|Year : 2018 | Volume
| Issue : 1 | Page : 19-24
Assessment of the effect of supine posture and phonation on modified mallampati grading and its applicability in prediction of difficult airway
Annappa Sankal, Kusuma Ramachandra Halemani, N Bhadrinath
Department of Anaesthesia, Kerala Institute of Medical Sciences, Trivandrum, Kerala, India
|Date of Web Publication||3-Apr-2018|
Dr. Kusuma Ramachandra Halemani
A3 “SAYANA”; “SUHA” Residency, Poonthi Road, Kumarapuram, Trivandrum - 695 011, Kerala
Source of Support: None, Conflict of Interest: None
Introduction: As it is not always possible to do Modified Mallampati Test (MMT) in sitting position, this study was designed to test the effect of supine position and phonation on classical MMT and use of such effect in predicting difficult laryngoscopical view or difficult intubation. Aim: To know the effect of phonation and supine position on classical MMT grade and to establish usefulness of modification in predicting difficult laryngoscopy or intubation. Objectives: 1. To compare classical MMT grades with those obtained in supine position with or without phonation. 2. To correlate MMT gradings obtained in all the three variations with Modified Cormack Lehane (MCML) grading and actual difficult intubations to obtain their powers in predicting difficult laryngoscopic view and difficult intubations. Material and Methods: A prospective observational study, conducted at a tertiary care hospital.Consenting, 130 adults, undergoing elective surgical procedures were included. MMT score in sitting position, in supine position with or without phonation was recorded in the preoperative area and MCML grading and actual difficulty for intubation were noted at the time of intubation. Emergency cases and patients with altered airway were excluded.Statistics: 'Kappa' agreement analysis was done to compare the agreement between various scores. Sensitivity, specificity, positive predictive value and negative predictive values were calculated. Results: Supine posture without phonation worsens the classical Mallampati grading whereas supine posture with phonation improves it. MMT in sitting and in supine position without phonation have very good agreement with each other in predicting difficult laryngoscopy and intubation. Conclusions: When the patient cannot sit for examination, MMT scoring can be done in supine position without phonation. Mallampati score in supine position with phonation is not recommended due to high false negatives.
Keywords: Airway assessment in supine position, Cormack–Lehane grading, difficult airway, Effect of posture and phonation on Mallampati grading
|How to cite this article:|
Sankal A, Halemani KR, Bhadrinath N. Assessment of the effect of supine posture and phonation on modified mallampati grading and its applicability in prediction of difficult airway. J Mahatma Gandhi Inst Med Sci 2018;23:19-24
|How to cite this URL:|
Sankal A, Halemani KR, Bhadrinath N. Assessment of the effect of supine posture and phonation on modified mallampati grading and its applicability in prediction of difficult airway. J Mahatma Gandhi Inst Med Sci [serial online] 2018 [cited 2022 Nov 26];23:19-24. Available from: https://www.jmgims.co.in/text.asp?2018/23/1/19/229148
| Introduction|| |
Modified Mallampati test (MMT) in sitting position without phonation is the most commonly used method for predicting potentially difficult intubation.,, Although applicable to majority of patients, airway evaluation in the sitting position may not be always convenient or advisable like elderly or very sick patients or patients with prolapsed disc and fracture spine or in emergency situations. A modification of the test, to allow it to be done in the supine position, has been suggested as an alternative approach.,,, Even though change in posture to supine and phonation produced a significant increase in the MMT grade, it is found to be correlating well with Modified Cormack–Lehane (MCML) grading.,, However, the applicability of such change in predicting difficult airway has to be further studied.
This prospective study was therefore designed to test the correlation of MMT in supine with or without phonation with classical MMT and MCML grading , and difficult intubation. If it is found to be correlating, it can be an useful tool in assessing airways of patients who cannot sit due to various reasons.
| Materials and Methods|| |
After taking written informed consent from each patient aged 18–65 years, 130 patients undergoing elective surgical procedure under general anesthesia (GA) were included in the study. Patients not consenting or belonging to American Society of Anesthesiologist III/IV or undergoing emergency procedures were excluded from the study. Other exclusions included were patients who cannot sit or cannot open the mouth, patients who have any other finding which will affect laryngoscopy and MCML grading (e.g., limited neck extension, mass in the oral cavity, edentulous patients or gap in frontal teeth, etc.), pregnant patients, obese patients with body mass index >35, and diabetic patients.
