|Year : 2018 | Volume
| Issue : 1 | Page : 17-23
Use of the “L-E-M-O-N” score in predicting difficult intubation in Africans
Danladi B Mshelia1, Elizabeth O Ogboli-Nwasor2, Erdoo S Isamade3
1 Department of Anesthesia, University of Abuja Teaching Hospital, Gwagwalada, Abuja, Nigeria
2 Department of Anesthesia, Ahmadu Bello University Teaching Hospital, Shika, Zaria, Kaduna State, Nigeria
3 Department of Anesthesia, University of Jos Teaching Hospital, Jos, Plateau State, Nigeria
|Date of Web Publication||23-Mar-2018|
Elizabeth O Ogboli-Nwasor
Department of Anesthesia, Ahmadu Bello University Teaching Hospital Shika, Zaria, Kaduna State
Source of Support: None, Conflict of Interest: None
Background: Endotracheal intubation is an integral part of airway management and is key to the practice of safe anesthesia. Prediction of a difficult airway can help reduce the incidence of failed or difficult intubation. We studied the use of “L-E-M-O-N” (Look-Evaluate-Mallampati-Obstruction-Neck mobility) scoring system to predict difficult intubation and determine the prevalence of difficult intubation among adult surgical patients. Materials and Methods: One hundred and sixty (160) consecutive ASA I–III surgical patients between 18 and 65 years of age were recruited from October to December 2011. A variety of airway tests using the “L-E-M-O-N” scoring were done during preoperative assessment; and at induction of anesthesia, airway assessment using Cormack and Lehane was performed and the results were recorded by a standardized record sheet. The variables evaluated were gender, age, weight, height, body mass index (BMI), dentition and a variety of airway tests using the “L-E-M-O-N” scale. SPSS version 17.0 was used for statistical analysis; and a P value <0.05 was considered significant. Results: Prevalence of difficult intubation using Cormack and Lehane score only was found to be 8.1%. The “LOOK” features had sensitivities of 99.1%, 96.6%, and 92.5% for facial trauma, large incisors, and beard or moustache, respectively, and positive predictive values of 0%. Combination of predictors in the “L-E-M-O-N” score showed that, as the mean “L-E-M-O-N” score of the patients increased, the likelihood of difficult visual laryngoscopy also increased. Conclusion: Combination of airway predictors in the “L-E-M-O-N” scoring system significantly improves the ability to predict difficult intubation.
Keywords: Africans, difficult intubation, L-E-M-O-N score
|How to cite this article:|
Mshelia DB, Ogboli-Nwasor EO, Isamade ES. Use of the “L-E-M-O-N” score in predicting difficult intubation in Africans. Niger J Basic Clin Sci 2018;15:17-23
|How to cite this URL:|
Mshelia DB, Ogboli-Nwasor EO, Isamade ES. Use of the “L-E-M-O-N” score in predicting difficult intubation in Africans. Niger J Basic Clin Sci [serial online] 2018 [cited 2018 Apr 25];15:17-23. Available from: http://www.njbcs.net/text.asp?2018/15/1/17/228359
| Introduction|| |
Prediction of difficult intubation is important to develop a strategy that best facilitates first-attempt intubation. Complex airway management is a multifaceted problem. The consequences of failed airway maintenance, endotracheal intubation, or both, can result in morbidity or mortality and can be devastating to the patient, the practitioner, and the health care system. We sought to determine the usefulness of the “L-E-M-O-N” (Look-Evaluate-Mallampati-Observe-Neck mobility) scoring system as a predictor of difficult intubation. The definition of the difficult airway varies in different literature sources. The American Society of Anesthesiologists Task Force on Management of the Difficult Airway defines it as the clinical situation in which a conventionally trained anaesthesiologist experiences difficulty with face mask ventilation of the upper airway, difficulty with tracheal intubation or both. Difficult intubation occurs when a trained anesthetist is unable to intubate after two optimal attempts. Difficult intubation is associated with many severe and fatal complications including airway trauma, laryngospasm, hypoxemia, and arrhythmias/potential cardiac arrest. Therefore, preoperative evaluation and prediction of potential difficult airway is very important. Various tests, such as the Mallampati classification and mouth opening by Wilson,, and measurements such as thyromental distance, sternomental distance, and ratio of height to thyromental distance have also been used to assess the airway and predict difficult intubation. Other parameters include history of difficult intubation, protrusion of the mandible, indirect laryngoscopy, tooth morphology, and radiographic evaluation of the head and neck.,,, However, accuracy of these tests vary probably because of different test thresholds and patient characteristics. It has been suggested that a combination of tests – Look, Evaluation, Mallampati, Obstruction and Neck mobility in the LEMON score will have better predictive value.
