Neck Circumference to Thyromental Distance Ratio and Neck Circumference to Thyromental Height Ratio as a Predictor of Difficult Intubation – A Hospital Based Cross Sectional Study
Author(s): Uma G, Padmapriya, Murali Manoj M, Raajaram Mu
Background: Administration of general anesthesia involves anticipation of a difficult airway and the arising complications. There are several anatomical and anthropometric measurements in clinical practice for predicting difficult intubation.
Objectives: To evaluate and assess the effectiveness of neck circumference (NC), thyromental distance (TMD), thyromental height (TMH), and derived ratios (NC/TMD and NC/TMH) in predicting difficult intubation among patients undergoing elective surgery.
Methods: This cross-sectional analytical study was done on 150 adult patients scheduled for elective surgery under general anesthesia. Preoperative airway assessments included measurements of NC, TMD, TMH, and calculations of NC/TMD and NC/TMH ratios. Intubation difficulty was assessed using the Intubation Difficulty Scale (IDS), with IDS >5 considered difficult. Statistical analysis with SPSS included ROC curve evaluation to determine the diagnostic accuracy of each parameter. Results: The mean age was 39 years. The mean IDS was 1.85, with 10% of participants classified as having difficult intubation (IDS ≥ 5).Statistical comparison showed weight was significantly higher in the difficult intubation group (p = 0.009), while other variables like age, BMI, NC, TMD, TMHT, and their ratios did not show significant differences (p>0.05). No predictor showed a statistically significant association with difficult intubation based on IDS when categorized by cut-off values (p>0.05), highlighting limited standalone predictive utility of these measurements.
Conclusion: Among all parameters tested, NC/TMHT emerged as the most clinically useful, followed closely by TMHT. NC/TMHT ratio can serve as a simple, non-invasive valuable adjunct to standard preoperative airway assessment and planning for difficult intubation.