Distances from vocal cords to mid-trachea for optimizing endotracheal tubes depth markers according to gestational age.

Background: adequate endotracheal tube positioning in preterm infants is complicated by the short length of the airway. Distal markers were designed to help with the insertion of endotracheal tubes at an appropriate depth below the vocal cords. However, those markers are not standardized between manufacturers, each tube size displays only one (sometimes two) marker to provide information for infants of various gestational ages, and indicated distances are often too long for extremely preterm infants.
Aim: The study aims to describe vocal cords to mid-tracheal distance for different gestational ages and suggest depth markers adjusted accordingly.
Methods: half the tracheal length added to the height of the posterior lamina of the cricoids approximates the distance between vocal cords and mid-trachea. Those dimensions were retrospectively retrieved from a database of laryngo-tracheal measurements obtained during autopsies of fetuses and newborn infants free of upper airway malformations. The equation of correlation between gestational age and distance from vocal cords to mid-trachea was used to calculate those distances for different gestational ages.
Results: data were derived from 114 patients. Vocal cords to mid-trachea distance is linearly correlated with gestational age (r=.90; distance =2.831+ 0.6208* gestational age). We suggest depth markers at 17.7, 19.0, 20.8, 22.7, 24.6 and 26.4 mm for gestational ages of 24, 26, 29, 32, 35 and 38 weeks respectively, indicated by contrasting colors.
Conclusions: the linear relationship between laryngo-tracheal size and gestational age offers the opportunity to revise endotracheal tubes depth markers for the smallest patients. Trials comparing those suggested markers with those currently in use are needed before implementation.