Assessment of the Thyromental Height Test as an Effective Airway Evaluation Tool

Comparison of airway assessment tests for prediction of difficult intubation in obese patients: importance of thyromental height and upper lip bite test

BACKGROUND

Prediction of difficult intubation (DI) has remained challenging for anesthesiologists and validity of airway assessment tests has not been fully investigated. This study aims to compare predictive values of these tests for prediction of DI in obese patients.

METHODS

196 patients with body mass index (BMI) ≥ 30 kg/m2 were included in this prospective study. Variables including intubation difficulty scale (IDS), thyromental height (TMH), hyomental distance (HMD) in extent and neutral neck position, HMD ratio (HMDR), sternomental distance (SMD), thyromental distance (TMD), ratio of height to TMD (RHTMD), width of mouth opening (MO), mandibular length (ML), Cormack-lehane (C-L) grade, upper lip bite test (ULBT), history of snoring, and obstructive sleep apnea were collected. Multiple logistic regression and receiver operating characteristic (ROC) curve analysis were used to determine independent predictors of DI (defined as IDS≥5) and their cut off points.

RESULTS

DI and difficult laryngoscopy (defined as C-L grade ≥3) were observed in 23% and 24.5% of the study population, respectively. Multiple logistic regression identified TMH (Odds ratio (OR):0.28, 95% confidence interval (CI):0.14-0.58, p=0.001), BMI (OR:1.18, 95% CI: 1.11- 1.26, p<0.001), HMDR (OR:0.45, 95% CI:0.36-0.56, p<0.001) and ULBT (OR: 3.91, 95% CI: 2.14-7.14, p<0.001) as independent predictors of DI. Sensitivity of TMH<4.8 cm, BMI>34.9 kg/m2, HMDR<1.4 and ULBT class≥2 were determined as 75.1%, 73.3%,62.3% and 93.3% respectively.

CONCLUSIONS

TMH and ULBT had the highest sensitivity for prediction of DI in obese patients in this study and it is recommended to be considered as part of airway assessment in this patient population.