We read with interest the recent article by Dr. Hunyady and colleagues.1While we acknowledge that mathematical formulae based on morphometric data may be useful guides, we caution against applying these formulae in lieu of clinical assessment. We conducted a randomized clinical trial to compare three common methods of endotracheal tube (ETT) placement: 1) deliberate mainstem intubation with subsequent withdrawal of the ETT 2 cm above the carina (“mainstem” method); 2) alignment of the double black line marker near the ETT tip at the vocal cords (“marker” method); or 3) placement of the ETT at a depth determined by the formula: ETT depth (cm) = 3 times ETT size (mmID) (“formula” method).2In our study, the formula method only placed the ETT at the appropriate depth 42% of the time. In addition, we retrospectively evaluated the efficacy of another formula, ETT depth (cm) = Age(yrs)/2 + 12,3but appropriate placement would have been achieved only 42% of the time as well. Identification of the carina via  auscultation, the mainstem method, was the preferred technique (73%, P = 0.006 vs.  the formula method).2 

Although our study did not specifically examine the efficacy of the Morgan and Steward formula,4neither did the study by Hunyady et al.  1The authors’ conclusion that the “.t.t.tMorgan formula provides good guidance for intubation in children .t.t.” is extrapolated based on their measurements and calculations.1The authors do not specify which technique was used to initially determine ETT depth in their study subjects or report the rates of correct versus  incorrect placement for the actual placement methods used. Based on the estimates by Hunyady et al. , the Morgan and Steward formula would have placed the ETT tip on average at the 90thpercentile for front teeth-to-carina distance and < 0.5 cm from the carina in 13 of their youngest subjects.1This is concerning since, as the authors astutely point out, the ETT is subject to movement with neck flexion or extension which may result in inadvertent endobronchial ETT placement.5–7 

Auscultation methods have their limitations as well,2,3and no clinical technique results in 100% success. When ETT placement is in question or when accurate ETT depth is mandatory for a particular surgical procedure (i.e. , prone position or head and neck surgery), we recommend intraoperative chest radiography, fluoroscopy, or fiberoptic bronchoscopy.

*University of California, San Diego Medical Center, San Diego, California. ermariano@ucsd.edu

Hunyady AI, Pieters B, Johnston TA, Jonmarker C: Front teeth-to-carina distance in children undergoing cardiac catheterization. Anesthesiology 2008; 108:1004–8
Mariano ER, Ramamoorthy C, Chu LF, Chen M, Hammer GB: A comparison of three methods for estimating appropriate tracheal tube depth in children. Paediatr Anaesth 2005; 15:846–51
Verghese ST, Hannallah RS, Slack MC, Cross RR, Patel KM: Auscultation of bilateral breath sounds does not rule out endobronchial intubation in children. Anesth Analg 2004; 99:56–8
Morgan GA, Steward DJ: A pre-formed paediatric orotracheal tube designed based on anatomical measurements. Can Anaesth Soc J 1982; 29:9–11
Donn SM, Kuhns LR: Mechanism of endotracheal tube movement with change of head position in the neonate. Pediatr Radiol 1980; 9:37–40
Rost JR, Frush DP, Auten RL: Effect of neck position on endotracheal tube location in low birth weight infants. Pediatr Pulmonol 1999; 27:199–202
Toung TJ, Grayson R, Saklad J, Wang H: Movement of the distal end of the endotracheal tube during flexion and extension of the neck. Anesth Analg 1985; 64:1030–2