Introduction
Gillespie1 and Bannister and Macbeth,2 provided the first analyses of the anatomical factors involved in difficult laryngoscopy. For Gillespie the solution was to attain adequate depth of anaesthesia and muscular relaxation. For Bannister and Macbeth it was so to position the head that the axes of the mouth, pharynx and larynx came into line. Cass, James and lines3 described 5 cases of difficult intubation and attempted to relate the difficulties to the dimensions of certain anatomical features such as angle of the mandible and the distance from incisors to its posterior border.
We carried out this study to determine the correlation of sternomental distance (SMD), thyromental distance (TMD), inter incisor gap (IIG), protrusion of mandible and modified mallampati test (MMT) with the larnygoscopic view as predictors of difficult intubation.
Methods
Aim
To compare the efficacy of SMD, TMD. IIG,degree of protrusion of mandible (MP) and MMT for predicting difficult intubation
Study Population
A total of 110 patients posted for surgery were enrolled in a tertiary health care institute during August 1998 to January 1999 after obtaining informed written consent. Patients with only ASA-I grade were enrolled. The exclusion criteria included patients with diabetes mellitus, rheumatoid arthritis, ankylosing spondylitis, neck swellings and obvious difficult airway such as T.M. joint ankylosis, mandibular fracture, maxillary tumours or any other airway pathology.
Airway was assessed in each patient preoperatively using Modified Mallampati test (MMT), Thyromental distance (TMD), Sternomental distance (SMD), Interincisor gap (IIG) and Degree of protrusion of mandible (MP).
Modified Mallampati Test (MMT)4
The patient was sitting upright in a chair keeping the head in neutral position, the patient was asked to open the mouth fully and protrude the tongue as far as possible. Looking from the patient's eye level the pharyngeal structure were inspected with a torch, without the patient phonating. The view was graded as follows :-
Grade I : Soft palate, uvula, fauces and pillars visible.
Grade II : Soft palate, uvula, fauces visible but pillars obscured.
Grade III : Soft palate only visible.
Grade IV : Soft palate not visible.
Thyromental Distance (TMD)
Sitting upright in a chair, the patient was asked to fully extend the neck from the neutral position. The distance from the bony point of the mentum to the thyroid notch was measured with a measuring scale. A distance greater than or equal to 6.5 cms was considered normal.
Sternomental Distance (SMD)
Sitting upright in a chair, the patient was asked to fully extend the neck from the neutral position. The distance from the bony point of the mentum to the upper border of manubrium sterni was measured with a measuring scale. A distance greater than 12.5 cms was considered normal.
Inter Incisor Gap (IIG)
Patient sitting upright in a chair was asked to open the mouth fully and the distance between the upper and lower incisor teeth was measured. Patients with IIG less than 5 cms were thought to be difficult intubation.
Degree of protrusion of Mandible (MP)
This was graded by asking the patient to push the chin as far as possible and was graded as :
A. If lower incisors could be protruded anterior to upper incisors.
B. If upper and lower incisors touch each other.
C. If lower incisors could not be brought forward to touch the upper incisors.
On the morning of surgery starvation was confirmed and consent was taken. Intravenous line was secured. Blood pressure monitor, cardioscope and pulse oximeter were attached. Pre-oxygenation was done for 3 minutes. General anaesthesia was induced with 2.5% thiopentone sodium 5 mg/kg body weight. After confirming ventilation, succinyl choline 2 mg/kg was used for muscle relaxation. After full muscle relaxation was achieved as evident by jaw relaxation laryngoscopy was performed by a qualified senior anaesthetist using a Macintosh blade. The laryngoscopist assigned a laryngeal view (LV) class based on the criteria of Cormack and Lehane.5
Class 1: Vocal cords visible.
Class 2: Only posterior commissure or arytenoids visible.
Class 3: Only epiglottis visible.
Class 4: No glottic structure visible.
After LV was graded, patient was intubated with appropriate sized endotracheal tube. Correct placement of the endotracheal tube was confirmed. Stylet, gum elastic bougie and long Macintosh curved blade were kept ready and used when required. In the event of failure of intubation, the senior consultant had taken over.
