Prediction of difficult laryngoscopy in obese patients by ultrasound quantification of anterior neck soft tissue

In 50 morbidly obese patients, we quantified the soft tissue of the neck from the skin to the anterior aspect of the trachea at the vocal cords using ultrasound. Thyromental distance, mouth opening, limited neck mobility, modified Mallampati score, abnormal upper teeth, neck circumference and sleep apnoea were assessed as predictors of difficult laryngoscopy. Of the nine (18%) cases of difficult laryngoscopy, seven (78%) had a history of obstructive sleep apnoea, compared with two of the 41 patients (5%) in whom laryngoscopy was easy (p < 0.001). Patients in whom laryngoscopy was difficult had more pretracheal soft tissue (mean (SD) 28 (2.7) mm vs. 17.5 (1.8) mm; p < 0.001) and a greater neck circumference (50 (3.8) vs. 43.5 (2.2) cm; p < 0.001). None of the other predictors correlated with difficult laryngoscopy. We conclude that an abundance of pretracheal soft tissue at the level of the vocal cords is a good predictor of difficult laryngoscopy in obese patients.