Background
Sternomental displacement (SMDD) is a surrogate indicator for cervical spine (C-spine) mobility. SMDD revealed good potential to predict difficult airway, but its validity in obese patients is not evident. Therefore, this study assessed the performance of SMDD with neck circumference (NC) in predicting difficult airway in obese surgical patients. The study involved 135 adult patients with body mass index (BMI) ≥ 35 kg/m scheduled for elective surgeries under general anesthesia with endotracheal tubes (ETT) inserted using Macintosh laryngoscopes. The airway was assessed using SMDD, NC, and modified Mallampati 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 BMI of 41.1 ± 3.3 kg/m. 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 had a good negative correlation ( =  − 0.6; 95% CI = 0.7 to 0.4;  = 0.0001). The NC/SMDD ratio had the best prediction for DLV (AUROC of 0.98 at a cut-off value  > 7.8).
Conclusions
In obese surgical patients, SMDD and NC/SMDD ratios are excellent predictors for DLV when the cut-off values are  < 5cm and  > 7.8, respectively.
Trial registration
ClinicalTrials.gov, NCT04524546. Registered in August 2020.