BRIEF REPORT

The Incidence of Class “Zero” Airway and the Impact ofMallampati Score, Age, Sex, and Body Mass Index onPrediction of Laryngoscopy GradeTiberiu Ezri, MD*, R. David Warters, MD†, Peter Szmuk, MD†, Husam Saad-Eddin, MD†,Daniel Geva, MD‡, Jeffrey Katz, MD†, and Carin Hagberg, MD†

*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 withHadassah Medical School, Jerusalem, Israel

The ability of a specific test (i.e., the Mallampatiscoring system) to predict a difficult intubation isdecreased by the variability of definitions of dif-

ficult intubation/laryngoscopy (1–4) and the inherentinaccuracy of numeric grading systems (5). However,the Mallampati scoring system is still widely used toevaluate airways before surgery. Ezri et al. (6) andMaleck et al. (7) have described a new class of airwayview, class zero, and propose to add this class to thefour modified Mallampati classes.

This study estimates the incidence of class zero air-way, determines the ability of a class zero view topredict laryngoscopy grade, and assesses the effect ofthe airway classes, age, sex, body mass index (BMI),and other factors on the prediction of the laryngos-copy grade.

MethodsDuring a 2-mo period, all patients greater than 18 yr ofage who spent time in the preoperative holding areabetween 8:00 am and 4:00 pm were enrolled in thisprospective study. With approval of the institutionalethics committee from the University of Texas atHouston, informed consent was obtained before eachassessment. We excluded patients receiving regionalanesthesia and patients receiving general anesthesiawithout endotracheal intubation. Also excluded werepatients with upper airway pathology (i.e., maxillofa-cial fractures, tumors, etc.), cervical spine fractures,and increased risk for aspiration of gastric contents.

The airway class was assessed according to theSamsoon and Young (8) modification of Mallampati’sclassification.

We added class zero (6) to the four classes of theMallampati system. Class zero is defined as the abilityto see any part of the epiglottis upon mouth openingand tongue protrusion (Fig. 1). All the airway assess-ments were done by the same anesthesiologist, in thesitting position, with the patient’s head in neutralposition, mouth fully open, tongue fully extended,and without phonation.

Previous difficult laryngoscopy, protruding upperteeth, loose teeth, thyro-mental distance �6 cm, inter-incisor gap �3 cm, and limited neck extension werealso recorded and correlated with airway classes 3 and4 and laryngoscopy grade III. Laryngoscopy was per-formed in “sniffing” position with a Macintosh blade,and stylettes were routinely used in the endotrachealtubes. The laryngoscopy grade was assessed by anattending anesthesiologist by using the Cormack andLehane grading scale (9). Difficult laryngoscopy wasdefined as grade III or IV laryngoscopy.

After 5 min of preoxygenation, anesthesia was in-duced with fentanyl (1 �g/kg), thiopental (3 mg/kg),and rocuronium (0.6 mg/kg). Patients with a BMI �35received succinylcholine (1 mg/kg) for endotrachealintubation.

Analysis of variance tests were used to determinewhether there were any significant differences in age,BMI, airway classes, and laryngoscopy grades. Stu-dent’s t-tests were performed to determine whetherthere were significant differences in age and BMI forpairwise comparison, and �2 or Fisher’s exact testswere performed to determine whether there were sig-nificant differences in sex among classes and grades.Linear regression analysis was performed to deter-mine whether there was a significant trend in age orBMI as airway class and laryngoscopy grade in-creased. Cochran-Armitage trend tests were used to

Presented in part at the annual meeting of the American Societyof Anesthesia, San Francisco, CA, October, 2000.

Accepted for publication May 15, 2001.Address correspondence and reprint requests to Peter Szmuk,

The University of Texas, Houston Medical School, Department ofAnesthesiology, 6431 Fannin, MSB 5.020, Houston, TX 77030. Ad-dress e-mail to Peter.Szmuk@uth.tmc.edu.

©2001 by the International Anesthesia Research Society0003-2999/01 Anesth Analg 2001;93:1073–5 1073

determine whether male sex was correlated with anincrease in airway class and laryngoscopy grade. Lo-gistic regression analysis was performed to determinethe independence of each factor in predicting difficultlaryngoscopy.

ResultsA 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 4airways, and 10.6% demonstrated a laryngoscopygrade of III. The distribution of age, sex, and BMIamong the five classes and three grades is presented inTable 1. Older mean ages were observed in thosepatients with airway class 4 and laryngoscopy gradeIII (57 and 53 yr, respectively).

Table 2 shows the statistical significance of the dif-ferences in age, BMI, and sex between the classes andgrades. All patients with class zero airways werewomen. Laryngoscopy grade III occurred twice asfrequently in males as in females. There was a signif-icant correlation between increased class with in-creased age and BMI. An increase in age but not BMIwas associated with high laryngoscopy grade.

Table 3 depicts the correlation between classes andgrades. All patients with class zero airways had agrade I laryngoscopy. Class 1 airway was associatedwith 10.9% grade II and 3.2% grade III laryngoscopy.There is a stepwise increase in the incidence of laryn-goscopy grade III as the airway class changes from 2 to3 and from 3 to 4. Classes 3 and 4 had a sensitivity,specificity and positive and negative predictive valuesof 84%, 71%, 97%, and 26%, respectively, for a gradeIII laryngoscopy view. With stepwise logistic regres-sion analysis, positive associations of grade III laryn-goscopy were found with increased age, male sex,

protruding upper teeth, loose teeth, and increasedairway class (Table 4). The incidence of failed intuba-tion or ventilation, as well as grade IV laryngoscopyview, was zero.

