Introduction: Unanticipated difficult laryngoscopic tracheal intubation accounts for a significant proportion of adverse anaesthetic outcome in clinical practice.

Hence, it is important to identify patients with difficult airway preoperatively.

In our study, we have compared the upper lip bite test with modified Mallampati classification in predicting difficulty in endotracheal intubation.

Materials and Methods: The study was conducted on 150 ASA I patients of either sex, aged more than18 years scheduled to undergo elective surgery under general anaesthesia and endotracheal intubation. Pre-operatively airways of the patients were evaluated using modified Mallampati test and upper lip bite test.

MMT class III and class IV and ULBT class III were considered potentially difficult intubation. Experienced anesthesiologists, unaware of pre-operative airway evaluation, will perform laryngoscopy and grade the glottic view as per Cormack and Lehane's classification. Grade III and IV were considered as difficult intubation. Sensitivity, specificity, accuracy, positive and negative predictive values of ULBT and MMT were calculated.

Results: MMT was more sensitive (71.43%) than ULBT (28.57%)). MMT had a specificity of 81.82 as compared to 96.5% for ULBT. Positive predictive value for MMT is 16.3% and 28.57% for ULBT.

Negative predictive value was 98.32% and 96.50% for MMT and ULBT respectively. Accuracy of MMT was 81.33% while it was 93.33% for ULBT.

Conclusions: Modified Mallampati test is an inherently better test at predicting difficult endotracheal intubation when compared to upper lip bite test. Both modified Mallampati and upper lip bite test are better predictors of easy intubation rather than as positive predictors of difficult intubation.

Keywords: Modified Mallampati Test, Upper Lip Bite Test.

The ULBT which involves the assessment of jaw subluxation and presence of buck teeth in a single test claims to have improved reliability and reduced interobserver variability.

In our study, we have compared the upper lip bite test with modified Mallampati classification in predicting difficulty in endotracheal intubation.

MATERIALS AND METHODS

The ethical committee approval was obtained and an observational blinded study was done prospectively in the Department of Anesthesiology, in a tertiary care teaching hospital in Kerala, India. The study was conducted on 150 ASA I patients of either sex, aged more than18 years scheduled for elective surgery under general anaesthesia and endotracheal intubation. Surgical specialities involved were general surgery and orthopaedics. Edentulous patients, patients with BMI>30, those unable to open the mouth, and any factor predicting difficult intubation were excluded from the study.

Pre-op Evaluation and consent

Detailed history, systemic examination, relevant and routine investigations were carried out. Procedure was explained to the patient and an informed written consent was obtained. Eligible patients fulfilling the inclusion criteria were included in the study. Pre-operatively two anaesthesiologists not involved in intubating the airways of the patients evaluated the patients by using the modified Mallampati test or the upper lip bite test.

Classification of the oropharyngeal view is done according to the MMT [14,15]:

Class I    -               Soft palate, fauces, uvula and pillars seen.

Class II -               Soft palate, fauces and uvula seen

Class III                -               Soft palate and base of uvula seen

Class IV -               Soft palate not visible

The examination to determine oropharyngeal view is done with the aid of the torch light. The patients in sitting position with mouth fully open, tongue maximally protruded and not phonating.

The Upper Lip Bite Test was performed according to the following criteria[1]:

In this study both MMT and ULBT is compared in 150 patients to predict difficult intubation which is evaluated using Cormack-Lehane (CL) grade. The incidence of difficult intubation in the present trial was 4.7%. The incidence of difficult intubation in Khan’s trial was 5.7% [1] where as in Leopold’s trial it was 12% [24]. Discrepancies in the incidence of difficult intubations in different studies may be attributed to the fact that sometimes the cases in which pressure was applied to the larynx were excluded from the ‘difficult intubation’ group.

The sensitivity of MMT in our study was 71.43% as compared to 28.57% for ULBT. A similar sensitivity of 70.2% was reported by Leopold et al [24] for MMT. Much lower sensitivities for MMT were reported by Savva et al (64%) [8] and Bhat et al (59%) [23] in their trials. Sensitivity of ULBT is 28.57% in this study which is comparable to that of Bhat et al (20.5%) [23]. The original study by Khan et al had a sensitivity of 76.5% for ULBT [1]. The difference in sensitivity could be due to the high incidence of ULBT Class 3 in Khan’s trial (15%). The current study demonstrated a specificity of 81.82% for MMT and 96.5% for ULBT. Lower specificities for MMT have been observed in studies conducted by Hester et al (75%) [25] and Leopold et al (61%) [24] trials.  Wide range of MMT specificities (61 – 84%) may be due to factors such as involuntary phonation and poor demarcation between the various classes. Zahid Hussain et al found a higher specificity for ULBT (88.7%) than the MMT (66.8%) [1]. In this study positive predictive value for MMT is 16.3% and 28.57% for ULBT. The positive predictive value for MMT in this study is comparable to that of Khan et al (13%) [1] and Leopold et al (19.5%) [24] trials. The positive predictive value of ULBT in this study is similar to that of Khan et al trial (28.9%) [1]. The negative predictive value was more than 90% for both the tests individually (98.32% - MMT, 96.50 % -ULBT), thus stressing upon the fact that these tests can be good predictors of easy intubation rather than as positive predictors of difficult intubation which has a very low incidence. This was one of the conclusions made by Leopold et al. The accuracy of prediction was frequent in the original study describing the ULBT by Khan et al [1]. The accuracy of ULBT was 88% compared to MMT 66.7%. This was replicated in the trial by Leopold et al, 84.9% for ULBT and 62.1% for MMT [24]. In our study, ULBT has a higher accuracy of 93.33% compared to that of MMT 81.33%.

