Combined Ultrasound and Upper Lip Bite Test Assessment of Difficult Laryngoscopy in Obese Patients

June 10, 2026 updated by: Makarious Morris Aboelkheir Shenouda, Cairo University

Ultrasound-Measured Hyomental Distance Ratio Combined With the Upper Lip Bite Test as a Predictor of Difficult Laryngoscopy in Obese Patients: A Prospective Observational Study

The aim of this observational study is to evaluate the accuracy of the HMDR combined with the ULBT as a predictor of difficult laryngoscopy in obese patients undergoing elective surgery under general anesthesia, regarding:

  • Correlation of HMDR-ULBT values with Cormack-Lehane grades during laryngoscopy.
  • Comparison of HMDR-ULBT with standard HMDR in predicting difficult laryngoscopy.

Study Overview

Status

Not yet recruiting

Conditions

Intervention / Treatment

Detailed Description

Airway management is a cornerstone of safe anesthesia practice. Difficult laryngoscopy and intubation remain a critical challenge for anesthesiologists. The ability to predict difficult airway situations preoperatively remains crucial, particularly in high-risk populations such as obese patients. These patients have significantly higher rates of difficult mask ventilation and tracheal intubation.

Numerous bedside screening tests have been established to predict difficult laryngoscopy, including the Mallampati classification, thyromental distance, the upper lip bite test (ULBT), and hyomental distance (HMD) measurements. However, none of these tests alone possesses sufficient sensitivity or specificity, and their predictive performance in obese individuals remains variable .

The Hyomental Distance Ratio (HMDR), defined as the ratio of the hyomental distance in maximal head extension to that in the neutral position , is a dynamic parameter reflecting upper airway compliance and anatomical displacement. An HMDR value <1.2 has been associated with increased risk of difficult laryngoscopy in several studies . Traditionally, the HMDR is measured either manually with a ruler or more objectively using ultrasound.

The Upper Lip Bite Test (ULBT) is a simple, validated bedside test assessing mandibular protrusion and temporomandibular joint mobility, two key factors influencing the success of glottic visualization . The ULBT is performed in a conscious state, making it a practical tool in airway assessment.

Given that the ULBT involves active mandibular protrusion, it may mimic the anterior displacement of airway structures achieved during head extension or jaw thrust. Therefore, measuring the hyomental distance while the patient performs the ULBT could serve as a novel dynamic modification of the traditional HMDR-potentially offering a more functional and patient-cooperative measure.

Recent studies have validated the HMDR (extension/neutral) as a useful predictor of difficult laryngoscopy by ultrasound, due to its capacity to evaluate the anterior neck space and upper airway alignment . However, these studies primarily assess neck extension without incorporating mandibular movement, despite its key role in airway visualization. To date, no published studies have evaluated the hyomental distance combined with the ULBT using ultrasound or compared it with the traditional HMDR, leaving an interesting gap in the literature.

Combining the anatomical advantages of anterior neck space assessment with functional jaw mobility via the HMDR combined with the ULBT may yield a more comprehensive and accurate predictor of difficult airway, especially in obese or anatomically challenging patients. This novel approach may detect subtle impairments in upper airway dynamics not captured by the static HMDR alone. To our knowledge, this application has not yet been explored in existing literature.

This study, therefore, aims to evaluate the accuracy of the HMDR combined with the ULBT as a predictor of difficult laryngoscopy in obese patients undergoing elective surgery under general anesthesia, using difficult laryngoscopy-defined as Cormack-Lehane grade 3 or 4-as the primary outcome .

Study Type

Interventional

Enrollment (Estimated)

134

Phase

  • Not Applicable

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Contact

Study Contact Backup

Study Locations

  • Egypt
    • Cairo Governorate
      • Cairo, Cairo Governorate, Egypt
        • Kasr Al-Ainy Hospital, Cairo University
        • Contact:
        • Contact:

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

  • Adult
  • Older Adult

Accepts Healthy Volunteers

No

Description

Inclusion Criteria:

  • Adult obese patients aged 18 to 65 years.
  • Both sexes.
  • American Society of Anesthesiologists (ASA) physical status II- III.
  • Body Mass Index (BMI) ≥ 30 kg/m² (classified as obese).
  • Scheduled for elective surgical procedures requiring general anesthesia with endotracheal intubation.
  • Ability to understand and provide informed written consent.
  • Cooperative and able to perform the ULBT on command.
  • Normal dentition (presence of upper and lower incisors to perform ULBT accurately).

