Difficult laryngoscopy and difficult tracheal intubation occur in 1.5% to 13% patients undergoing general anesthesia and has always been a concern for anesthesiologist’s.

ULBT (Upper Lip Bite Test) is a representation of the temporomandibular joint movement. Multiple factors such as weight, head and neck mobility, jaw movement, receding mandible and buck teeth are included in the ULBT, it would be expected to offer a higher predictive value for assessment of a difficult airway in patients having jaw subluxation combined with buck teeth.

In ULBT three classes: class I, patient is able to raise the lower incisors above the vermilion line; class II, upper lip below the vermilion line; and class III, unable to bite the upper lip.

Another method for difficult airway prediction is measurement of the thyromental distance (TMD). The distance between the laryngeal prominence of the thyroid cartilage and the mental protuberance of the mandible was measured. A TMD less than or equal to 6 cm was considered to be predictive of difficult intubation.

The current study was carried out in the form of a prospective, observational, single-blind evaluation, with the objective of determining the sensitivity, specificity, and positive and negative predictive values of the ULBT compared with TMD for predicting difficult intubations.

Inclusion Criteria

• Patient willing to sign the written& informed consent.
• Patients of either gender aged between 18 and 60 years.
• Patients belonging to American Society of anesthesiologists grade I and II
• Patients scheduled for elective surgery under general anesthesia requiring endotracheal intubation.

Exclusion Criteria

• Patient’s refusal from taking part in the study.
• Patients with previous history of burn or trauma to airway.
• Patients having tumors or mass in the laryngeal, facial and cervical region.
• Patients with restricted mobility of the neck and mandible.

In this prospective, observational, study, non-blinded study 30 patients who required inhaled general anesthesia with endotracheal intubation for elective surgery were enrolled for evaluation of the accuracy in predicting difficult intubation by TMD measurement and ULBT.  In the ULBT, the capacity of biting the upper lip is categorized into three classes: class I, a patient is able to raise the lower incisors above the vermilion line; class II, a patient is able to bite the upper lip below the vermilion line; and class III, a patient is unable to bite the upper lip. The TMD of the subjects was measured in the upright sitting position with the head in complete extension. The distance between the laryngeal prominence of the thyroid cartilage and the mental protuberance of the mandible was measured with a ruler.

A TMD less than or equal to 4 cm was considered to be predictive of difficult intubation After induction of anesthesia with a standard protocol, the patient's grade of laryngeal view by the Cormack-Lehane classification was documented by an anesthesiologist with at least 3 years' experience who was unaware of prior evaluations. A TMD equal to or less than 4 cm and a class III ULBT were considered to be predictive of difficult intubation. A Cormack-Lehane class III or IV was considered a difficult intubation.

Data will be analysed by SPSS (statistical package for social scientist) 15.0. The characteristics and demographic data of each group  are  presented  descriptively  in  terms  of  percentage,  mean, and  standard  deviation.  Categorical data was analyzed by chi – square mtest or Fisher’s exact test. Ordinal data will be analyzed by chi- square   test   or   by   the   Kolmogorov - Smirnovtest.   The significance value used was α - 5% with 80% power.

Of 30 patients involved in the study two had difficult intubation. Sensitivity, specificity, positive and negative predictive values and accuracy were 100%, 94.44%, 66.67%, 100% and 95%  for ULBT, and 50%, 77.78%, 20%, 93.33% and 75% for TMD .Sensitivity, Specificity, positive predictive value and accuracy were found to be significantly higher for the ULBT than for TMD (p < 0.05).

Table 1:  Depicts ULBT Prediction for Difficult Intubation.

Table 2: Depicts TMD Prediction for Difficult Intubation.

Table 3: Comparison between both ULBT and TMD.

Of 30 patients involved in the study two had difficult intubation. Sensitivity, specificity, positive and negative predictive values and accuracy were 100%, 94.44%, 66.67%, 100% and 95%  for ULBT, and 50%, 77.78%, 20%, 93.33% and 75% for TMD .Sensitivity, Specificity, positive predictive value and accuracy were found to be significantly higher for the ULBT than for TMD (p < 0.05).

Early  detection  of  difficult  airway  is  important  because  failed intubation  can  have  serious  consequences  which  lead  to  high morbidity and mortality of the patient [2], [3] .The ability to predict a  difficult  tracheal  intubation  permits  anesthesiologists  to  take precautions to decrease the risk [4]. bIn  2003,  Khan  et  al  introduced  a  simple  method  for  predicting difficult intubations known as the upper lip bite test (ULBT). ULBT is a  representation  of  the  temporomandibular  joint  movement. Multiple  factors  such  as  weight,  head  and  neck mobility,  jaw movement,  receding  mandible  and buck teeth are included in the ULBT, it would be expected to offer a higher predictive value for assessment of a difficult airway in patients having jaw subluxation combined with buck teeth [5].The  TMD  of  the  subjects  was  measured  in  the  upright  sitting position with the head in complete extension. The distance between the laryngeal prominence of the thyroid cartilage and the mental Protuberance of the mandible was measured. A TMD less than or equal   to   6   cm   was considered   to   be   predictive   of   difficult intubation. In  this  study  it  was  noted  that  upper  lip  bite  test  had  a  better sensitivity,  specificity,  positive  predictive  value  and  negative predictive value compared to thyromental distance in the prediction of  difficult  intubation  and  efficiently  predicated  and  prevented morbidity and mortality that could have happened without accurate prediction of difficult intubation.This  study  was  consistent  with  study  done  in  2018  by  Elnaz Faramarzi  which  concluded  that  Upper  lip  bite  test  has  moderate sensitivity  and  positive  predictive  value  and  high  specificity  and accuracy and can be  used as  useful bedside  test for evaluation of patient airway in patients requiring general anesthesia. Considering that the ULBT is a simple objective evaluation that is not dependent on particular circumstances or specific instruments, it is of utmost importance to evaluate and re-evaluate it in various conditions and make comparisons with alter-native tests.As for the issue of questionable reliability of the TMD, it may not appear to be an appropriate test, but both tests were contrasted with the gold standard, and not directly compared with each other. The current  study  provided  further  information  for  the  database  of literature regarding both methods.The  limitation  in  our  study  is  that  the  study  was  conducted  in  a short period of time with a small sample size. Conducting the study for a longer duration of time and with a larger sample size would yield better results. Other parameters detecting difficult airway was not assessed. This study was concerned only with elective surgical patients, and emergency patients were neglected. This study is non blinded hence some observer bias is present.

ULBT is a useful bedside test for evaluation of patient airway before the general anesthesia with greater sensitivity, specificity, positive predictive value negative predictive value and accuracy than TMD.

The authors are thankful to the patients and technical staff without whom this publication would not be possible.

Nil

None declared

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