A comparison of the ratio of patients height to thyromental distance with upper lip bite test and modified mallampati test in predicting difficult laryngoscopy

Abstract

BACKGROUND: Preoperative airway assessment is essential for predicting difficult laryngoscopy and intubation but which airway predictors and clinical factors are best predictors is controversial.
OBJECTIVES: To compare the predictive value of modified Mallampati test, upper lip bite test and the ratio of height to thyromental distance in isolation and in various combinations in predicting difficult laryngoscopy and intubation.
PARTICIPANTS: Total 300 adult patients having ASA I-III status scheduled for elective abdominal, gynecological and urological surgeries under general anesthesia.
STUDY DESIGN: Prospective observational study
METHODS: We collected data on 300 consecutive patients scheduled for elective surgery under general anaesthesia requiring endotracheal intubation and the modified Mallampati test, the upper lip bite test and the ratio of height to thyromental distance tests were evaluated in all patients before surgery. An experienced anaesthesiologist, not informed of the preoperative airway evaluation , performed laryngoscopy and grading as per Cormack and Lehane’s classification. Sensitivity, specificity, and positive and negative predictive value, Receiver operating characteristics(ROC) curve and the area under ROC Curve(AUC) for each airway predictor in isolation and in combination were determined.
RESULTS: Difficult laryngoscopy(Grade III&IV) occurred in 88 patients. The main end point of the present study , the AUC of the ROC was significantly lower for the MMT(AUC,0.73, p value 0.106) than the upper lip bite test(AUC,0.82 ,p value 0.024) and the ratio of height to thyromental distance score(AUC,0.85, p value 0.015).
CONCLUSION: By using various statistical parameters it was found that the ratio of height to thyromental distance(RHTMD) when used alone is the most sensitive and specific test in predicting difficult laryngoscopy and intubation (Sensitivity 89.62%, specificity 94.32%). Combination of these three tests have better predictive value for difficult laryngoscopy and intubation as compared to these tests in isolation.
IMPLICATIONS: No single test can accurately predict difficult laryngoscopy and intubation Combination of tests are required to accurately predict difficult laryngoscopy and intubation.