BACKGROUND: Many parameters are being used today to assess difficulty of intubation. This study was done to determine the validity of a new device, the Lee Thyromental Ruler (LTR), in the prediction of degree of difficult intubation. METHODS: A prospective, single-blinded cross sectional study was used. 187 patients scheduled for elective surgery under general endotracheal anesthesia were enrolled in the study. All residents of the Department of Anesthesiology of the Veterans Memorial Medical Center were taught how to use the LTR. Preoperative assessments were done on each patient using the following stepwise evaluation plan: (1) thyromental distance measurement in terms of fingerbreadths, (2) airway asseSsment using the Mallampati classification, (3) assessment of range of neck flexion and extension, and (4) thyromental distance measurement using the LTR. These were correlated with the number of attempts to intubate and the degree of glottic exposure during laryngoscopy by Cormack and Lehane as measures for difficulty of intubation RESULTS: The study showed that TMD by LTR using 5.3 cm had higher sensitivity (90 percent) and specificity (83.6 percent) than TMD by fingerbreadth for prediction of degree of difficulty of intubation as measured by the number of attempts to intubate. There was no significant difference in the number of attempts among patients distributed according to Mallampati classification and range of neck flexion and extension. Only the Mallampati classification showed a significant difference among the distribution of subjects according to the Cormack and Lehane grading of glottic exposure during laryngoscopy. CONCLUSION: The Lee Thyromental Ruler is therefore a more valid measure of the thyromental distance as compared to use of fingerbreadths. It is inexpensive, reliable, easy to use and its design allows its use in patients with different anatomical variations. It would thus aid in the prediction of difficult intubation and avoid the complications associated with multiple intubation attempts and failed intubation. (Author)
Human ; INTUBATION ; ANESTHESIA ; ENDOTRACHEAL ; SURGERY ; ELECTIVE, ANESTHESIOLOGY