# Comparison of the Ratio of Neck Circumference to Thyromental Distance and the Ratio of Neck Circumference to Inter-Incisor Gap in Predicting Difficult Intubation

## TL;DR

This study compares two ratios to predict difficult intubation, finding both effective but with different strengths in accuracy and sensitivity.

## Contribution

The study introduces a comparative evaluation of two novel airway assessment ratios for predicting difficult intubation.

## Key findings

- RNTMD had higher diagnostic accuracy (AUC 0.96) compared to RNCIIG (AUC 0.80).
- RNCIIG was more sensitive (80%) than RNTMD (69%) in predicting difficult intubation.
- Both ratios showed comparable specificity and predictive values.

## Abstract

Background

Airway management is central to anaesthetic practice, with endotracheal intubation pivotal in both elective and emergency settings. Although various assessment tests aim to predict a difficult airway, their predictive performance varies widely. Comparative evaluation is therefore required to identify the most reliable predictor.

Objective

The study was conducted to compare the two index ratios, the ratio of neck circumference to thyromental distance (RNTMD) and the ratio of neck circumference to inter-incisor gap (RNCIIG), to determine their effectiveness in predicting difficult intubation.

Methods

This prospective observational study consisted of 118 participants undergoing elective surgeries under general anaesthesia. Measurements of neck circumference, thyromental distance, and inter-incisor gap were recorded preoperatively. RNTMD and RNCIIG were calculated. Ease of intubation was determined using the Intubation Difficulty Scale (IDS). Predictive indices and diagnostic accuracy were calculated for both indices.

Results

Both parameters were comparable in terms of specificity, positive and negative predictive values, and diagnostic accuracy. The area under the curve, as calculated from the receiver operating characteristic (ROC), was 0.80 for RNCIIG and 0.96 for RNTMD. However, RNCIIG was found to be more sensitive (80%) than RNTMD (69%).

Conclusion

We conclude that both airway assessment indices, RNCIIG and RNTMD, are effective predictors of a difficult airway. A ratio of two indices provides superior diagnostic accuracy and reliability than when a single parameter is used alone.