Patient-controlled transcutaneous electrical nerve stimulation for postoperative pain after abdominal surgery: a randomized pilot trial in an enhanced recovery after surgery hospital

Patients will be allocated into 2 groups, both receiving the intervention at different intensities. Group 1 will have TENS applied and titrated to a stimulation intensity that is the maximal tolerable by the patient without being painful or inducing muscle contraction. Stimulation intensity set by each individual patient at the start of each session whereby patients will titrate it up. Once patients are satisfied with intensity, patients will be instructed not to change it for the rest of the session. It is anticipated final intensity will be approximately 30mA based on previous studies but this will vary depending on what the patient deems non-painful. There is no minimum/maximum intensity provided. After the patient is taught how to administer the treatment by a study investigator, the patient will self-administer the treatment postoperatively. Patients will receive a TENS unit providing an asymmetric square biphasic wave form at a frequency of 80 pulses/s and a pulse width of 250 µs. TENS will be applied starting 1 hour post-surgery once patients are awake and alert, with each session applied for a duration of 30 minutes for the first 48hours postoperatively. Patients will be instructed to apply the TENS when they feel pain for pre-set 30-minute durations. Patients can terminate the session early if they experience discomfort or want to; we will ask patients to record events like this. The intervention will occur on the hospital recovery ward. Patients will be given a written form to track the intensity, timing and duration of each application. The TENS machine will be modified so only intensity can be changed to prevent tampering. Patients and the TENS unit will be checked on twice daily to monitor adherence.