The principal investigator in the preoperative patient holding area did preliminary airway assessment and a secondary investigator (senior anesthesiologist) blinded to preoperative airway assessment did the laryngoscopical MCML grading. The principal investigator was not involved in laryngoscopy. Difficult intubation is defined as >3 attempts to intubate by senior anesthetist/use of gum elastic bougie/McCoy laryngoscope for intubation.
First, the patient was made to sit up with head in neutral position, mouth fully opened, and tongue maximally protruded without phonation. The MMT score [Figure 1] was assessed by the investigator at eye-to-eye level with the patient. Later, the patient was asked to lye supine, open the mouth fully, and protrude the tongue without the phonation, while the investigator looks vertically downward from above the head end of the patient. MMT score was recorded. Later, in the same position, the patient was asked to say “ah” and MMT was recorded.
After shifting to the operation theatre, preinduction monitors were connected and the patient was premeditated with injection midazolam 1 mg and injection glycopyrrolate 0.2 mg intravenously (IV). Anesthesia was induced with injection fentanyl 2 μg/kg IV, injection propofol 2 mg/kg IV. After loss of response to verbal commands, the maximum amplitude of train of four (TOF) was checked and then neuromuscular blockade was achieved with injection atracurium 0.5 mg/kg IV. Once TOF count was zero, direct laryngoscopy was performed with head in sniffing position by the secondary investigator. The view of the glottis obtained was noted as per MCML grading [Figure 2]. If there was any difficulty in intubation, it was noted down.
Statistical analysis was done using IBM SPSS version 16 software (downloaded from www.ibm.com/us-en/marketplace/spss-statistics. International Business Machines (IBM) Corporation, Armonk, New York, United States of America). All the values were expressed in relative values (number) and absolute values (percentage). P < 0.05 is considered as significant. “Z” test was used for significance sex distribution in the population. “Kappa” agreement analysis was done to compare the agreement between various scores. Four quadrant tables were used to calculate the true positive and true negative cases when grades III and IV in MMT and grades IIb, III, and IV in MCML scores were considered as predictors of difficult laryngoscopic view/difficult intubation. Statistical parameters like sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were calculated.
| Results|| |
A total of 130 adult patients were included in the study. The group was comparable in terms of gender distribution (P = 0.158). Other parameters were as follows: mean age 41.8 ± 12.3 years, mean weight 67.34 ± 10.4 kg, mean height 162.40 ± 7 cm, and mean body mass index (BMI) 25.6 ± 3.4.
MMT in supine position without phonation worsens the grading of MMT assessed in sitting position and MMT in supine position with phonation improves the view [Table 1] and Graph 1].
|Table 1: Percentage distribution of sample according to Mallampati scoring in various modifications|
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Only 14.6% of patients had difficulty in intubation even though 23.1% were showing difficult laryngoscopic view [Table 2] and Graph 2].
|Table 2: Percentage distribution of sample according to difficult Modified Cormack–Lehane scoring versus actual difficult intubation|
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MMT in the sitting position and MMT in the supine position without phonation have better agreement between each other [Table 3].
|Table 3: Agreement analysis between modified Mallampati test in the sitting position versus modified Mallampati test in other modifications when modified Mallampati test in the sitting position is the gold standard|
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MMT in the sitting position and MMT in the supine position with phonation are moderately effective in detecting difficult laryngoscopic view whereas MMT in supine without phonation is fairly effective [Table 4].
|Table 4: Agreement analysis of modified Mallampati test in various modifications in predicting difficult laryngoscopic view when modified Cormack–Lehane grading is the gold standard|
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Among the three MMT gradings, MMT in the supine position without phonation shows the highest sensitivity and lowest specificity. It also shows high false-positives (59.4%), indicating overprediction of difficult laryngoscopic view [Table 5].
|Table 5: Predictive power of grade III/IV in modified Mallampati test in various alterations, in detecting difficult laryngoscopic view, when modified Cormack–Lehane grading is considered as the gold standard|
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MMT in the supine position with phonation shows the highest specificity, indicating that it is better in predicting easy intubations. With highest true positives, positive likelihood ratio, and PPV, the probability of facing difficult laryngoscopic view is the highest when MMT in this position is in grade III/IV. But with 12.5% false-negatives, it becomes less effective in ruling out difficulty in laryngoscopy.
