A study of the neck circumference to thyromental distance ratio to predict difficult intubation in patients scheduled for elective surgeries under general anaesthesia

Introduction. A comprehensive airway assessment requires an understanding of the anatomical features of the neck and upper airway. Accurately predicting a potentially difficult airway is a multifactorial challenge, dependent on patient-related factors, clinical context, and the anesthesiologist’s proficiency. Failure to anticipate a difficult airway remains a common cause of anesthesia-related complications.

The objective was to evaluate the relationship between the neck circumference to thyromental distance ratio (NC/TMD) and the incidence of difficult intubation in adult patients scheduled for elective surgeries under general anesthesia.

Materials and method. This study included 100 patients undergoing elective surgeries under general anesthesia with endotracheal intubation of ASA grades I and II. Patients were examined preoperatively and intraoperatively. Data collection using the patient proforma which includes the demographic data, body mass index (BMI), NC/TMD ratio, thyromental distance (TMD), and Modified Mallampati Test (MMT). Statistical software (SPSS 20.0) was used for statistical analyses of the data.

Results. In cases of difficult intubation, TMD was significantly lower (mean = 6.07 cm, SD = 0.892) than in its absence (7.31 cm, SD = 0.877, P = 0.02994). The values of the ratio between neck circumference and TMD in individuals without difficult intubation were lower: 4.78 (SD = 0.466) versus 5.71; SD = 0.183 (P < 0.001).

Conclusion. The NC/TMD ratio is a simple, effective, and non-invasive predictor of difficult intubation. It demonstrates superior sensitivity and specificity compared to NC and MMT. Routine incorporation of this measurement in preoperative airway assessment could improve the safety of anesthesia.

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