|Year : 2019 | Volume
| Issue : 1 | Page : 22-27
Correlation of anticipated difficult airway with concurrent intubation: A prospective observational study
Gayatri Rajeev Sakrikar1, Prerana Nirav Shah2
1 Department of Anaesthesiology, Bharat Ratna Dr Babasaheb Ambedkar Hospital, Mumbai, Maharashtra, India
2 Department of Anaesthesiology, Seth GS Medical College and KEM Hospital, Mumbai, Maharashtra, India
|Date of Web Publication||25-Apr-2019|
Dr. Gayatri Rajeev Sakrikar
1, Pavankumar Society, Sant Janabai Road, Vileparle East, Mumbai - 400 057, Maharashtra
Source of Support: None, Conflict of Interest: None
Background: Neither all anticipated difficult airways prove to be difficult intubations nor can all difficult intubations be accurately predicted. We conducted this prospective observational study to evaluate the incidence of anticipated difficult airway and concurrent difficult intubation and look for any correlation between them. Patients and Methods: In this study, 352 patients aged >18 years posted for elective surgery requiring general anaesthesia with the placement of endotracheal tube were recruited after obtaining the Ethical Committee approval and written informed consent. The airway was examined at the time of preanaesthetic check up and assigned the modified Mallampati class and Wilson's score. The modified Mallampati Class III/IV and Wilson's score of >4 were considered a difficult airway. Concurrent intubation was graded according to the Cormack–Lehane classification on laryngoscopy. Other parameters such as the duration of laryngoscopy, time taken for intubation and number of attempts were also noted. The incidence of anticipated and unanticipated difficult airway was calculated separately for each score along with its sensitivity, specificity, positive predictive value and negative predictive value. The significance of this association was analysed using the Chi-square test. Results: The incidence of the anticipated difficult airway by the modified Mallampati classification was 6.8%, whereas that by Wilson's score was 2.5%. The incidence of actual difficult intubation was 13%. Actual difficult airways out of those anticipated by the modified Mallampati classification were only 8, whereas those anticipated by Wilson's score were 27. Correlation between them was calculated using the Chi-square test with P < 0.05 considered as statistically significant. Conclusions: Modified Mallampati classification could fairly predict the true-negative results and Wilson's score even though not routinely used is a better indicator for true-positive values. Thus, Wilson's score should be included in routine preanaesthetic evaluation.
Keywords: Anticipated difficult airway, difficult intubation, modified Mallampati class, Wilson's score
|How to cite this article:|
Sakrikar GR, Shah PN. Correlation of anticipated difficult airway with concurrent intubation: A prospective observational study. Airway 2019;2:22-7
|How to cite this URL:|
Sakrikar GR, Shah PN. Correlation of anticipated difficult airway with concurrent intubation: A prospective observational study. Airway [serial online] 2019 [cited 2019 Aug 18];2:22-7. Available from: http://www.arwy.org/text.asp?2019/2/1/22/257042
| Introduction|| |
Difficult airway is a clinical situation in which a conventionally trained anaesthesiologist experiences difficulty with facemask ventilation and/or difficult laryngoscopy and/or difficult intubation. Difficult laryngoscopy is a situation in which it is not possible to visualise any portion of vocal cords even after multiple attempts with conventional laryngoscopy. Difficult intubation is inability to pass the endotracheal tube through vocal cords in the presence or absence of tracheal pathology.
The incidence of failed intubation in elective cases ranges from 1 in 1000 to 2000, 1 in 250 in obstetric cases and 1 in 100 in emergency cases. Difficulty with tracheal intubation, especially in patients with unanticipated difficult airway, remains a frequent cause of anaesthesia-related morbidity and mortality.
The All India Difficult Airway Association described a difficult airway algorithm in 2016 for the management of unanticipated difficult airway in adults. There exist many preoperative tests for the evaluation of difficult airway such as the modified Mallampati classification, interincisor distance, thyromental distance, sternomental distance, upper lip bite test and neck and jaw movements. Nevertheless, the sensitivity and accuracy of the different criteria vary among different studies and no single test is accurate enough to predict a difficult airway. Moreover, anticipation of difficult airway does not necessarily lead to difficult intubation and vice versa. In this study, we have used the modified Mallampati classification and Wilson's score for the prediction of difficult airway and attempted to correlate this prediction with actual results.
The study aimed to evaluate the incidence of the difficult airway and difficult intubation and their association if any using the modified Mallampati classification and Wilson's score. The primary objective was to evaluate the incidence of the anticipated difficult airway using the modified Mallampati classification and Wilson's score and its correlation with the incidence of difficult intubation with the Cormack–Lehane grade visualised at the time of laryngoscopy. The secondary objective was to evaluate the duration of laryngoscopy, time taken for intubation and number of attempts for successful intubation.
| Patients and Methods|| |
The study was conducted on 352 patients. Adults aged >18 years of either gender posted for elective surgery under general anaesthesia with endotracheal intubation were included in the study. Patients requiring rapid sequence induction and intubation, pregnant women and those with pathological conditions that could alter the anatomy of face and neck such as burns-related contractures, tumours or swellings involving the head-and-neck area were excluded from the study.
