Comparison Of Upper Lip Bite Test And Modified Mallampati Classification In Predicting Difficult Intubation
R Bhat, S Mishra, A Badhe
area under a receiver operating curve auc of a roc-curve, cormack lehane, modified mallampati mmp, upper lip bite test ulbt
R Bhat, S Mishra, A Badhe. Comparison Of Upper Lip Bite Test And Modified Mallampati Classification In Predicting Difficult Intubation. The Internet Journal of Anesthesiology. 2006 Volume 13 Number 1.
The sensitivity, specificity, positive predictive value, negative predictive value and accuracy were calculated. The accuracy of the tests was further assessed using Likelihood ratio and Odds ratio. The discriminating power of the tests was calculated using Area under a Receiver Operating Curve (AuC of a ROC-curve)
Endotracheal intubation may be rendered difficult or impossible due to coexisting diseases or abnormal physical features like restricted neck movements, restricted jaw movements, or restricted mouth opening.
Unanticipated difficulty in intubation in patients for elective surgical procedures can occur in 1.5 to 13 percent cases with none of the above mentioned abnormalities resulting in both morbidity and mortality.
Other clinical predictors of difficult intubation include thyro-mental distance, sterno-mental distance, receding mandible, buck teeth, and obesity. Several studies have however cast doubts on these pre-op predictors including Modified Mallampati Classification to reliably predict unanticipated difficult intubation.
In 2003, Khan et al 4 proposed and studied a new test the Upper Lip Bite Test (a simple bed side technique) which involves the assessment of jaw subluxation, and presence of buck teeth in a single test which they concluded would improve its reliability and reduce inter-observer variability.
Aims and objectives
To assess the ability of Upper Lip Bite Test (ULBT) to predict difficult intubation.
To compare the sensitivity, specificity, accuracy, positive predictive value and negative predictive value of Upper Lip Bite Test and Modified Mallampati Classification.
To assess the combined accuracy of Upper Lip Bite Test and Modified Mallampati Classification.
Material and methods
After obtaining institutional approval and informed consent obtained from the patients Five hundred ASA-1/2 patients were assessed. Included in study are, Age above 16 years undergoing elective surgical procedure requiring endotracheal intubation for providing anesthesia.
Excluded from the study are edentulous patients, restricted mouth opening, Restricted cervical movement Presence of oropharyngeal / laryngeal pathology
Modified Mallampati Classification.
Upper Lip Bite Test
Cormack and Lehane grading of laryngeal exposure.
Modified Mallampati Classification
Classification of oropharyngeal view was assessed with the patient in sitting position with the neck in neutral position and tongue fully protruded without phonation (fig 1).
Soft palate, fauces, uvula and pillars seen, class 1
Soft palate, fauces and uvula seen, class2
Soft palate and base of uvula seen, class3
Soft palate not seen,class4.
Upper Lip Bite Test
Upper lip bite test was assessed with patient sitting, head in neutral position. Ability of the patient to bite his / her upper lip was assessed and graded by the investigator after a proper demonstration of the test to the patient (fig 2).
Lower incisors can bite upper lip above the vermilion line.
Lower incisors can bite below the vermilion line.
Cannot bite upper lip.
This assessment was done by the candidate and these findings were not disclosed to the anaesthesiologist intubating the patient.
Cormack and Lehane classification
The anaesthesiologist conducting the case recorded the degree of laryngoscopic evaluation according to fig 3.
Full view of glottis, only posterior commisure visible, only epiglottis visible.
No glottic structure visible.
Direct laryngoscopy was done using Macintosh blade by an anaesthesiologist with at least two years of experience .Induction was done with inj. Thiopentone 5 mg /kg iv and intubation was done after giving suxamethonium 1.5mg/kg .The grade of glottic visualization and number of attempts was noted down on the proforma by the intubator after intubation.Grade 1 and 2 were considered as easy and grade 3 and 4 were considered as difficult intubation.
Data was collected from 500 patients scheduled to receive general anesthesia and endotracheal intubation.
The age group of patients in the study was 16 to 67. Females comprised 286(57.2%) of the study population where as 214(42.8%) were males. Most of the females were in the age group 28-48 years and males in the age group 26 -55, (Graph 1).
