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Scientific Oral Presentations

Laryngology/Broncho-Esophagology

Session: Scientific Oral Presentations 4 - Laryngology/Broncho-Esophagology

Ratio of Height to Interincisor Distance (RHIID): Preoperative Assessment of Difficult Laryngeal Exposure

Tuesday, October 14, 2025

10:06 AM - 10:12 AM EDT

Location: 120

Disclosure(s):

Lily A. Stevenson, BS:

faculty for this accredited education activity has no relationship(s) with ineligible companies to disclose.

Niklas Hillig, MS-4:

faculty for this accredited education activity has no relationship(s) with ineligible companies to disclose.

Introduction: The Ratio of Height to Interincisor Distance (RHIID) is a novel metric proposed for assessing laryngeal exposure. Anatomic ratios controlling for height, such as the Ratio of Height to Thyromental Distance (RHTMD), are associated with difficult laryngeal exposure among anesthesiologists. This study examines the correlation between RHIID and force metrics, as measured by the Laryngeal Force Sensor (LFS), during suspension laryngoscopy.

Methods: Data from 476 adult patients (2017–2024) were analyzed in a prospective clinical trial examining force metrics during suspension laryngoscopy. Height, thyromental (TMD), and interincisor (IID) distance were measured, and RHTMD and RHIID were calculated dividing height (cm) by their respective variables (cm). Average and maximum forces (N) during direct laryngoscopy were recorded using the LFS. Multiple regression models were developed in R Studio, and several linear models were selected as the best fit for identifying associations between these variables.

Results: RHIID’s associations with force metrics were twice as strong as those observed with individual anatomical variables, including height, TMD, and IID. Patients with higher RHIID values exhibited significantly greater average and maximum forces during suspension microlaryngoscopy (p < 0.001). Although RHIID and RHTMD displayed comparable predictive strength for average force, RHIID consistently showed stronger correlations with maximum forces.

Conclusions: RHIID is a new ratio that strongly correlates with force metrics, outperforming individual variables such as height, TMD, and IID. Incorporating these anatomic ratios into preoperative assessments provides clinicians with another tool for predicting laryngeal exposure during direct laryngoscopy.

Presenting Author(s)

LS

Lily A. Stevenson, BS

Research Assistant/ Procedural Assistant
Massachusetts Eye and Ear
Boston, MA, United States

Disclosure(s):
faculty for this accredited education activity has no relationship(s) with ineligible companies to disclose.
Niklas Hillig, MS-4

Medical Student
Universitätsmedizin Greifswald
Greifswald, Mecklenburg-Vorpommern, Germany

Disclosure(s):
faculty for this accredited education activity has no relationship(s) with ineligible companies to disclose.

Senior Author(s)

PS

Phillip C. Song, MD

Assistant Professor
Mass Eye and Ear
Boston, MA, United States

Disclosure information not submitted.

Co-Author(s)

MN

Matthew R. Naunheim, MD, MBA

Assistant Professor
Massachusetts Eye and Ear Infirmary/Harvard Medical School
Boston, MA, United States

Disclosure information not submitted.
Allen L. Feng, MD

Assistant Professor of Otolaryngology - Head & Neck Surgery
Massachusetts Eye and Ear Infirmary / Harvard Medical School
Arlington, MA, United States

Disclosure information not submitted.
Ramon A. Franco, Jr., MD

Associate Professor
Harvard University School of Medicine
Boston, MA, United States

Disclosure information not submitted.