BJA Advance Access originally published online on April 24, 2007
British Journal of Anaesthesia 2007 98(6):785-791; doi:10.1093/bja/aem084
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Feasibility study for the administration of remifentanil based on the difference between response entropy and state entropy
1 Department of Anesthesiology, St Vincent Catholic Medical Centers – St Vincent's Hospital, Manhattan, New York, NY 10011, USA
2 New York Medical College, Valhalla, New York, USA
3 Department of Anaesthesia, Ghent University Hospital, Ghent, Belgium
4 Demed Engineering, Temse, Belgium
* Corresponding author: Department of Anesthesiology, St Vincent Catholic Medical Centers – St Vincent's Hospital, Manhattan, 170 West 12th Street, NR 408, New York, NY 10011, USA. E-mail: dmathews{at}svcmcny.org
Background: Facial electromyography (FEMG) may have utility in the assessment of nociception during surgery. The difference between state entropy (SE) and response entropy (RE) is an indirect measure of FEMG. This study assesses an automated algorithm for remifentanil administration that is based on maintaining an entropy difference (ED) that is less than an upper boundary condition and greater than a lower boundary condition.
Methods: The algorithm was constructed with a development set (n = 40), and then automated and studied with a validation set (n = 20) of patients undergoing anterior cruciate ligament repair. The percentage of time that the ED was maintained between the two boundary conditions was determined. Remifentanil and propofol predicted effect-site concentrations (Ce) were determined at surgical milestones and, after drug discontinuation, the time to response to verbal stimulation and orientation was measured.
Results: The median (25th–75th percentile) per cent of time that the ED was recorded between the boundary conditions was 99.3% (98.1–99.8%). Predicted propofol (µg ml–1) and remifentanil (ng ml–1) Ce (SD), respectively, were 3.5 and 4.0 at induction, 1.9 (0.8) and 7.2 (3.7) at the end of surgery, and 1.1 (0.5) and 3.2 (2.2) at eye opening. The median time to eye opening and orientation was 3.8 and 6.8 min, respectively.
Conclusion: This feasibility study supports the concept that remifentanil may be delivered using an algorithm that maintains the difference between SE and RE between the upper and lower boundary condition.
Keywords: anaesthetic techniques, i.v. infusion; anaesthetics i.v., propofol; analgesics, opioid, remifentanil; drug delivery, computerized; monitoring, depth of anaesthesia
Declaration of interest. A patent application has been submitted by the principal author for the algorithm utilized in the investigation.
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