DIFFICULT LARYNGOSCOPY;

THE PREDICTIVE VALUE OF RATIO OF HEIGHT TO THYROMENTAL DISTANCE VERSUS OTHER COMMON PREDICTIVE TESTS OF UPPER AIRWAY

Abstract

Background: Preoperative evaluation of anatomical landmarks and clinical factors helps to identify potentially difficult
laryngoscopies; however, its predictive reliability is unclear. As the ratio of height to thyromental distance (RHTMD) is a newer upper airway
predictive test for difficult laryngoscopy, the predictive value and odds ratios of RHTMD versus mouth opening, thyromental distance(TMD),
neck movement, and oropharyngeal view (modified Mallampati) were evaluated. Methods: Data of 407 consecutive patients scheduled for
elective surgery with general anesthesia requiring endotracheal intubation were collected and all five factors were assessed before surgery.
Four senior anesthesiology residents, not aware of the recorded preoperative airway assessment, performed the laryngoscopy and grading (as
in Cormack and Lehane’s classification). Results: Difficult laryngoscopy (Grade 3 or 4) occurred in 94 patients (23.1%). In the multivariate
analysis, three criteria were found independent for difficult laryngoscopy (neck movement ≤80 degrees; Mallampati Class 3 or 4, and RHTMD
≥ 24). Neck movement (NM) ≤ 80 degrees had a higher sensitivity, specificity and PPV than the other factors. After neck movement,
Mallampati class 3 and 4, IIG ≤ 3.5 cm and then RHTMD ≥ 24 were valuable with lowest NPV. The multivariate analysis Odds ratio (95%
confidence interval) of the NM, Mallampati class, IIG and RHTMD were 18.16 (9.634 – 34.265), 12.498 (6.744 – 23.16), 11.183 (6.571 – 19.03)
and 3.123 (1.933 – 5.047) respectively.TMD ≤ 6.5 cm was not recognized as independent variable for difficult laryngoscopy. Conclusions:
RHTMD is a useful and valuable screening test for preoperative prediction of difficult laryngoscopy along with common predictive examinations.