Introduction:

The significance of difficult or failed tracheal intubation is well recognized as a major cause of morbidity and mortality in anaesthetic practice. The importance of preoperative prediction of a difficult airway is obvious from the fact that 85% of all mistakes regarding airway management result in permanent cerebral damage and up to 30% of all anaesthetic deaths can be attributed to the management of difficult airways.

Study procedure:

We conducted a prospective observational study to evaluate Upper lip bite test(ULBT) and Thyromental height(TMHT) in predicting difficult laryngoscopy. After ethical committee approval, the study was conducted on 109 patients satisfying the inclusion and exclusion criteria.

Patients included in the study underwent a routine pre anaesthetic check-up and routine preoperative investigations and investigations relevant to the surgery were obtained. Age, gender, weight, BMI, Medical history and ASA physical status of all patients were recorded. Preoperative assessment included airway assessment by Modified Mallampati Test(MMT), Upper Lip Bite Test(ULBT) and Thyromental height test(TMHT) and the findings were recorded by the principal investigator who was not involved in doing laryngoscopy of the subjects.

On the day of surgery, it was confirmed that patients had fasted for at least 6 hours prior to surgery. After being taken in the operation theatre, routine institutional protocol was followed for general anaesthesia. After the induction of anaesthesia, the patient’s head and neck were kept in sniffing position, laryngoscopy was done using Macintosh laryngoscope with blade no 3 or 4 depending upon personal preferences by an senior anaesthesiologist with at least 2 years of experience. Glottic view was graded without any external pressure or other manoeuvres applied according to the Cormack and Lehane(CL) grading and the reading noted in anaesthesia sheet. CL grade 3 and 4 were considered as difficult intubation.

Result summary:

In this study, using  MMT there were 1(0.9%) true positive; 5(4.6%) false positive; 15(13.8%) false negative and 88 (80.7%) true negatives. The sensitivity of MMT was found to be 6.25%%. The specificity was 94.62%, positive predictive value was 16.67% and the negative predictive value was 85.43%. The accuracy of MMT was 81.65% in this study.

With ULBT, true positives were 3(2.7%), false positive were 2(1.8%), true negatives were 91(83.4%) and false negative were 13(11.9%) respectively. The sensitivity, specificity, positive predictive value and negative predictive value and was 18.75%, 97.85%, 60.0% and 87.5% respectively. The accuracy of ULBT in this study was found to be 86.23%.

With TMHT, true positives were 13(11.9%), false positives were NIL, true negatives were 93(85.3%) and false negatives were 3(2.8%) respectively. The sensitivity of TMHT test was found to be 81.25% and specificity was found to be 100%. Positive predictive value was found to be 100%, negative predictive value was 96.87% and accuracy was 90.62% in our study.

All the validity parameters for TMHT were found to be superior to MMT and ULBT and were statistically significant as per Mc Nemar’s test.

Combining the ULBT and TMHT was of statistical significance than that of ULBT alone. Also combination of two test had the added clinical advantages of both the tests. Also, both the tests have high negative predictive value (87.5% for ULBT and 96.87% for TMHT) thus stressing the fact that both these tests can be good predictors of easy intubation.

Conclusion:

Thus, our study suggests that TMHT is a better predictor of difficult intubation as compared to ULBT and MMT. Combination of ULBT and TMHT don’t have statically significant than the TMHT alone.