An assessment of the ratio of height to thyromental distance compared to thyromental distance as a predictive test for prediction of difficult tracheal intubation in Thai patients

Abstract

Background and rationale: Preoperative evaluation is important in the detection of patients at risk for difficult tracheal intubation. Thyromental distance (TMD) is often used for these purposes, but its value as an indicator for difficult intubation is questionable, as it varies with patient size and body proportions. The purpose of the present study was to evaluate and compare the accuracies of the ratio of patient's height to TMD (ratio of height to TMD = RHTMD) and TMD alone in the prediction of difficult tracheal intubation in Thai patients.

Material and methods: The authors collected data on 382 consecutive patients scheduled to receive general anesthesia requiring endotracheal intubation for elective surgery. Thyromental distance and RHTMD were evaluated preoperatively. Difficult intubation was defined in the present study by Cormack and Lehane grade 3 or 4. The optimal predictive value was chosen using a receiver operating characteristic (ROC) curve. The areas under the ROC curves (AUC) of TMD and RHTMD were compared to determine the performance of the different predictive tests used. The sensitivity, specificity, and positive and negative predictive values of each of the predictive tests were calculated according to standard formulae.

Results: Difficult intubation occurred in 42 patients (10.9 %). The predictive advantage of RHTMD has a similar specificity with improved sensitivity in comparison with TMD. The AUC of RHTMD was significantly greater than the AUC of TMD (p = 0.00). The authors concluded that RHTMD had better accuracy in predicting difficult intubation than TMD.