Diagnostic criteria: L-E-M-O-N scoring system
L – Look. Four criteria are used for the look category: facial trauma, large incisors, beard or moustache, large tongue.
E – Evaluate. Evaluation is done using the 3-3-2 rule.
- Inter-incisor distance: patient's mouth is opened adequately to allow the placement of three fingers between the upper and lower teeth
- Hyomental distance: three finger breadths are used
- Thyromental distance: two finger breadths are used
M – Mallampati. This is done with the patient seated with the head in the neutral position and mouth fully open and the tongue protruded maximally without phonation while the interviewer looks from the front at the patient's eye level and inspects the pharyngeal structures with a pen torch without the patient phonating.
The views are graded as follows: Class I: soft palate, uvula, fauces, and pillars visible; Class II: soft palate, uvula, fauces visible; Class III: soft palate, base of uvula visible; Class IV: hard palate only visible.
O – Obstruction. Patients are evaluated for stridor, foreign bodies, and other forms of sub- and supraglottic obstructions including tumors, abscesses, inflamed epiglottis, or expanding hematoma.
N – Neck mobility. This is a vital requirement for successful intubation. It is assessed by the patient in the sitting position to place their chin down onto their chest and then to extend their neck so they are looking towards the ceiling.
To our knowledge, this is the first attempt at validating the “L-E-M-O-N” assessment in the elective surgical setting in Nigeria; however, it has been validated by Reed et al.in the emergency department setting and the resuscitation room in the United States of America. If a screening test such as this is to be useful, it must be performed on all patients who might need to be intubated; it must therefore be quick to perform and also give reliable results. No screening test can be 100% sensitive; however, it should have a high sensitivity, be specific, and possess a high positive predictive value with few false positive predictions.
| Materials and Methods|| |
This study is a prospective observational study of 160 patients. Preoperatively, informed written consent was sought and obtained from each patient. Ethical approval was obtained from the Hospitals' Ethical Committee before the commencement of the research, carried out at Ahmadu Bello University Teaching Hospital Zaria tertiary/referral health facility. The pre-anesthetic assessment and intubation was carried out by a senior registrar anesthetist with over 5 years experience.
All elective surgical patients who underwent general anesthesia with endotracheal intubation at the hospital between October and December 2011 and met the inclusion criteria were included.
Patients aged between 18 and 64 years who underwent elective surgery under general anesthesia, patients in American Society of Anesthesiologists (ASA) 1–III risk classification, and patients who consented to participate were included in the study.
Patients who declined to participate in the study, patients classified as ASA IV and V, patients below 18 years or older than 65 years, patients who were unable to sit, patients with gross anatomical abnormality of the head and neck, patients who recently had surgery/trauma of the head and neck, patients who had severe cardiorespiratory disorders, patients requiring rapid sequence induction or an awake intubation, patients going for obstetric surgery, patients who had a history of difficult intubation, patients having regional anesthesia or conscious sedation, and patients undergoing emergency surgical procedures.
The primary outcome measure was to find the ability of the “LEMON” scoring system to actually predict difficult intubation, i.e., the positive predictive value of the “L-E-M-O-N” score. The secondary outcome measures were to determine the incidence of difficult intubation in the study population and to find the usefulness of different airway features in predicting difficult intubation.
“L-E-M-O-N” score calculation: The airway assessment score was calculated thus:
'LOOK' Criteria: Facial trauma (Absent = 0 point, Present = 1 point), Large incisors (Absent = 0 point, Present = 1 point), Beard or moustache (Absent = 0 point, Present = 1 point), Large tongue (Absent = 0 point, Present = 1 point).
'EVALUATE' Criteria: Inter incisorGap (≥3 fingers breadths = 0 point, ≤2 finger breadths = 1 point), Hyomental distance (≥3 fingers breadths = 0 point, ≤2 finger breadths = 1 point), Thyromental distance (2 fingers breadths = 0 point, 1 finger breadths = 1 point),
Mallampati classification: class 1 or 2 = 0 point, class 3 or 4 = 1 point
Obstruction to the neck: Absent = 0 point, Present = 1 point
Neck mobility: Good = 0 points, Poor = 1 point
The airway assessment score for each of the predictors was then added up to give the 'L-E-M-O-N' score with maximum score possible being 10 and the minimum score zero.
