|Year : 2020 | Volume
| Issue : 1 | Page : 33-37
A comparative study of acromio-axillo-suprasternal notch index with upper lip bite test and modified Mallampati score to predict difficult laryngoscopy
Rupesh Sunkam1, Vinayak Seenappa Pujari2, Balakrishna Kailasnatha Shenoy2, Yatish Bevinaguddaiah2, Leena Harshad Parate2
1 Department of Anaesthesiology, Bhaskar Medical College, Hyderabad, Karnataka, India
2 Department of Anaesthesiology, MS Ramaiah Medical College, Bengaluru, Karnataka, India
|Date of Submission||06-Oct-2019|
|Date of Decision||31-Oct-2019|
|Date of Acceptance||03-Nov-2019|
|Date of Web Publication||13-Feb-2020|
Dr. Vinayak Seenappa Pujari
Department of Anaesthesiology, MS Ramaiah Medical College, Bengaluru - 560 054, Karnataka
Source of Support: None, Conflict of Interest: None
Background: The current bedside predictors of the difficult airway are not perfect. A new test, the acromio-axillo-suprasternal notch index (AASI), has been found to be superior to conventional predictors. In this study, we have compared the accuracy of AASI with upper lip bite test (ULBT) and modified Mallampati (MMP) test to predict difficult laryngoscopy and the time taken to complete each test.
Methods: Institutional ethical committee clearance was obtained, and written informed consent was taken from 150 patients posted for elective surgery under general anesthesia with endotracheal intubation. Preoperative airway examination was carried out with AASI, ULBT, and MMP score. AASI ≥0.49, ULBT Class III, and MMP score III/IV were considered as predictive of difficult visualization of larynx (DVL). After the induction of anesthesia, the laryngeal view was recorded according to Cormack–Lehane (CL) grade. Sensitivity, specificity, predictive values, and accuracy were calculated for all the three tests.
Results: DVL (CL Grades 3/4) was observed in 18 (12%) patients. AASI was found to have higher specificity (93.2%), positive predictive value (PPV) (55%), and accuracy (89.3%) when compared to MMP and ULBT. MMP was found to have the highest sensitivity (77.8%), and ULBT was found to have least sensitivity (50%). Time taken for AASI was higher (13.01 ± 1.03 s) when compared to ULBT (7.49 ± 1.95 s) and MMP (3.97 ± 0.49 s).
Conclusion: We conclude that the MMP is the most sensitive and fastest test to predict DVL when compared to AASI and ULBT. AASI is a better predictor for DVL as it has higher specificity, PPV, accuracy, and odds ratio when compared to standard tests such as MMP and ULBT.
Keywords: Airway management, laryngoscopy, predictive value of tests, sensitivity, specificity
|How to cite this article:|
Sunkam R, Pujari VS, Shenoy BK, Bevinaguddaiah Y, Parate LH. A comparative study of acromio-axillo-suprasternal notch index with upper lip bite test and modified Mallampati score to predict difficult laryngoscopy. Indian Anaesth Forum 2020;21:33-7
|How to cite this URL:|
Sunkam R, Pujari VS, Shenoy BK, Bevinaguddaiah Y, Parate LH. A comparative study of acromio-axillo-suprasternal notch index with upper lip bite test and modified Mallampati score to predict difficult laryngoscopy. Indian Anaesth Forum [serial online] 2020 [cited 2020 Dec 3];21:33-7. Available from: http://www.theiaforum.org/text.asp?2020/21/1/33/278190
| Introduction|| |
Airway management is safest when airway problems are identified in the preanesthetic check, enabling the anesthetist to plan thus, reducing the risk of complications. The incidence of difficult airway is varied and is reported in the range of 1.5%–20%. The American Society of Anesthesiologists (ASA) database analysis of adverse respiratory events has found that majority of airway-related events can lead to brain damage or death.
Conventional tests for prediction of the difficult airway which are commonly used in daily practice such as modified Mallampati (MMP) score, thyromental distance, and upper lip bite test (ULBT) use simple anatomical landmarks., These bedside screening tests are quite simple, but they require patient's cooperation to be performed right and thus assessed correctly.
