Aim To test the hypothesis that: The black mark at the tip of endotracheal tube guides the optimal insertion distance during neonatal intubation.
Background There are several formulae and graphs that are used to calculate the length of orally or nasally inserted endo-tracheal tube (ETT) in a neonate. These aim to place the in tip in mid-tracheal position (or against T2 vertebra) on chest x-ray. It is widely practised that the black mark at the end of ETT is the appropriate depth for insertion. Our unit uses VYGON tubes and the black mark begins at 7 mm and ends at 25 mm distance from the tip in tubes of all sizes.
Method The authors retrospectively studied CXRs of sequential neonates who were admitted to the neonatal unit over 8 months. The admission CXR was studied if the exposure contained neck and chest, regardless of whether intubated or reason for admission. The authors attempted to predict the distance of mid-trachea from vocal cords by studying digital chest x-rays (CXR). Neonatal vocal cords are super-imposed against C4 vertebra on frontal CXR. We estimated the vocal cord to mid-trachea distance from middle of C4 vertebra to middle of T2 vertebra. The C4 to T2 measurements were plotted on a scatter chart against the birth weight.
Results The authors obtained x-rays for 78 babies with a weight range from 560 to 4160 g. The authors found that even in the smallest neonates, mid-trachea lies 15 mm below vocal cords, whereas this distance is 35 mm in the large term babies. There is a linear relation with birth weight and the r2 is calculated to be 0.86.
Discussion The black mark at the tip of neonatal VYGON endotracheal tube is located at a fixed distance, regardless of the diameter. For the smallest neonates, the black mark will lie half-way and for the largest babies, more than the full length through the vocal cords.
Conclusion Passing the black mark through the cords leads to bronchial intubation in extreme preterm babies, and high ETT for term infants. One cannot use the black mark to guide how far the ETT should be inserted beyond the vocal cords to be adequately positioned.