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
Banjong Krobbuaban MD*, Siriwan Diregpoke BN*, Sujarit Kumkeaw BN*
Affiliation : * Division of Anesthesiology, Chaiyaphum Hospital, Chaiyaphum
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.
Materials 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 predict-
ing difficult intubation than TMD.
Keywords : Laryngoscopy, Difficult, Predictive test
