Assessing the difficult airway

Airway assessment if a fundamental part of patient assessment. It helps predict a difficult airway and can help reduce the incidence of failed or difficult intubation. Several airway assessment tools have been developed to assess the many parameters involved in airway management. Some of these tools are simple, and fail to address important factors, whilst others are too complex and become impractical as a clinical tool.1 In this article we review the tool LEMON which has been used in different clinical settings.

There are several patient characteristics that have been associated with difficult airway intubation: obesity, head and neck movement, jaw movement, receding mandible, long upper incisors, Mallampatti score, maxillary incisor characteristics, male sex, age 40-59, decreased mouth opening, shortened thyromental distance, and short neck.1

LEMON has been developed to assess these patient characteristics and facilitate first-attempt intubation.2

The LEMON Tool
L – Look Check for facial trauma, large incisors, beard or moustache, large tongue
E – Evaluate 3-3-2

i. Inter-incisor distance: patient's mouth is opened adequately to allow the placement of three fingers between the upper and lower teeth

ii. Hyomental distance: three finger breadths are used

iii. Thyromental distance: two finger breadths are used

M – Mallampati

Patient seated with the head in the neutral position, mouth fully open and the tongue protruded maximally without phonation while the clinician inspects the pharyngeal structures

The views are graded as: 

Class I: soft palate, uvula, fauces, and pillars visible; 

Class II: soft palate, uvula, fauces visible; 

Class III: soft palate, base of uvula visible; 

Class IV: hard palate only visible.

O – Obstruction Patients are evaluated for stridor, foreign bodies, and other forms of sub- and supraglottic obstructions including tumours, abscesses, inflamed epiglottis, or expanding hematoma
N – Neck mobility This is a vital requirement for successful intubation. It is assessed by the patient in the sitting position to place their chin down onto their chest and then to extend their neck so they are looking towards the ceiling

Applying LEMON

Some studies have investigated the use of LEMON in emergency and trauma situations where there is limited time for patient assessment.

Reports of a modified LEMON where Mallampati is not assessed in emergency situations still affirm this tool as a good predictor of difficult airway.1,3,4 And alternative modified LEMON has also been suggested to include oxygen saturation as part of the assessment.4

The proposed LEMONS refers to the patient whose oxygen saturation is 100% following preoxygenation as having “adequate reserve”; above 90% but less than 100% as having “limited reserve”; and less than 90% despite appropriate preoxygenation as having “no reserve.”4

About the author

My name is Andreia Trigo RN BSc MSc, I am a nurse consultant with over a decade of experience in anaesthesia, sedation and pain management.

This involves patient care, as well as lecturing at post grad level on these topics, presenting at conferences and co-developing a very successful sedation course at SedateUK. My passion for creating safer environments for patients and professionals led me to collaborate with Medtronic and share my knowledge and expertise with our professional community.


The content of this article is written by a blogger with whom Medtronic has a relationship. However, the contents represent the personal objective views, comments and techniques of the blogger and are not statements from Medtronic. To the extent this material might contain images of patients or any material where a copyright is held by a third party, all necessary written permissions from the patient or copyright holder, as applicable, with respect to use, distribution or copying of such images or copyrighted materials has been obtained by the blogger.

  • 1. Reed MJ, Dunn MJG, McKeown DW (2005) Can an airway assessment score predict difficulty at intubation in the emergency department? Emergency Medicine Journal ; 22:99-102.

  • 2. Mshelia et at (2018) Use of the “L-E-M-O-N” score in predicting difficult intubation in Africans. Nigerian Journal of Basic and Clinical Sciences; 15:17-23 Available at;year=2018;volume=15;issue=1;spage=17;epage=23;aulast=Mshelia

  • 3. Sung-Mi Ji et al (2018) Correlation between modified LEMON score and intubation difficulty in adult trauma patients undergoing emergency surgery. World J Emerg Surg. 13: 33. Available at

  • 4. Braude (2006) Difficult Airways are “LEMONS”: Updating the LEMON Mneumonic To Account for Time and Oxygen Reserve. Annals of Emergency Medicine. Vol 47, Issue 6, Page 581 Available at