Response entropy changes after noxius stimulus.

Small changes in the frequency of the electromyography could reflect an inadequate anesthetic or analgesic level, and it could be more specific than the hemodynamic monitors. The Datex-Ohmeda S/5 Entropy Module includes information about the electromyographic activity of the face muscles (response entropy--RE). The aim of our study is compare entropy and BIS ability to detect a nociceptive stimulus during a sevoflurane anesthesia. We designed an observational, prospective and descriptive study that included 20 patients. We performed sevoflurane anaesthesia induction, the end-tidal was kept at 3 and 4 %, during 15 min at each concentration, with no analgesic drug and no neuromuscular blocking agent, and we applied a nociceptive stimulus: tetanus 100 Hz, during 5 s. We set the standard monitorization, BIS, RE, and state entropy (SE) along the study. There was a significant difference between RE and SE post-noxious stimulus values at 3 and 4 % end-tidal sevoflurane (p < 0.05). Only RE changed significantly at the moment of the noxious stimulation at both sevoflurane concentrations studied (p < 0.05). In patients under general anesthesia only carried out with sevoflurane at concentrations that inhibit the movement to painful stimuli, the RE is a single parameter able to detect variations after the nociceptive stimulation.