Statistical Analysis
Patients with LV Class 3 and 4 were taken as difficult intubation cases.
In order to compare the clinical performance of the five indices, sensitivity, specificity were calculated. Correlation was determined between the five parameters and laryngoscopic view by using Karl Pearson’s coefficient of correlation (r).6
Results
110 adult patients with ASA I were studied. The age of the patients ranged from 20 to 70 years. The mean age was 38.4 yrs + 10%. 85% of patients belonged to 20-50 years age group. 61% were females as compared to 39% males. Mallampati score was I in 70 patients, II in 22 patients, III in 18 patients. No patient had a score of IV. TMD was more than 6.5 cms in 106 cases and less than 6.5 cms in 4 patients. Mean TMD was 8.6 cms with standard deviation of + 1.2 cms. SMD was more than 12.5 cms in 103 cases and less than 12.5 cms in 7 patients. Mean SMD was 14.1 cms with standard deviation of + 3.8 cms. IIG was more than 5 cms in 72 cases and less than 5 cms in 38 patients. Mean IIG was 4.4 cms with standard deviation of + 0.85 cms. Regarding MP 101 patients belonged to Group A, 8 patients belonged to group B and only one patient was in group C. Laryngoscopic view (LV) which was taken as the decisive factor for difficult intubation showed Easy view (I and II) in112 patients and difficult view (III and IV) in 8 patients (Table 1).
| Table 1 : Correlation of the five parameters with laryngoscopic view |
| Test |
No. of cases |
Laryngoscopic view |
| |
Normal |
Difficult |
| I |
II |
III |
IV |
| Sternomental distance |
7 |
2 |
0 |
5 |
0 |
| < 12.5 cm |
103 |
94 |
6 |
3 |
0 |
| >= 12.5 |
n=110 |
|
|
|
|
| Thyromental distance |
|
|
|
|
|
| < 6.5 |
4 |
3 |
0 |
1 |
0 |
| >= 6.5 |
106 |
96 |
3 |
7 |
0 |
Modified
mallampati |
|
|
|
|
|
| I and II |
92 |
87 |
4 |
1 |
0 |
| III and IV |
18 |
10 |
1 |
7 |
0 |
| Inter incisor gap |
|
|
|
|
|
| < 5 cm |
70 |
64 |
3 |
3 |
0 |
| >= 5 cm |
40 |
33 |
2 |
5 |
0 |
| Mandibular protrusion |
|
|
|
|
|
| A,B |
109 |
96 |
5 |
8 |
0 |
| C |
1 |
1 |
0 |
0 |
0 |
|
| Table 2 : “r” value, sensitivity and specificity of the five parameters in difficult to intubate patients |
| Name of the test |
r Value |
Sensitivity |
Specificity |
| 1. Sternomental distance |
0.82 |
88.8% |
96% |
| 2. Modified Mallampati |
0.70 |
80% |
91% |
| 3. Thyromental distance |
0.63 |
66.6% |
97% |
| 4. Inter incisor gap |
0.50 |
61.6% |
72% |
| 5. Mandibular protrusion |
0.44 |
6% |
98% |
|
The five parameters viz; SMD,TMD, IIG, MMT and MP were compared to LV by using correlation analysis. The karl Pearsons coefficient of correlation i.e. r value, sensitivity and specificity was determined for each parameter (Table 2).
SMD had the highest sensitivity (88.8%) and specificity of 96% and correlated best with Laryngoscopic view (r=0.91) (Fig.1). TMD had highest specificity (97%), but did not correlate well with LV. MMT showed a borderline correlation (0.72) in the general population but a stronger correlation (0.84) in the difficult to intubate patients. MP and IIG had practically no correlation with LV. 6 out of 8 difficult patients had 2 or more of the five airway evaluation indices abnormal. Complications observed in the 8 difficult patients were oropharyngeal trauma in 4 patients, more than 2 attempts for endotracheal intubation, use of assistance in the form of external laryngeal pressure and stylet in all 8 patients. Long blade was used in 3 patients.
