New Predictor of Difficult Intubation???

Dr. C. Chon

Neck circumference to thyromental distance ratio: a new predictor of difficult intubation in obese patients

Kim, W.H., et al. British Journal of Anaesthesia. 2011 Feb 24;doi:10.1093/bja/aer024

Anesthesiologists from an academic medical center in Seoul, South Korea enrolled 260 ASA I or II patients undergoing general anesthesia with tracheal intubation. 123 patients were assigned to the obese group (BMI ³ 27.5, as per the WHO’s Asian obesity criteria) and 125 patients were assigned to the non-obese group (BMI < 27.5). 12 patients were excluded because of incomplete data.

Using the intubation difficulty scale (IDS), difficult intubation -- defined by an IDS ³ 5 -- was more frequent in the obese group than the non-obese group (13.8% vs 4.8%; P=0.016). Multivariate analysis revealed the Mallampati score, the Wilson score, and neck circumference-to-thyromental distance ratio (NC/TM) were independently associated with difficult intubation. Among these, NC/TM showed a higher sensitivity and negative predictive value than the other airway measures.

Numerous studies looking at preoperative airway measures have suggested that single tests have limited value in predicting difficult intubations. However, combining numerous measures and risk factors, as is done to when calculating the El-Ganzouri or Wilson scores, can be cumbersome and time-consuming. This study combines two valuable risk factors (neck circumference and thyromental distance), which the researchers say “may increase the diagnostic value while not increasing the burden of [testing].”