Can the "Face Index"; an Anthropometric Measurement, Predict Difficult Laryngoscopy and Intubation?

August 20, 2026 updated by: Nilay Tas, Ordu University

Patient safety is the cornerstone of anesthetic practice, and maintaining adequate respiration represents its most critical initial step. In situations where spontaneous breathing cannot be sustained-such as during general anesthesia-the airway must be mechanically secured. While simple face masks may be sufficient in some cases, endotracheal intubation remains the most reliable method for airway control in conditions associated with respiratory depression.

Airway management may be challenging due to various patient-related anatomical factors, including facial and mandibular structure, obesity, limited mouth opening, facial hair, sunken cheeks, wide facial morphology, and a short or muscular neck. These challenges are collectively described as difficult ventilation and difficult intubation (cannot ventilate-cannot intubate), which may occur unexpectedly or be anticipated. A difficult airway is defined as difficulty encountered by a trained anesthesiologist in face mask ventilation, tracheal intubation, or both.

Several predictors of difficult airway are widely accepted, such as thyromental and sternomental distances, neck circumference, Mallampati classification, upper lip bite test, mouth opening, and interincisor distance. Thorough preoperative airway evaluation is mandatory, as difficult mask ventilation and failed intubation remain major contributors to anesthesia-related morbidity and mortality. Although numerous studies have examined these predictors, research focusing on facial morphology and anthropometric indices-particularly the face index-is extremely limited.

Facial morphology varies considerably among individuals and can be evaluated anthropometrically using simple, noninvasive tools such as a digital caliper. Anthropometric analysis is commonly applied in forensic medicine and reconstructive surgery but has rarely been incorporated into airway assessment.

This study aims to introduce face index analysis as a novel predictor of difficult airway alongside conventional methods. By evaluating measurements such as trichion-gnathion distance, total facial index, upper facial index, and nasal index, the study investigates whether airway difficulty can be predicted using a single index value. All measurements are standard, noninvasive, and routinely performed during preoperative assessment.

Study Overview

Status

Not yet recruiting

Conditions

Intervention / Treatment

Other: Face index

Detailed Description

Patient safety is the most critical aspect of anesthetic practice, and the first step in ensuring this safety is the maintenance of adequate respiratory function. Under anesthesia, or in any situation where spontaneous respiration cannot be sustained, the upper and lower airways must be mechanically secured. Airway control can often be achieved using simple face masks; however, in cases of general anesthesia or similar conditions associated with respiratory depression, airway management must be ensured through the more reliable method of endotracheal intubation.

During artificial ventilation, numerous physical characteristics such as facial structure, mandibular anatomy, obesity, limited mouth opening, the presence of a beard, a thin face with sunken cheeks, a wide facial structure, and a short, muscular neck may pose challenges for the anesthesiologist. These situations, defined in the medical literature as "difficult ventilation - difficult intubation" (cannot ventilate - cannot intubate), are not uncommon and may present as either anticipated or unanticipated difficult airways. A difficult airway is defined as a clinical situation in which a trained anesthesiologist experiences difficulty with face mask ventilation, tracheal intubation, or both, due to upper airway conditions (1,2).

Universally accepted predictors of difficult airway among anesthesiologists and the scientific community include physical measurements and classifications such as thyromental distance, sternomental distance, neck circumference, upper lip bite test, Mallampati classification, mandibular length, mouth opening, and interincisor distance (1,3,4). A comprehensive preoperative airway evaluation is both necessary and mandatory during the physical examination of patients scheduled for general anesthesia (5,6). One of the most common-and arguably the most significant-causes of anesthesia-related morbidity and mortality is difficult mask ventilation and failed intubation. In daily anesthetic practice, these classifications are frequently used to reduce the risk of airway difficulty and enhance patient safety, and numerous studies and theses addressing these physical examination criteria are available in the literature.

