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GENERAL ARTICLES

Craniocervical Extension Improves the Specificity and Predictive Value of the Mallampati Airway Evaluation

George A. Mashour, MD, PhD^*, and Warren S. Sandberg, MD, PhD^*

From the *Department of Anesthesia and Critical Care, Massachusetts General Hospital; and Department of Anaesthesia, Harvard Medical School, Boston, Massachusetts.

Address correspondence and reprint requests to George A. Mashour, MD, PhD, 55 Fruit St., Clinics 309, Boston, MA 02114. Address e-mail to gmashour{at}partners.org.

	Abstract

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BACKGROUND: The modified Mallampati (MMP) classification is a standard airway examination that assesses mouth opening and structures within the oral cavity. Recent data suggest that maximal mouth opening (as measured by interdental distance) is possible only with extension of the craniocervical junction. Because the MMP examination is performed with the head in a neutral position, the airway may appear worse because of submaximal interdental distance. We hypothesized that adding craniocervical extension to the MMP would allow for greater mouth opening, lower scores, and less false positives than the traditional MMP examination.

METHODS: Multiple clinicians with at least 1 yr of airway experience evaluated adult airways (n = 60) with the MMP examination (with head in neutral position). The same examination was then repeated with the addition of craniocervical extension (Extended Mallampati Score, EMS).

RESULTS: On average, craniocervical extension decreased the MMP class (P < 0.002). The EMS improved specificity from 70% to 80% and positive predictive value from 24% to 31% when compared with the traditional MMP. The sensitivity (83%) was the same for MMP and EMS.

CONCLUSIONS: Craniocervical extension improves the specificity and positive predictive value of the MMP airway evaluation while retaining sensitivity of the traditional MMP examination. The introduction of the EMS into clinical practice should be considered.

	Introduction

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The Mallampati evaluation is a standard method of assessing the airway for potentially difficult intubation. First formulated as a hypothesis (1), it was later demonstrated in a prospective study to be predictive of difficult laryngoscopy (2). Samsoon and Young (3) modified the original Mallampati classification system by including a fourth class of airway, in which the soft palate could not be visualized. The modified Mallampati (MMP) Class 4 airway was shown to be associated with difficult tracheal intubation in a retrospective study of the obstetric population. The proposed anatomic basis for this examination is the relationship of the tongue to the oral cavity: when the base of the tongue is disproportionately large, the glottis may be obscured during laryngoscopy.

The MMP examination is performed with the patient sitting upright, the head in neutral position, and the tongue maximally protruded (3). Lewis et al. (4) demonstrated that the predictive value of the MMP is dependent on the position of the cervical spine and recommended that the MMP be performed with extension of the craniocervical junction. It has been demonstrated more recently that mouth opening is also dependent on cervical spine positioning: to achieve maximal interdental distance, the craniocervical junction must be extended (5). When patients were kept in the neutral position and prevented from full extension, mouth opening was limited by an average of 12 mm. Similarly, when craniocervical extension is limited with soft cervical collars, mouth opening is also limited (6). These biomechanical studies suggest that when the head is in the neutral position with respect to the cervical spine, mouth opening is limited and submaximal.

Because the MMP airway evaluation is performed with the head in the neutral position, the degree of mouth opening seen by the examiner is less than what could be achieved with craniocervical extension. This creates the possibility of the airway appearing worse than it actually is, as the relationship of the tongue to the apparent size of the oral cavity is also dependent on the degree of mouth opening. The consequent result of a false positive examination (where a "positive" is predictive of difficult laryngoscopy) may decrease the specificity and predictive value of the MMP.

We hypothesized that performing the MMP examination with craniocervical extension (Extended Mallampati Score or EMS) would allow for greater mouth opening, lower classification scores, and less false positive examinations. We conducted a paired-design cohort study in which 60 patients were assessed with both the MMP and EMS, for a total of 120 airway evaluations. We report that the EMS is associated with lower oropharyngeal classification scores, improved specificity, and improved positive predictive value when compared with the standard MMP.

	METHODS

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Ethical Considerations
The IRB of the Massachusetts General Hospital approved this study, and informed consent was obtained for all patients participating (Protocol No. 2005-P-001894/1).

Experimental
Multiple examiners with at least 1 yr of airway management experience evaluated adult patients (n = 60) using the standard MMP examination: sitting, head in neutral position, mouth opened fully, tongue maximally protruded, and no phonation. Patients with cervical spine disease were excluded from the study. Examiners were instructed to view the patient eye-to-eye in a "mirror" fashion and then circle a graphical representation of the MMP class that best corresponded to their view. The EMS was then performed with the patient's head extended in relation to the cervical spine, mouth open, tongue maximally protruded, no phonation, and the examiner eye-to-eye. The EMS view was recorded with a duplicate graphical representation. The evaluating clinician thereafter performed direct laryngoscopy and recorded Cormack–Lehane grades as a description of laryngoscopic view (7). Direct laryngoscopy was not standardized, allowing the laryngoscopist to choose the technique judged best to achieve optimal visualization in each particular patient. The recorded Cormack–Lehane grade was without cricoid pressure, except in two instances (noted in Table 1). Examiners were aware that the goal of the study was to compare the MMP and EMS.

Statistical Analysis
Wilcoxon matched-pairs test for comparison of ordinal data was used to compare the classification scores of the MMP and EMS. The Spearman correlation test was used to compare the MMP or EMS with Cormack–Lehane grades. MMP or EMS classifications of 3 or 4 were considered predictive of difficult laryngoscopy on the basis of the original studies of Mallampati et al. (2) as well as Samsoon and Young (3). Cormack-Lehane grades of 3 or 4 were confirmed difficult laryngoscopies, in agreement with the study of Iohom et al. (8). Therefore, this study assessed difficult laryngoscopies as the outcome measure, rather than difficult intubations or difficult airways. Sensitivity and specificity were calculated on the basis of standard methods.

