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BACKGROUND: In healthy patients, the narrowest diameter of the subglottic upper airway is the width of the air-column at the level of the cricoid cartilage. This diameter governs the selection of the endotracheal tube size, as excessive tube diameter may damage the tracheal mucosa leading to postextubation stridor or subglottic stenosis. Unfortunately, selecting endotracheal tube size based on height, weight, or age does not reliably lead to the proper tube. The knowledge of airway diameter, especially using a bedside noninvasive tool, could therefore be helpful in anesthesia and intensive care. METHODS: We studied 19 healthy volunteers (27 +/- 3 yr, nine females) to compare the transverse diameter of the cricoid lumen assessed by ultrasonography and magnetic resonance imaging. RESULTS: We found a strong correlation between the two techniques (r = 0.99, P < 0.05) confirmed by Bland-Altman analysis with a bias of 0.14 mm, a precision of 0.33 mm, and limits of agreement of -0.68 mm/0.96 mm. CONCLUSION: In young healthy adults, ultrasonography appeared to be a reliable tool to assess the diameter of the subglottic upper airway.
Lakhal et al. (2007) studied this question.