2.4. Randomization and masking
Participants enrolled in this trial will be equally allocated to the TEAS-2Hz group, TEAS-10Hz group, or usual care group by block randomization. The computer-generated random sequence will be created by an independent statistician and preserved by an investigator not involved in this trial. Every patient’s random number is to be accessed by telephone from the noninvolved investigator. Due to the trial design, participants of the usual care group will inevitably know about their grouping.To ensure that the participants receiving TEAS and the TEAS operators will remain blinded to the allocation (2Hz or 10Hz) during the entire study, an independent investigator will set up the frequency of the stimulation device in advance and then cover the frequency display site. The distribution of the 3 groups will be hidden from the outcome evaluators and data analysts.