Discussion
 |
| Fig. 1: Sensitivity and specificity of five parameters. |
Visualisation of the glottic aperture by direct laryngoscopy is usually easy due to profound muscular relaxation produced with muscle relaxation. However, many a time, in an apparently normal individual inspite of using the best positioning and most profound relaxation, visualization of glottic aperture proves difficult or sometimes impossible.
In the present study, 110 normal adult patients were studied. The five bedside airway parameters were measured in each patient. Laryngoscopic view (LV) was classified as per Cormack and Lehane.5 Coefficient of correlation was determined between each of these and LV and whether this correlation helped in predicting difficult intubation.
Age of the patients ranged from 20 to 70 years. The mean age was 38.4 yrs + 10 yrs. 85% of patients belonged to 20-50 years age group. 61% were females as compared to 39% males. The average height was 155.5 + 7.2 cms. The weight of the patients ranged from 30 to 84 kg. The mean weight was 54.7 + 10.5 kg.
The incidence of difficult intubation in our study was 7%. In the study done by J.D.L.Oates et al,7 it was 1.8%. Wilson et al found an incidence of 1.5%. Mallampati et al4 gave an incidence of 13%.
The mean SMD in our study was 14.1 + 3.8 cms. A distance of less than 12.5 cms was considered to be suggestive of difficult intubation. There were 7 patients with SMD less than 12.5 cms and 5 of these patients had an LV of Grade III. This test had a sensitivity of 88.8% and specificity of 96%. Coefficient of correlation i.e. “r” value in the 110 patients was 0.82 and in the difficult to intubate patients was 0.91. These values suggest a strong correlation between SMD and LV. In the study done by D. Savva in 1994,9 SMD had a sensitivity of 82.4% and specificity of 88.6% and it was the best predictor of difficult intubation. Our study showed a better predictability and correlation.
MMT grade III and IV was present in 18 patients. Six patients had LV of Grade III. This test had a sensitivity of 80% and specificity of 91%. This test has a better ability to identify the truly negative i.e. patients with normal evaluation index and who had normal laryngoscopy. This test is thus more specific than sensitive. The coefficient of correlation was 0.72 in the 110 patients & in the 8 difficult patients it was 0.84. Thus in general population this test has a borderline correlation.
In the study done by Frerk in 1991,10 this test showed a sensitivity 81.2% and specificity of 81.5% but he had included Grade two patients in whom a bougie was used to facilitate intubation in his difficult group. If these are excluded as suggested by I.Calder11 the incidence of difficult intubation becomes 1.6% in Frerk’s study, in contrast to 4.2%. Savva in his study had a sensitivity of 64.7% and specificity of 66.1% for this test which was much lesser than our study. In a study by Oates et al,7 it was found that twice as many patients were predicted to be difficult by MPT than by Wilson risk sum.8
The mean TMD in our study was 8.6 + 1.2 cms. A distance of less than 6.5 cms was considered to be suggestive of difficult intubation as per Savva’s study. There were 4 patients with TMD less than 6.5 cms. One of these had an LV of Grade III. The other 7 patients with an LV of grade III had TMD more than or equal to 6.5 cms. This test had a sensitivity of 66.6% which is similar to D. Savva’s9 study of 64.7%. Hence this test had a poor ability to detect the true positive patients i.e. patients with abnormal airway and who would have difficult laryngoscopy. The specificity of the test was 97%. The r value was 0.63 for all the 110 patients which indicate a poor correlation. In the difficult to intubate patients, it was 0.6. M.Mathew et al12 showed that with a TMD of less than 6 cms combined with horizontal length of mandible less than 9 cms had a good correlation with class III and IV LV and had a higher probability of difficult intubation. Frerk’s10 study showed a sensitivity of 90.9% and a specificity of 81.5%. He assumed a distance of 7 cms or less as a predictor for difficult intubation.
