Neck circumference to inter-incisor gap ratio: a new predictor of difficult laryngoscopy in cervical spondylosis patients

BACKGROUND Preoperative airway assessment help anticipate a difficult airway. We hypothesized that a close association existed between difficult laryngoscopy and the neck circumference/inter-incisor gap ratio (RNIIG). Our aim was to determine its utility in predicting difficult laryngoscopy in cervical spondylosis patients. METHODS Two hundred thirteen consecutive patients, aged 20-70 years, scheduled to undergo cervical spine surgery under general anesthesia, were recruited. Preoperative assessments included inter-incisor gap (IIG), thyromental distance (TMD), neck circumference (NC), NC/IIG ratio (RNIIG), NC/TMD ratio (RNTMD) and modified Mallampati test (MMT). Cormack-Lehane scales were assessed during intubation. The anesthesiologist was blinded to the airway assessments. RNIIG's ability to predict difficult laryngoscopy was compared with that of established predictors. RESULTS Difficult laryngoscopy incidence was 16.4%. Univariate analysis showed that male gender, increased age, weight, NC, RNIIG and RNTMD, decreased IIG and TMD, and MMT 3 and 4 were associated with difficult laryngoscopy. Binary multivariate logistic regression analyses identified only one factor that was independently associated with difficult laryngoscopy: RNIIG. The odds ratio and 95% confidence interval (95% CI) were 1.932 (1.504-2.482). RNIIG (≥9.5) exhibited the largest area under the curve (0.80; 95% CI 0.73-0.86) and the highest sensitivity (88.6%; 95% CI 78.1-99.1) and negative predictive value (96.6%; 95% CI 94.0-99.2), confirming its better predictive ability. CONCLUSIONS RNIIG is a new and simple predictor with a higher level of efficacy, and could help anesthetists plan for difficult laryngoscopy management in cervical spondylosis patients. TRIAL REGISTRATION ChiCTR-OON-16008320 (April 19th, 2016).