For laryngoscopy, the patient was placed in the supine position with the head in the sniffing position. Monitoring was carried out with a pulse oximeter, electrocardiogram and non-invasive arterial blood pressure monitoring using the Dash 4000 multi-purpose monitor by General Electric medical systems (2003). Baseline vital signs (Blood pressure, Pulse Rate, SPO2, temperature and Respiratory Rate) were obtained and recorded. Induction was performed with the patient in the supine position with 5mg·kg –1 of sodium thiopental or Propofol 2mg·kg –1 intravenously. Suxamethonium chloride 1mg·kg –1 was administered intravenously to facilitate endotracheal intubation. After the disappearance of fasciculations, a Macintosh #3 or #4 blade was used to visualize the larynx and the laryngeal view was graded according to the Cormack and Lehane's scale. Grade I: vocal cords visible, Grade II: only posterior commissure visible, Grade III: only epiglottis visible, Grade IV: none of the fore going visible. No external laryngeal pressure was applied for grading of the laryngoscopic view. Difficult visual laryngoscopy (DVL) was defined as grade III or IV while a grade I or II view on direct laryngoscopy was classified as easy visual laryngoscopy (EVL).
Data sources and measurement
Statistical analysis was performed using the Statistical Package for Social Sciences (SPSS) version 17.0. Descriptive statistics of means and standard deviations were used for quantitative variables. The Chi-square and the student's t-tests were used for inter group comparisons. The sensitivity, specificity, and positive predictive values of each of the predictors were calculated. Tables and diagrams like bar charts and pie charts were used to illustrate the results. P value less than 0.05 were considered statistically significant.
Sample Size Determination: Minimum sample size was determined using the formula by Araoye.
| Results|| |
The 160 patients recruited for this study were made up of 69 males (43.1%) and 91 females (56.9%) with a male: female ratio of 1.5:2. The age range of the patient was between 18-65 years [Figure 1], with a mean age of 40.2 ± 12.8 and a mean weight of 63.3 kg ± 12.4, while the average height of the patients was 1.6±0.0 m. The mean BMI for the patients was 25.2 ± 4.5 but was on average higher for the females (26.2 ± 4.8) than the males (23.9 ± 3.7), as in shown in [Table 1]. There were no significant differences in mean age weight, height and Body Mass Index (BMI) between the difficult visual laryngoscopy (DVL) and easy visual laryngoscopy (EVL) patients.
Out of the patients assessed, 90 (56.3%) was classified as ASA 2, 52 (32.5%) was classified ASA 1 and 18 (11.3%) was classified as ASA 3 as shown in [Figure 2]. In the patients' distribution according to Cormack and Lehane, 100 (62.5%) belong to class 1, and 1 (1%) belongs to class 4, as shown in [Figure 3].
|Figure 3: Distribution of patients in the study according to their Cormack and Lehane class|
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From the demographic characteristics of patients with DVL and EVL shown in [Table 2], it was observed that 13 patients (8.1%) had DVL compared to the 147 (91.9%) with EVL. There was no significant difference between the ages of the two groups, also, there was no significant difference in demographic data of the height (P value = 0.916), weight (P value = 0.815), and body mass index (P value = 0.815).
|Table 2: Distribution of DVL and EVL according to sociodemographic characteristics of patients|
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Results of the four 'LOOK' features shown in [Figure 4] reveals that the predictors; facial trauma, large incisors, beard or moustache and large tongue were found in only 1, 5, 11 and 3 patients respectively. The outcome of these four features is summarized in [Table 3]. [Table 4] shows the sensitivity, specificity and positive predictive values of the four “LOOK” predictive tests. The test for large tongue had sensitivity of 15.3%, specificity of 99.3 5 and a positive predictive value of 66% while the other features of facial trauma, large incisors and beard/moustache had 0% sensitivity and specificities of 99.1%, 96% and 92.5% respectively.
|Figure 4: Distribution of “LOOK” features among patients involved in the study|
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|Table 4: Sensitivity, specificity, and positive predictive value of “LOOK” airway predictors|
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[Table 5] shows the distribution of the three “evaluates” predictors of inter- incisor gap, hyomental distance and thyromental distance.
[Table 6] shows that 16 (10%) and 32 (20%) were found to have 2 finger breadths during the measurement of the inter incisor and hyomental distance respectively, while 24 (15%) had one finger breadth measurement in the assessment of the thyromental distance.
However, [Table 6] shows that of the 16 patients with inter incisor gap of 2 fingers breadths, only 5 patients had difficult visual laryngoscopy (DVL). A similar trend was also noticed where 24 of the 32 patients who had 2 finger breadths as their hyomental distance had an easy laryngoscopy while eight patients had DVL. Likewise of the 24 patients with 1 finger breadth as a measurement of their Thyromental distance only 8 had a difficult laryngoscopy.
