Sternomental Displacement and Neck Circumference. A New Look for the Neck as a Difficult Airway Predictor in Obese Surgical Patients. A Cohort Study

Abstract

Background Sternomental displacement (SMDD) is a surrogate indicator for cervical spine (C-spine) mobility. SMDD revealed good potentials to predict difficult airway, but its validity in obese patients is not evident. This study assessed the performance of SMDD with neck circumference (NC) in predicting difficult airway in obese surgical patients. Methods The study involved 135 adult patients with BMI ≥ 35 kg/m2, scheduled for elective surgeries under general anesthesia with endotracheal tubes (ETT) inserted using Macintosh laryngoscopes. The airway was assessed using SMDD, NC, and Modified Malampati test (MMT). Difficult laryngoscopy view (DLV) was defined as Cormack–Lehane (C-L) grade ≥ 3. The accuracy of the SMDD in predicting DLV was set as the primary endpoint, while the accuracy of the SMDD compared to that of NC, MMT, and NC/SMDD ratio in predicting difficult airway was set as the secondary endpoint. Results The DLV cases were 28 of 135 (20.7%), with a mean body mass index (BMI) of 41.1 ± 3.3 kg/m2. SMDD < 5cm and NC > 43 cm could predict DLV with an area under the receiver operating characteristic curve (AUROC) of 0.97 and 0.83 respectively. SMDD and NC revealed a good negative correlation (r = - 0.6; 95% CI= 0.7 to 0.4; p= 0.0001). The NC/SMDD ratio had the best predition for DLV (AUROC of 0.98 at a cut-off value > 7.8). Conclusion In obese surgical patients, the SMDD and NC/SMDD ratio are excellent predictors for DLV when the cut-off values are < 5cm and > 7.8, respectively. Trial registration : ClinicalTrials.gov identifier: ID: NCT04524546 Registered in August 2020.