Changes in a surgical stress index in response to standardized pain stimuli during propofol-remifentanil infusion

Abstract

Background. The surgical stress index (SSI) is based on a sum of the normalized pulse beat interval (PBI) and the pulse wave amplitude (PPGA) time series of the photoplethysmography. As a measure of the nociception-anti-nociception balance in response to a standardized pain stimulus, SSI was compared with EEG changes in state and response entropy (SE and RE), PPGA, and heart rate (HR) during various targeted pseudo-steady-state concentrations of propofol and remifentanil. Methods. Forty ASA I patients were allocated to one of the four groups to receive a remifentanil step-up/-down effect-compartment target-controlled infusion (Ceremi) of 0, 2, 6, 2, 0 ng ml-1, or 6, 2, 0, 2, 6 ng ml-1, and an effect-compartment target-controlled propofol infusion (Ceprop) to keep the SE between 30 and 50 or 15 and 30, respectively. At each steady-state Ceremi, maximum change in SSI, SE, RE, PPGA, and HR after a noxious stimulus was compared with the baseline value. A correlation and prediction probability (PK) with Ceprop and Ceremi was measured. Results. Static and dynamic values of SSI correlated to Ceremi better than SE, RE, HR, and PPGA. SSI was independent of Ceprop, in contrast to SE and RE. The PK for Ceremi both before and during a noxious stimulus was better with SSI. Conclusions. SSI appeared to be a better measure of nociception - anti-nociception balance than SE, RE, HR, or PPGA. © The Board of Management and Trustees of the British Journal of Anaesthesia 2007. All rights reserved.