A comparison of the ratio of patient's height to thyromental distance with the modified Mallampati and the upper lip bite test in predicting difficult laryngoscopy

Abstract

Background:The aim of the present study was to compare the ability to predict difficult visualization of the larynx from the following preoperative airway predictive indices, in isolation and combination: modified Mallampati test (MMT), the ratio of height to thyromental distance (RHTMD) and the Upper-Lip-Bite test (ULBT).Methods:We collected data on 603 consecutive patients scheduled for elective surgery under general anesthesia requiring endotracheal intubation and then evaluated all three factors before surgery. An experienced anesthesiologist, not informed of the recorded preoperative airway evaluation, performed the laryngoscopy and grading (as per Cormack and Lehane's classification). Sensitivity, specificity, and positive and negative predictive value, Receiver operating characteristic (ROC) Curve and the area under ROC curve (AUC) for each airway predictor in isolation and in combination were determined.Results:Difficult laryngoscopy (Grade 3 or 4) occurred in 41 (6.8%) patients. The main endpoint of the present study, the AUC of the ROC, was significantly lower for the MMT (AUC, 0.511; 95% CI, 0.470–0.552) than the ULBT (AUC, 0.709; 95% CI, 0.671–0.745, P=0.002) and the RHTMD score (AUC, 0.711; 95% CI, 0.673–0.747, P=0.001). There was no significant difference between the AUC of the ROC for the ULBT and the RHTMD score. By using discrimination analysis, the optimal cutoff point for the RHTMD for predicting difficult laryngoscopy was 21.06 (sensitivity, 75.6%; specificity, 58.5%).Conclusion:The RHTMD is comparable with ULBT for prediction of difficult laryngoscopy in general population.

Evaluation of difficult airway in paediatric population ranging from 5-12 years age group

“…The diagnostic accuracy of this test is also less among all the other tests. Safavi et al [27] in their study on 603 adult subjects for comparing ULBT, RHTMD with MMT for difficult laryngoscopy and intubation found that RHTMD has some limitations. It depends on accurate measurement of patient's TMD and height that lessens simplicity of this method.…”

The predictive value of the ratio of neck circumference to thyromental distance in comparison with four predictive tests for difficult laryngoscopy in obstetric patients scheduled for caesarean delivery

“…RHTMD measurement has high sensitivity than other tests and is sufficiently sensitive to detect possible difficulties with laryngoscopy and intubation. [ 20 21 ]…”

Prediction of Difficult Laryngoscopy in Pregnant Women Undergoing Cesarean Section Using the Hyomental Distance in fully extended and neutral position of neck, in Comparison With four usual bedside tests: A prospective blinded study

“…The ratio was calculated [5] . RHTMD: Thyromental distance was measured from the bony point of the mentum while the head was fully extended with close mouth.Then the ratio of height to TMD was calculated [7] .…”

“…Recently "i" studies have shown that NC/TMD is a sensitive test to predict diicult airway in general population [5] and obstetrics [6] . Also RHTMD (Ratio of Height to Thyromental Distance) that has high sensitivity, is suiciently sensitive to detect possible diiculties with laryngoscopy and intubation in obstetrics(AUC = 0.627, 95% CI, 0.589-0.664) [7] . The modiied Mallampati classiication has poor prognostic value [2,[6][7][8] in many studies.…”

“…Also RHTMD (Ratio of Height to Thyromental Distance) that has high sensitivity, is suiciently sensitive to detect possible diiculties with laryngoscopy and intubation in obstetrics(AUC = 0.627, 95% CI, 0.589-0.664) [7] . The modiied Mallampati classiication has poor prognostic value [2,[6][7][8] in many studies. In addition, Savva [8] showed that modiied Mallampati test (MMT) was neither sensitive nor speciic enough as a single test in predicting diicult intubation in parturient patients.…”