Exclusion Criteria:

  • History of maxillofacial trauma, surgery, or congenital facial anomalies affecting mandibular movement or neck anatomy.
  • Known or suspected difficult airway requiring awake intubation.
  • Patients with limited neck mobility (e.g., cervical spine disease or immobilization).
  • Temporomandibular joint disorders or restricted mandibular mobility.
  • Pregnancy.

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

  • Primary Purpose: Other
  • Allocation: N/A
  • Interventional Model: Single Group Assignment
  • Masking: None (Open Label)

Arms and Interventions

Participant Group / Arm
Intervention / Treatment
Other: HMD measured by US in neutral head position , maximum head extension and during upper lip bite test
Hyomental distance will be measured using ultrasound in three positions: neutral head position, maximum head extension, and during the upper lip bite test (ULBT).
Diagnostic test: Hyomental distance measured using ultrasound in neutral head position, maximum head extension and during upper lip bite test
Hyomental distance will be measured using ultrasound in three positions: neutral head position, maximum head extension, and during the upper lip bite test (ULBT).

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Prediction of difficult laryngoscopic view, defined as Cormack-Lehane Grade 3 or 4 on the first laryngoscopy attempt without external laryngeal manipulation.
Time Frame: Day of surgery from preoperative assessment to first laryngoscopy attempt after induction of general anethesia and after three minutes of mask ventilation.

Difficult laryngoscopic view is defined as Cormack-Lehane Grade III or IV during the first laryngoscopy attempt without external laryngeal manipulation

Cormack-Lehane classification for laryngoscopic view :

grade 1: most of the vocal cords is seen; grade 2: only the posterior part of the vocal cords or the arytenoid cartilages are seen; grade 3: only epiglottis is seen; grade 4: epiglottis is not seen.
Day of surgery from preoperative assessment to first laryngoscopy attempt after induction of general anethesia and after three minutes of mask ventilation.

Secondary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Determination of an optimal cutoff value for HMDR-ULBT to predict difficult laryngoscopy.
Time Frame: From preoperative airway assessment until completion of the first laryngoscopy attempt during induction of anesthesia on the day of surgery
Receiver operating characteristic (ROC) curve analysis will be performed to determine the optimal cutoff value of the hyomental distance ratio measured during the upper lip bite test (HMDR-ULBT) for predicting difficult laryngoscopic view, defined as Cormack-Lehane Grade III or IV on the first laryngoscopy attempt without external laryngeal manipulation. The area under the ROC curve (AUC), sensitivity, specificity, positive predictive value, and negative predictive value corresponding to the optimal cutoff value will be calculated.
From preoperative airway assessment until completion of the first laryngoscopy attempt during induction of anesthesia on the day of surgery
Comparison of HMDR-ULBT with standard HMDR in predicting difficult laryngoscopy.
Time Frame: From preoperative airway assessment until completion of the first laryngoscopy attempt during induction of anesthesia.
The predictive performance of the hyomental distance ratio measured during the upper lip bite test (HMDR-ULBT) will be compared with that of the standard hyomental distance ratio (HMDR) for predicting difficult laryngoscopic view, defined as Cormack-Lehane Grade III or IV during the first laryngoscopy attempt without external laryngeal manipulation. Diagnostic accuracy parameters, including sensitivity, specificity, positive predictive value, negative predictive value, and area under the receiver operating characteristic (ROC) curve, will be compared between the two methods.
From preoperative airway assessment until completion of the first laryngoscopy attempt during induction of anesthesia.

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

Cairo University

Publications and helpful links

The person responsible for entering information about the study voluntarily provides these publications. These may be about anything related to the study.

General Publications

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Estimated)

July 1, 2026

Primary Completion (Estimated)

February 1, 2027

Study Completion (Estimated)

March 1, 2027

Study Registration Dates

First Submitted

June 7, 2026

First Submitted That Met QC Criteria

June 7, 2026

First Posted (Actual)

June 11, 2026

Study Record Updates

Last Update Posted (Actual)

June 12, 2026

Last Update Submitted That Met QC Criteria

June 10, 2026

Last Verified

June 1, 2026

More Information

Terms related to this study

Keywords

Other Study ID Numbers

  • Airway Ultrasound

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

NO

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

No

Studies a U.S. FDA-regulated device product

No

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

Clinical Trials on Airway Assessment

Search Similar Trials

Sponsors and Collaborators

Medical Conditions

Drug Interventions

CROs by country

CROs in Lithuania

Conditions

Rare Diseases

Drug Interventions

Dietary Supplements

Sponsor/Collaborators

Locations

Subscribe