Can the “Sympatho‐Galvanic Reflex” (Skin Conductance Response) Be Used to Evaluate the Extent of Sympathetic Block in Spinal Analgesia?

The skin conductance response (SCR) (the “sympatho-galvanic reflex”) was studied in volunteers and in a few patients undergoing spinal analgesia. Electrical stimulation over the clavicle, breath-holding during inspiration, a short, deep breath and a sharp sound provoked a marked change in conductance not only in the hand and foot but also in dermatomes T5, T9, T12-L1. Thus, the SC response can be used to study sympathetic activity not only in the hand and foot, but also on the chest and abdomen. Electrical stimulation over the clavicle or a short, deep breath were the best means of provoking SC responses in patients receiving spinal analgesia. This restricted pilot study indicates that skin conductance response is maintained at dermatome levels far below anaesthetised levels during spinal analgesia, and a larger study is now under way to investigate these results further.