The sensitivity, specificity and positive predictive value of the 'evaluate' predictive tests is shown in [Table 7] and it reveals that the hyomental distance had the highest sensitivity amongst the three predictors of 61.5%, while the measurement of inter incisor gap had the greatest specificity of 92.5% and a corresponding higher positive predictive value of 31.25% as compared with the other two tests where each had a positive predictive value of 25%.
|Table 7: The sensitivity, specificity, and positive predictive value of “EVALUATE” airway predictors|
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[Figure 5] shows that 35% (56) of the patients were classified as Mallampati grade 1, 60% (97) were grade 2, while 6 (4%) of the patients were grade 3 and only one patient (1%) had a Mallampati grade 4 score. [Table 8] shows that of the seven patients (4.4%) with Mallampati grade 3 and 4 only two had difficult visual laryngoscopy while of the 153 (95.6%) patients with Mallampati grades 1 and 2, 142 (93%) had easy visual laryngoscopy (EVL). [Table 9] shows that the sensitivity of the Mallampati grading among the patients was 15.9%, while the specificity was 96.6% and the positive predictive value was 28.8%.
|Table 9: Sensitivity, specificity, and positive predictive value of some airway predictors|
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From this study, 9% (15) of the patients had neck obstruction. [Table 8] shows that of the fifteen (15) patients with neck obstruction, only 3 patients had DVL.
[Table 9] shows that neck obstruction as a predictor of difficult intubation had a sensitivity of 23%, a specificity of 98.5% and a positive predictive value of 20%.
From [Table 8] it can be seen that 8% (13) of the patients had limited neck mobility and out of this number only 4 had difficult visual laryngoscopy (DVL).
[Table 9] shows that the test for neck mobility had a positive predictive value of 30.8%, a specificity of 93.9% and a sensitivity of 30.8%.
As seen in [Table 10], a comparison of the mean scores of the two groups shows that the mean score of the patients with DVL was higher with a score of 2.3 ± 1.8 as compared to the mean value of 0.7 ± 1.0 for the EVL group, a finding which is statistically significant (P = 0.001).
|Table 10: Comparison of mean scores of “L-E-M-O-N” score for EVL and DVL groups|
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[Table 11] shows that 91 (56.8%) of the 160 patients studied had a 'L-E-M-O-N' score of zero and of this Table, 90 (98.9%) of them had easy-visual laryngoscopy (EVL) whereas one patient who had a total score of six had difficult visual laryngoscopy (DVL). This was found to be statistically significant using the student t test.
| Discussion|| |
This study showed that of the four 'LOOK' criteria used, only the predictive test for the 'large tongue' had a sensitivity of 15.3% while the others had a sensitivity of 0%. The 'LOOK' features of beard/moustache, large incisors facial trauma and large tongue had very high specificities of 92.5%, 96.6%, 99.1% and 99.3% respectively. This is unlike the study carried out in the emergency department setting by Reed et al. where the patients with the large incisors had a poor view on laryngoscopy (DVL). This variation could be due to racial and anthropometric differences since most of the patients in that study are Caucasians while this study consisted only of black Africans or Negros.
The “evaluate” predictors in this study showed that the hyoid mental distance had a high number of true positives (61.5%) as compared to the results for the inter- incisor gap (38.4%) and the thyromental distance with 46%. The specificity values for the ‘evaluate’ predictors were high at 83.7% for the hyoid mental distance, 87.7% for the thyromental distance and 92.5% for the inter incisor gap.
The moderate sensitivity of the hyomental distance (61.5%) and specificity found in this study is comparable to the values of 46% and 81% for sensitivity and specificity respectively as found by Jin Huh et al. in an Asian population in Seoul, South Korea.
In this study thyromental distance of less than 2 fingers was not a good indicator of difficult intubation as it had a moderate sensitivity of 46% and a specificity of 87.7% with a positive predictive value of 25%. This is in contrast to the study done by Merah et al. who found a lower sensitivity of 15%. Tse et al. reported a similarly low sensitivity of 32% and positive predictive value of 20%. However the majority of reports had much higher values like that of Frerk who found a sensitivity and specificity of 90.9% and 81.5%, respectively. The discrepancy between our findings and that of Frerk can be explained partly by the different definitions used for difficult intubation in the two studies. Frerk defined difficult intubation as 'a need to use a gum elastic bougie. Other definitions have been made by the American Society of Anaesthesiologists as difficult tracheal intubation occurring when tracheal intubation requires multiple attempts in the presence or absence of tracheal pathology while the Italian Society Of Anaesthesiology Analgesia Reanimation And Intensive Care (SIAARTI) in its guidelines for difficult intubation and for difficult airway management defined difficult intubation as a procedure which is characterised by difficult laryngoscopy or that required at least 4 attempts or more than 5 minutes for its execution independent of the Anaesthesiologists' degree of experience.
