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*Department of Anesthesiology, Wolfson Medical Center, Holon, Affiliated with Sackler Medical School, Tel-Aviv, Israel; University of Texas, Houston Medical School, Houston, TX; and the Kaplan Medical Center, Rehovot, Affiliated with Hadassah Medical School, Jerusalem, Israel
Address correspondence and reprint requests to Peter Szmuk, The University of Texas, Houston Medical School, Department of Anesthesiology, 6431 Fannin, MSB 5.020, Houston, TX 77030. Address e-mail to Peter.Szmuk{at}uth.tmc.edu
Abstract
IMPLICATIONS: In an earlier study we proposed the addition of a new airway class, zero (visualization of the epiglottis), to the four classes of the modified Mallampati classification. In this prospective study, 764 surgical patients were assessed with regard to their airway class (including class zero), laryngoscopy grade, and the effect of the airway class and other predictors on the laryngoscopy grade.
The ability of a specific test (i.e., the Mallampati scoring system) to predict a difficult intubation is decreased by the variability of definitions of difficult intubation/laryngoscopy (1–4) and the inherent inaccuracy of numeric grading systems (5). However, the Mallampati scoring system is still widely used to evaluate airways before surgery. Ezri et al. (6) and Maleck et al. (7) have described a new class of airway view, class zero, and propose to add this class to the four modified Mallampati classes.
This study estimates the incidence of class zero airway, determines the ability of a class zero view to predict laryngoscopy grade, and assesses the effect of the airway classes, age, sex, body mass index (BMI), and other factors on the prediction of the laryngoscopy grade.
Methods
During a 2-mo period, all patients greater than 18 yr of age who spent time in the preoperative holding area between 8:00 AM and 4:00 PM were enrolled in this prospective study. With approval of the institutional ethics committee from the University of Texas at Houston, informed consent was obtained before each assessment. We excluded patients receiving regional anesthesia and patients receiving general anesthesia without endotracheal intubation. Also excluded were patients with upper airway pathology (i.e., maxillofacial fractures, tumors, etc.), cervical spine fractures, and increased risk for aspiration of gastric contents. The airway class was assessed according to the Samsoon and Young (8) modification of Mallampati’s classification.
We added class zero (6) to the four classes of the Mallampati system. Class zero is defined as the ability to see any part of the epiglottis upon mouth opening and tongue protrusion (Fig. 1). All the airway assessments were done by the same anesthesiologist, in the sitting position, with the patient’s head in neutral position, mouth fully open, tongue fully extended, and without phonation.
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After 5 min of preoxygenation, anesthesia was induced with fentanyl (1 µg/kg), thiopental (3 mg/kg), and rocuronium (0.6 mg/kg). Patients with a BMI >35 received succinylcholine (1 mg/kg) for endotracheal intubation.
Analysis of variance tests were used to determine whether there were any significant differences in age, BMI, airway classes, and laryngoscopy grades. Student’s t-tests were performed to determine whether there were significant differences in age and BMI for pairwise comparison, and 
2 or Fisher’s exact tests were performed to determine whether there were significant differences in sex among classes and grades. Linear regression analysis was performed to determine whether there was a significant trend in age or BMI as airway class and laryngoscopy grade increased. Cochran-Armitage trend tests were used to determine whether male sex was correlated with an increase in airway class and laryngoscopy grade. Logistic regression analysis was performed to determine the independence of each factor in predicting difficult laryngoscopy.
Results
A total of 764 patients (52% men, aged 44.4 ± 17 yr, BMI 28 ± 8, mean ± SD) were enrolled in the study. Class zero airway occurred in 1.18% of patients. Thirty-five percent of the patients had class 3 or 4 airways, and 10.6% demonstrated a laryngoscopy grade of III. The distribution of age, sex, and BMI among the five classes and three grades is presented in Table 1. Older mean ages were observed in those patients with airway class 4 and laryngoscopy grade III (57 and 53 yr, respectively).
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In this study the incidence of class zero airway was 1.18%. All patients with class zero airways were women and had grade I laryngoscopy. The fact that all patients with class zero airways were women may be explained by differences in neck fat deposition between the sexes, as demonstrated in a magnetic resonance imaging study by Whittle et al. (10). This may also explain the larger percentage of difficult laryngoscopies found in our male patients.
