# Comparative Evaluation of Airway Assessment Parameters for Predicting Difficult Intubation: A Prospective Observational Study

## TL;DR

This study compares three airway assessment methods to predict difficult intubation, finding that the ratio of height to thyromental distance is the most accurate predictor.

## Contribution

The study provides a comparative evaluation of RHTMD, MPC, and SMD for predicting difficult intubation using a prospective observational design.

## Key findings

- RHTMD had the highest predictive accuracy with an AUC of 0.84 and a strong correlation of 0.52.
- Combining multiple airway assessment parameters improved diagnostic reliability for difficult intubation.
- Patients with RHTMD ≥ 25 were at significantly increased risk of difficult intubation.

## Abstract

Background: Difficult intubation remains a significant concern in anesthetic practice because of its association with airway trauma, hypoxemia, and increased perioperative morbidity. Although multiple bedside airway assessment tests are routinely employed, their predictive accuracy varies, and no single parameter has proven universally reliable. This underscores the need for comparative evaluation of commonly used predictors in specific clinical populations. This study aimed to evaluate and compare the diagnostic accuracy of the modified Mallampati classification (MPC), sternomental distance (SMD), and the ratio of height to thyromental distance (RHTMD) in predicting difficult intubation, using the Intubation Difficulty Scale (IDS) as the reference standard.

Methods: A prospective observational study was conducted among 57 adult patients undergoing elective surgical procedures under general anesthesia with tracheal intubation. Preoperative airway assessment included MPC, SMD, and RHTMD measurements. Laryngoscopy and intubation were performed using standard techniques, and intubation difficulty was graded using the IDS. An IDS score > 5 was considered indicative of difficult intubation. Statistical analysis comprised receiver operating characteristic (ROC) curve analysis with area under the ROC curve (AUC), logistic regression to estimate odds ratios (ORs), and correlation testing to assess associations between predictors and difficult intubation.

Results: The incidence of difficult intubation in the study population was 12 (21.1%). Among the three parameters, RHTMD demonstrated the highest predictive accuracy, with an AUC of 0.84, an adjusted odds ratio (aOR) of 6.5, and a statistically significant association (p < 0.001). MPC also showed a significant predictive value (aOR 4.2, p = 0.018), followed by SMD (aOR 3.8, p = 0.032). ROC analysis confirmed the superior discriminatory ability of RHTMD compared to MPC and SMD. RHTMD had the strongest correlation (r = 0.52), followed by MPC (r = 0.41) and SMD (r = 0.38). Patients with RHTMD ≥ 25 were at significantly increased risk of difficult intubation.

Conclusion: RHTMD emerged as the most accurate single predictor of difficult intubation in this cohort. However, combining multiple airway assessment parameters improved diagnostic reliability. A multimodal preoperative airway assessment strategy may enhance patient safety and reduce the risk of unanticipated difficult intubation.