	RESULTS

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A total of 120 airway examinations by 23 examiners were performed in 60 different adult patients. With craniocervical extension, MMP Class 1 airways (n = 15) did not significantly change. Craniocervical extension did lead to lower scores for MMP Class 2, 3, and 4. MMP Class 2 airways (n = 24) decreased to a mean class of 1.6; Class 3 airways (n = 15) decreased to a mean of 2.6; and Class 4 airways (n = 6) decreased to a mean of 3.5. On average, EMS class values were significantly lower than MMP (P < 0.002) when compared using the Wilcoxon matched-pairs test. Original ordinal data are shown in Table 1 and are expressed as mean values in Table 2.

EMS classification demonstrated a positive correlation with the Cormack–Lehane grade (r = 0.618, P < 0.0001) similar to MMP (r = 0.567, P < 0.0001). MMP examination was associated with a sensitivity of 83% and specificity of 70%, whereas EMS was associated with an equal sensitivity of 83% and an improved specificity of 80% (Table 3). The positive predictive value was 24% for MMP and 31% for EMS; the negative predictive value was 97% for MMP and 98% for EMS (Table 3).

	DISCUSSION

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Predicting difficult laryngoscopy and tracheal intubation continues to be a challenging clinical task, and the MMP classification has been a standard method of evaluation. Although in routine use, a recent meta-analysis of airway assessment concluded that the MMP is of marginal diagnostic value (9). This conclusion was based on the heterogeneity of sensitivity and specificity in the studies analyzed and a potential lack of standardized conditions for the examination, including head position. One of the significant findings of the present study is the direct demonstration that MMP scores are dependent upon the position of the head in relation to the cervical spine. EMS evaluation of patients in the position of craniocervical extension differs significantly from the standard MMP examination, in which the patient is sitting with the head in neutral position. This highlights the importance of standardized examination conditions for meaningful evaluation and comparison.

Airway evaluation with the EMS resulted in significantly lower airway classification scores than did the standard MMP. Despite the decrease in oropharyngeal class, the EMS demonstrated a correlation with Cormack–Lehane grades that was comparable to the MMP (r = 0.618, P < 0.0001 for EMS, r = 0.567, P < 0.0001 for MMP). Although the correlation coefficient for the EMS was higher than that for the MMP, the power of the study did not allow us to assess whether this difference was statistically significant. The sensitivity of the MMP and the EMS was precisely the same (83%), indicating that the lower classification scores of the EMS did not compromise the ability to predict a difficult laryngoscopy when compared with the traditional MMP. The overall incidence of difficult laryngoscopy of 10% (CL grade of 3 or 4; 6/60) noted in our study was comparable to the 9% incidence found in the study of Iohom et al. (8). The central finding of the present investigation was that the EMS improved specificity by 10% and positive predictive value by 7% (a 29% increase over the conventional MMP examination). Given the routine and widespread use of the MMP in airway evaluation, even relatively small improvements in accuracy may result in a substantial benefit to clinical practice. The paired design of this study, in which patients serve as their own control, strengthens these findings by diminishing interindividual variability.

These data are consistent with the findings of Lewis et al. (4), who showed that craniocervical extension was associated with the best predictive value of the MMP. The present study differs, however, in that laryngoscopic positioning or method was not standardized. Furthermore, there were considerably more examiners in the present study (n = 23 compared with n = 2 in Lewis et al.), and they were not involved in study design or interpretation. Thus, the EMS was evaluated under conditions that more closely reflect the heterogeneity of clinical practice and suggests greater clinical relevance.

In conclusion, our results indicate that airway evaluation using the MMP examination is dependent upon craniocervical positioning, and that the EMS is associated with decreased oropharyngeal scores, improved specificity, and improved predictive value. On the basis of our findings and those of Lewis et al., the use of the EMS should be considered for routine airway evaluation and further study in other patient populations.

	Footnotes

 
Accepted for publication June 30, 2006.

Supported by departmental and institutional funds.

	REFERENCES

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1. Mallampati SR. Clinical sign to predict difficult tracheal intubation (hypothesis). Can Anaesth Soc J 1983;30(3 Pt 1):316, 317.
2. Mallampati SR, Gatt SP, Gugino LD, et al. A clinical sign to predict difficult tracheal intubation: a prospective study. Can Anaesth Soc J 1985;32:429–34.[Web of Science][Medline]
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4. Lewis M, Keramati S, Benumof JL, Berry CC. What is the best way to determine oropharyngeal classification and manidublar space length to predict difficult laryngoscopy? Anesthesiology 1994;81:69–74.[Web of Science][Medline]
5. Calder I, Picard J, Chapman M, et al. Mouth opening: a new angle. Anesthesiology 2003;99:799–801.[Web of Science][Medline]
6. Goutcher CM, Lochhead V. Reduction in mouth opening with semi-rigid cervical collars. Br J Anaesth 2005;95:344–8.[Abstract/Free Full Text]
7. Cormack RS, Lehane J. Difficult tracheal intubation in obstetrics. Anaesthesia 1984;39:1105–11.[Web of Science][Medline]
8. Iohom G, Ronayne M, Cunningham AJ. Prediction of difficult tracheal intubation. Eur J Anaesthesiol 2003;20:31–6.[Web of Science][Medline]
9. Shiga T, Wajima Z, Inoue T, Sakamoto A. Predicting difficult intubation in apparently normal patients: a meta-analysis of bedside screening test performance. Anesthesiology 2005;103:429–37.[Web of Science][Medline]

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