After approval from the Institutional Ethics Committee and registering with the national authority (CTRI/2016/12/007520), a written informed consent was obtained from the patients before enrolling them in the study. Patient's demographic details and type of surgery was noted. One day before surgery, patients were examined in the sitting position with the head in neutral position. Patients were asked to open the mouth as wide as possible with the tongue maximally protruded and the modified Mallampati classification was noted. Modified Mallampati Class III and IV were considered as the predictors for difficult intubation.
Wilson's score is based on a sum of constitutional and anatomical structures and was calculated after evaluating clinical parameters such as body weight, interincisor distance, subluxation of the jaw, jaw movement, degree of neck extension, the presence of retrognathia and buck teeth. Patients with Wilson's scores between 2 and 4 were considered possibly difficult intubations while those with a score > 4 were often difficult intubation.
After preoxygenation, the patients were given standard general anaesthesia. After achieving muscle relaxation, laryngoscopy was performed by the anaesthesiologist with at least 6 months of experience using a standard Macintosh blade with the head placed in 'sniffing the morning air' position. Difficult intubation was graded according to the view of vocal cords obtained during laryngoscopy as described by the Cormack–Lehane classification. Cormack–Lehane Grade III and IV were considered as difficult to intubate.
Successful tracheal intubation was confirmed by misting of the endotracheal tube, chest wall movement, auscultation and capnography. The lungs were ventilated with oxygen in between attempts if >1 attempt was needed. Vital parameters such as pulse, blood pressure and oxygen saturation were monitored every minute for the next 10 min. In case of failure to intubate after the second attempt or oxygen desaturation <95%, the procedure was taken over by a senior anaesthesiologist. Rescue tracheal intubation was done with the aid of a bougie or laryngeal mask airway as needed. Complications such as trauma to lips, teeth or pharynx were looked for and managed accordingly. Duration of laryngoscopy, which was the time taken from removal of the face mask and insertion of laryngoscope to the visualisation of the vocal cords, was noted. Time from the visualisation of vocal cords to the insertion of endotracheal tube and confirmation of correct tracheal placement were noted as the duration of intubation. The number of attempts for intubation was also noted. When there was a failed intubation at the first attempt, but the second attempt was successful, the sum of time taken for the first unsuccessful attempt and the next successful attempt was noted.
The incidence of anticipated and unanticipated difficult airway was calculated separately for each score along with its sensitivity, specificity, positive predictive value and negative predictive value. The significance of such an association was evaluated using the Chi-square test.
| Results|| |
In the present study, patients aged ≥18 years were included in the study [Table 1]. The distribution was almost equal between the genders [Table 2]. The incidence of easy airway anticipated by the modified Mallampati Class I/II was 93.2% (n = 328) and that of difficult airway was 6.8% (n = 24) [Table 3]. The efficacy of modified Mallampati class in predicting a possible difficult airway is shown in [Table 4] and [Table 5].
|Table 4: Efficacy of modified Mallampati classification in predicting difficult intubation|
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|Table 5: Efficacy of modified Mallampati classification in predicting difficult intubation|
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We considered a Wilson's score ≥2 as probable difficult airway and >4 as definitive difficult airway. It was found that Wilson's score of 0–1 was present in 85.8% of patients. Nearly 11.7% of patients had a Wilson's score of 2–3, while 2.6% had a Wilson's score of 4–5. Therefore, 14.3% of patients were anticipated to have difficult airway according to Wilson's score [Table 6]. The efficacy of Wilson's score in predicting a possible difficult airway is shown in [Table 7] and [Table 8].
Nearly 26% (12/46) of the difficult airways were unanticipated by both modified Mallampati class and Wilson's score. Thus, not every anticipated difficult airway proved to be difficult intubation and vice versa [Table 9].
The average duration of laryngoscopy was 19 s with a maximum 170 s and a minimum of 8 s, whereas the average duration of intubation was 6.73 s with maximum 60 s and minimum 3 s. Nearly 89% of patients were intubated in the first attempt. Thirty patients required two attempts for intubation, whereas nine patients required more than two attempts for successful intubation.
| Discussion|| |
The establishment of difficult airway algorithms has led to more and more successful intubations and decreased airway-related morbidity. Even after years of research and development of various instruments and newer techniques for intubation, the 'cannot intubate-cannot ventilate' scenario still remains the most dreaded situation faced by anaesthesiologists worldwide. Hence, there is a constant search for better tests to predict the ease of intubation.