The patients in the study were in the height range of 140 to 184cm. Most of the men were in the range of162 to 172cm, where as women were in the range of 148 to158cm, (Graph 2).
The patients in the study were in the weight range 28 to 92kgs. Most of the men were in the range 44 to 62kgs where as the females were in the 42-58kgs range, (Graph 3)
The BMI ranged from 13 to 42kgm-2. Most of the females had BMI ranging from18-24kgm-2, where as males had a range of16 to 22kgm-2, (Graph 3)
Modified Mallampati Class (MMP)
The number of patients in each class of Modified Mallampati Class was as given in the Table13 & Graph 5
The number of patients in class 1&2(164+238) predicted easy intubation is 402 (80.4%) where as class 3&4(83+15) predicted difficult intubation was 98(19.6%)
The number of patients in each class of Upper Lip Bite Test was as given in the Table14 & Graph 6
Upper Lip Bite Test distribution
The table and graph above show that 12 cases have class 3 ULBT class hence predicted as difficult intubation.
The number of patients in each class of Cormack and Lehane classification of glottic exposure is as given in the Table15. It shows that only 39 patients were grade 3 I.e. difficult intubation and there were no cases of grade 4 visualization.
Distribution of Cormack & Lehane's grades of glottic exposure
Effect Of External Laryngeal Manouvre
The table above shows that in 148 cases belonging to grade 2 and grade 3 glottic exposure, external laryngeal maneuver was applied and it improved the visualization to grade 1 in 109 cases, grade 2 in 38 cases and remained grade 3 in one case.
The table above shows that 479 cases were intubated in first attempt, 17 cases required 2nd attempt and 4 cases required 3rd attempt. There were no cases of failed intubation.
The above graph and table shows that 3 patients with class1 exposure out of 164 patients,14 patients with class 2 out of 238 patients , 19 patients with class 3 out of83 patients and 3 patients with class 4 out of 15 patients had difficult intubation.
The table and graph show that 9 patients out of 382 class1 ULBT patients had grade 3 Cormack and Lehane's ,22 out of 106 patients with class2 ULBT had grade 3 Cormack and Lehane's and 8 patients out of 12 with class 3 ULBT had grade 3 glottic exposure.
Modified Mallampati Vs Cormack Lehane's
The p value of 0.004 for sensitivity and 0.000 for specificity show that the difference in sensitivity and specificity between MMP & ULBT is significant
The p value of 0.000 for sensitivity and 0.000 for specificity show that the difference in sensitivity and specificity between MMP &
The p value of 0.063 for sensitivity and 0.500 for specificity show that the difference in sensitivity and specificity between ULBT and MMP &ULBT in series using McNemar test is not significant
The p value of 0.063 for sensitivity and 0.688 for specificity show that the difference in sensitivity and specificity between MMP &
The p value of 0.000 for sensitivity and 0.000 for specificity show that the difference in sensitivity and specificity between ULBT and MMP &ULBT in parallel using McNemar test is significant
The p value of 0.000 for sensitivity and 0.000 for specificity show that the difference in sensitivity and specificity between MMP & ULBT in series and MMP &ULBT in parallel using McNemar test is significant
The likelihood ratio incorporates both the sensitivity and specificity of the test and provides a direct estimate of how much a test result will change the odds of having a disease. The
The AUCofROC curve for Modified Mallampati class is 0.712 with a 95% confidence interval 0.618 to 0.807
The AUCofROC curve for ULBT class is 0. 598 with a 95% confidence interval 0.494 to 0.703
The AUCofROC curve for MMP or ULBT class in parallel is 0. 779 with a 95% confidence interval 0.694 to 0.863
The AUCofROC curve for MMP & ULBT class in series is 0.536 with a 95% confidence interval 0.437 to 0.636
The incidence of unanticipated difficult intubation varies between 1.3% to 13% in various studies and the search for predictive tests that has ease of applicability, reliability and accuracy continues.
The incidence of difficult intubation in our trial was 7.8% i.e. 39 out of the total 500 people assessed turned out to have difficult intubation, of these only 23 were correctly predicted as difficult by Modified Mallampati test where as only 8 were predicted as difficult by ULBT. The incidence of difficult intubation in Khan's trial was 5.7% where as in Leopold's trial it was 12%.
