Ultrasound and a new videobronchoscopic technique to measure the subglottic diameter.

OBJECTIVE: The aim of this study was to evaluate ultrasound (US) and a new videobronchoscopic (VB) technique in the measurement of the subglottic lumen diameter.

DESIGN: This blind prospective animal study of 62 recently sacrificed rabbits was conducted at the Montreal Children's Hospital.

METHODS: Three different diameter measurements of the subglottis were assessed using B-mode US on each intact animal. The same diameter measurements, as well as a fourth, were estimated with a VB measuring technique. Finally, the subglottic area was surgically exposed allowing for direct caliper measurements of all four corresponding diameters. All three US measurements on each of the 62 rabbits and all four VB measurements on each of the 60 rabbits were compared with the gold standard corresponding caliper measurements.

RESULTS: Statistical analysis revealed strikingly convergent values in subglottic lumen diameter measurements using US and calipers. The mean difference between these methods for all 186 observations was 0.11 mm. With 95% confidence, the maximum discordance was less than 0.30 mm on the smallest evaluated lumen. Convergent values were also demonstrated in subglottic lumen diameter measurements using VB and calipers. The mean difference between these methods for all 240 observations was 0.16 mm. With 95% confidence, the maximum discordance was less than 0.37 mm on the smallest evaluated lumen. Pearson's correlation coefficient supported a strong and positive relationship between US and caliper measurements as well as VB and caliper measurements. Simple linear regression model indicated that the subglottic lumen diameter could be predicted by both US and our VB technique.

CONCLUSION: This work represents the first attempt to validate B-mode US and a VB technique as measuring tools for the subglottic lumen diameter. Our results have clearly shown that both methods are precise measuring modalities for this purpose. With further studies, these two objective methods of measuring the subglottic diameter could be adopted universally. The precise knowledge of this diameter could help physicians recognize and describe the severity of a narrowed lumen. Reporting results in such a standardized fashion, by either US or VB, could facilitate communication among clinicians and institutions.