Anesth Analg 2002;95:783
© 2002 International Anesthesia Research Society
LETTERS TO THE EDITOR
A Further Consideration on Mallampati Class and Laryngoscopy Grade
Hsiu-chin Chou, MD, and
Tzu-lang Wu, MD
Kaiser Permanente Medical Center, Hayward, California
To the Editor: We read with great interest the recent report by Ezri et al. (1) on Mallampati class and laryngoscopy grade. Ezri et al. defined direct visualization of epiglottis as class "zero" airway, determined it an indicator for easy laryngoscopy, and showed its prevalence in female sex and younger age. Since its introduction in 1983 (2) the Mallampati airway classification has been widely used as a difficult airway predictor; however, thus far, the anatomic basis behind this clinical sign has not been fully identified or explained.
Combining Ezri et al. and Mallampati’s airway classes, we see a progressive loss of sight in the epiglottis, tonsil pillars, uvula, and soft palate as the airway class advances from zero to 4 and the visualization of glottis becomes more difficult (1). The challenge for clinicians is how to explain this phenomenon. Mallampati’s own explanation (2) is based only on the concept of a large tongue size relative to the oral cavity. We believe that the upper airway anatomy and their rostrocaudal relationships (3–7) should also be taken into consideration.
The epiglottis, arising from thyroid cartilage and positioned posterior to the hyoid, marks the transition from tongue base to larynx. Typically, there is a rostrocaudal distance of 3–4 cm from the tip of epiglottis to the glottic opening (per our cervical soft tissue studies). The mandibular ramus, hinging rostrally with the base of the skull and extending caudally into the cervical region, determines the floor level of the oral cavity and the size of oropharyngeal space. A short ramus raises the floor of the oral cavity and reduces the oropharyngeal space (3). Applying these anatomic facts clinically explains how we can see the epiglottis upon mouth opening in Mallampati class zero; the position of the larynx has to be very high (rostral) and/or the oropharyngeal space has to be very large (e.g., a long mandibular ramus). In these patients, the tongue is mostly contained in the oral cavity and the mandibulohyoid distance (MHD) is small, making direct laryngoscopy easy (3). On the other end, in Mallampati class 3 and 4, the larynx is low (caudally positioned) or the oropharyngeal space is relatively small (e.g., a short mandibular ramus). In these patients, a large portion of the tongue mass is collected in the hypopharynx, the MHD is long, and direct laryngoscopy becomes difficult (3,7). Incorporating the new concepts of short ramus, caudal larynx, long MHD (3), and large hypopharyngeal tongue (7), with the original "large tongue" explanation, we can therefore better understand the Mallampati sign. Also, in Ezri et al.’s study, the prevalence of class zero airways in the female sex and younger age can be better explained, respectively, by the facts that females tend to have smaller MUD (3), and laryngeal structures descend caudally with increases in age (7,8).
Lastly, as we have reiterated previously (3–6), direct laryngoscopy is the result of a complex and dynamic interaction of multiple favorable and unfavorable factors. Other factors that may affect upper airway mobilityand space(4,6) may further influence the Mallampati class and/or laryngoscopy grade. For example, immobility of temporomandibular joint may restrict mouth opening and reduce oropharyngeal space, thus increasing both Mallampati class and laryngoscopy grade. However, immobility of atlanto-occipital joint may limit head extension and increase laryngoscopy grade, and yet, may not affect the Mallampati class. Therefore, we agree with Ezri et al. that use of Mallampati classification should be combined with other predictors.
References
- Ezri T, Warters RD, Szmuk P, et al. The incidence of class "zero" airway and the impact of Mallampati score, age, sex, and body mass index on prediction of laryngoscopy grade. Anesth Analg 2001; 93: 1073–5.[Abstract/Free Full Text]
- Mallampati SR. Clinical sign to predict difficult tracheal intubation (hypothesis) [letter]. Can Anaesth Soc J 1983; 30: 316–7.[Web of Science][Medline]
- Chou H-C, Wu T-L. Mandibulohyoid distance in difficult laryngoscopy. Br J Anaesth 1993; 71: 335–9.[Abstract/Free Full Text]
- Chou HC, Wu TL. Thyromental distance—shouldn’t we redefine its role in the prediction of difficult laryngoscopy? [letter]. Acta Anaesthesiol Scand 1998; 42: 136–7.[Web of Science][Medline]
- Benumof JL. Prediction of difficult intubation [letter] . Acta Anaesthesiol Scand 1998; 42: 128.[Web of Science][Medline]
- Chou UC, Wu TL. Rethinking the three axes alignment theory for direct laryngoscopy. [letter]. Acta Anaesthesiol Scand 2001; 45: 261–2.[Web of Science][Medline]
- Chou UC, Wu TL. Large hypopharyngeal tongue: a shared anatomic abnormality for difficult mask ventilation, difficult intubation, and obstructive sleep apnea? [letter]. Anesthesiology 2001; 94: 936–7.[Web of Science][Medline]
- Schwartz DS, Keller MS. Maturational descent of the epiglottis. Arch Otolaryngol Head Neck Surg 1997; 123: 627–8.[Abstract/Free Full Text]
Response
Tiberiu Ezri, MD,
Robert D. Warters, MD, and
Peter Szmuk, MD
Department of Anesthesiology, Wolfson Medical Center, Holon, Tel-Aviv, Israel
The University of Texas, Houston Medical School, Houston, TX
In Response: We congratulate Chou and Wu for their interesting hypothesis regarding the mechanisms explaining the variations between different Mallampati classes.
We agree that the anatomical differences are related to complex factors. Among them we consider young age as a prominent predictor for class zero owing to the fact that in children the larynx lies higher than in adults (1). A lack in the descent of the larynx may explain the view of epiglottis upon mouth opening in certain patients.
Consequently, a class zero view may be more frequent (personal unpublished observation) in pediatric patients.
References
- Cauldwell CB. Induction, maintenance and emergence. In: Gregory GA ed. Pediatric anesthesia. New York: Churchill Livingstone, 1994: 227–260.
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