ELECTROPHYSIOLOGICAL PROPERTIES OF AURICULAR ACUPUNCTURE POINTS IN PATIENTS DURING SURGERY UNDER GENERAL ANESTHESIA

There is experimental and clinical evidence that the major lesions (pain, inflammation, surgery) will be reflected on the surface of the ear and can be identified using the measurement of skin resistance, although the physical basis of these measurements is not clearly understood [ 1 - 3 ]. As for detection of auricular acupuncture points (AAP) by measuring the electrical skin resistance in patients before, during and after surgery, evaluation of possibilities for this simple technique still needs continuation. The aim of the present work was to study the frequency of the AAP detection using the skin resistance measurement in the external ear during surgery under general anesthesia. The AAP were examined by means of electrical resistance measurement in 25 patients (mean age 66.3 years) scheduled for elective orthopedic surgery. Twenty of them received a hip joint replacement A surgical Hallux valgus correction was performed in another 5 patients. 15 healthy volunteers, matched to the patient group according to age, were examined and results compared to the preoperative findings in patients. Surgery was performed under general anesthesia with endotracheal intubation and controlled mechanical ventilation. The first AAP examination was performed in the evening before surgery. The second examination took place during the most painful phase of surgery, which was the surgical manipulation on the lower extremity. The third ear examination was performed several hours after surgery in the postoperative care unit, when the patients were awake, but slightly sedated with piritramid (an opioid analgesic drug). It delivered through a patient controlled analgesia pump for postoperative pain relief. We detected AAP that had lower skin resistance, using SVESA neural pen (Neuralstift SVESA 1070, SVESA, Munchen, Germany). The neural pen generates maximal electric potential of 2 V. If the potential on the gate of the booster exceeds 1 V during examination, the light indicator will be activated. A referent “zero” value of resistance was adjusted for every measurement on the lateral margin of ear lobule, which is free of acupuncture points [ 4 ]. Detected points were compared to the map of AAP and classified according to WHO classification [ 5 ]. Both ears were examined. The AAP was considered to be found, if it was represented at least on one side. However, if the AAP was detected on both sides, it was included in further analysis only once. We defined the “frequently detected” AAP as those in more than 5 of patients (25%). The frequency of AAP detection was further analyzed statistically and compared to those in 15 healthy volunteers. The logistic regression model with logic link and exchangeable covariance structure was fit to analyze the dichotomous data (AAP detected or not). The analysis was performed using the SAS procedure GENMOD [ 6 ]. A single blinded observational study on the detection of AAP measuring electrical skin resistance in patients scheduled for orthopedic surgery compared with healthy volunteers was performed, liie following AAP were detected in more than 50% of patients: MA-SF5 (clavicle), MA-IC1 (lung), MA-TF1 (shen-men), and AAP corresponding to the site of surgery. The point MA-SF5 (clavicle) was found in 64% of patients before, 68% during and 60% after the operative procedure and in 60% of volunteers. MA-TF1 (shen-men) was found in 60% of patients, whereas during and after the operative procedure it was represented only in 32% and 16% (p<0.05). The area corresponding to the hip joint (mapped in the lower third of Crus anthelicis superior) was detected more frequently during the operative procedure (p<0.05) in 20 patients scheduled for total hip replacement. The patients scheduled for Hallux valgus surgery showed lower skin resistance in the corresponding ear area (upper third of Crus anthelicis superior) also only during the operative procedure (4 out of 5 patients). The point MA-TF1 (shen-men) was detected in the patient group before surgery more frequently in comparison with healthy controls (60% vs. 7%; p<0.05). The side of examination showed no significant differences throughout the study. We did not expect that the frequency of AAP detection by means of electrical skin resistance measurement during the surgery under general anesthesia would exceed the pre- and postoperative level. Although all the patients received appropriate standard analgesia with fentanyl during surgery, the highest detection frequency of the points, corresponding to the surgery sites, was registered during the operative procedure under general anesthesia. It was probably due to acute pain in the most painful phase of the surgery, whilst the hemodynamic parameters remain constant. Moreover, it seems that the measurement of skin resistance/conductance is more sensitive to intra-operative pain than standard monitoring of the depth of anesthesia. Our findings would support a classical physiological theory on the changes of skin resistance/conductance due to the activation of sympathetic nervous system, where the activation of sudomotor sympathetic nerves leads to the changes of skin moisture. The high incidence of the MA-TF1 (shen-men) identification in patients before surgery can be explained with the increased level of preoperative anxiety. The detection and subsequent needling of that point was effective to treat that disorder in sham controlled studies with healthy volunteers and ambulatory surgery patients [ 7 ]. In general data obtained support the theory of a somatotopic representation of the body on the human auricle [ 2 , 8 ]. The frequently found AAP with lower skin resistance in patients during orthopedic surgery can be useful for treatment of preoperative anxiety (MA-TF1, shen-men) and/or postoperative pain relief (MA-IC1, lung and the AAP corresponding to the site of surgery) in addition to standard auricular acupuncture prescriptions.