The Performance of the Neck Circumference for a Difficult Laryngoscopy in Obese Patients.

BACKGROUND AND OBJECTIVE There is conflicting evidence as to whether neck circumference (NC) is related to a difficult laryngoscopy in obese patients. The objectives of this study were to determine the performance of the NC in defining a difficult laryngoscopy, and to identify factors predicting a difficult laryngoscopy among those obese patients. MATERIAL AND METHOD This prospective study was conducted in adult patients with a body mass index (BM) of greater or equal to 30 kg/m² who underwent conventional endotracheal intubation. Preoperative NC, the modified Mallampati test (MMT), the thyromental distance (TM) and the sternomental distance (SM) were measured. A difficult laryngoscopy was defined as a Cormack-Lehane laryngoscopic view of grade III or IV. RESULTS Five hundred patients (366 females; 134 males), with a mean BMI of 34.3 ± 4.6 kg/m² (minimum = 30.0 kg/m², and maximum = 68.4 kg/m²) and who had elective surgery planned, were enrolled. The incidence of a difficult laryngoscopy was 7.2%. The overall performance of the NC using the area under the receiver operating characteristic curves of a difficult laryngoscopy was 0.574, with a 95% confidence interval (CI) of 0.53 to 0.618. The optimal cutoff point of the NC for a difficult laryngoscopy was 37.1 centimeters. It provided sensitivity and specificity of 75.5% (95% CI 57.8, 87.9) and 42.5% (95% CI 37.9, 47.2). The positive and negative predictive values were 9.2% and 95.6%. After multivariate analysis, factors affecting a difficult laryngoscopy were high grades of MMT (odds ratio (OR) 2.23, 95% CI 1.10, 4.50) and NC/TM (OR 1.78, 95% CI 1.15, 2.74). CONCLUSION The NC per se was not a good predictor of a difficult laryngoscopy. However the ratio of the NC to the TM and the MMT were factors predicting a difficult laryngoscopy in obese patients.