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Updated: Feb 12, 2026

Point-of-Care Ultrasound: A Review of Ultrasound Parameters for Predicting Difficult Airways
Published on: April 7, 2023
Cervical collar makes difficult airway: a simulation study using the LEMON criteria
Moonsu Yuk1, Woonhyung Yeo1, Kangeui Lee1
1Department of Emergency Medicine, National Medical Center, Seoul, Korea.
Objective:
Endotracheal intubation is extremely difficult to perform in patients wearing a cervical collar for a head and neck injury. Therefore, we analyzed actual measurements using the look externally, evaluate 3-3-2, Mallampati score, obstruction, and neck mobility (LEMON) criteria before and after cervical collar application to investigate the causes of a difficult airway.
Methods:
This simulation study was performed in 76 healthy volunteers. We measured the mouth opening, modified Mallampati classification, and neck extension before and after cervical collar application.
Results:
The mean inter-incisor distance significantly decreased from 4.3 to 2.6 cm (P<0.001). Fifty-seven participants classified as I and II were newly classified as III and IV according to the modified Mallampati classification after cervical collar application (16% to 91%). The angles of neck extension significantly decreased from 44° to 22° after cervical collar application (P<0.001). Before cervical collar application, our simulations predicted that 14 of 76 participants (18%) would have a difficult airway, whereas after cervical collar application, 76 of 76 (100%) were predicted to have a difficult airway.
Conclusion:
All values for the LEMON criteria (mouth opening, modified Mallampati classification, and neck extension) worsened significantly after cervical collar application. Additionally, a difficult airway was predicted in all participants after cervical collar application.
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