With moderate specificity and moderate sensitivity, MMT in the sitting position shows an accuracy of 75.4% in predicting difficult laryngoscopic view.
MMT in the sitting position and MMT in the supine position without phonation are fairly effective in predicting difficult intubation, whereas MMT in the supine position with phonation is moderately effective [Table 6].
|Table 6: Power of the modified Mallampati test in various positions in predicting difficult intubation|
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MMT in the supine position without phonation has the highest sensitivity and lowest specificity. It shows the lowest false negatives but also shows the highest false-positives, indicating that it overpredicts difficulty in intubation [Table 7].
|Table 7: Predictive power of grade III/IV in modified Mallampati test in various alterations, in detecting difficult intubation, when actual difficulty in intubation is considered as the gold standard|
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MMT in the supine position with phonation shows the highest specificity and lowest sensitivity. It also shows a high number of false negatives than the other two.
With moderate specificity and moderate sensitivity, MMT in the sitting position shows an accuracy of 74.6% in predicting difficult intubation.
| Discussion|| |
MMT test is a common and popularly used technique for predicting difficult airway. However, its requirement of sitting position limits its applicability in bedridden and majority of patients requiring emergency intubation.
After analysis, we found that when the patient is not phonating during the MMT test, changing the posture from sitting to supine significantly worsened Mallampati grade in 18 (28.1%) patients (grade I/II became grade III/IV on supine), and our finding is consistent with most of other studies.,,, In contrast, MMT in the supine position with phonation significantly improved the grading, leading to the exclusion of a significant number of patients (22.4%) who were otherwise considered as difficult airway by MMT in the sitting position. This is similar to the results of Singhal et al. However, Tham et al. described a small non significant change in MMT score when assessed in the sitting and supine positions and the change did not affect the predictive power of the MMT test. As Singhal et al. did not compare MMT in both positions with Cormack–Lehane gradings, they were unable to say whether there is any effect on predictive power of MMT test when done in the supine position.
In short, supine posture without phonation worsens the grading of that from MMT in the sitting posture whereas supine posture with phonation improves the grading. This leads to overprediction of difficulty in intubation when MMT is done in the supine position without phonation and underprediction when done in the supine position with phonation in comparison to MMT in the sitting position.
Agreement analysis shows that there is a substantial agreement between MMT in the sitting position and MMT in the supine position without phonation and a moderate degree of agreement with MMT in the supine position with phonation in predicting difficult airway. MMT in the supine position without phonation correlated better with classical MMT and hence can be used instead of the other.
Our study differs from Tham et al. in which MMT in the supine position with phonation correlated better with MMT in the sitting position. This might be because of the possibility of interobserver variation in their study as agreed by the authors themselves. In our study, we excluded this by limiting the study to only two investigators as done by Singhal et al.
Among a total of 130 patients studied, 30 patients (23.1%) had difficult laryngoscopic view which is very high compared to the previous incidences of 5% by Koh et al. and 6% by Khatiwada et al. This could be because of the use of modified CML grading  in our study, wherein grade IIb is included as difficult laryngoscopic view as compared to classic Cormack–Lehane grading where grade II without subdivision is considered as easy, thus excluding the majority of patients. This is in consensus with Cohen et al.
Out of 30 patients, only 19 (14.6%) patients actually had difficulty in intubation. They needed more than three attempts at intubation or an additional help in the form of gum elastic bougie/McCoy blade for intubation. All others were intubated with little assistance like external laryngeal manipulation. None of the patients needed fiberoptic intubation or cancellation of surgery due to difficulty in intubation. None of the patients suffered any injury or damage due to difficult intubation.
Difficult laryngoscopic view
Out of 30 patients with difficult laryngoscopic view, MMT in the sitting position identified 22 patients (sensitivity 73.3%) as difficult airway; MMT in the supine position without phonation identified 26 patients (sensitivity 86.6%); and MMT in the supine position with phonation identified 17 patients (sensitivity 56.6%). In other words, MMT in the sitting position missed difficult airway in 8 patients, MMT in the supine position without phonation missed difficult airway in 4 patients, and MMT in the supine position with phonation missed difficult airway in 13 patients.
