Comparative evaluation of Narcotrend, Bispectral Index, and classical electroencephalographic variables during induction, maintenance, and emergence of a propofol/remifentanil anesthesia.

UNLABELLED: In the present study, we sought to compare the abilities of Narcotrend (NT) with the Bispectral Index (BIS) electroencephalographic system to monitor depth of consciousness immediately before induction of anesthesia until extubation during a standardized anesthetic. We investigated 26 patients undergoing laminectomy. Investigated states of anesthesia were: awake, loss of response, loss of eyelash reflex, steady-state anesthesia, first reaction, and extubation during emergence. NT, BIS, spectral edge frequency, median frequency, relative power in delta, theta, alpha, beta, and hemodynamics were recorded simultaneously. The ability of all variables to distinguish between awake versus loss of response, awake versus loss of eyelash reflex, awake versus steady-state anesthesia, steady-state anesthesia versus first reaction and extubation were analyzed with the prediction probability. Effects of remifentanil during propofol infusion were investigated with Friedman's and post hoc with Wilcoxon's test. Only NT and BIS were able to distinguish all investigated states accurately with a prediction probability >0.95. After start of remifentanil infusion, only hemodynamics changed statistically significantly (P < 0.05). NT and BIS are more reliable indicators for the assessment of anesthetic states than classical electroencephalographic variables and hemodynamics, whereas the analgesic potency of depth of anesthesia could not be detected by NT and BIS. IMPLICATIONS: The modern electroencephalographic monitoring systems Narcotrend and Bispectral Index are more reliable indicators for the assessment of anesthetic states than classical electroencephalographic and hemodynamic variables to predict anesthetic conditions from before induction of anesthesia until extubation during a standardized anesthetic regime with propofol and remifentanil. The analgesic potency of depth of anesthesia could not be detected by Narcotrend and Bispectral Index.

Alaris AEP monitor's "Click Detection" does not help to detect inadvertent disconnection of headphones during anesthesia.

UNLABELLED: Auditory evoked potentials (AEP) can be suppressed by anesthetics dose dependently, but may fail to be registered because of the absence of adequate auditory stimuli. The Alaris AEP monitor includes the "Click Detection" (CD) (generating the message "NO AEP" or "LOW AEP") to detect the loss of auditory stimuli. We investigated the accuracy of the CD in 17 patients awake (AWAKE) and during anesthesia (ANESTHESIA) with accurately placed headphones (HP) and after disconnected HP (No HP) over 5 min each, respectively. Alaris AEP ARX index, CD, and Bispectral Index were recorded each minute. Changes were evaluated with the Friedman and Wilcoxon test. Sensitivity (SEN) and specificity (SPE) and receiver operating characteristic curve were analyzed for the accuracy of the CD. During AWAKE after disconnection of the HP, Alaris AEP ARX index decreased significantly (P < 0.05). The CD was able to detect No HP after 2 min with a SEN of 88% and a SPE of 97%. During ANESTHESIA, no changes were found after HP disconnection. CD detected No HP with a SEN of 100% and a SPE of 20%. The CD of the Alaris AEP monitor is not able to detect unnoticed disconnection of HP during ANESTHESIA. IMPLICATIONS: Signal transmission of auditory evoked potentials can be suppressed by anesthetics, but also by disconnection of headphones. In the present study, we demonstrate that even the Alaris AEP monitor with the very new feature "Click Detection" was not able to detect the loss of headphones during general anesthesia with propofol and remifentanil.