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).