Comparison of Focused Upper Airway Ultrasonographic and Anthropometric Measurements for Predicting Difficult Intubation: A Prospective Observational Study.

Background and

Objectives

The prediction of difficult laryngoscopic view remains an important component of preoperative airway assessment. Conventional bedside tests are widely used, but their diagnostic performance may be limited by subjectivity and interobserver variability. Focused upper airway ultrasonography may provide objective anatomical information and complement standard clinical evaluation. This study aimed to evaluate the diagnostic accuracy of focused upper airway ultrasonographic and conventional anthropometric measurements for predicting difficult laryngoscopic view in adult patients scheduled for tracheal intubation. Materials and

Methods

This single-center, prospective, observational study included 212 adult patients with American Society of Anesthesiologists physical status I-III who were scheduled for elective surgery under general anesthesia requiring tracheal intubation. Preoperative airway assessment included the Modified Mallampati classification, upper lip bite test, mouth opening, thyromental distance, and sternomental distance. Focused ultrasonographic measurements included hyoid-skin distance and epiglottis-skin distance. Difficult laryngoscopic view was defined as a Cormack-Lehane grade III-IV view recorded during the initial direct laryngoscopic assessment. Diagnostic performance was evaluated using receiver operating characteristic curve analysis, and independent predictors were assessed using multivariable logistic regression.

Results

Difficult laryngoscopic view was identified in 44 of 212 patients (20.8%). Patients with difficult laryngoscopic view had significantly higher body weight and body mass index, smaller mouth opening, and greater hyoid-skin distance. Hyoid-skin distance was significantly greater in patients with difficult laryngoscopic view than in those without difficult laryngoscopic view (12.00 ± 2.79 mm vs. 10.33 ± 3.16 mm; p = 0.002). Mouth opening was significantly smaller in patients with difficult laryngoscopic view (4.39 ± 0.72 cm vs. 4.74 ± 0.99 cm; p = 0.030). Epiglottis-skin distance did not differ significantly between groups. In receiver operating characteristic analysis, hyoid-skin distance showed an area under the curve of 0.682, with a cut-off value of ≥12.05 mm, sensitivity of 47.73%, and specificity of 83.33%. In multivariable logistic regression analysis, body mass index and hyoid-skin distance were independently associated with difficult laryngoscopic view, whereas greater mouth opening had a protective effect. The combined multivariable model showed an area under the curve of 0.734; however, at a probability cut-off value of 0.5, its sensitivity was low at 15.9%, despite high specificity of 97.0%.

Conclusions

Focused upper airway ultrasonography may provide complementary objective information when used together with conventional preoperative airway assessment. Hyoid-skin distance was independently associated with difficult laryngoscopic view and demonstrated relatively high specificity; however, its discriminatory performance was modest and its sensitivity was limited. Therefore, hyoid-skin distance and the combined model should not be interpreted as standalone screening tools for excluding difficult laryngoscopic view. Their main clinical value may be as adjunctive parameters that support risk stratification and advance airway management planning in selected patients.