Conclusion
A reliable method of estimating the nasopharyngeal depth will lend confidence and clarity to healthcare providers of important nasopharyngeal diagnostic tests and will guide other applications relying on accurate blind estimations of this distance, including nasogastric tube placement and NP temperature probe placement. This study has demonstrated a near 1:1 ratio of nasopharyngeal depth to the tragus-to-philtrum coronal plane distance and has confirmed its persistence between sex and ethnicity in subgroup analysis. As such, individually optimized nasopharyngeal depth seems to be a supportive tool for safe NP procedures and can be clinically predicted by simply measuring the distance from the tragus to a plane perpendicular to the philtrum on a lateral view.