The mean IIG in our study was 4.4 + 0.8 cms. An IIG of 5 cms or three finger breadths is considered normal. 3 patients out of the 8 difficult patients had IIG less than 5 cms, the minimum distance being 3 cms. The sensitivity of this test was 61.6% and specificity was 72%. Wilson and colleagues suggested that IIG less than 2 cms rather than 5 cms is a predictor of difficult intubation. They said that difficult intubations had mean IIG of 3.8 cms. Our study had a mean IIG of 4.4 cms in the difficult patients. Coefficient of correlation was 0.5 for this test, so in our study IIG had no correlation with LV. Savva’s9 study also did not find any correlation between IIG and LV.
Out of the 8 difficult patients 7 had MP grade A and I had grade B. Only 1 patient had grade C of MP. This test had a sensitivity of only 6% and specificity of 98%, thus is an unreliable test to predict difficult intubation. Savva’s study reveals a sensitivity of 29.4% and a specificity of 85%. Our value for sensitivity is much lesser as compared to Savva’s study. The coefficient was 0.44 which suggests that there is no correlation between LV and MP.
All of the 8 patients were intubated in more than 2 attempts. One of our patients developed bradycardia and ventricular ectopics and was given appropriate treatment and was intubated at the fourth attempt. Oropharyngeal trauma occurred in 4 out of 8 patients. Long bladed laryngoscope had to be used in 3 patients. External laryngeal pressure and stylet had to be used in all 8 patients.
Conclusions
SMD of less than 12.5 cms has the highest sensitivity for predicting difficult intubation. MMT had a sensitivity better than TMD but as less sensitive than SMD. TMD had a high specificity but was not a reliable index due to low sensitivity. IIG and MP neither correlate with LV nor are reliable indices of predicting difficult intubation.
References
- Gillespie NA. Endotracheal Anaesthesia Madison : U. Wisconsin Press. 1941.
- Bannister FB, Macbeth RG. Direct laryngoscopy and tracheal intubation. Lancet 1944; 2 : 651.
- Cass NM, James NR, Lines V. Difficult direct laryngoscopy complicating intubation for anaesthesia. British Medical Journal 1956; 1 : 488.
- Mallampati SR, Gatt SP, Gugino LD, et al. A clinical sign to predict difficult tracheal intubation : a prospective study. Canadian Anaesthetists Society Journal 1985; 32 : 429-34.
- Cormack RS, Lehane J. Difficult tracheal intubation in obstetrics. Anaesthesia 1984; 39 : 1105-11.
- Gupta SP. Statistical methods. Publishers Sultanchand and sons revised edition 1995.
- Oates JDL, Macleod AD, Oates PD, et al. Comparison of two methods for predicting difficult intubation. British J Anaesthesia 1991; 66 : 305-09.
- Wilson ME, Spiegelhalter D, Robertson JA, Lesser P. Predicting difficult intubation. British J Anaesthesia 1988; 61 : 211-16.
- Savva D. Prediction of difficult tracheal intubation. British J Anaesthesia 1994 ; 73 :149-53.
- Frerk CM. Predicting difficult intubation. Anaesthesia 1991 ; 46 : 1005 -08.
- Calder I. Predicting difficult intubation. Anaesthesia 1992; 47 : 528-29.
- Mathew M, Hanna LS , Aldrete JA. Preoperative indices to anticipate difficult tracheal intubation. Anaesthesia Analgesia 1989; 68 : S1-S321.
EPILEPSY IN ELDERLY
Around 1-% of elderly people have epilepsy, often secondary to cerebrovascular disease; presentation is often non-specific, and many other conditions can mimic an epileptic seizure. With appropriate pharmacological treatment, most elderly people with epilepsy will remain seizure-free.
When choosing an antiepileptic drug, particular attention should be paid to side effects and potential for drug-drug interactions. Randomised clinical trials suggest that lamotrigine and gabapentin are better tolerated than carbamazepine in elderly people.
Development of epilepsy is common in later life. The prognosis in terms of seizure control may be better than in younger populations. The choice of antiepileptic drugs should focus on avoidance of side effects and adverse drug-drug interactions.
BMJ, 2005; 331 : 1321. |
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