Modified Mallampati classification
Mallampati et al. reported the sensitivity of their classification as 100% and specificity of 80% which was not reproduced in the studies that followed. The test has a large interobserver variation and is dependent on the patient position and phonation. Error due to patient positioning was minimised in the present study by standardising the position for an examination. Observational discrepancy at the time of airway evaluation was removed as the examination was done by the same person throughout the study.
In this study, 93.2% (n = 328) had modified Mallampati Class I/II, of which 88.42% (n = 290) had Cormack–Lehane Class I/II and 11.58% (n = 38) had Cormack–Lehane Class III/IV. A total of 24 patients were reported to have modified Mallampati Class III/IV, of which 66.67% (n = 16) were Cormack–Lehane class I/II and 33.3% (n = 8) were Class III/IV. The correlation was found to be statistically significant (P = 0.002) by the Chi-square test [Table 4].
Wanderley et al. studied 81 patients and reported modified Mallampati Class I/II in 64.2% (n = 52), of which 96.2% (n = 50) were Cormack–Lehane I/II and 3.8% (n = 2) were Cormack–Lehane III/IV. Out of 81 patients studied, 35.8% (n = 29) patients were reported to have modified Mallampati Class III/IV, of which 93.1% turned Cormack–Lehane Class I/II and 6.9% were reported to have Class III/IV. This correlation was found to be insignificant (P = 0.54). The study mentions that even though results are statistically insignificant, they are fairly inclined with those of Lundstrom et al. and statistically significant results could be obtained with larger sample size.
Lundstrøm et al. considered 55 studies and found that only 35% were correctly predicted to be difficult by the modified Mallampati classification which is consistent with our finding of 33.3%. They found that sensitivity and specificity ranged from 0.0 to 1 and 0.44 to 1.0, respectively and positive and negative predictive values varied from 0.48 to 48.38 and 0.13 to 1.18, respectively.
Wilson et al. concluded that the sensitivity of their score is 42% and specificity is 95% when a score of ≥2 was considered as difficult airway with false-positive rate of 12%. In our study, 14.2% of patients were anticipated to have difficult airway according to Wilson's score when score ≥2 was considered difficult. Out of 50 (14.2%) patients anticipated to have difficult airway by Wilson's score, 54% (n = 27/50) were correctly predicted to have difficult intubation, whereas 23/50 (46%) patients did not have a difficult intubation. The correlation was found to be statistically significant using the Chi-square test (P < 0.01) [Table 7].
Wanderley et al. studied 81 patients and found that Wilson's score of 0–1, 2–3 and ≥4 was present in 63%, 34.6% and 2.5%, respectively with 100% of sensitivity, and the correlation was found to be statistically significant (P = 0.01). The study concluded that Wilson's score is highly sensitive predictor of difficult airway even though its specificity is low.
Shiga et al. considered 35 studies and found that the pooled sensitivity and specificity of Wilson's score was 36%–56% and 85%–92%, respectively. The present study found the sensitivity and specificity of Wilson's score is 58.7% and 92.5% respectively [Table 8] which is fairly consistent with the pooled data from Shiga et al.
The high sensitivity and positive predictive value of Wilson's score as compared to the modified Mallampati classification might be due to consideration of multiple factors and anatomical characteristics for the calculation of Wilson's score. Furthermore, the standardisation of measurement of each factor leads to lesser interobserver bias.
The lower threshold of Wilson's score used in the present study for the anticipation of difficult airway makes it a more sensitive predictor.
The discrepancy in the duration of laryngoscopy, intubation and number of attempts taken for successful intubation in a difficult airway has varied in the present study as laryngoscopy was performed by different anaesthesiologists. However, the performing anaesthesiologist had at least 6 months of experience at laryngoscopy. Thirty-eight patients and 19 patients identified as easy airway by the modified Mallampati classification and Wilson's score, respectively resulted in difficult intubation. Although 12 patients were not anticipated to be a difficult airway by both the tests, they still turned out to be difficult intubations. Therefore, not all anticipated difficult airways result in difficult intubation and vice versa [Table 9].
The incidence of actual difficult intubation in this study was found to be 13%. There was no incidence of failed intubation. Hence, to conclude, the modified Mallampati classification could fairly predict the true-negative results. Although not routinely used, Wilson's score was a better indicator for the true-positive values.
However, in clinical practice, anaesthesiologists are more concerned about the false-negative values, i.e., those that are anticipated to be an easy airway but actually turn out to be a difficult intubation. In this study, Wilson's score had lesser false-negatives along with true-positive results, and hence is better for anticipation of difficult airway. Thus, Wilson's score should be included in routine preanaesthetic evaluation.
| Conclusion|| |
Modified Mallampati classification could fairly predict the true-negative results and Wilson's score even though not routinely used is a better indicator for true-positive values. Thus, Wilson's score should be included in routine preanaesthetic evaluation.
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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], [Table 6], [Table 7], [Table 8], [Table 9]