Can changes in skin impedance be used to monitor sedation after midazolam and during recovery from anesthesia?

It has been suggested that sympathetic activity, measured as changes in electrical skin impedance (SI), can be used to assess the adequacy of general anesthesia. Our prospective study investigated if measurements of skin impedance can determine levels of sedation induced by midazolam. Twenty-seven patients scheduled for arthroscopy requiring general anesthesia were served as their own control. These were blinded to the order of injections by telling them that they will be randomly administered a placebo (saline) orsedative agent. A DM 3900 multimeter was used for SI measurements. The degree of sedation was measured using the modified Observer's Assessment of Alertness and Sedation (mOAAS) scale. Resting SI values were noted, and all participants were then administered the placebo followed 5 min later by midazolam 2 mg i.v. Five min after that, patients were administered standard general anesthesia with propofol, oxygen, nitrous oxide 60 %, and isoflurane 1 MAC via a laryngeal mask, and sufentanil 5 - 10 µg. SI significantly increased after administration of midazolam and induction of anesthesia. There were no significant differences between pre-administration (baseline) and placebo and end of surgery and end of anesthesia with closed eyes. There were highly significant differences (p<0.001) between pre-administration vs. midazolam, placebo vs. midazolam, pre-administration vs. induction of anesthesia. We found slight correlation between mOAAS and SI. There were no significant changes between the end of surgery and the end of anesthesia with closed eyes, but SI significantly decreased (p<0.01) after eyes opened.