The conventionally used predictors of difficult airway have poor-to-moderate discrimination when used alone. This may improve further when the combination of tools are used. A recent study on acromio-axillo-suprasternal notch index (AASI) by Rajkhowa et al. found that AASI was a good predictor of difficult visualization of larynx (DVL) at direct laryngoscopy. AASI was proposed by Kamranmanesh et al. it is a bedside test based on surface anatomy. They observed that DVL was found in patients whose neck was situated deep in the chest, and they described it as subjects with a sloping clavicle. They used the portion of the arm-chest junction above the level of suprasternal notch might estimate DVL and proposed a new index the AASI.
The present study was planned to evaluate the accuracy of AASI and to compare it with ULBT and MMP for assessing DVL in patients requiring endotracheal intubation under general anesthesia.
| Methods|| |
This prospective observational study was conducted during September 2016–July 2018 on 150 ASA physical status I/II patients aged between 18 and 75 years undergoing elective surgeries requiring endotracheal intubation. The institutional ethical committee clearance was obtained, and the study was registered with clinical trial registry of India (CTRI/2018/01/011337). Written informed consent was obtained from the participants. The exclusion criteria were recent head and neck surgery, mouth opening <3 cms, edentulous patients, gross external head/neck deformities, and pregnancy.
AASI, ULBT, and MMP were assessed by an independent evaluator during the preanesthetic evaluation [Table 1]. ULBT of Class III and MMP Class III/IV was considered predictive of DVL. The AASI was measured with the patient lying in a supine position and their arms by the side of the trunk. A vertical line was drawn from the top of the acromion process to the superior border of the axilla (A). Another line (B) was drawn perpendicular to line A from the suprasternal notch. The portion of line A that lies above the intersection was labeled as line C. The length of line C divided by line A will give the AASI (AASI = C/A). AASI of ≥0.49 was predictive of DVL [Figure 1]. The time taken to complete each test was calculated from the time the evaluator explains the test to the patient till the endpoint of each test was noted.
|Table 1: Upper lip bite test, Mallampati test, and Cormack-Lehane grading|
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|Figure 1: Acromioaxillosuprasternal notch index calculation acromio-axillo-suprasternal notch index is defined as C divided by A (acromio-axillo-suprasternal notch index = C/A)|
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In the operation theater, after connecting to the monitor, baseline parameters were noted. Patients were preoxygenated for 3 min; anesthesia was induced with fentanyl 2 μg/kg, propofol 2 mg/kg, and atracurium 0.5 mg/kg. Patients were ventilated for 3 min using appropriate sized mask. Direct laryngoscopy was then done using size 3 Macintosh blade with head in sniffing position, and the best possible laryngoscopic view was noted. The laryngoscopy was done by an anesthesiologist with minimum of 2 years of clinical experience and they were blinded to preoperative assessment grade of the airway. Cormack–Lehane (CL) Grades I/II were considered as easy visualization of larynx (EVL) and III/IV was considered as DVL [Table 1]. If the airway could not be secured, the Difficult Airway Society guidelines for the management of unanticipated difficult intubation were followed.
Sample size calculation
In an earlier study, it was found that the sensitivity of AASI was 78.9% in predicting difficult laryngoscopy as compared to 52.4% sensitivity of MMP test. The sample size was calculated assuming similar difference in sensitivity when comparing the AASI, ULBT, and MMP with power of 99% and alpha error of 1% sample size was calculated to be 150. Continuous variables were expressed as mean ± standard deviation numerical data were analyzed using an unpaired Student's t-test. Categorical data were analyzed by the Chi-square test. The differences among the three groups were analyzed using the one-way analysis of variance test. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), accuracy, and likelihood ratios were calculated for each of these tests. Statistical analysis was performed using the Statistical software IBM©SPSS© (Statistical Package for the Social Sciences) version 18 (IBM © Corp., Armonk, NY, USA).
| Results|| |
All 150 patients recruited completed the study. We analyzed the results according to the CL grade. CL Grade I/II being EVL and CL Grade III/IV being DVL. There were 18 patients who had CL Grade III/IV; these grades were significantly more common in older subjects. Although the patients with DVL were heavier and had a higher body mass index, demographic profiles were comparable between two groups [Table 2].
