Thyromental height test as a predictor of difficult airway. Single test versus multivariate predictive models. A cohort study

Abstract

Background Thyromental height test (TMHT) revealed good potential to predict difficult airway but with variable cut-off values. This study aimed to assess the validity of TMHT either as a sole test or within multivariable models for predicting difficult airway.Methods The study included 612 patients aged ≥18 years who were scheduled for elective surgeries under general anaesthesia with an endotracheal tube. Airway was assessed with TMHT, Thyromental distance (TMD), Sternomental distance (SMD), inter-incisor distance (IID), and Modified Mallampati test (MMT). The difficult laryngoscopy (DL) was defined as Cormack–Lehane (C-L) grade > 2. The primary outcome was the validity of TMHT as a predictor for DL.Results Cases with DL were 56 (9.2%) patients, while cases with difficult intubation (DI) were 7 (1.1%). The TMHT was significantly shorter in cases with DL compared to easy laryngoscopy (45.82 ± 8.21 versus 56.93 ± 8.83 mm, respectively) and in cases with DI compared to easy intubation (42 ± 7.19 versus 56.07 ± 9.24 mm respectively). TMHT was a good predictor for both DL and DI at a cut-off value of ≤ 48 mm with an AUROC (Area Under the Receiver Operating Characteristic) curve of 0.82 (95% CI: 0.79 to 0.85) and 0.89 (95% CI: 0.82 to 0.92), respectively. The logistic regression analysis incorporated the TMHT within two multivariable predictive models for DL and DI with better predictive ability.Conclusion In adult surgical patients, TMHT is a good objective predictor for DL and DI. The predictive ability increased when incorporated into two multivariable models.Trial registration ClinicalTrials.gov, ID: NCT04264338 in February 2020.

Keywords

• Thyromental height test
• thyromental distance
• sternomental distance
• modified mallampati
• airway predictive models
• difficult intubation