Why is a grade 0 Mallampatti score considered a difficult intubation?

Grade 0 Mallampati Score and Difficult Intubation

Grade 0 Mallampati score is not associated with difficult intubation unless other airway characteristics contribute to difficulty. 1

Understanding Mallampati Classification

The Mallampati classification is a critical tool for predicting difficult intubation and is given the highest score (5 points) in the MACOCHA score, reflecting its importance in airway assessment 2. The standard classification includes:

• Class I: Soft palate, fauces, uvula, and anterior and posterior pillars are visible 2
• Class II: Soft palate, fauces, and uvula are visible 2
• Class III: Soft palate and base of the uvula are visible 2
• Class IV: Soft palate is not visible 2

Grade 0 Mallampati and Intubation Difficulty

• Grade 0 Mallampati (sometimes called "Class Zero") refers to exceptional visibility of oropharyngeal structures beyond what is seen in Class I 1
• Research indicates that Grade 0 Mallampati per se is not associated with difficult intubation 1
• In a prospective study of patients with Mallampati class zero, all had "easy" tracheal intubation (Cormack & Lehane grade 1 or 2) 1

Important Considerations with Grade 0 Mallampati

• Despite excellent visualization of oropharyngeal structures, some anatomical features may still present challenges:
  • In 37% of Mallampati class zero patients, the epiglottis was described as "large" upon direct laryngoscopy 1
  • Some patients (7.4%) with Mallampati class zero had "difficult" mask ventilation 1

Risk Factors for Difficult Intubation

The MACOCHA score identifies key predictors of difficult intubation:

• M: Mallampati score III or IV (5 points) 2, 3
• A: Obstructive sleep apnea syndrome (2 points) 2, 3
• C: Limited cervical spine mobility (1 point) 2, 3
• O: Mouth opening less than 3 cm (1 point) 2, 3
• C: Coma (1 point) 2, 3
• H: Hypoxemia (1 point) 2, 3
• A: Untrained anesthesiologist or non-anesthesiologist (1 point) 2, 3

Clinical Implications

• Difficult intubation is defined as requiring two or more attempts at endotracheal intubation 3
• The incidence of difficult intubation is higher in ICU settings (8-23%) compared to operating rooms 3, 2
• A cut-off of 3 or more in the MACOCHA score is suitable for ruling out difficult intubation with high negative predictive value (97-98%) 3, 2

Limitations of Mallampati Assessment

• The Mallampati score lacks adequate sensitivity for identifying difficult laryngoscopy, difficult intubation, and difficult bag-valve-mask ventilation 4
• It generates numerous false-positive warnings for each correct prediction of a difficult airway 4
• Inter-observer reliability is poor, with independent observers commonly grading it differently 4
• Cannot be evaluated in young children and uncooperative patients 4

Best Practice Recommendations

• All ICU patients should be considered at risk of complicated intubation 3
• Risk factors for complicated intubation must be distinguished from predictors of difficult intubation 3
• Intubation procedures should be standardized with assessment of risk factors for difficult intubation 3, 2
• A combination of several parameters should be used for effective prediction (BMI, head and neck movement, dentition status, upper lip bite test, interincisor gap, thyromental distance) 5

Conclusion

While higher Mallampati scores (III and IV) are associated with difficult intubation, Grade 0 Mallampati is not inherently linked to difficult intubation unless other airway characteristics contribute to the difficulty 1. Clinicians should use multiple parameters for airway assessment rather than relying solely on the Mallampati classification 5, 4.