|Year : 2013 | Volume
| Issue : 1 | Page : 105-109
Comparison between different tests and their combination for prediction of difficult intubation: An analytical study
Sandip Roy Basunia, Sarmila Ghosh, Susmita Bhattacharya, Indranil Saha, Atanu Biswas, Anu Prasad
Department of Anaesthesiology, Burdwan Medical College and Hospital, Burdwan, West Bengal, India
|Date of Web Publication||26-Jun-2013|
Sandip Roy Basunia
Department of Anaesthesiology, 64/1b Raja Rammohan Roy Road, Priyanka Apartment Flat - 105, Kolkata - 700 008, West Bengal
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Context: There is an impelling need for accurate tests to predict difficult intubation, as failure to achieve endotracheal intubation causes significant morbidity and mortality in anesthetic practice.
Aim: To calculate the validity of the different tests along with their combination and agreement when compared with endotracheal intubation in predicting difficult intubation.
Settings and Design: Operation theaters, analytical study.
Materials and Methods: Three hundred patients aged between 16 and 60 years of American society of anesthesiologist (ASA) physical status I and II, scheduled for elective surgical procedures requiring endotracheal intubation were studied during January-July 2012. Mallampati grade (MP), sternomental distance (SMD), thyromental distance (TMD), and Delilkan and Calder test were recorded for every patient. Endotracheal intubation was performed by an experienced anesthesiologist blinded to the measurements and recorded grading of intubation. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), likelihood ratio (LR), odds ratio (OR), and kappa coefficient of tests individually and in combination were calculated.
Statistical Analysis Used: IBM SPSS software (version 16.0) and Epi-info software (version 3.2).
Results: Difficult and failed intubation was 13.3% and 0.6%, respectively. Difficult intubation increased with age. TMD and Calder test showed highest sensitivity individually and Dellilkan's test showed least sensitivity. Among the combination of tests, MP with SMD and MP with Calder test had the highest sensitivity.
Conclusion: Among individual test TMD and Calder are better predictive tests in terms of sensitivity. Combination of tests increases the chance of prediction of difficult intubation.
Keywords: Delilkan and Calder test, difficult intubation, Mallampati grade, sternomental and thyromental distance
|How to cite this article:|
Basunia SR, Ghosh S, Bhattacharya S, Saha I, Biswas A, Prasad A. Comparison between different tests and their combination for prediction of difficult intubation: An analytical study. Anesth Essays Res 2013;7:105-9
|How to cite this URL:|
Basunia SR, Ghosh S, Bhattacharya S, Saha I, Biswas A, Prasad A. Comparison between different tests and their combination for prediction of difficult intubation: An analytical study. Anesth Essays Res [serial online] 2013 [cited 2020 Jul 15];7:105-9. Available from: http://www.aeronline.org/text.asp?2013/7/1/105/114014
| Introduction|| |
Airway management and endotracheal intubation are the primary concern in the field of anesthesiology. Patent airway is essential for adequate oxygenation and ventilation as failure to maintain a patent airway results in life-threatening consequences like hypoxia, brain damage, and death.  Closed claim study of American society of anesthesiologist has reported 17% adverse respiratory events occurring to difficult intubation and 85% of these cases either died or suffered brain damage.  So pre-operative evaluation of airway is mandatory in all surgical patients irrespective of anesthetic technique.
Various tests are performed to evaluate airway. But none of the available indices are able to predict all difficult intubation.  So there is always a chance of unanticipated difficult intubation. On the other hand, sometimes airway is falsely predicted to be difficult when intubation proves easy. The present study was conducted to find out the validity of different tests namely modified Mallampati (MMP) grade, sternomental distance (SMD), Thyromental distance (TMD), and Delilkan and Calder test individually and in combination and their agreement were compared with endotracheal intubation in predicting difficult intubation.
| Materials and Methods|| |
The present study was an analytical cross-sectional study, carried out between January and July 2012 in a tertiary health center, Burdwan Medical College and Hospital, Burdwan, West Bengal. Study population comprising patients aged between 16 and 60 years of either sex belonging to American society of anesthesiologist physical status (ASA PS) I and II scheduled for elective surgical procedures requiring endotracheal intubation. A total of 300 such patients were found during the data collection period and studied. Thus complete enumeration method was followed while selecting the patients. Patients with intra-oral growth, unable to open mouth, chin on chest, mentally challenged person, pregnancy, previous history of difficult intubation, and congenital and acquired disorders of head and neck were excluded from the study. Study was initiated only after permission from Ethics Review Board (ERB) of our institution and informed written consent was obtained from each patient. Pre-operatively anesthesiologists who were not involved in intubation in the operation theatre evaluated airway by assessing MMP and Delilkan and Calder test were measured TMD and SMD.
