We thank Dr. Mariano and colleagues for their comments. As stated in the article, we believe that “sole reliance on a specific formula is not advisable, and careful auscultation is necessary to ensure appropriate position.”1The stethoscope is indeed a useful, albeit not infallible, tool.

The endotracheal tube (ETT) was positioned according to the preferred method of the attending anesthesiologist. The Morgan formula2(ETT length at front upper teeth [cm]= 0.10 × height [cm]+ 5) was therefore not used in all patients, but the actual ETT tip position was within ±5% of the calculated Morgan formula distance in 138 of the 170 patients.

It is correct that we did not test different intubation depth formulas directly, instead we utilized the front teeth-to-carina data to assess whether different intubation formulas would result in bronchial intubation or not. We believe this is a reasonable approach. It is our understanding that Mariano et al.  used a similar method to assess the appropriateness of alternative ETT positions in their study.3 

We agree with Mariano et al.  3and Phipps et al.  4that the 3 × ETT size formula can be misleading, perhaps because “correct” ETT size varies with tracheal dimensions and depends on whether a cuffed or uncuffed ETT is used. In our patients, three neonates intubated with 3.5 uncuffed ETT’s would have been bronchially intubated if this formula had been applied.

The Morgan formula, on the other hand, is based on the reasonable assumption that the length of the airway tends to increase linearly with the length of the individual. No patient would have been bronchially intubated had the Morgan formula been applied, but thirteen infants and one older child (8%) would have had an ETT tip-to-carina distance of less than 0.5 cm. Although this is less than the 12% noted by Mariano et al.  when using the “mainstem method,”3we share their concern. As mentioned in our paper, it might be helpful to use a modified Morgan formula in infants less than 3 months [ETT length at front upper dental ridge (cm) = 0.10 × height (cm) + 4].1This does not abolish the risk for low ETT position; one 5-month-old and one 6-yr-old in our study would still have had an ETT tip-to-carina distance of less than 0.5 cm had this modification been added. Still, we have found that the ETT position seldom needs to be readjusted when these formulas are applied, and we therefore prefer to first tape the ETT in place and then confirm the position with auscultation.

We rarely use fluoroscopy, chest X-ray, or bronchoscopy to document the ETT position in the operating room. In our experience, intraoperative bronchial intubation is commonly precipitated by a cranial move of the carina, such as occurs during laparoscopic surgery, making such initial documentation less useful.

*Seattle Children’s Hospital, Seattle, Washington. christer.jonmarker@seattlechildrens.org

Hunyady AI, Pieters B, Johnston TA, Jonmarker C: Front teeth-to-carina distance in children undergoing cardiac catheterization. Anesthesiology 2008; 108:1004–8
Morgan GAR, Steward DJ: Linear airway dimensions in children: including those with cleft palate. Can Anaesth Soc J 1982; 29:1–8
Mariano ER, Ramamoorthy C, Chu LF, Chen M, Hammer GB: A comparison of three methods for estimating appropriate tracheal tube depth in children. Pediatr Anesth 2005; 15:846–51
Phipps LM, Thomas NJ, Gilmore RK, Raymond JA, Bittner TR, Orr RA, Robertson CL: Prospective assessment of guidelines for determining appropriate depth of endotracheal tube placement in children. Pediatr Crit Care Med 2005; 6:519–22