|Table 2: Comparison of demographic and clinical variables according to Cormack-Lehane grading|
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AASI of <0.49 was found in 130 patients and 123 of them had an EVL. Whereas AASI of ≥0.49 was found in 20 patients and among them 11 had DVL. MMP III/IV was found in 64 patients and 14 had DVL. ULBT score of III was found in 47 patients and 9 had DVL. AASI was found to have higher specificity, PPV, and accuracy to predict DVL when compared to MMP and ULBT. MMP was found to have the highest sensitivity (77.8%) to predict DVL when compared to AASI and ULBT. AASI had higher sensitivity than ULBT. Odds ratio is more for AASI when compared to MMP and ULBT, which indicates a strong correlation between AASI of ≥0.49 and DVL [Table 3].
|Table 3: Correlation of acromio-axillo-suprasternal notch index, modified Mallampati and upper lip bite test with Cormack-Lehane Grading|
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MMP takes significantly lesser time (3.97 ± 0.49 s) to assess when compared to ULBT (7.49 ± 1.95 s) and AASI (13.01 ± 1.03 s) [Table 4].
In our study, AASI was found to have higher specificity, PPV, accuracy, and odds ratio to predict DVL when compared to MMP. AASI was found to have higher sensitivity, specificity, PPV, NPV, accuracy, and odds ratio to predict difficult visualization of larynx (DVL) when compared to ULBT. MMP was found to have higher sensitivity, PPV, NPV, and odds ratio to predict DVL when compared to ULBT whereas specificity and accuracy are more for ULBT when compared to MMP.
| Discussion|| |
Accurate prediction of difficult laryngoscopy preoperatively would be ideal, but there is no single test yet which is both sensitive and with a low false-positive rate. A screening test to predict difficult airway should have high sensitivity to identify patients in whom the airway will really be difficult. It should also have a high PPV so that only few patients with airways who are actually easy to manage would be subjected to the protocol of difficult airway management. A test should also have a high NPV to rightly predict the ease of laryngoscopy.
The incidence of DVL in our study was 12%, which is in the reported in the range of 1.7% and 20.2%. The specificity of MMP in this study is 62.1% which is lower when compared to other studies., 8, ,,, The sensitivity of MMP in this study was 77.8% which was comparable to the sensitivity observed by Gupta et al. A major disadvantage of MMP is its sensitivity is highly variable. In this study, AASI predictive values such as specificity, NPV are comparable to other studies., However, the sensitivity and PPV were lower than reported by Kamranmanesh et al. The predictive values such as sensitivity, specificity, PPV, and NPV of this study were almost similar to Safavi study [Table 5]. An odds ratio of 21.47 indicates that an AASI of ≥0.49 increases the chance of DVL by more than 21 times. Kamranmanesh et al. have estimated an odds ratio of 31.5. The differences may be due to differences in population used between the two studies. In our study, ULBT was found to be less sensitive and specific to predict DVL compared to other studies. The test with higher sensitivity will have lower false negatives. MMP has a lesser false-negative rate when compared to AASI.
|Table 5: Comparison of predictive values of modified Mallampati, upper lip bite test and acromio-axillo-suprasternal notch index obtained in this study and other studies|
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We found that AASI was more specific and had lesser false-negative rate when compared to ULBT. The time tested MMP takes lesser time to assess and is a more sensitive test as compared to AASI. AASI is a new simple bedside test done in supine position; it is of great value in patients who cannot be seated, cannot cooperate, or are unable to perform properly other airway predictive tests due to mental/physical disability. AASI is derived from measurements and thus is less subjective.
There are a few limitations of this study, we evaluated patients who had no factors predicting difficult airway at the preanesthetic visit, and there is evidence that comorbidities may predispose the patient to the risk of difficult airway. The inference of difficult laryngoscopy in our study was established only using the CL grade which has its own limitations. Another limitation of the study is that the grading of DVL was done by different anesthesiologists.
| Conclusion|| |
We conclude that the MMP is still the fastest and most sensitive test to predict DVL when compared of AASI and ULBT. The new bedside test AASI is a better predictor for DVL as it has higher specificity, PPV, accuracy, and odds ratio when compared to MMP and ULBT.
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Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]