Samsoon and Young's modification of Mallampati  grading was performed in patient in sitting position, mouth open as wide as possible, and tongue stuck out without phonation. Observer's eye was at the level of the patient's open mouth. Following four grades were noted:
Grades 1 and 2 were predicted as easy laryngoscopy and Grades 3 and 4 were taken as difficult viewing of glottis.
- Grade 1: Faucial pillars, uvula, soft, and hard palate visible.
- Grade 2: Uvula, soft, and hard palate visible.
- Grade 3: Base of uvula or none, soft, and hard palate visible.
- Grade 4: Only hard palate visible.
While performing Delilkan's test the patient was asked to look straight ahead. The head was held in the neutral position. The index finger of the left hand of the observer was placed under the tip of the jaw, whereas the index finger of the right hand was placed on the patient's occipital tuberosity. The patient was now asked to look at the ceiling. If the left index finger became higher than the right, extension of atlanto-occipital joint was considered normal. If the left index finger remained at the same level or lower of the right, extension was abnormal. In Calder test, the patient was asked to protrude the lower jaw as far as possible. The lower incisors were lying either anterior to or aligned with or posterior to the upper incisors. The latter two were suggested as reduced view at laryngoscopy. The SMD was measured with the head fully extended and with the mouth closed. The straight distance between the upper border of the manubrium sterni and the bony point of the mentum was measured.  SMD < 12.5 cm was considered as a reduced view at laryngoscopy. For TMD, the straight distance between the upper border of the thyroid cartilage and the bony point of mentum was measured.  TMD < 6.5 cm was considered reduced view at laryngoscopy. All the findings were recorded in patients' record form.
In the operating room, 18G intravenous cannula was inserted and ringer lactate infusion was started. Standard monitors were attached to the patient. Intravenous midazolam 0.05 mg/kg, glycopyrrolate 0.005 mg/kg, ondansetron 0.1 mg/kg, and fentanyl 2μg/kg were given before induction. After pre-oxygenation for 3 min, patients were induced with propofol 2 mg/kg and after mask ventilation was ensured, succinylcholine 1 mg/kg was given. In sniffing position (neck flexion 20-25° and head extension 80-85° by putting a pillow of 8-10 cm below occiput which helps in alignment of the oral, pharyngeal, and laryngeal axis), laryngoscopy was performed after 1 min of succinylcholine administration with a Macintosh No. 3/4 blade and trachea was intubated. Grading of intubation was noted. Grading was carried out by an experienced anesthesiologist who was blinded to the pre-operative observations. Grading of intubation is as follows:
Grades 1 and 2 were considered as easy and Grades 3 and 4 as difficult intubation. In Grade 4, where anesthesiologist failed using conventional technique, a gum elastic bougie, video laryngoscope, or fiber optic bronchoscope was considered.
- Grade 1: No extrinsic manipulation of the larynx is required.
- Grade 2: External manipulation of the larynx is necessary to intubate.
- Grade 3: Intubation possible only when aided by a stylet.
- Grade 4: Failed intubation.
Collected data were compiled on Microsoft Excel worksheets (Microsoft, Redwoods, WA, USA). Validity of the tests was expressed by sensitivity and specificity by judging grade of intubation by endotracheal intubation as gold standard. Diagnostic power of the different tests was expressed by predictive value. Likelihood ratio (LR) was computed to determine the increase or decrease in the probability of intubation grading if the respective options were positive or negative . Kappa coefficient was also computed to see what extent the reading of two different methods agreed beyond which we would expect by chance alone. Relationship between two variables and difference between two independent mean values was determined by Spearman's correlation coefficient (ρ) and unpaired Student's t-test, respectively, computed by IBM SPSS software (version 16.0). Epi-info software (version 3.2) was used to calculate odds ratio (OR). P <0.05 was considered as statistically significant.
| Results|| |
Out of 300 patients the difficult intubation (Grades 3 and 4) occurred in 40 cases (13.3%) and failed intubation (Grade 4) occurred only in two cases (0.6%) where fibreoptic bronchoscope was used. In this difficult intubation group, majority, i.e., 60% (24) were males and rest 40% (16) were females. Mean age of the patients was higher among difficult intubation group (45.32 ± 8.22 years) when compared with easy intubation group (41.39 ± 9.49 years). This difference was significant statistically by unpaired Student's t-test (t = 2.48, P = 0.013). Overall, there was a significant positive correlation between age and difficult intubation (Spearman's ρ =0.353, P = 0.00), which indicated that with increase in age there was increase in difficult intubation [Table 1].
