Analysis of the analgesic mechanism of TENS-WAA in colonoscopy using the EEG-fNIRS system: a study protocol for a randomised controlled trial

Introduction Colonoscopy is an essential procedure for the early diagnosis of colorectal conditions; however, over 60% of patients undergoing non-sedated colonoscopy report moderate to severe pain. This study aims to investigate the central analgesic mechanisms of transcutaneous electrical nerve stimulation based on wrist-ankle acupuncture theory (TENS-WAA). A multimodal approach combining electroencephalography (EEG) and functional near-infrared spectroscopy (fNIRS) will be employed to assess pain-related brain activity, with artificial intelligence applied to model the relationship between objective neurophysiological signals and subjective pain experience. Methods This is a single-centre, randomised, double-blind, controlled trial involving 60 patients undergoing colonoscopy without anaesthesia. Participants will be randomly allocated (1:1) to either an electrical stimulation group receiving TENS-WAA or a sham stimulation group. EEG and fNIRS data will be acquired before, during and after the procedure. The primary outcome is the analysis of EEG-fNIRS signals to characterise cerebral responses associated with pain modulation. Secondary outcomes include patient-reported pain using the Visual Analogue Scale (VAS), total colonoscopy duration and the correlation between EEG-fNIRS indicators and VAS scores. A deep learning framework will be used to enhance pain prediction accuracy. Ethics and dissemination This study has received ethical approval from the Ethics Committee of Changhai Hospital, Shanghai (approval reference CHEC2025-006), and has been registered at ClinicalTrials.gov. Written informed consent will be obtained from all participants. Findings will be disseminated in peer-reviewed academic journals and at relevant scientific conferences, regardless of outcome, contributing to evidence-based, non-pharmacological pain management strategies. Trial registration number ClinicalTrials.gov, NCT06813703 .