Changes in skin conductance as a tool to monitor nociceptive stimulation and pain.

PURPOSE OF REVIEW The skin conductance algesimeter (SCA) reflects the sympathetic nervous system influenced by changes in emotions, which releases the acetylcholine that acts on muscarine receptors, causing a subsequent burst of sweat and increased skin conductance. The SCA reacts immediately and is not influenced by hemodynamic variability or neuromuscular blockade. The use of SCA for pain and nociceptive assessment is outlined in this review. RECENT FINDINGS When pain was monitored by verbal reporting in postoperative patients, the SCA had a sensitivity of about 90% and specificity up to 74% to identify the pain, better than heart rate and blood pressure. In general anesthetized patients, both the sensitivity and specificity were about 90% to detect responses to noxious stimulation when compared with clinical stress variables. The SCA reflects changes in norepeinephrine levels induced by nociception better than heart rate, blood pressure, and electroencephalograph (EEG) monitors. Unlike EEG monitors, the SCA response is sensitive to experimental noxious stimuli during general anesthesia, and the measured response was attenuated by analgesic medication. This SCA response is significantly associated with genetically modulated pain sensitivity. Moreover, noxious stimuli in artificially ventilated patients and in preterm infants increase the SCA index, and the increase correlates to the clinical discomfort. SUMMARY The SCA detects nociceptive pain fast and continuously, specific to the individual, with higher sensitivity and specificity than other available objective methods.