Effect‐site concentration of remifentanil attenuating surgical stress index responses to intubation of the trachea

Surgical Stress Index has been proposed for assessment of surgical stress and analgesia. It is a numeric index based on the normalised pulse beat interval and photoplethysmographic pulse wave amplitude. We determined the effect-site concentration of remifentanil for attenuation of Surgical Stress Index responses to intubation of the trachea. Thirty ASA 1-2 patients received either deep or normal anaesthesia and then target-controlled remifentanil. Burst suppression was maintained in the deep group and state entropy at 40-60 (scale 0-91) in the normal group. Mean (SD) effect-site concentrations of remifentanil attenuating responses in 50% of patients were 2.13 (0.25) ng x ml(-1) and 3.05 (0.27) ng x ml(-1) in deep and normal groups, respectively (p = 0.034). From probit analysis, EC(50) and EC(95) of remifentanil (95% CI) were 2.34 (1.97-2.71) ng x ml(-1) and 3.19 (2.69-3.69) ng x ml(-1) in deep group and 3.17 (2.67-3.67) ng x ml(-1) and 3.79 (3.21-4.37) ng x ml(-1) in the normal group, respectively. The values from probit analysis and up-and-down method did not differ significantly.