Diagnostic Accuracy of Neck Circumference and Thyromental Distance Ratio for Assessing Difficult Intubation in Obese Patients: a Validation Study

Abstract

Various tools for airway assessment are include Mallampati score, upper lip bite test, Wilson scoring and extent of mouth opening; none have high investigative precision especially in obese patients. Objectives: To assess the diagnostic accuracy of neck circumference and thyromental distance ratio for assessing difficult intubation in obese patients using intubation difficulty score as gold standard. Setting: Department of Anesthesiology in East and West operation theatres of Mayo hospital Lahore. Duration: 12 months (From Oct 2015 – Oct 2016) Sample Size: 220 obese patients Methods: Patients undergoing elective surgery were enrolled. Height, weight and body mass index was documented. At the cricoid cartilage level, the neck circumference was measured. All tracheal intubations were conducted by a three-year-experienced anaesthesiologist who was unaware of the study's findings. Cormack and Lehane's grading system was used to rate the laryngoscopy image. Difficult intubation was assessed according to intubation difficulty scoring. Results: The diagnostic accuracy of neck circumference and thyromental distance ratio in assessment of difficulty intubation (DI) among obese patients was 47%, sensitivity 85% and specificity of 37%. Conclusion: NC/TM ratio was a good interpreter in assessing difficult intubation in obese patients. This variable can be incorporated in our preoperative assessment for difficult intubation (DI). It is simple, requires very less time and is economical. Keywords: Airway management, obese, difficult intubation, neck circumference, laryngoscopy, tracheal intubation.