RATIO OF HEIGHT TO STERNOMENTAL DISTANCE;

A COMPARISON OF COMMON UPPER AIRWAY TESTS FOR PREDICTING DIFFICULT LARYNGOSCOPY IN ELECTIVE SURGICAL PATIENTS

Abstract

Background: Preoperative evaluation is important in predicting the risk of difficult airway management. Ratio of height to
sternomental distance is a new test for predicting difficult laryngoscopy. Design: Analytical cross – sectional study. Setting: Guilan University
of Medical Sciences, Rash-Iran. Period: 1st Oct, 2009 to 30th Dec, 2010. Methods: 470 consecutive patients scheduled for elective surgery
undergoing general anesthesia and requiring endotracheal intubation. The tests that were used to predict difficult laryngoscopy included:
mouth opening range, body mass index (BMI), thyromental distance, sternomental distance, and neck movement range, ratio of height to
thyromental distance, ratio of height to sternomental distance and assessment of oropharyngeal view by modified Mallampati classification.
After general anesthesia, glottic visualization was assessed during laryngoscopy using Cormack and Lehane classification. Multivariate
analysis and 95 percent confidence interval with SPSS 14 statistical package were used to compare the results of study. Results: Neck
movement range≤80 degrees had the highest sensitivity and specificity. Then Mallampati class 3 or 4 and RHSMD ≥ 12.5 were valuable
respectively. Odds ratio (95 percent confidence interval) of the neck movement range ≤ 80 ̊, Mallampati class 3 or 4, RHSMD ≥ 12.5 and
RHTMD ≥ 23.5 were 17.7(9.57 – 49.76), 12.28 (7.6 – 47.04), 12.22 (22.8 – 76.6), 9.35 (2.29 – 10.52),5.6 (0.88 – 0.89), 3.78 (0.022 – 0.595)
respectively. RHSMD had the least false negative value. Cut off point of RHSMD ≥ 12.5 and RHTMD ≥ 23.5 was not different between men
and women. Conclusions: RHSMD is a useful and valuable clinical screening test for predicting difficult laryngoscopy.