Sonoanatomy of the difficult airway. A case-control study.

Introduction and objectives: The occurrence of a difficult airway during intubation is a critical event in anaesthesia. Despite the usefulness of clinical predictors, difficult intubation frequently arises unexpectedly. The aim of this study was to determine the utility of airway ultrasound in detecting these patients.

Materials and methods: This was a case-control study. The patients in the case group were identified from the registry of patients with reports of difficult laryngoscopy (Cormack III and IV). The controls were selected from among patients classed as Cormack I who underwent surgery under general anaesthesia. Fifty patients (25 cases and 25 controls) participated in the study. All patients underwent ultrasound to obtain 3 measurements: distance from the skin to the hyoid bone, distance from the skin to the epiglottis, and distance from the skin to the vocal cords.

Results: A skin-to-hyoid bone distance greater than 9.8 mm (50% of the sample) generated an odds ratio of 5.46 (p = 0.005); a skin-to-epiglottis distance greater than 21.3 mm (50% of the sample) generated an odds ratio of 6.62 (p = 0.002). There was no significant difference in the skin-to-vocal cords distance.

Conclusions: Ultrasound has proven to be a useful tool for predicting difficult laryngoscopy. Despite the low sensitivity of clinical predictors, they appear to improve the detection of patients with difficult laryngoscopy when integrated into predictive models alongside ultrasound values.