title: Novel measurements of the length of the subglottic airway in infants and young children.
abstract: BACKGROUND
  To date, the lengths of the subglottic and tracheal airway segments have been measured from autopsy specimens. Images of the head and neck obtained from computerized tomography (CT) provide an alternate method. Our objective in this study was to identify anatomic landmarks from CT scans in infants and young children to estimate the lengths of the subglottic and tracheal airway segments and to correlate these lengths with age.
  
  
  METHODS
  We performed a retrospective analysis of CT images of the neck for various diagnostic indications in children ≤3 years. We obtained planes of reconstruction at the level of the vocal cords (VCs), cricoid cartilage, and carina (C) which were parallel to each other and perpendicular to sagittal long axis of the trachea. The lengths of the subglottic airway (LengthSG) and total length of the laryngotracheal airway (LengthVC-C) were measured from the distance between, respectively, the VC versus cricoid cartilage and the VC versus C planes of reconstruction. Tracheal length was then calculated as the difference between LengthVC-C and LengthSG.
  
  
  RESULTS
  Fifty-six children met the inclusion criteria. There were 29 boys. The median weight was 10.7 kg (range 3.1-19.0 kg). Regression analysis yielded mean LengthSG (mm) = 7.8 + 0.03·corrected age (months), r(2) = 0.07, P = 0.056; lower and upper 95% confidence interval for β = 0.03 were -0.001 and 0061. The mean LengthSG was 8.4 mm with an SD of 1.4 mm. The 95th percentile for LengthSG was 10.8 mm, and the 5% to 95% interquartile range was 4.9 mm. The estimate for the 95% confidence interval of the 95th percentile was between 10.2 and 11.3 mm. The LengthVC-C increased with age: mean LengthVC-C (cm) = 5.3 + 0.05·corrected age (months), r(2) = 0.7, P < 0.001. Tracheal length also increased with age: mean tracheal length (cm) = 4.5 + 0.05·corrected age (months), r(2) = 0.6, P < 0.001.
  
  
  CONCLUSIONS
  We report a novel estimate method for the lengths of the airway segments between the VC and C in 56 infants and young children and suggest that the growth characteristics of the subglottic and tracheal airway may differ.
authors.affiliation: Department of Pediatric Anesthesia, Montreal Children’s Hospital, Montreal, Quebec, Canada.
authors.forename: Metee
authors.initials: M
authors.lastname: Sirisopana
authors.forename: Christine
authors.initials: C
authors.lastname: Saint-Martin
authors.forename: Ning Nan
authors.initials: NN
authors.lastname: Wang
authors.forename: John
authors.initials: J
authors.lastname: Manoukian
authors.forename: Lily H P
authors.initials: LH
authors.lastname: Nguyen
authors.forename: Karen A
authors.initials: KA
authors.lastname: Brown
mesh_terms: D000367:Age Factors; D059925:Anatomic Landmarks; D001835:Body Weight; D002675:Child, Preschool; D003413:Cricoid Cartilage / Q000000981:diagnostic imaging; D005260:Female; D005931:Glottis / Q000000981:diagnostic imaging* / Q000254:growth & development; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007442:Intubation, Intratracheal / Q000295:instrumentation; D008297:Male; D056888:Patient Positioning; D011237:Predictive Value of Tests; D011873:Radiology Information Systems; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed; D014132:Trachea / Q000000981:diagnostic imaging; D014827:Vocal Cords / Q000000981:diagnostic imaging