Limitations of the study –This study was conducted exclusively with elective surgical patients. Emergency patients and those who were recognized to be difficult airway were excluded. Hence it may not be applicable to all subgroups of the general population .ULBT requires the patient’s cooperation, ability to move the mouth and the presence of teeth; only participants meeting those criteria were included. Furthermore the inter-observer reliability was not evaluated and that would influence the result.

CONCLUSION

Modified Mallampati test is an inherently better test at predicting difficult endotracheal intubation when compared to upper lip bite test.

1.       Khan ZH, Kashfi A, Ebrahimkahani E. A comparison of the upper lip bite test (a simple new technique) with modified Mallamapti classification in predicting difficulty in endotracheal intubation: a prospective blind study. Anesth Analg. 2003;96(2): 595-9.

2.       Shiga T,Wajima Z,InoueT,Sakamoto A.Predicting difficult intubation in apparently normal patients:A meta-analysis of bedside screening performance.Anesthesiology.2005:103:429-37.

3.        Cormack RS, Lehane J. Difficult tracheal intubation in obstetrics. Anaesthesia 1984; 39: 1105-1111

4.       Mhyre J M,Healy D.The unanticipated difficult intubation in obstetrics.Anesth Analg 2011:112:648-52.

5.       Lyons G.Failed intubation.Six years’experience in teaching maternity unit.Anesthesia.1985:40:759-62.

6.       SwapnilGaneshAswar,SwatiChhatrapati,AnjanaSahu,AmitDalvi,RishirajBorhazowal. Comparing Efficacy of Modified Mallampati Test and Upper Lip Bite Test to predict difficult intubation. International Journal of Contemporary Medical Research2016:3(9):2715-19.

7.       Cheney FW, Posner KL, Caplan RA: Adverse respiratory events infrequently leading to malpractice suits. Anesthesiology 75:932-939, 1991. NLM PubMed, Journal Website.

8.       Savva.D. Prediction of difficult tracheal  intubation. Br J Anaesth 1994; 73: 149-53

9.       Rose DK, Cohen  MM. The airway : problems and predictions in 18,500 patients.  Can J Anaesth 1994 ; 41 : 372- 83.

10.    Tse JC, Rimm EB, Hussain A. Predicting difficult endotracheal intubation in surgical patients scheduled for general anaesthesia: a prospective blind study. Anesth Analg. 1995 ; 81 (2) : 254 – 8.

11.    Naguib M, Scamman FL, O’ Sullivan C, Aker  J, Ross AF, Kosmach S. Predictive performance of  three multivariate difficult tracheal intubation models: a double blind case -controlled study . Anesth Analg. 2006; 102(3) : 818 – 24.

12.    Lee A, Fan L T, Karmakar M K, Kee WD. A systematic review (meta-analysis) of the accuracy of the Mallampati testrs to tests to predict the difficult airway. Anesth Analg. 2006; 102(6): 1867 -78.

13.    Pearce A. Evaluation of the airway and preparation for difficulty. Best practice & Research Clinical Anaesthesiology. 2005; 19(4): 559-79.

14.    Mallampati SR, Gatt SP, Gugino LD, Desai SP, Warakasa B, Feriberger D, et al. A clinical sign to predict difficult tracheal intubation : a prospective study. Can Anaesh Soc J. 1985; 32(4): 429-34.

15.    Samsoon GLT, Young JRB. Difficult tracheal intubation: a retrospective study. Anaesthesia 1987; 42: 487 – 90.

16.    Zahid Hussain Khan,Mostafa Mohammadi,Mohammad .R.Rasouli,Fahimeh Farrokhnia. The diagnostic value of the upper lip bite test combined with sternomental distance,thyromental distance and interincisor distance for prediction of easy laryngoscopy and iintubation: A prospective study.Anesth Analg.2009;109:822-4

17.    Reed MJ, Dunn MJG, McKeown DW. Can an airway assessment score predict difficulty at intubation in the emergency department? Emerg Med J 2005; 22: 99-102.

18.    Ovassapian A, Glassenberg R, Randel GI et al: The unexpected difficult airway and lingual tonsil hyperplasia. A case series and a review of the literature, Anesthesiology 2002; 97: 124

19.     William. H. Rosenblatt. Clinical Anaesthesia. IV^th Ed; 614-615

20.     A1 Ramadhani. Sternomental distance as the sole predictor of difficult laryngoscopy in obstestric anaesthesia. Br J Anaesth 1996; 77: 312-316

21.    Oates J. D. Comparison of two methods for predicting difficult intubation. Br J Anaesth 1991 ; 66 : 305-309

22.     Yamamoto, Tsubokawa. Predicting difficult intubation with indirect laryngoscopy. Anaesthesiology 1997 ; 86: 316 – 321

23.    Bhat RR, Mishra SK, Badhe AS. Comparison of the upper lip bite test and modified Mallampti classification in predicting difficult intubation. The internet journal of anesthesiology [serial on the internet]. 2007 [cited 2008 Feb 7].

24.    Eberhart LH, Amt C, Cierpka T, Schwanekamp J, Wulf H, Putzke C. The reliability and validity of the upper lip bite test compared with the Mallampati classification to predict difficult laryngoscopy: an external prospective evaluation. Anesth Analg. 2005; 101(1) : 284-9.