• Neonatology
• Clinical Procedures
• Intensive Care

When intubating a newborn, the aim was to place the endotracheal tube (ETT) in the midtrachea to allow for even distribution of ventilation and surfactant to both lungs. An ETT is considered correctly positioned if the tip is visible between the upper border of the first and the lower border of the second thoracic vertebra on chest x-ray (CXR).1 A number of methods are used to estimate the depth of insertion, including use of the vocal cord guide.2 ,3 The vocal cord guide was originally described as a 2-mm-wide solid black line added to neonatal ETTs with the upper border of the line at a distance of 24 mm, 26 mm and 28 mm from the tip of size 2.5, 3.0 and 3.5 ETTs, respectively.3 It is recommended that the ETT should be advanced until the guide is visible at the vocal cords on direct laryngoscopy and secured at this depth.3 ,4 Using this vocal cord guide was reported to eliminate main stem bronchus intubation in a series of 28 intubations in an unspecified number of infants.3

We suspected that the vocal cord guide may differ between ETTs and so examined five models of ETTs made by three manufacturers (Portex cuffless tracheal tube and Portex cuffless with standard sideport connector, Smiths Medical International Ltd, Kent UK; Mallinkrodt cuffless and Mallinkrodt cuffed, Covidien Ireland Ltd, Tullamore, Ireland; and KimVent Microcuff, Kimberley Clarke, Roswell, Georgia, USA) of internal diameter 2.0–4.0 mm where available. We noted the design of the vocal cord guide on each ETT and measured the distance from the ETT tip to its proximal end, as this is the distance that determines insertion depth.3 ,4 We independently measured this distance using the same steel ruler.

The design of the vocal cord guide differed between manufacturers and between different ETTs made by the same manufacturer (figure 1). The vocal cord guide on some ETTs were continuous black lines, while on others it was a broken line or, in some cases, absent. We found marked differences in the position of the proximal end of the vocal cord guide between different models of all sizes of ETTs (table 1). The largest difference was 21 mm between the size 3.0 Portex cuffless ETT with sideport and the Mallinkrodt cuffed ETTs (figure 1, table 1). The distance from the tip of the cuffless Mallinkrodt ETTs to the proximal end of the vocal cord guide was similar in all sizes from 2.0 to 4.0. Using the vocal cord guide to estimate insertion depth with these ETTs would therefore suggest that it would be appropriate to place a similar length of ETT beneath the vocal cords for babies of 500 g and 4 kg.

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Figure 1

Five models of size 3.0 endotracheal tubes (top to bottom: Portex without sideport, Portex with sideport, Mallinkrodt cuffless, Mallinkrodt cuffed, KimVent Microcuff).

We found that the design and position of the vocal cord guide on ETTs used in newborns differ between different models of ETT. Using the vocal cord guide to estimate insertion depth may therefore produce different results depending on the model of ETT used.