How Far Is Far Enough? Measuring a Baby's Face to Place a Breathing Tube Safely

A study of 50 very small premature babies at a New York children's hospital compared three simple bedside methods for deciding how deep a breathing tube should go

When a very premature baby needs a breathing tube, doctors must decide in seconds how far to push it in — and the safe zone is less than half an inch wide. A new study of 50 babies weighing under 1,500 grams found that the two methods most widely taught today tend to push the tube in slightly too far, while a third method — measuring from the corner of the mouth to the top of the ear — landed almost exactly on target and gave the same answer no matter who did the measuring.

Why This Question Matters

If your baby was born very early, there is a good chance a breathing tube was part of their first hours. The tube, called an endotracheal tube, passes through the mouth, down past the voice box, and into the windpipe. A machine then pushes gentle breaths of air through it into lungs that are not yet ready to do the job alone. It is one of the most common and most life-saving things done in a neonatal intensive care unit. The study described here [1] asked one narrow question about that tube: how far in should it go?

The tube has to end up in exactly the right place. The windpipe of a baby born at 26 weeks is only about as long as a AAA battery, and it splits at the bottom into two branches, one going to each lung. Doctors aim for the tip of the tube to sit in the middle of that short stretch — described on an X-ray as being level with the first and second bones of the upper spine [2]. If the tube stops too short, it can slip out when the baby is moved, or fail to deliver breaths properly. If it goes too far, it slides into the branch leading to the right lung and inflates only that one — which can collapse the left lung, or overinflate the right one until air leaks out of it. Studies of babies arriving at hospitals after transport have found tubes sitting outside the safe zone often enough to be a real concern [3], and careful X-ray reviews in extremely premature babies have shown just how little room there is for error [4]. These are not just plumbing problems: air leaking from an overinflated lung has long been linked to bleeding in the fragile brain of a premature baby [5].

How Doctors Used to Decide

For most of the past fifty years, the answer came from a rule of thumb published in 1979: take the baby's weight in kilograms and add six [6]. A one-kilogram baby got seven centimetres, a two-kilogram baby got eight, a three-kilogram baby got nine — easy to remember, easy to teach, and repeated in delivery rooms around the world. The trouble was that nobody had carefully checked whether it worked. When researchers finally did, they found the rule tended to push the tube in too deep, and that the problem was worst in the smallest babies [7] — exactly the ones with the least room to spare.

So the field looked for something better, and settled on measuring the baby instead of relying on a formula. In 1997 a group proposed measuring from the base of the nose to the small flap of cartilage just in front of the ear canal — a distance called the naso-tragus length — and adding one centimetre [8]. This felt like an improvement because it takes account of how big this particular baby's head is. But faces are not built to a single template. A study in Taiwan found that the naso-tragus measurement, plus its fixed one centimetre, did not fit babies there nearly as well [9], which raised an uncomfortable question about whether a method developed in one population can simply be applied everywhere.

The other option now taught to newborn resuscitation teams is a printed table: look up the baby's gestational age — how many weeks of pregnancy had passed at birth — and read off a recommended depth [10]. When that table was actually compared with the old weight rule in a proper randomised study in Dublin, the two performed about the same [11]. In other words, the newer official methods replaced the old rule without ever having been shown to be better than it.

That is the situation this new research set out to address. A team at Stony Brook Children's Hospital in New York had earlier reported that a different facial measurement — from the corner of the mouth to the rim of the ear, called the oro-helix length — worked better than the old weight rule [12]. What nobody had tested was how that measurement compares with the two methods doctors are currently trained to use.

What the Researchers Did

Between April 2022 and February 2024, the team enrolled 50 babies weighing 1,500 grams or less who needed a breathing tube in their neonatal intensive care unit [1]. Parents gave written permission before a baby joined the study. On average these were very small, very early babies: born at about 26 and a half weeks of pregnancy and weighing about 950 grams — roughly two pounds.

For each baby, three predictions of the right depth were made: one from the mouth-to-ear measurement, one from the nose-to-ear measurement plus a centimetre, and one from the gestational-age table. Two staff members took the facial measurements separately, with a paper tape marked in centimetres, and neither knew what the other had found. Then a routine chest X-ray — the same one that would have been taken anyway after any intubation — was read by a children's radiologist who did not know the baby was in a study. The depth the X-ray showed to be ideal became the answer key, and all three predictions were scored against it. Importantly, no baby's care was changed by the study; the researchers only compared numbers that were being generated anyway.

What They Found

The average correct depth turned out to be 6.22 centimetres, measured at the lip.

The mouth-to-ear measurement predicted an average of 6.06 centimetres — off by just 0.15 centimetres, a difference so small it could easily be chance. It was the only one of the three that did not differ meaningfully from the right answer.

The nose-to-ear method predicted an average of 6.83 centimetres, overshooting by 0.61 centimetres. To put that in perspective, the researchers themselves defined anything more than half a centimetre off as a misplaced tube. The gestational-age table also aimed too deep, though by less: 0.20 centimetres on average.

Counting how often each method landed inside the safe zone tells the same story. The mouth-to-ear measurement got 46 of the 50 babies right. The gestational-age table got 40 right. The nose-to-ear method got 37 right — meaning roughly one baby in four would have had a tube placed outside the safe range if that method alone had been trusted.

One more finding is worth knowing about, because it speaks to whether a method can be relied on in the real world. When two different staff members measured the same baby's mouth-to-ear distance without conferring, their answers agreed almost perfectly. That kind of consistency matters: a measurement is only useful if it gives the same number in different hands, at three in the morning, under pressure.

