A new formula for estimating endotracheal tube insertion depth in neonates

The majority of extremely preterm infants require endotracheal intubation in the delivery room and neonatal intensive care units. Although the use of early nasal continuous positive airway pressure significantly reduces the intubation rate in extremely low birth weight infants, one-fourth of those who survive require reintubation within 7 days after extubation.1Miksch R.M. Armbrust S. Pahnke J. Fusch C. Outcome of very low birthweight infants after introducing a new standard regime with the early use of nasal CPAP.Eur J Pediatr. 2008; 167: 909-916Crossref PubMed Scopus (22) Google Scholar, 2Wang S.H. Liou J.Y. Chen C.Y. Chou H.C. Hsieh W.S. Tsao P.N. Risk factors for extubation failure in extremely low birth weight infants.Pediatr Neonatol. 2017; 58: 145-150Abstract Full Text Full Text PDF PubMed Scopus (14) Google Scholar When placed correctly, the tip of the endotracheal tube (ET) must be positioned in the midtracheal region, halfway between the inferior clavicle and the carina. The tip will reside in the main stem bronchus (usually on the right side) if the ET is inserted too far. This may lead to volutrauma in the right lung (pneumothorax, pulmonary interstitial emphysema), atelectasis of the left lung, and unilateral surfactant replacement. These findings indicate that an accurate predictive formula is crucial in the management of preterm infants. Several formulas have been proposed to estimate the depth of ET insertion to place it at the midtracheal position. Tochen described a simple formula for the determination of the depth of ET insertion for orotracheal intubations based on birth weight in 1979.3Tochen M.L. Orotracheal intubation in the newborn infant: a method for determining depth of tube insertion.J Pediatr. 1979; 95: 1050-1051Abstract Full Text PDF PubMed Scopus (88) Google Scholar The estimated depth of ET insertion = 1.17 × birth weight (kg) + 5.58. This can be translated for an infant weighing 1 kg being intubated to a depth of 7 cm, a 2-kg infant being intubated to a depth of 8 cm, and a 3-kg infant being intubated to a depth of 9 cm. The calculation converts to the "7-8-9 rule" and continues to be recommended by the American Academy of Pediatrics. The rule was also used by a majority of neonatal intensive care units in Canada to estimate the depth of an oral ET insertion.4Sakhuja P. Finelli M. Hawes J. Whyte H. Is it time to review guidelines for ETT positioning in the NICU? SCEPTIC-survey of challenges encountered in placement of endotracheal tubes in Canadian NICUs.Int J Pediatr. 2016; 2016: 7283179Crossref PubMed Google Scholar However, the "7-8-9 rule" is not always accurate, in particular, for the extremely low birth weight infants. In this issue of Pediatrics and Neonatology, the study conducted by Chung et al.5Chung H.W. Lee W.T. Chen H.L. Reexamining the ideal depth of endotracheal tube in neonates.Pediatr Neonatol. 2018; 59: 258-262Abstract Full Text Full Text PDF Scopus (8) Google Scholar has retrospectively compared the final ideal ET insertion depth using the Tochen's formula, determined the correlation between neonatal clinical factors and the final ideal ET insertion depth, and devised an accurate predictive formula that can be applied for Taiwanese neonates. They enrolled 139 neonates and found that the final ideal ET insertion depth was in concordance with the Tochen's formula in 19 neonates (13.7%), relatively deeper in 30 (21.6%) neonates, and shallower than the values obtained using the Tochen's formula in 90 (64.7%) neonates. The multiple regression analysis revealed that birth weight and gestational age together provided the best prediction for estimating the final ideal ET insertion depth. They concluded that the Tochen's formula might not be appropriate to predict ET insertion depth for neonates in Taiwan and developed a new formula = 4.0 + 1.0 birth weight (kg) + 0.05 gestational age (weeks) to estimate the final ideal ET insertion depth. The limitations of this study are the small sample sizes and that the chin position was not recorded during X-ray examinations. The strength of this study is that half of the neonates weighed <1500 g and one-third of the neonates weighed <1000 g. This sample composition may compensate for the shortcoming of the "7-8-9 rule" that placed the ET significantly below the midtracheal position in infants weighing <750 g.6Peterson J. Johnson N. Deakins K. Wilson-Costello D. Jelovsek J.E. Chatburn R. Accuracy of the 7-8-9 rule for endotracheal tube placement in the neonate.J Perinatol. 2006; 26: 333-336Crossref PubMed Scopus (76) Google Scholar Neonatal resuscitation warrants rapid and correct ET insertion. The 7th edition Neonatal Resuscitation Program recommends using the gestation-based "initial endotracheal tube insertion depth" table or measuring the newborn's nasal–tragus length and adding 1 cm to determine the correct ET insertion depth.7Weiner G.M. Zaichkin J. Kattwinkel J. Textbook of neonatal resuscitation. 7th ed. American Academy of Pediatrics and American Heart Association, Elk Grove Village, IL2016Crossref Google Scholar However, these methods are affected by the ethnic background and only estimates of correct insertion depth are obtained. Auscultation of breath sounds and the use of a carbon dioxide detector are recommended to confirm the correct ET placement. The author declares no conflicts of interest.

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