Figure 1. Class zero airway: the epiglottis is seen at the back of themouth view.

Table 1. Distribution of Age, Body Mass Index, and SexAmong Airway Classes and Laryngoscopy Grades

Age (yr)Body mass

index

Sex

Male Female

Class0 31 (19–38) 24 � 7 0 1.21 39 (18–54) 27 � 8 11 9.42 45 (20–63) 27 � 6 22.5 21.23 48 (32–65) 29 � 7 17.7 14.94 57 (45–70) 41 � 23 0.8 1.2

GradeI 41 (25–58) 28 � 9 21.8 23.7II 46 (35–65) 28 � 6 23.2 20.7III 53 (38–75) 29 � 8 7.1 3.5

Values are expressed as mean (range), mean � sd, or percentage of total(764 cases).

Table 2. Statistical Significance of the CorrelationBetween Classes and Grades Versus Age, Body MassIndex, and Sex

Variable AgeBody mass

index Sex

Class0 vs 1 0.106 0.245 0.0010 vs 2 0.023 0.154 0.0020 vs 3 0.002 0.047 0.0010 vs 4 0.0001 0.019 0.0521 vs 2 0.0003 0.683 0.6281 vs 3 0.0001 0.017 0.9421 vs 4 0.0001 0.041 0.3052 vs 3 0.027 0.0002 0.5152 vs 4 0.006 0.0001 0.3843 vs 4 0.019 0.0001 0.284

GradeI vs II 0.0001 0.918 0.192I vs III 0.0001 0.278 0.002II vs III 0.0007 0.226 0.025

Numbers represent P values. P � 0.05 was considered statistically signif-icant.

Chi-square test or Fisher’s exact test were used for categoric variables(class, grade, and sex), and Student’s t-test was used for continuous variables(age and body mass index).

Table 3. Distribution of the Four Laryngoscopy GradesAmong the Five Airway Classes

Class

Grade

I II III IV

0 9 (100%) 0 0 0%1 134 (85%) 17 (10.9%) 5 (3.2%) 0%2 155 (46.3%) 172 (51.3%) 8 (2.4) 0%3 48 (19.3%) 144 (57.8%) 57 (22.9%) 0%4 2 (13.3%) 2 (13.3%) 11 (73.3%) 0%

Number of cases (percentage of the total number of patients from eachclass and the respective grade).

1074 BRIEF REPORT ANESTH ANALG2001;93:1073–5

DiscussionIn this study the incidence of class zero airway was1.18%. All patients with class zero airways werewomen and had grade I laryngoscopy. The fact that allpatients with class zero airways were women may beexplained by differences in neck fat deposition be-tween the sexes, as demonstrated in a magnetic reso-nance imaging study by Whittle et al. (10). This mayalso explain the larger percentage of difficult laryn-goscopies found in our male patients.

As the airway class increased, so did the laryngos-copy grade (Table 3). The 10- to 30-fold increase in theincidence of grade III from classes 0–2 to classes 3 and4 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 IIIlaryngoscopy, compared with none in class 1.

Some studies have shown obesity to be a risk factor fordifficult intubation (12,13), yet others (14,15) have foundthat the incidence of difficult intubation in morbidlyobese patients is not more frequent than in normal sub-jects. In our patients, an increased BMI was not corre-lated with a high laryngoscopy grade. By using magneticresonance imaging measurements in obese patients withand without obstructive sleep apnea, Horner et al. (16)found more fatty tissues in areas surrounding the col-lapsible segments of the pharynx in patients with sleepapnea. This may explain why some obese patients areeasy to intubate or ventilate and others are not.

Age between 40 and 59 years may carry a risk fordifficult intubation (13). In our study, an increase in agewas consistent with increase in both airway classes andlaryngoscopy grades. Osteoarthritic changes and poordentition may explain the age-related difficultlaryngoscopy.

Logistic regression analysis revealed that grade IIIlaryngoscopy had a positive correlation with ad-vanced age, male sex, protruding upper teeth, looseteeth, and increased airway class, but not with BMI,interincisor distance, or thyro-mental distance.

The 71% specificity of the Mallampati test demon-strates that 29% of our patients who were not Mallam-pati 3 and 4 still experienced a difficult laryngoscopy.Combined with the low positive predictive value, thissuggests that for a better prediction of difficult intuba-tion, the Mallampati scoring should be combined withother predictors.

Class zero airway had an incidence of 1.18% andproved to be an excellent predictor of grade I laryn-goscopy. All patients with class zero airways werewomen. Class 1 airway was not as good as class zerofor predicting an easy intubation. An airway class �2was a good predictor of difficult laryngoscopy (gradeIII). An increased laryngoscopy grade had a positivecorrelation with increased age, male sex, protrudingupper teeth, loose teeth, and increased airway class,but not with increased BMI.

We thank Professor Jacques Chelly and Dr. Sam Lurie for theirsupport in preparing this manuscript.

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Table 4. Stepwise Logistic Regression: Laryngoscopy Grade III Versus Grade I and II

Variable Variable estimate se P value Odds ratio

Age 0.0248 0.00812 0.0022 1.05Male 0.7995 0.2781 0.004 2.224Protruding upper teeth 1.5172 0.7475 0.0424 4.559Loose teeth 1.4759 0.6827 0.0306 4.375Airway class 1.7714 0.2350 0.0001 5.879

ANESTH ANALG BRIEF REPORT 10752001;93:1073–5