Epidural anesthesia and postoperative analgesia for major abdominal surgery increases wound tissue oxygen tension compared with general anesthesia and intravenous morphine analgesia.

Objectives: The efficacy of transcutaneous electrical nerve stimulation (TENS) for pain relief has not been reliably established. Inconclusive findings could be due to inadequate TENS delivery and inappropriate outcome assessment. Electronic monitoring devices were used to determine patient compliance with a TENS intervention and outcome assessment protocol, to record pain scores before, during and after TENS and measure electrical output settings. Methods:Patients with chronic back pain consented to use TENS daily for two weeks and to report pain scores before, during and after 1-hour treatments. A ≥30% reduction in pain scores was used to classify participants as TENS-responders. Electronic monitoring devices 'TLOG' and 'TSCORE' recorded time and duration of TENS-use, electrical settings and pain scores.Results: Forty-two patients consented to participate. 1/35 (3%) patients adhered completely to the TENSuse and pain score reporting protocol. 14/33 (42%) were TENS responders according to electronic pain score data. Analgesia onset occurred within 30-60 minutes for 13/14 (93%) responders. It was not possible to correlate TENS amplitude, frequency or pulse width measurements with therapeutic response. Discussion:Findings from TENS research studies depend on the timing of outcome assessment; pain should be recorded during stimulation. TENS device sophistication might be an issue and parameter restriction should be considered. Careful protocol design is required to improve adherence and monitoring is necessary to evaluate the validity of findings. This observational study provides objective evidence to support concerns about poor implementation fidelity in TENS research.