What This Means for Families

If your baby is intubated, nothing about this study should worry you. The chest X-ray taken after a breathing tube is placed is precisely the safety check this research relies on, and it remains the final word. The authors are clear that even the best of these bedside measurements is a starting estimate, not a substitute for confirming the position on film [1].

What the study offers is a modest, practical improvement in that starting estimate — which matters most in the minutes before an X-ray is available: in a delivery room, in an ambulance, or during a transfer between hospitals. If a first guess is closer to correct, there is less repositioning, less handling of a fragile baby, and less time spent with a tube in the wrong place.

It is also worth being honest about the study's size. Fifty babies at a single hospital is a small foundation. The researchers point out that their group was not diverse enough to answer the question of whether facial proportions differ enough between populations to matter — the very question raised by the Taiwanese findings. A larger comparison from India, for example, found the gestational-age table performing considerably less well than it did here [13], which suggests that local habits of taping and securing the tube may shape the results as much as the measurement itself.

What Comes Next

Researchers working on this question have three tasks ahead. The first is repeating the study across many hospitals and a much more diverse group of babies, so that the role of facial differences can be properly examined rather than guessed at. The second is agreeing on how much error is acceptable — this team chose a stricter standard than earlier studies used, and that choice deserves a wider conversation. The third and most important is a randomised study: rather than comparing predictions on paper, actually assign teams to use one method or the other and count how many tubes end up in the wrong place. Earlier work comparing the nose-to-ear method in that way has already been done [14], and the same approach applied to the mouth-to-ear measurement would settle the question.

Until then, the message is a small and reassuring one: a measuring tape, two easily found landmarks on a baby's face, and a confirming X-ray remain the safest combination available.

References

  1. Agorastos S, Hou W, Maduekwe ET. Comparative accuracy of oro-helix length, naso-tragus length, and gestational age-based methods for endotracheal tube depth prediction in neonates ≤1,500 g. Frontiers in Pediatrics. 2026;14:1861978. doi:10.3389/fped.2026.1861978 ↩
  2. Blayney MP, Logan DR. First thoracic vertebral body as reference for endotracheal tube placement. Archives of Disease in Childhood — Fetal and Neonatal Edition. 1994;71(1):F32–F35. doi:10.1136/fn.71.1.F32 ↩
  3. Mainie P, Carmichael A, McCullough S, Kempley ST. Endotracheal tube position in neonates requiring emergency interhospital transfer. American Journal of Perinatology. 2006;23(2):121–124. doi:10.1055/s-2006-931915 ↩
  4. Thayyil S, Nagakumar P, Gowers H, Sinha A. Optimal endotracheal tube tip position in extremely premature infants. American Journal of Perinatology. 2008;25(1):13–16. doi:10.1055/s-2007-995221 ↩
  5. Hill A, Perlman JM, Volpe JJ. Relationship of pneumothorax to occurrence of intraventricular hemorrhage in the premature newborn. Pediatrics. 1982;69(2):144–149. doi:10.1542/peds.69.2.144 ↩
  6. Tochen ML. Orotracheal intubation in the newborn infant: a method for determining depth of tube insertion. The Journal of Pediatrics. 1979;95(6):1050–1051. doi:10.1016/S0022-3476(79)80309-180309-1) ↩
  7. Peterson J, Johnson N, Deakins K, Wilson-Costello D, Jelovsek JE, Chatburn R. Accuracy of the 7-8-9 rule for endotracheal tube placement in the neonate. Journal of Perinatology. 2006;26(6):333–336. doi:10.1038/sj.jp.7211503 ↩
  8. Shukla HK, Hendricks-Munoz KD, Atakent Y, Rapaport S. Rapid estimation of insertional length of endotracheal intubation in newborn infants. The Journal of Pediatrics. 1997;131(4):561–564. doi:10.1016/S0022-3476(97)70062-370062-3) ↩
  9. Wang TC, Kuo LL, Lee CY. Utilizing nasal-tragus length to estimate optimal endotracheal tube depth for neonates in Taiwan. Indian Journal of Pediatrics. 2011;78(3):296–300. doi:10.1007/s12098-010-0278-8 ↩
  10. Weiner GM, ed. Textbook of Neonatal Resuscitation. 9th ed. Elk Grove Village, IL: American Academy of Pediatrics; 2025. ↩
  11. Flinn AM, Travers CP, Laffan EE, O'Donnell CPF. Estimating the endotracheal tube insertion depth in newborns using weight or gestation: a randomised trial. Neonatology. 2015;107(3):167–172. doi:10.1159/000369375 ↩
  12. Lee D, Mele PC, Hou W, Decristofaro JD, Maduekwe ET. The oro-helical length accurately predicts endotracheal tube insertion depth in neonates. The Journal of Pediatrics. 2018;200:265–269.e2. doi:10.1016/j.jpeds.2018.04.045 ↩
  13. Priyadarshi M, Thukral A, Sankar MJ, Verma A, Jana M, Agarwal R, et al. 'Lip-to-tip' study: comparison of three methods to determine optimal insertion length of endotracheal tube in neonates. European Journal of Pediatrics. 2021;180(5):1459–1466. doi:10.1007/s00431-020-03919-7 ↩
  14. Uygur Ö, Öncel MY, Şimşek GK, Okur N, Çelik K, Bozkurt Ö, et al. Is nasal septum-tragus length measurement appropriate for endotracheal tube intubation depth in neonates? A randomized controlled study. American Journal of Perinatology. 2021;38(7):728–733. doi:10.1055/s-0039-3400982 ↩