Dear Editor,

We read the recent article by Embleton et al with interest.[1] We accept their conclusion that foot length is an accurate predictor of nasotracheal tube length in neonates, and is at least as accurate as the conventional weight based estimation. We however wish to point out that palpation of the tip of the endotracheal tube (ETT) in the suprasternal fossa continues to provide the simplest means to ensure its correct placement during emergency tracheal intubation when weighing the neonate or measuring its foot length may not be practical or appropriate.[2,3] Given that the “safety zone” for the tracheal tube tip placement in neonates is only ~2.5 cms, the natural tendency is for the ETT to be located too distally.[3] The placement of the ETT tip in the suprasternal fossa helps avoid the consequences of intubation of the right main bronchus. We have found this method useful in achieving optimal placement of the ETT for emergency intubation as well as for elective intubation and surfactant instillation in high-risk neonates (e.g. birth weight £1000 grams, those with congenital diaphragmatic hernia). We have observed that if the tip of the tube can not be felt in the suprasternal fossa,it is too far down into the right main bronchus. If the position of the ETT is confirmed to be in the airway, withdrawal of the tube by a centimeter achieves its optimal placement.Confirmation of the suprasternal location of the tip of the ETT is facilitated by minimal forward and backward gentle movement of the tube at the nares or the lip depending on the route of intubation.Prospective assessment of this simple technique is warranted.

PATOLE SK, JOG SM, WHITEHALL JS

References
(1) Embleton ND, Deshpande SA, Scott D, Wright C, Milligan DWA. Foot length, an accurate predictor of nasotracheal tube length in neonates Arch Dis Child Fetal Neonatal Ed 2001; 85: F60-F64.
(2) Finer NN. Flexible fiber-optic bronchoscopy. In: Spitzer AR, ed. Intensive Care of the fetus and neonate. St. Louis: Mosby, 1996: 531-7.
(3) Kuhns LR, Poznaski AK. Endotracheal tube position in the infant. Jr Pediatr 1971; 78:991-6.

Dear Editors

The study by Embleton et al. (Arch Dis Child Fetal Neonatal Ed 2001;85:F60-F64) highlights the difficulty estimating nasotracheal tube length in neonates and provides foot length as a potentially useful surrogate measurement. Evolutionary and embryological insights may explain why these lengths are correlated.

Lung-based gas exchange and limb-dependent locomotion may be appreciated as adaptations to land-based living.[1] This evolutionary link is supported by recent findings that both lung and limb development share an essential requirement for a specific fibroblast growth factor (FGF) and its cognate receptor (FGFR). Deletion of FGF10 or its receptor FGFR2IIIb abrogates both lung and limb development in transgenic mice. [2-4] Airway and limb morphogenesis are therefore developmentally linked and plausibly related in evolutionary terms. This may then provide an attractive explanation for the otherwise serendipitous correlation between foot and nasotracheal lengths. Furthermore it remains possible that other aspects of pulmonary anatomy are for the same reason correlated to limb dimensions.

Transgenic techniques continue to expose previously unrecognised developmental relationships between organ systems. These links may prove useful to clinicians searching for novel predictors of visceral dimensions in neonates.

References

(1) Farmer CG. Evolution of the vertebrate cardio-pulmonary system. Annu Rev Physiol 1999;61:573-92.

(2) Min H, Danilenko DM, Scully SA, Bolon B, Ring BD, Tarpley JE, et al. Fgf-10 is required for both limb and lung development and exhibits striking functional similarity to Drosophila branchless. Genes Dev 1998;12:3156-3161.

(3) Sekine K, Ohuchi H, Fujiwara M, Yamasaki M, Yoshizawa T, Sato T, et al. Fgf10 is essential for limb and lung formation. Nat Genet 1999;21:138-41.

(4) Arman E, Haffner-Krausz R, Gorivodsky M, Lonai P. Fgfr2 is required for limb outgrowth and lung-branching morphogenesis. Proc Natl Acad Sci U S A 1999;96:11895-9.

Dear Editor

We were interested to read Embleton et al's study in which they presented a well researched argument for using foot length as a predictor of nasotracheal tube length in neonates [1]. While we do not doubt the accuracy of this method we question some of the intubation techniques described, particularly in an emergency situation.

It is generally recommended that emergency intubation should be oral because it can be performed more rapidly than nasotracheal intubation and is more reliable [2]. Once the patients condition is stabilised the endotracheal tube can be changed electively to one via the nasal route under direct vision. We note that in this study 13/72 (18%) of infants could not be successfully intubated nasally and are concerned at the possible morbidity associated with this failed intubation rate.

Whichever method is used to estimate the length of the endotracheal tube at the lip or nares the most important check for the intubator to make is the length of the tube at the cords. This is often forgotten, particularly by inexperienced personnel, but is a reliable way of ensuring a tube is neither too long nor too short.

Finally we would argue strongly against pre-cutting endotracheal tubes to within 0.5cm of estimated length as described as it leaves little room for error. We note that 9/55 infants intubated nasally in the study had high endotracheal tube placements on chest radiographs. With tubes cut so short this means re-intubation and unnecessary instrumentation of the larynx in 16% of infants.

References

(1) Embleton ND, Deshpande SA, Scott D et al. Foot length, an accurate predictor of nasotracheal tube length in neonates. Arch Dis Child Fetal Neonatal Ed 2001;85:F60-F64.
(2) American Heart Association. Pediatric Advanced Life Support. Texas: American Heart Association, 1997:4-16.