In our study we found the sensitivity of Modified Mallampati Class was 59% which was less than the study conducted by Khan et al (82.4%) , but this was comparable with many other studies like that of Savva et al (64%).
The specificity of Modified Mallampati class in our study is 83.5%which is more than that of Khan et al (66.8%) and Leopold et al (61%). Higher specificity similar to our study been reported by Oates et al (82%) and Freck (84%)
The wide variation in reported specificity and sensitivity in various studies may be because of incorrect evaluation of the test because of inter observer variability seen in Modified Mallampati class assessment as was found by
The difference in sensitivity was significant when MMP and ULBT were compared (p=0.004), when MMP and MMP& ULBT in series were compared (p=0.000), when ULBT and MMP or ULBT were compared in series (p=0.000) and when MMP or ULBT in parallel is compared with MMP &ULBT in series (0.000)
The difference in specificity is significant when MMP & ULBT were compared (p =0.000), when MMP and MMP& ULBT in series were compared (p=0.000), when ULBT and MMP or ULBT were compared in series(p=0.000) and when MMP or ULBT in parallel is compared with MMP &ULBT in series (p=0.000).
When ULBT and Modified Mallampati class were done in parallel (27.5%) the positive predictive value was more than that for modified mallampati class alone (23.2%) and this increased to 60% when ULBT and modified mallampati class were done in series.
The negative predicted value was more than 90% for both the tests individually (96% - MMP, 93.7% - ULBT) and also when considered in parallel and series (ULBT or MMP- 97.2%, ULBT & MMP – 92.7%) thus stressing upon the fact that all 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. The accuracy of ULBT was (88%) compared to modified mallampati class (67.7% )this was almost replicated in the trial by Leopold et al (84.9% )for ULBT and( 62.1% )for modified mallampati class. In our study the ULBT had higher accuracy of 93% compared to that of MMP (81.6%), MMP or ULBT in parallel (83%) and MMP & ULBT in series (92.4%).
We have further tried to analyse the accuracy using
In our study the likelihood ratio for ULBT was 22.7 followed by ULBT and modified mallampati class in series 19.25 followed by ULBT and modified mallampati class in parallel 4.45. The least value was for modified mallampati class 3.57. This value for Modified Mallampati class (3.57) in our study is high compared to Leopold et al (1.8) and khan et al (2.48). We found a high likelihood ratio for ULBT 22.77 compared to Leopold et al (3.78) and khan et al (6.76).
We calculated the
We also calculated area under curve of receiver operating characteristics
AUCofROC curve with confidence level of 95% was 0.598(0.494—0.703) for ULBT in the present study which was less than 0.826 (calculated by Leopold et al for) Khan et al and almost same to that for ULBT in Leopold's trial. The AUCofROC curve thus reveals that the pre–hoc probability of correct prediction is improved from 50% (random guess) to 59.8% when applying the ULBT, an improvement that is far from being of clinical relevance. This disappointing result may be caused by the low sensitivity of the test due to large proportion of false negatives
AUCofROC curve with confidence level of 95% for modified mallampati class was 0.743 (0.663-0.822) which was similar to Khan et al trial (0.746) but more than that calculated for Modified Mallampati class in Leopold's trial (0.656),which again is more compared to ULBT in our study . AUC value more than 0.7 is considered to be clinically relevant.
AUCofROC curve with confidence level of 95% for MMP or ULBT in parallel is 0.779(0.694-0.863). A combination of ULBT and Modified Mallampati in combination improves the predictive ability.
AUCofROC curve with confidence level of 95% for MMP and ULBT in series is 0.536 (0.437-0.636). This combination has poor predictive value.
Thus in our study we found that
The accuracy of ULBT 93% is much higher than that of Modified Mallampati alone 81.6% or Modified Mallampati and ULBT in series 92.4% or in parallel 83
Upper Lip Bite Test cannot be used as a single bed side test for predicting unanticipated difficult intubation.
A combination of Upper Lip Bite Test and Modified Mallampati Test in parallel is more sensitive, specific and has a higher discriminative power which is clinically relevant than Modified Mallampati Test or ULBT alone.
The high negative predictive values of both the tests alone and in parallel and series indicate that they are good predictors of possible easy intubation rather than difficult intubation.