# Flexible intubating video endoscope-guided determination of optimal oral endotracheal tube depth in infants: a prospective observational study

## TL;DR

This study evaluates formulas for predicting endotracheal tube depth in infants and proposes a new height-based formula that aligns better with direct visualization.

## Contribution

A new height-based predictive formula for endotracheal tube depth in infants, validated using flexible intubating video endoscopy.

## Key findings

- APLS and NRP formulas overestimated tube depth in 12.5% of neonates and 30.1% of older infants.
- Height showed the strongest correlation with optimal tube depth in infants aged 1–12 months (r = 0.952).
- A new formula (depth = 4.5 + 0.1 × height) was developed and showed better agreement with FIVE-referenced depth.

## Abstract

To assess the accuracy of Advanced Pediatric Life Support (APLS) and Neonatal Resuscitation Program (NRP) formulas for predicting oral endotracheal tube (ETT) depth in Chinese infants undergoing elective surgery, and to develop a flexible intubating video endoscope (FIVE)-verified predictive formula for this population.

In this prospective study, 189 infants (including term neonates and infants aged 1–12 months) who required oral intubation for elective surgery were enrolled. Demographics were recorded, and ETT depths were calculated using APLS and NRP formulas. A reference insertion depth was determined using FIVE, with the tube tip positioned 1 cm above the carina (a pragmatic reference position rather than a universal “ideal”). Correlations between patient characteristics and optimal depth were assessed, and new formulas were developed by linear regression.

In neonates, FIVE-confirmed depth correlated with height (r = 0.670, P < 0.001), weight (r = 0.488, P < 0.001), and body surface area (BSA) (r = 0.536, P < 0.001). In infants aged 1–12 months, stronger correlations were found with height (r = 0.952, P < 0.001), weight (r = 0.895, P < 0.001), BSA (r = 0.926, P < 0.001), and age in months (r = 0.871, P < 0.001). APLS and NRP formulas produced deeper predicted depths than the FIVE-referenced depth in 12.5% of neonates and 30.1% of older infants. New predictive formulas were: infants 1–12 months: depth (cm) = 4.5 + 0.1 × height (cm).

The weight-based APLS formula may be less applicable to Chinese infants undergoing elective surgery. A height-based formula demonstrated closer agreement with the FIVE-referenced depth. Because the model was developed and assessed in the same cohort, it should be considered preliminary and requires independent external validation (preferably multicenter) before widespread clinical use, particularly in non-elective or critically ill populations.