Predicting Difficult Airways: 3-3-2 Rule or 3-3 Rule? March 2015
T Yu, B Want, X J Jin, R R Wu, H Wu, J J He, D Yao, Y H Li
Irish Journal of Medical Science 2015 March 5
Background: The goal of this study was to assess the value of the 3-3 rule and the 3-3-1 rule in predicting difficult airways.
Methods: The authors conducted an observational study over a 6-month period. For each consenting adult patient undergoing general anesthesia, preoperative patient characteristics and data regarding difficult airway assessments and airway outcomes were collected. The 3-3-2 rule, 3-3-1 rule and 3-3 rule were included in preoperative difficult airway assessments. The 3-3-1 rule is defined as interincisor distance (IID) less than three fingers, a hyoid-mental distance (HMD) less than three fingers, and a hyoid-thyroid cartilage distance (HTD) less than one finger.
Results: Among the 732 patients who were successfully recruited in this study, 67 patients had difficult laryngoscopy (DL) (9.2%), and 25 patients had difficult intubation (DI) (3.4% of the total). All of the DI patients were also DL patients (25/67, 37.3%). The AUC of the 3-3-2, 3-3 and 3-3-1 rules for predicting difficult laryngoscopy were 0.702, 0.709, and 0.631, respectively. Significant differences between the 3-3-2 and 3-3-1 rules as well as between the 3-3 and 3-3-1 rules were evident. The AUC values for the 3-3-2, 3-3, and 3-3-1 rules for predicting DI were 0.830, 0.822, and 0.725, respectively.
Conclusions: The 3-3 rule and the 3-3-2 rule are similar regarding their ability to predict difficult airways. A HTD less than two fingers or one finger is not predictive of DV or DI.