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The gold standard for confirming ETT position is a chest xray, but this can often be delayed while the patient is stabilized. Many physicians will estimate ETT insertion depth to be 3x the ETT size, but this is based on selection of the correct tube. There are several other published formulas, including the PALS guidelines [age in years/2 + 12] which applies to children older than one year. In 1982, there was an article published that cited the formulas of [Height (cm) x 0.1 +5] or [Weight(kg)/5 + 12].
This was a retrospective study where the ideal position of cuffed ETT (from the front teeth) was determined by looking at post intubation xrays of 167 patients between 28 days and 18 years. The individual optimal ETT insertion depth was plotted against age, weight and height for all children. This study showed that there is not a fully linear relationship between age, height or weight which is a flaw of all of these formulas. Calculations using the patients’ weight performed the worst. Age based and height formulas performed the best.
References
Ebenebe et al. Recommendations for endotracheal tube insertion depths in children. Emerg Med J 2023; 0:1-5. epub ahead of print.