Endotracheal tubes and the cricoid: Is there a good fit?

Choosing an appropriately sized endotracheal tube (ETT) is important in pediatric patients as an inappropriately sized ETT may result in multiple endotracheal intubation attempts or excessive pressure on the tracheal mucosa with the potential for airway damage. Although age-based formulas are generally used with choice of an ETT based on the internal diameter (ID), measurements of the outer diameter (OD) of the ETT would seem to be a more scientific approach to determine the proper size of an ETT. However, the variable OD of the ETT despite the same ID makes the selection of a proper sized ETT more difficult. The current study compares airway dimensions measured using computed tomography (CT) with the OD of ETTs from various manufacturers.

The outer diameter of commonly used ETTs (12 cuffed and 5 uncuffed) were measured and compared with CT-based cricoid measurements obtained from a previous study involving 130 pediatric patients, ranging in age from 1 month to 10 years. These data were used to determine the likelihood of a clinically acceptable match.

The differences of the cricoid dimensions between the 5th and the 95th percentile in each group ranged from a minimum of 2.23mm to a maximum of 6.51mm. Depending on the manufacturer, there was significant variation in the OD of the ETTs with the same ID. These discrepancies, which varied according to manufacturer and were greater with uncuffed as compared to cuffed ETTs, impacted the chances of an acceptable fit with the cricoid diameters.

When choosing an ETT, age-based formulas which use the ID may not be uniformly accurate in ensuring the appropriately-sized ETT given the variation in the OD despite the same ID. These issues further support the use of cuffed ETTs as the variation in fit can be adjusted by inflation of the cuff to provide an adequate tracheal seal.