Comparison of sonographic hyomental distance ratio and thyromental height as predictors of difficult intubation

Abstract

Background

Preoperative airway assessment has always been dynamic to quantify a single parameter that identifies difficult airway reliably and therefore newer modalities are introduced, researched and compared amongst themselves. Thyromental height (TMH) and hyomental distance ratio (HMDR) have been recently developed and validated as good diagnostic tools for difficult airway prediction. However, they have not been compared with respect to each other as to define the superiority amongst the two and thus present trial was designed to assess the same.

Method

400 patients >18 years of age undergoing elective surgery under general anaesthesia were enrolled in the study. In addition to the standard airway parameter assessment, preoperative TMH and sonographic HMDR was also recorded which was correlated with Cormack Lehane (CL) grade and percentage of glottic opening (POGO) score of laryngoscopy to grade a difficult airway.

Results

HMDR (83 %) was found to be more accurate in predicting difficult intubation than TMH (56.5 %). Though the sensitivity of TMH (70.83 %) and HMDR (68 %) were comparable, HMDR (84.66 %) was found to be more specific than TMH (54.83 %) for a difficult airway prediction. The cut off values for HMDR and TMH for predicting difficult intubation, derived from the present study from the ROC curves and AUC was found to be 1.26 and 5.05 cm respectively.

Conclusions

HMDR outstrips TMH with a good sensitivity and specificity for difficult airway prediction. In conclusion, we recommend the use of sonographically derived HMDR as a reliable airway assessment parameter to predict a difficult airway.