Working with estimation-formulas to predict nasopharyngeal airway insertion depth in children: Looking at magnetic resonance images - A prospective observational study (WEND:LI-Study)

To determine the accuracy of the recently proposed landmark-method 'nostril-to-tragus minus 10 mm' and compare with ERC-recommended distances for nasopharyngeal airway length sizing in children.We conducted a prospective observational study in sedated children 12 years. Nasopharyngeal airways were inserted following 'nostril-to-tragus minus 10 mm'. Primary outcome was the rate of nasopharyngeal airway tips between soft palate and epiglottis on magnetic resonance imaging (MRI) indicated for medical reasons. An optimal placement was defined when the tip lied within 25-75% of the total soft palate-to-epiglottis distance. Between 0-100% of this distance, placement was still considered acceptable, below 0% too proximal or above 100% too distal. Secondary outcomes were the rate of adverse events, the qualitative positions of airway tips, and the comparison of ́nostril-to-tragus minus 10 mḿ with the ERC-recommended distances 'nostril-to-angle of the mandible' and 'nostril-to-tragus' with objective MRI measurements.We analysed 92 patients with a mean age of 4.3 years. Nasopharyngeal airways were optimally placed in 37.0% (8.7% too proximal-77.2% acceptable-14.1% too distal). Three qualitative malpositions, but no airway-associated adverse event occurred. Objective measurements on MRI revealed the probability of 40.2% optimally placed nasopharyngeal airways (5.4%-67.4%-27.2%) for 'nostril-to-tragus minus 10 mm', 38.0% (17.4%-58.7%-23.9%) for 'nostril-to-mandible' and 13.0% (0%-28.3%-71.7%) for 'nostril-to-tragus', respectively.No landmark-method predicted nasopharyngeal airway position reliably. 'Nostril-to-tragus minus 10 mm' seems the least inaccurate one and could be a valuable approximation until another estimation-formula proves more accurate. During insertion, careful clinical evaluation of airway patency is crucial.German Clinical Trials Register; DRKS00021007.