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From the Department of Anesthesiology, Hospital Clínic Universitari of Barcelona, Barcelona, Spain.
Address correspondence to: Dr. M.A. Ayuso, Servicio Anestesiología y Reanimación, Hospital Clinic Universitari, C/Villarroel 170, 08034 Barcelona, Spain. Phone: 34-932275558; E-mail: 6691ayc{at}comb.es
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Abstract |
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Methods: The study included 181 patients. The variables evaluated were: Mallampati grade, thyromental distance, mouth opening, temporomandibular joint movement, tooth morphology, maxillary deficiency, head and neck movement, receding mandible, body mass index, and clinical symptoms of laryngeal and supraglottic disease. To establish the score, regression coefficients of the statistically significant variables were used on adjusted logistic regression analysis.
Results: DI was present in 50 patients (28%) and orotracheal intubation was impossible in four (2%). Except for obesity, all the variables evaluated were predictive of DI. A simple predictive test was established based on logistic regression analysis including all the variables except temporomandibular joint movement. To determine the optimum cut-off for the new test, a receiver operating characteristic curve analysis was applied. A score 
5 in the proposed test provided a sensitivity of 94% and a specificity of 76%.
Conclusion: The index we describe is aimed at predicting DI in a very specific population with a high risk of this complication. This index uses a series of variables which may be measured easily during the preoperative period and provides an excellent predictive capacity with a high sensitivity and specificity when the index is 5.
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Introduction |
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Methods |
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Preoperative evaluation was carried out by an anesthesiologist with experience in otorhinolaryngology (ENT) surgery. The variables evaluated are shown in Table I
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Intubation was considered difficult in the following cases: a) when intubation was not achieved, and b) when intubation was achieved but the glottic view during laryngoscopy was Cormack grades III or IV; or anatomical alterations impeded the identification of the laryngeal structures and the glottic lumen; or auxillary equipment was required to achieve OTI (rigid stylet, fibroscope intubation or transtracheal jet ventilation).
Statistical analysis was performed using the SPSS 10.0 statistical package for Windows. The different variables were analyzed independently to evaluate their statistical influence on DI by univariate tests (Chi-square). Sensitivity, specificity and odds ratio were determined for each of the independent variables with statistical significance. To evaluate the influence of the different variables studied in the prediction of difficult tracheal intubation an unsaturated logistic regression model was used. Regression coefficients (B) of the statistically significant variables included in the regression analysis were used, (adjusted for relative weight) to create a simple test capable of predicting DI preoperatively. To determine the optimum cut off point of this simple test, a receiver operating characteristic (ROC) curve analysis was performed.
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Results |
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The grades of laryngoscopic view obtained according to the Cormack and Lehane scale were I in 84 patients (46.4%), II in 47 (26%), III in 34 (18.7%), and IV in 12 (6.6%). In four (2.2%) cases the glottic space was not recognized due to a large tumoral deformation of all the larynx.
The incidence of DI according to the predefined criteria was 30% (54 patients), intubation was impossible in four (2.2% of the patients) and tracheostomy was carried out. Intubation was possible in the remaining 50 patients (28%). Table II details the cases of DI.
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On univariant statistical analysis all the variables, except BMI, showed DI to be statistically significant (P < 0.05). However, individually, these variables showed low predictive reliability as demonstrated by the values of sensitivity, specificity and positive and negative predictive value (Table III).
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). A simplified risk score was calculated by adding the adjusted B values obtained (Table IV). On analysis of the ROC curve with the simple score, the optimum cut-off was 5 (a score 5 provides a sensitivity of 94% and a specificity of 76%). With a cut-off of 4 the sensitivity was 100% and the specificity was 64%; being 89% and 89%, respectively with a cut-off of 6.
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Discussion |
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5. The elevated incidence of DI observed may be largely explained by all aspects of laryngeal disease (airway tumour, dental pathology, previous radiotherapy, etc...). In the general population the incidence of DI ranges from 0.5–2%,8 and in ENT surgery DI ranges from 8–10%.4 Nonetheless, the incidence of DI rises to 28%4 when the patient presents a tumour of the airway, as was the case in our study.