As the airway class increased, so did the laryngoscopy grade (Table 3). The 10- to 30-fold increase in the incidence of grade III from classes 0–2 to classes 3 and 4 is in agreement with the results of Mallampati et al. (11), which showed that of the 15 patients with class 3 (15 of 210 patients, 7.14%) airways, 60% had grade III laryngoscopy, compared with none in class 1.
Some studies have shown obesity to be a risk factor for difficult intubation (12,13), yet others (14,15) have found that the incidence of difficult intubation in morbidly obese patients is not more frequent than in normal subjects. In our patients, an increased BMI was not correlated with a high laryngoscopy grade. By using magnetic resonance imaging measurements in obese patients with and without obstructive sleep apnea, Horner et al. (16) found more fatty tissues in areas surrounding the collapsible segments of the pharynx in patients with sleep apnea. This may explain why some obese patients are easy to intubate or ventilate and others are not.
Age between 40 and 59 years may carry a risk for difficult intubation (13). In our study, an increase in age was consistent with increase in both airway classes and laryngoscopy grades. Osteoarthritic changes and poor dentition may explain the age-related difficult laryngoscopy.
Logistic regression analysis revealed that grade III laryngoscopy had a positive correlation with advanced age, male sex, protruding upper teeth, loose teeth, and increased airway class, but not with BMI, interincisor distance, or thyro-mental distance.
The 71% specificity of the Mallampati test demonstrates that 29% of our patients who were not Mallampati 3 and 4 still experienced a difficult laryngoscopy. Combined with the low positive predictive value, this suggests that for a better prediction of difficult intubation, the Mallampati scoring should be combined with other predictors.
Class zero airway had an incidence of 1.18% and proved to be an excellent predictor of grade I laryngoscopy. All patients with class zero airways were women. Class 1 airway was not as good as class zero for predicting an easy intubation. An airway class >2 was a good predictor of difficult laryngoscopy (grade III). An increased laryngoscopy grade had a positive correlation with increased age, male sex, protruding upper teeth, loose teeth, and increased airway class, but not with increased BMI.
Acknowledgments
We thank Professor Jacques Chelly and Dr. Sam Lurie for their support in preparing this manuscript.
Footnotes
Presented in part at the annual meeting of the American Society of Anesthesia, San Francisco, CA, October, 2000.
References
This article has been cited by other articles:
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  J. Huh, H.-Y. Shin, S.-H. Kim, T.-K. Yoon, and D.-K. Kim Diagnostic Predictor of Difficult Laryngoscopy: The Hyomental Distance Ratio Anesth. Analg., February 1, 2009; 108(2): 544 - 548. [Abstract] [Full Text] [PDF]
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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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B. Fang, J. Norris, V. K. Grover, R. Mahajan, T. Ezri, P. Szmuk, Y. Cohen, and R. D. Warters Class Zero Airway and Laryngoscopy * Response * Response Anesth. Analg., March 1, 2004; 98(3): 870 - 871. [Full Text] [PDF]
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E. Okamoto, T. Sakuragi, Y. Sugi, S. Shono, and K. Higa Endotracheal Intubation and a Laryngeal Mask Airway in a Child with Mallampati Class Zero Airway Anesth. Analg., February 1, 2004; 98(2): 557 - 557. [Full Text] [PDF]
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T. Ezri, P. Szmuk, D. Warters, J. Katz, P. Juvin, E. Lavaut, H. Dupont, P. Lefevre, M. Demetriou, J.-L. Dumoulin, et al. Tracheal Intubation in Obese Patients * Response Anesth. Analg., January 1, 2004; 98(1): 272 - 273. [Full Text] [PDF]
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V. K. Grover, R. Mahajan, and M. Tomar Class Zero Airway and Laryngoscopy Anesth. Analg., March 1, 2003; 96(3): 911 - 911. [Full Text] [PDF]
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H.-c. Chou, T.-l. Wu, T. Ezri, R. D. Warters, and P. Szmuk A Further Consideration on Mallampati Class and Laryngoscopy Grade * Response Anesth. Analg., September 1, 2002; 95(3): 783 - 783. [Full Text] [PDF]
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X. Xie, X. Au-Truong, A. J. Klowden, N. J. Joseph, and M. Ramez Salem Mallampati Class "Zero" Anesth. Analg., May 1, 2002; 94(5): 1371 - 1371. [Full Text] [PDF]
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