Ultrasonography in the preoperative difficult airway assessment

To evaluate the utility of ultrasound for detection of the difficult intubation in a preoperative setting. PubMed, Ovid, CINAHL Plus Full Text, and Google Scholar searches using [“difficult airway” OR “difficult intubation” OR “difficult laryngoscopy” OR “difficult ventilation”] AND [ultrasonography OR sonography OR ultrasound] without date limitations. Abstracts without publications, case reports, letters, textbooks, unrelated topics, or foreign language articles were excluded. Ancestry references were included from the reviewed articles. Two reviewers independently performed the query. Each study was reviewed using the STARD checklist to assess blinding, incomplete data reporting, subject attrition, and selection of appropriate statistical tests. Ten studies were included. All used convenience sampling of adult subjects requiring direct laryngoscopy in elective surgical settings. One study is retrospective and nine are prospective observational. Populations included non-obese, obese, pregnant, and thyroidectomy patients in the United States, Turkey, Israel, Canada, Portugal, and China. Airway locations scanned are variable using different protocols and patient positioning. The outcome variable is uniformly the Cormack–Lehane Grade. 114 of the 681 total subjects had difficult laryngoscopies. Significance for sonographic prediction of difficult laryngoscopy occurred at three locations: hyomental distance [52.6 ± 5.8 mm (p < 0.01)], anterior tissue at the hyoid bone [16.9 mm (95 % CI 11.9–21.9) and 15.9 ± 2.7 mm (p < 0.0001)], and the thyrohyoid membrane [34.7 mm (95 % CI 28.8–40.7) and 23.9 ± 3.4 mm (p < 0.0001) and 28.25 ± 4.43 mm (p < 0.001)]. The vocal cords and sternal notch levels have conflicting significance. Limitations include the heterogeneous populations and lack of standard scanning protocols.