Vagal sensory evoked potentials disappear under the neuromuscular block - an experimental study.

BACKGROUND: Transcutaneous vagal nerve stimulation is a promising treatment modality in patients suffering mood disorders and chronic pain, however, the mechanisms are still to be elucidated. A recently developed technique of EEG responses to electrical stimulation of the inner side of the tragus suggests that these responses are far field potentials, generated in the vagal system - Vagal Sensory Evoked Potentials (VSEP). OBJECTIVE: To reproduce the VSEP technique free from myogenic artifacts. METHODS: Fourteen ASA I-II patients scheduled for elective surgery in standardized Total Intravenous Anesthesia (TIVA) were enrolled. Transcutaneous electrical stimulation was applied to the inner side of the right tragus. Averaged EEG responses were recorded from the electrode positions C4-F4 and T4-O2 before and after induction of TIVA, during the maximal effect of the non-depolarizing muscle relaxing agent, cis-atracurium (C-AR) and after recovery from C-AR under TIVA. RESULTS: Typical response curves with P1, N1 and P2 peaks could be reproduced in all patients before and after anesthesia induction. The response curves disappeared during the C-AR action and re-appeared after recovery from C-AR under TIVA. CONCLUSION: The disappearance of the scalp responses to electrical tragus stimulation under the neuromuscular block suggests a muscular origin of these potentials.

The effect of auricular acupuncture on fentanyl requirement during hip arthroplasty: a randomized controlled trial.

OBJECTIVES: Although auricular acupuncture (AA) is suggested to be effective in treatment of pain, it has not yet been used for intraoperative analgesia. Therefore, we studied whether the AA reduces intraoperative analgesic requirement during total hip arthroplasty (THA). METHODS: One hundred and twenty patients scheduled for THA were enrolled in this patient-anesthesiologist-blinded study. The patients were randomly assigned to receive needling of specific AA points or a sham procedure (needling of 3 nonacupoints on the ear helix) ipsilateral to the surgery site. Fixed indwelling AA needles were placed in the evening before THA and withdrawn on the day after surgery. The patients received general anesthesia with desflurane, which end-tidal concentration was kept within 3.5 volume % to 5.5 volume % to maintain the Bispectral Index within 40% to 55%. The anesthesiologists were asked to titrate fentanyl to keep the heart rate and blood pressure within 20% of baseline values. The primary outcome was fentanyl amount given during surgery. The secondary outcome measures were incidence of nausea and vomiting and time to first request of analgesics in the recovery room. The success of patients' and anesthesiologist blinding was also documented. RESULTS: The data of fentanyl requirement of 116 patients were available for the final analysis. Patients from AA group required 15% less fentanyl during surgery than the controls (4.6±1.1 µg/kg vs. 5.2±1.3 µg/kg; mean±SD; P=0.008). Demographic data and secondary outcome measures were comparable in both groups. DISCUSSION: Regarding the modest clinical effect, AA should be further investigated for its clinical usefulness for complementary analgesia during the surgery.