|Table 1: Distribution of the patients according to intubation grading and age|
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Different airway tests were performed on each patient and compared with intubation grading. For each of the measured parameters LR, OR, and kappa coefficient were calculated in [Table 2] and sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) is shown in [Table 3]. Individually, MP alone had highest LR, OR, and kappa coefficient. Again, in combination with MP, OR, LR, and kappa coefficient had increased with SMD and DL [Table 2].
|Table 2: Likelihood ratio, odds ratio, and kappa coefficient of different tests in predicting difficult intubation|
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|Table 3: Sensitivity, specificity, positive predictive value, and negative predictive value of the measured parameters indicative of difficult intubation|
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TMD and Calder showed highest sensitivity (65%) individually, followed by MP and Dellikan's test that showed least sensitivity (47.5%). MP alone had highest positive predictive value, specificity (93.4%), and negative predictive value (94.1%). Among the combination of tests, MMP with SMD and MMP with Calder test had the highest sensitivity (90%) [Table 3], [Figure 1] and [Figure 2]. Greatest agreement was seen between MMP, MMP with SMD, and MMP with Delilkan and grading of intubation (kappa coefficient = 0.5).
| Discussion|| |
Predictors of difficult intubation can be grouped as individual and group indices. Individual indices may be physical examination and radiological indices. Physical examination indices includes assessment of cervical and atlanto-occipital (Delilkan's test) and temporo-mandibular joint (Calder test, Upper lip bite test), mandibular space (TMD and SMD), adequacy of oropharynx (MP grading), glottic view by laryngoscopy (Cormack and Lehane's classification, Grading ease of intubation), and ratio of patient height to TMD. Radiological assessment include ratio of mandibular length with posterior depth, distance between occiput and spinous process of C1, and posterior depth of mandible. But these are time-consuming and are probably no better than the above clinical tests. Group indices include Wilson's scoring system (weight, head and neck movement, jaw movement, receding mandible, and buck teeth), Benumof's 11 parameter analysis, Arne's simplified score, and rapid airway assessment etc., Rapid airway assessment include 1 finger test (for sliding movement of mandible), 2 finger test interincisor gap), and 3 finger test (sub-mandibular space). Among the individual tests MMP, SMD, TMD, and Delilkan and Calder are most useful tests. This study was designed to evaluate the accuracy of measurements of MMP, SMD, TMD, and Delilkan's and Calder test individually and in combination of MMP with each of the other tests in prediction of difficult intubation.
In our study, among 300 patients the incidence of difficult intubation was 13.3% and failed intubation was 0.6%. This occurrence is quiet similar as found in previous studies which ranged from 1 to 18%. ,, This wide range might be due to wide racial variation. Among the difficult intubation group, the majority were male (60%), similar to other studies.  This male preponderance of difficult intubation may be explained by increased muscle mass and neck rigidity present in male.  With increase in age there is an increase probability of difficult intubation, as evident from the present study, that might be related to decreased neck mobility, increased articular stiffness, and irregular dentition with advanced age. 
In our study, MMP had a lower sensitivity (62%) and high specificity (93%) which corroborated with previous study of Lundstrom et al.  TMD and Calder test individually had higher sensitivity (65%) when compared with MMP. Khan et al.  also found similar sensitivity with TMD.
Among the combinations with different tests, MMP with SMD and MMP with Calder test had the highest sensitivity (90%). Domi and Sava had found similar sensitivity with MMP combined with SMD in their respective studies. , MMP with Delilkan's test had highest specificity (83%) but lower sensitivity (87%) when compared with MMP with SMD and MMP with Calder test, whereas MMP with TMD had least sensitivity (77.5%) among the combinations.
Prediction of difficult intubation of individual and combination of tests was assessed by different statistical methods like OR, LR, and Kappa coefficient. We found OR > 1 in all of the tests which denoted good association between test and intubation grading.  LR was more than 1 in all the tests which signified that the probability of test positively coincided with the intubation grading. We found good agreement between MMP, SMD, MMP with SMD, MMP with Delilkan's test, and intubation grading where kappa value was between 0.4 and 0.75. We also found combination of all tests that were statistically significant (P < 0.05).
Ideal test for prediction would have perfect sensitivity and specificity. But sensitivity and specificity are interdependent and increase in one whereas decreases in other. We considered sensitivity the most important parameter as our target was to identify more number of difficult intubation cases to avoid the potentially serious outcome of unanticipated difficult tracheal intubation.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3]