[Stellate ganglion block with transcutaneous electric nerve stimulation (TENS): a double-blind study with healthy...

Blockade of the stellate ganglion is an established and highly effective diagnostic and therapeutic procedure for management of certain acute and chronic pain syndromes or other disorders. The paratracheal injection of a local anaesthetic is the simplest and most frequently used approach for blocking the cervicothoracic sympathetic nerves (ganglion stellate). However, since serious complications can occur during or following the anterior paratracheal technique including accidental intravenous or intraarterial injection, non-invasive methods for blockade of the stellate ganglion have been suggested. In 1980 Jenkner (15) reported the successful interruption of the sympathetic outflow from the stellate ganglion together with the relief of pain by transcutaneous electrical nerve stimulation (TENS), followed by the development of an "optimal wave form" in 1981 (14). Since we were unable to reproduce Jenkner's results of sympathetic blockade in our patients, this study was designed to investigate the effects of TENS on the sympathetic activity of the stellate ganglion in healthy volunteers.

50 healthy volunteers were randomised into two groups (n = 25). In group I the left stellate ganglion was stimulated for 20 min by the mode described by Jenkner (monophasic pulse, small anode, large cathode, frequency 20 Hz), while group II was stimulated by conventional TENS (biphasic pulse, electrodes of identical size, frequency 100 Hz). The method of stimulation was blinded to both the investigator and the subjects investigated. Measurements included cutaneous blood flow of the volar forearm (laser Doppler), skin temperature on two sites of the cheeks (thermistor), pupil diameter and size of the palpebral fissures, sweat production (ninhydrine test) and global sensitivity and pain perception thresholds on both sides (electrical stimulation). Measurements were performed before TENS of the stellate ganglion, after 5, 10, 15 and 20 min of stimulation and 10 min after termination of TENS. Statistical analysis of the obtained data was performed by Friedman-Test and by Mann-Whitney-U-Test. p < 0.05 was assigned statistical significance.

Skin temperature increased in both groups and on both sides by 1.2 degrees C, while skin perfusion rate, pupil size, size of the palpebral fissure and sweat production remained unchanged. Global sensitivity and pain perception thresholds of forehead decreased in both groups and on both sides, while there was no change of both parameters on the hands.

No signs and symptoms of sympathetic blockade could be demonstrated in any of the groups, neither by TENS of the stellate ganglion as described by Jenkner nor by unspecific TENS. Thus, pain relief by TENS of the stellate ganglion as reported in the literature must involve other mechanisms than sympathetic blockade. In addition, TENS may not replace traditional blockade of the stellate ganglion by local anesthetics, if sympathetic blockade is required for diagnostic and therapeutic purposes.