Different factors determine the incidence of DI including the criteria adopted to define DI.8 According to the criteria of Tse9 and Pottecher,8 we considered that a Cormack grade 3 laryngoscopy may be associated with technical difficulties in tracheal intubation. On the other hand, other factors such as a severe stenosis of the glottic lumen impeding the introduction of the endotracheal tube and a large supraglottic tumour making localization of the position of the glottis or recognition of the laryngeal anatomical structures difficult, have been considered criteria for DI.4 We took numerous criteria into account to improve the prediction of DI in an attempt to decrease the morbidity associated with anesthesia in patients with pharyngo-laryngeal disease.
Predictive tests applicable to the general population are not adequate for use in patients with laryngeal disease. The Mallampati test applied in the general population presents a sensitivity of 84% but its subjectivity has been criticized10 as has its low sensitivity in specific groups. Thus, in ENT surgery, the sensitivity of this test decreases to 60% having a specificity of 72%.3 Application of the Wilson index to a general population has a sensitivity of 75% with a specificity of 88%.2 Nonetheless, when it is applied to patients with an airway tumour, the sensitivity decreases to 9%, with a specificity of 93%.4 Therefore, the specific aspects of pharyngo-laryngeal disease should be considered when developing a test applicable for the screening of DI in the preoperative period. The simple test we propose demonstrates a sensitivity of 94% and a specificity of 76% when score results 5. This is probably due to the inclusion of an important factor such as the supraglottic localization of the lesion which may present great difficulties in localization of the glottis since our objective was exclusively for laryngeal disease and not for other ENT surgical pathologies.
The statistical methodology applied in the study by Arné et al.5 was similar to that developed in our study and was based on logistic regression analysis of the different variables predicting DI. This statistical analysis requires a high number of cases to be reliable. The high incidence of DI and the application in such a specific population makes the results of the statistical analysis more reliable and reproducible. However, contrary to the study by Arné et al.,5 we did not include a validation group of patients.
In conclusion, we developed a simple index aimed at predicting DI in a very specific population of patients undergoing laryngeal microsurgery with a high risk of DI. This index uses a series of variables which may be measured easily during the preoperative period and provides an excellent predictive capacity with a high sensitivity and specificity when the index result is 5. However, a validation study remains necessary.
Revision received October 18, 2002. Accepted for publication June 3, 2002.
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References |
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2 Wilson ME, Spiegelhalter D, Robertson JA, Lesser P. Predicting difficult intubation. Br J Anaesth 1988; 61: 211–6.
3 Bergler W, Maleck W, Baker-Schreyer A, Ungemach J, Petroianu G, Hormann K. The Mallampati score. Prediction of difficult intubation in otolaryngologic laser surgery by Mallampati score (German). Anaesthesist 1997; 46: 437–40.[Medline]
4 Descoins P, Arné J, Bresard D, Ariès J, Fusciardi J. Proposal of a new multifactorial score to predict difficult intubation in ENT and stomatological surgery. A preliminary study (French). Ann Fr Anesth Réanim 1994; 13: 195–200.[Medline]
5 Arné J, Descoins P, Fusciardi J, et al. Preoperative assessment for difficult intubation in general and ENT surgery: predictive value of a clinical multivariate risk index. Br J Anaesth 1998; 80: 140–6.
6 Frerk CM. Predicting difficult intubation. Anaesthesia 1991; 46: 1005–8.[Medline]
7 Cormack RS, Lehane J. Difficult tracheal intubation in obstetrics. Anaesthesia 1984; 39: 1105–11.[Medline]
8 Pottecher TH, Velten M, Galani M, Forrler M. Compared predictive value of clinical signs of difficult intubation in women (French). Ann Fr Anesth Reanim 1991; 10: 430–5.[Medline]
9 Tse JC, Rimm EB, Hussain A. Predicting difficult endotracheal intubation in surgical patients scheduled for general anesthesia: a prospective blind study. Anesth Analg 1995; 81: 254–8.[Abstract]
10 Charters P, Perera S, Horton WA. Visibility of pharyngeal structrures as a predictor of difficult intubation (Letter). Anaesthesia 1987; 42: 1115.
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  A. Lee, L. T. Y. Fan, T. Gin, M. K. Karmakar, and W. D. Ngan Kee A systematic review (meta-analysis) of the accuracy of the mallampati tests to predict the difficult airway. Anesth. Analg., June 1, 2006; 102(6): 1867 - 1878. [Abstract] [Full Text] [PDF]
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