The inter incisor gap had a sensitivity of 38.4%, specificity of 92.5% and a positive predictive value of 31.25%. These findings are slightly higher than that found by Gupta et al. in a Kashmir population where they found a sensitivity of 18.8%, specificity of 94.14% and a positive predictive value of 6.6% in using the inter incisor gap to test for difficult intubation. The results of this study are however similar to the findings in the study done by Merah et al. in which the sensitivity, specificity and positive predictive values were 30.8%, 97.3% and 28.6% respectively making the inter incisor gap on its own not a very good indicator of difficult intubation.
The Mallampati test in this study had a sensitivity of 15.9% that is; preoperatively the test identified only 2 of the 13 patients who later had a difficult intubation. The test's positive predictive value was 28.8%; it identified 7 patients who would have a difficult intubation, but, in fact, 5 of them had an easy intubation. It was useful when the score was one or two, i.e., of the 147 intubations predicted to be easy (with a score of one or two) 138 had easy visual laryngoscopy (sensitivity 96.6%).
These findings are in concordance with the findings of Jin Huh et al. who also found a sensitivity of 12% for the Mallampati test among a group of patients in South Korea  and Reed who did not find any association between a high Mallampati score and difficult intubation. However studies carried out by Merah et al. found higher values with a sensitivity, specificity and positive predictive value of 61.5%, 98.4%, and 57.1% respectively. A sensitivity of greater than 80% was reported by Frerk in a European population and also Ita et al. in Nigeria.,
Mallampati et al.reported a sensitivity of 53% and a positive predictive value of 93%, however, repeated studies have not obtained this high positive predictive value.,,,, The discrepancy between their results and the findings of our study has three possible sources.
First, is inter-observer variability as reported by Karkouti et al. In this study the same person who did the preoperative evaluation also graded the laryngoscopy view, thereby introducing the possibility of bias into the assessment. However in the study by Tse, a patient's assignment to an oropharyngeal class and the laryngoscopic examination were always performed by a different Anesthesiologist.
Secondly, the uncertainties created by the ambiguous definition of Mallampati Class three increases with the number of evaluators in a study as a result of inter individual variations in interpretation. In this study there was one evaluator for the preoperative assessment, however the investigation by Mallampati et al. used twenty two evaluators.
Thirdly, prevention of phonation was shown by Tham et al. to be a critical factor in achieving a reliable score, as many automatically say 'Ah' or simulate phonation, which falsely improves the view but in this study it was done without phonation.
The tests for neck mobility and neck obstruction all had a low sensitivity (30.8%and 23% respectively) with equally low positive predictive values (30.8% and 20%). This is in contrast to the findings by Reed in the emergency department where he found that patients with neck obstruction and reduced neck mobility have a poor view at laryngoscopy. A study looking at a larger population may show that these factors are also associated with DVL.
Individually these predictors generally have low sensitivity and low positive predictive values but when using the' LOOK', 'Evaluate', Mallampati, Neck Obstruction and neck mobility combined in the 'L-E-M-O-N' score the ability to predict a difficult airway is improved.
The results of this study shows that as the mean score of the patient increases there is likely to be a difficult intubation (DVL) and this was found to be statistically significant with a P value of. 001. Similar findings were also discovered by Reed in the emergency department setting where airway assessment score based on criteria of the 'L-E-M-O-N' method was able to successfully stratify the risk of intubation difficulty in the emergency department.
We therefore conclude that an airway assessment score based on criteria of the 'L-E-M-O-N' method is able to successfully stratify the risk of difficult intubation. When all these airway predictors are combined and used as the 'L-E-M-O-N' assessment score the ability to predict a difficult intubation is greatly improved, as there is a greater possibility of a difficult intubation in patients with a higher score on a scale of zero to ten than those with lower scores. However, when these assessments are used individually they are not very good predictors of difficult intubation. The large tongue and reduced Hyomental distance are more likely to have DVL than the other predictors i.e., facial trauma, large incisors, beard/moustache, inter incisor gap, Mallampati, neck obstruction and degree of neck mobility.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7], [Table 8], [Table 9], [Table 10], [Table 11]