Despite the abundance of such studies, research evaluating facial morphology and anthropometric measurements-including the "face index"-is almost nonexistent. Facial morphology varies widely among individuals worldwide. It can be analyzed anthropometrically using various measurements and indices, which are currently most commonly applied in fields such as forensic medicine and aesthetic or reconstructive surgery. Anthropometric measurement is a technique that examines metrically definable body characteristics and can be performed easily using a simple measurement tool such as a digital caliper (7).

The primary aim of this study is to introduce a novel perspective on difficult airway assessment by incorporating face index analysis as an additional airway predictor alongside traditional measurement methods that have long been used in anesthesiology. Specifically, the study seeks to determine whether airway difficulty can be predicted using a single index value rather than multiple measurements in patients with different facial morphologies.

Airway management involves sequential steps, beginning with ventilation via a face mask, followed by visualization of the vocal cords (laryngeal inlet and vocal folds) using laryngoscopy, and finally placement of an endotracheal tube into the trachea. Facial measurements may identify physical factors that contribute to difficulty at any of these stages. This study primarily investigates the predictive value of conventional difficult airway assessments in comparison with components of the face index, including trichion-gnathion length (Tri-Gn), total facial index, upper facial index, and nasal index, in determining airway management difficulty.

All measurements employed in this study are standard, noninvasive, and harmless physical examination methods routinely used by anesthesiologists worldwide and are mandatory components of preoperative assessment.

Study Type

Observational

Enrollment (Estimated)

1000

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

Name: Yasir İlyas, Ass. Prof.
Phone Number: +904522252344
Email: yasirilyas@odu.edu.tr

Study Contact Backup

Name: Halil Yılmaz, Ass. Prof.
Phone Number: +904522252344
Email: halilyilmaz855@gmail.com

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

Sampling Method

Non-Probability Sample

Study Population

All patients who have general anesthesia

Description

Inclusion Criteria:

Adult patients over the age of 18
Patients who received general anesthesia

Exclusion Criteria:

A prior history of difficult airway
All patients who have undergone facial deformities
All patients who have tracheostomy

5. Children patients 6. Pregnant patients

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

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Face index and face mask ventilation Time Frame: Preoperative period (before induction of anesthesia)	Facial Anthropometric Measurements: Facial anthropometric measurements, including trichion-gnathion distance, upper face height (subnasale-stomion), total face height (nasion-gnathion), bizygomatic width, and alar width, measured preoperatively and recorded for each participant.	Preoperative period (before induction of anesthesia)
1. The facial index: Unit of Measure: Ratio (dimensionless) 2. Upper Face Height: Unit of Measure: mm 3. Total Face Height: Unit of Measure: mm 4. Mallampati: Categorical (Class I-IV) 5. Difficult Airway: Categorical (yes / no) Time Frame: Preoperative period (before induction of anesthesia)	The facial index in will be calculated as the ratio of total face height (nasion-gnathion) to bizygomatic width measured preoperatively. Upper Face Height: Linear distance between subnasale and stomion measured preoperatively. Total Face Height: Linear distance between nasion and gnathion measured preoperatively. Mallampati Categorical (Class I-IV): Airway classification assessed preoperatively. Difficult Airway: Categorical (yes / no): Defined as the presence of difficult mask ventilation and/or difficult intubation.	Preoperative period (before induction of anesthesia)

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Facial Index and Preoperative Airway Assessment Parameters Time Frame: Preoperative period (before induction of anesthesia)	Facial index values and preoperative airway assessment parameters, including Mallampati classification, thyromental distance, sternomental distance, mandible length, interincisor gap, Upper Lip Bite Test, and atlanto-occipital joint angle, measured preoperatively and recorded for each participant prior to intubation.	Preoperative period (before induction of anesthesia)

Collaborators and Investigators

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

Sponsor

Ordu University

Investigators

Principal Investigator: Nilay Taş, Prof. Dr., Ordu University School of Medicine, Türkiye

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)

November 1, 2026

Primary Completion (Estimated)

November 1, 2027

Study Completion (Estimated)

November 1, 2027

Study Registration Dates

First Submitted

January 18, 2026

First Submitted That Met QC Criteria