Randomization and blinding
A trained researcher (B.W) allocated the participants the TEAS group or sham group in a 1:1 allocation according to a computer-generated random sequence. M.Z enrolled participants, and another two researchers (M.N.L and J.L.L) assigned participants to interventions. Concealed allocation was attained using sequentially numbered, opaque, and sealed envelopes. The attending anesthesiologists, surgeons, data collectors and the patients were unaware of the allocation. The participants were informed that they may feel various sensations, such as strong or mild tickling, or nothing during the TEAS procedure. They were told that just one parameter of TEAS was tested, so it was impossible for the participants to distinguish whether placebo or real TEAS [