Assessment of Ratio of Height to Rhinion-Mentum Distance as a Predictive Tool for Difficult Tracheal Intubation

Document Type : Original Article


1 Anesthesiology Research Center, School of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran

2 Department of Anesthesiology, Imam Khomeini Hospital Complex, Tehran University of Medical Sciences, Tehran, Iran.


Background: Difficult Intubation (DI) is a constant concern for anesthesiologists and being able to predict it will improve patient safety. Different tests have been presented in anesthesiology practice to increase the accuracy of the DI prediction. Since there is no single sensitive and specific test, most of the practitioners use a combination of them. Here we report a new and novel index of ratio of height to rhinion-mentum distance (RHRMD) to improve the prediction.
Materials and Methods: Four hundred adult patients’ candidate for elective surgery were enrolled into the study. Initially, patients’ data such as weight, height and rhinion-mentum distance (RMD) were recorded by the first anesthesiologist. After anesthesia induction, the second anesthesiologist performed laryngoscopy and recorded the Cormack-Lehane (CL) score. CL score III or higher was considered as DI. Finally, sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) for RHRMD was calculated.
Results: DI was reported in 7.75% of patients. RHRMD is related with CL grade: as the former increased, the latter decreased. RHRMD with cut-off point 25.4 has 90.6% sensitivity, 29.9% specificity, 10.1% PPV and 97.3% NPV in predicting DI.
Conclusion: RHRMD with 90.6% sensitivity and 97.3% NPV could be a valuable tool for prediction of DI.