Reply to “Use of radiologic indicators to predict difficult laryngoscopy in patients with cervical spondylosis”

Sir: We thank professor F. S. Xuefor the comments on our article. Regarding the first point, operator experience had an important impact on the results of the study. We could not agree with it more. In view of this, during the study, the operation and laryngeal classification was determined during Macintosh laryngoscopy by the same senior anesthesiologist who had worked for more than 5 years. We have clarified this in the method section. Also, the laryngeal classification (Macintosh 3-4 blade) used in our study was defined according to the method of Cormack and Lehane, in which the initial view should be performed without the application of external laryngeal pressure. We admitted that external laryngeal pressure was widely used in clinical practice during laryngoscopy with Macintosh laryngoscope. However, any external pressure on the neck might have a potentially detrimental effect on the cervical disease. Besides, it was difficult to quantify the impact of strength of external pressure on laryngoscopy. In order to achieve the consistency of the study result, we did not give external laryngeal pressure for all study objectives. Secondly, the ideal indicator for prediction of difficult laryngoscopy would need to have perfect sensitivity and specificity. Sensitivity and specificity are dependent on each other: the increase in one of them usually results in a decrease in the other. We admit that Youden index is not a perfect evaluation index. If we choose the maximum value of Youden index, indicators will have different sensitivity and specificity. In order to facilitate the comparison of the five indicators, we try to have similar specificity and find the optimal sensitivity. Considering the practical application and clinical safety, we pay more attention to sensitivity, which helps to screen out potentially difficult laryngoscopy. According to the ROC curve, the optimal sensitivity and specificity values for distance from the highest point of the hyoid bone to the mandibular body (X4) were in the range of 19.25 to 22.3 mm, and are shown in Table 1. To facilitate clinical application, a cutoff value equal to 20 mm was chosen. Thirdly, no single factor can reliably predict difficult laryngoscopy and combinations of individual indictor or risk factors would add some incremental diagnostic value compared to that of each test alone. However, the clinical value of the combined screening tests for predicting difficult laryngoscopy remains limited if the individual indictor had only poor to moderate discriminative power when used alone. In this study, we found three independent risk factors, of which the accuracy of modified Mallampati test score is low (AUC=0.620). Even though we give a combination of several risk factors, the accuracy of evaluation is not high enough. This study aims to find out the most accurate radiologic indicator for difficult laryngoscopy in patients with cervical spondylosis. Multi-parameter evaluation should combine the best index of radiologic indicators and physical features, which can improve the accuracy of prediction. We hope to establish a new difficult airway assessment system by combining multiple tests with high discriminative power when used alone and the related research is in progress. We hope above explanation could clarify the findings of our study.