3530) g. The regression equations with 95% prediction intervals were calculated to estimate the optimal nasotracheal length from foot length. In a randomised trial, 59 neonates were nasally intubated acco rding to foot length and body weight based estimates to assess the achievem ent of "optimal" and "satisfactory" tube placements. Results-In the direct measurements of the airway at autopsy, foot length wa s a better predictor of nasotracheal distances (r(2) = 0.79) than body weig ht, gestational age, and head circumference (r(2) = 0.67, 0.58, and 0.60 re spectively). Measurement of foot length was easy and highly reproducible. I n the randomised controlled trial, there were no significant differences be tween the foot length and body weight based estimates in the rates of optim al (44% v 56%) and satisfactory (83% v 72%) endotracheal tube placements. Conclusions-Foot length is a reliable and reproducible predictor of nasotra cheal tube length and is at least as accurate as the conventional weight ba sed estimation. This method may be particularly valuable in sick unstable i nfants.