Application of the new ‘XU-line’ in the dynamic ultrasonographic evaluation of the spatial displacement of anterior cervical tissues for airway management: protocol for a prospective observational study

INTRODUCTION: Patients with cervical spondylosis have a high incidence of difficult airway, and unpredicted difficult intubation may be life-threatening. Traditional predictors and imaging data may suggest a difficult airway, but these data have limited predictive value, with low sensitivity and specificity. Ultrasonography is a non-irradiating, reproducible, inexpensive and simple tool that provides good imaging of the cervical soft tissue for airway assessment. This study will use the new ‘XU-line’ in the dynamic ultrasonographic airway evaluation of the spatial displacement of the anterior cervical tissues to determine whether preoperative ultrasonographic assessment of the neck anatomy can predict difficult airway. METHODS AND ANALYSIS: This prospective, observational study will be conducted in a single centre. Four hundred and eleven patients scheduled for anterior cervical decompression and fusion under general anaesthesia will be recruited. The parallel trunk reference line through the mentum is defined as the XU-line, and the spatial displacement of the anterior cervical soft tissue relative to the XU-line at six anatomical levels in the transverse plane and two distances in the sagittal plane will be measured on ultrasonography with the patient in the supine position and the sniff position. The spatial displacement distances of soft tissue structures relative to the XU-line will be compared between the ‘easy intubation’ and ‘difficult intubation’ groups (in accordance with the Cormack-Lehane classification). Receiver operating characteristic curves will be used to determine the sensitivity and specificity of the ‘difficulty prediction capability’ of each ultrasonographic and physical measurement. Multiple logistic regression analysis will be performed to determine the independent predictors of difficult intubation. ETHICS AND DISSEMINATION: Ethical approval for this study has been obtained from the Peking University Third Hospital Medical Science Research Ethics Committee. The results of this study will be disseminated via a peer-reviewed publication and national and international conferences and workshops. TRIAL REGISTRATION NUMBER: ChiCTR2000034446.