Submandibular Sonography

Abstract

The aim of this study was to evaluate the feasibility of sonography as a tool to measure the hyomental distance ratio and tongue size in obese patients with a large neck circumference. The hyomental distance ratio is a predictor of difficult laryngoscopy that may result in difficult intubation. Five obese and 7 morbidly obese adult patients with a history of either difficult or easy intubation had a submandibular sonographic examination performed in the supine position. The hyomental distance was measured while the head was placed in the neutral position and then in a hyperextended position, and the ratio of two distances (hyomental distance ratio) was calculated. Their tongue volumes were derived from multiplication of the midsagittal cross-sectional area of the tongue by its width obtained from transverse sonograms. The mean hyomental distance ratios ± SD in 6 patients with difficult intubation and 6 with easy intubation were 1.02 ± 0.01 and 1.14 ± 0.02 (P < .002), respectively. Tongue volumes did not differ statistically between the two groups: 137 ± 29 cm(3) (difficult intubation) and 168 ± 34 cm(3) (easy intubation). The mean body mass indices were 36.3 ± 6.0 and 43.2 ± 7.2 kg/m(2) in the difficult and easy intubation groups. The mean neck circumferences were 44.5 ± 7.4 and 46.8 ± 7.0 cm in the difficult and easy intubation groups. Sonography allows bedside measurements of the hyomental distance ratio and tongue size in morbidly obese patients. Preoperative assessment of the hyomental distance ratio may predict difficult laryngoscopy resulting in difficult intubation.