New Method for Evaluation of Difficult Intubation in Adults (intubation)

Evaluation of Height/Thyromental Distance Ratio Combined With Obstruction and Neck Mobility for Predicting Difficult Endotracheal Intubation in Adults : A Prospective Observational Study

There are multiple scores used for airway assesment ,the commonest one is LEMON score. LEMON is an airway assessment score that measures factors associated with difficult intubation such as obesity, head and neck movement, jaw movement , receding mandible, long upper incisors, Mallampatti scores, maxillary incisor characteristics, decreased mouth opening ,shorten thyromental distance and short neck.

The Height-to-Thyromental Distance ratio (H/TMD) has emerged as a simple, objective, and reproducible anatomical predictor of difficult laryngoscopy, as it normalizes mandibular space to patient height. However, airway difficulty is not purely anatomical; functional factors such as airway obstruction and cervical spine mobility significantly affect intubation success.

Therefore, combining H/TMD with two highly predictive functional elements from the LEMON score - Obstruction (O) and Neck Mobility (N) - may provide a more accurate, simplified, and clinically applicable model for predicting difficult airway. This combination is referred to as the HON Model (Height/TMD + Obstruction + Neck mobility).

Study Overview

• Status: Active, not recruiting
• Conditions: Difficult Airway Intubation
• Intervention / Treatment: Other: evaluation of difficult intubation

• Study Type: Observational
• Enrollment (Estimated): 350

Contacts and Locations

Study Locations

• Egypt
  • Nasser City
    • Sohag, Nasser City, Egypt
      • Faculty of medicine sohag university

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Child; Adult
• Accepts Healthy Volunteers: Yes

• Sampling Method: Probability Sample

Study Population

The sample size calculation was performed using G. power 3.1.9.2 (Universitat Kiel, Germany) and total sample size will be 350. It was calculated according to a previous study (Pal et al., 2025, Rista et al., 2025) based the sensitivity of Height/Thyromental Distance Ratio and L.E.M.O.N score as to best of our knowledge our study will be the first to assess Height/Thyromental Distance Ratio Combined with Obstruction and Neck Mobility (HON Model) to predict difficult intubation (Power : 0.8, α error: 0.05).

Description

Inclusion Criteria:

• Adult patients from 15- 60 yrs old
• Patients who require endotracheal intubation for surgery under general anesthesia.
• Patients with ASA I - II
• Patients who provide informed consent

Exclusion Criteria:

• Patients with history of previous difficult intubation.
• Patients with inability to sit/stand, heamodinamiclly unstable and need for rapid sequence induction .

Study Plan

How is the study designed?

Number of groups / cohorts

1

Cohorts and Interventions

Group / Cohort

Intervention / Treatment

- Adult patients from 15- 60 yrs old - Patients who require endotracheal intubation for su

Other: evaluation of difficult intubation; The Height-to-Thyromental Distance ratio (H/TMD) has emerged as a simple, objective, and reproducible anatomical predictor of difficult laryngoscopy, as it normalizes mandibular space to patient height. However, airway difficulty is not purely anatomical; functional factors such as airway obstruction and cervical spine mobility significantly affect intubation success. Therefore, combining H/TMD with two highly predictive functional elements from the LEMON score - Obstruction (O) and Neck Mobility (N) - may provide a more accurate, simplified, and clinically applicable model for predicting difficult airway. This combination is referred to as the HON Model (Height/TMD + Obstruction + Neck mobility).

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Time Frame
The primary outcome evaluate using Ratio of Patient's Height to Thyromental Distance Combined with Obstruction and Neck Mobility (HON Model) as a new practical scoring system in predicting Difficult Laryngoscopy .	30 minutes

Collaborators and Investigators

• Sponsor: Sohag University

Study record dates

Study Major Dates

• Study Start (Actual): January 5, 2026
• Primary Completion (Estimated): June 15, 2026
• Study Completion (Estimated): July 15, 2026

Study Registration Dates

• First Submitted: March 5, 2026
• First Submitted That Met QC Criteria: March 5, 2026
• First Posted (Actual): March 10, 2026

Study Record Updates

• Last Update Posted (Actual): April 17, 2026
• Last Update Submitted That Met QC Criteria: April 14, 2026
• Last Verified: April 1, 2026

More Information

Terms related to this study

• Other Study ID Numbers: Soh-Med-26-2-15MS

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: UNDECIDED