Cormack – Lehane Grading System


Grade 1: full view of the glottis
Grade 2a: partial view of the glottis
Grade 2b: arytenoids only
Grade 3: epiglottis only
Grade 4: neither glottis or epiglottis identified


Originally described by Cormack and Lehane in 1984, the Cormack-Lehane grading system has been present in medical education as a model for describing views in intubation.  It was studied in obstetric anesthesia and reading the article demonstrates its antiquity.  The article gives a personal shout out to Sir Robert MacIntosh, as in the inventor of the MacIntosh blade.  The score was updated in 1998 by Yentis et al to include partial views of Grade 2, namely Grade 2a and 2b.  Intuitively, worse scores are less frequent and associated with difficult intubation as demonstrated:

MCLS Percentage of patients Percentage with difficult intubations
1 74 <1
2a 21 13
2b 3 65
3 2 80
4 <1 100

Anesthesia and Intensive Care 2002 – 605 patients undergoing elective surgery and with direct laryngoscopy.  Overall 5.1% with difficult intubations, difficult meaning requiring a second attempt or airway adjuncts.  Percentages of difficult intubations by grade.  Also looked at thyromental distance of less than 6cm being 42% sens and 88% specific for difficult intubations.

The MCLS was challenged by the POGO score or Percentage of Glottic Opening score.  Also intuitively described, this measures the glottic opening on a scale of 0-100% with 0% being a non-visualized glottis.  A study in 1999 demonstrated higher inter-rater reliability when using the POGO compared to the MCLS.  Regardless of which description you use, being able to accurately describe your view while intubating keeps everyone in the room on the same page.



Cormack, R. S., and J. Lehane. “Difficult Tracheal Intubation in Obstetrics.” Anaesthesia 39 (1984): 1105-111

Ochroch, E. Andrew, Judd E. Hollander, Scott Kush, Frances S. Shofer, and Richard M. Levitan. “Assessment of Laryngeal View: Percentage of Glottic Opening Scorevs Cormack and Lehane Grading.” Canadian Journal of Anesthesia/Journal Canadien D’anesthésie 46.10 (1999): 987-90

Koh, L. K. “The Modified Cormack-Lehane Score for the Grading of Direct Laryngoscopy: Evaluation in the Asian Population.” Anaesthesia and Intensive Care, 2002.