As per agreement analysis, MMT in the supine position with phonation is more effective in predicting difficult laryngoscopic view (accuracy 85.4%) when compared to MMT in the sitting position (accuracy 75.4%) and MMT in the supine position without phonation (accuracy 67.7%).
The positive predictive power and positive likelihood ratio of MMT in the supine position with phonation are significantly higher than the other two positions. This means when an airway is graded as difficult in this position, the likelihood of difficult laryngoscopic view is also high. But with high false-negatives (12.5%), low NPV, and low sensitivity, it becomes ineffective in excluding the difficult laryngoscopy. MMT in the sitting position also has more false-negatives (9.5%) than MMT in the supine position without phonation (6.1%).
The preanesthetic examination of the airway should be primarily aimed at detecting as many patients with difficult airway as possible. This is necessary for minimizing the risk of unanticipated difficult/failed intubation. From this point of view, the sensitivity of a test may be a more valuable parameter for predicting difficult intubation than its specificity. Hence, with lowest sensitivity, MMT in the supine position with phonation is not a good test for predicting difficult laryngoscopic view. Hence, MMT in the supine position without phonation with lowest false-negatives and highest sensitivity is better to predict difficult laryngoscopic view.
Actual difficult intubation
Out of the 19 patients with actual difficulty in intubation, MMT in the sitting position identified 16 patients (sensitivity 84.2%) as difficult airway; MMT in the supine position without phonation identified 18 patients (sensitivity 94.7%); and MMT in the supine position with phonation identified 13 patients (sensitivity 68.4%).
In other words, MMT in the sitting position could not detect difficult airway in three patients, MMT in the supine position without phonation missed difficult airway in only one patient, and MMT in the supine with phonation missed difficult airway in six patients. Agreement analysis shows that MMT in the sitting position and MMT in the supine position without phonation are fairly effective in predicting difficult intubation, whereas MMT in the supine position with phonation is moderately effective.
The likelihood of getting true positives to predict difficult intubation is significantly higher (positive likelihood ratio 6.8) in the supine position with phonation than the other two variations. But as it is showing lowest sensitivity (68.4%) and highest percentage of false-negatives (5.6%), it is not a good test for using in preoperative examination as explained earlier.
None of the three tests have 100% sensitivity. With lower positive likelihood ratio (3.04) and higher negative likelihood ratio (0.35), classical MMT in the sitting position is also less efficacious for predicting difficult laryngoscopic view as well as difficulty in intubation. This is consistent with various meta-analysis or studies done so far ,, (sensitivity of MMT in the sitting position for predicting difficult intubation is 84.2% and specificity is 72.9%). However, due to its simplicity, it is still being used as a routine test for assessment of airway. Some combinations , or modifications ,, to classical MMT tests are being considered to improve its sensitivity, for example, MMT performed in the sitting patient with extension of the craniocervical junction.
The test for predicting difficult intubation should have high accuracy, sensitivity, and PPV to identify all patients in whom intubation will be difficult. Among the three, MMT in the supine position without phonation appears to meet almost all criteria for predicting both difficult laryngoscopic view and difficult intubation except PPV, indicating a high number of false-positives.
The limitations of our study were that, we did not study the combination of MMT in the sitting position and MMT in the supine position without phonation or MMT in the sitting position and MMT in the supine position with phonation in predicting difficult airway. We suggest further study on these lines. Other limitation would be that we did study on a single population. As the anatomy varies with different people from different ethnic backgrounds, the findings may vary. Future studies should be performed considering these factors.
Apparently, no clinical test, the Mallampati scoring system being no exception, can meet perfect criteria when used alone. Effective and reliable prediction requires a combination of several parameters (e.g., age, height, weight, BMI, MMT, head and neck movement, dentition status, upper lip bite test,,,, interincisor gap, and thyromental distance ,,).
Usually, the more parameters are used, the higher is the accuracy of prediction. On the other hand, it is impractical to perform a large number of time-consuming tests before GA. It follows, therefore, that the anesthesiologist must always be prepared to manage difficult airway when such a problem arises.
| Conclusion|| |
We recommend using MMT testing in the supine position without phonation in patients who cannot sit due to various reasons. Even though it is highly sensitive test, because of it's low positive predictive power it can give false alarms that the airway is going to be difficult when that is actually not. How ever with cautious approach and combining with other parameters, it can be as helpful as MMT in the sitting position. Mallampati score in supine position with phonation is not recommended due to high false negatives.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7]