Detection of positional airway obstruction in neonates by acoustic reflection

In neonates intubated with an uncuffed endotracheal tube (ETT), positional changes of the head may induce obstruction (side position-related ETT obstruction [SPRO]) due to abutment of the beveled distal ETT orifice against the tracheal wall. We studied whether the acoustic reflection (ACR) method, a 4-s measurement that maps cross-sectional area as a function of the distance along the ETT and the airways, could detect SPRO. Eleven preterm newborns intubated with 2.5-mm ETTs and clinically suspected of having SPRO were studied with the head oriented to the left and to the right. In all patients there was a marked decrease in the ACR-measured area beyond the distal tip of the ETT in the presence of obstruction (decrease = 38 +/- 22% [mean +/- SD] of the ETT inside area), while the ACR-measured area increased markedly in the absence of obstruction (increase = 49 +/- 17%). For six of the 11 infants, we also recorded the maximal flow produced by a set mechanical inflation pressure. This maximal flow decreased in the presence of obstruction (decrease = 47 +/- 18%), and was constantly associated with a decrease in ACR-measured area beyond the ETT. In conclusion, ACR measurement is an efficient method for diagnosing positional ETT obstruction in intubated newborns.