Automated assessment of circulatory response to surgical stimuli is unsolved. Would detection of cardiac baroreflex inhibition assess adequacy of intra-operative anti-nociception upon incision, as performed on-line on a beat-by-beat basis by a cardiovascular index, CARDEAN™? 18 ASA I-II patients undergoing spinal disc repair were studied, in a prospective randomized single-blinded trial (observational study). During infusion of propofol to maintain bispectral index between 40 and 60, patients were allocated to receive an effect site target-controlled infusion of remifentanil at Ce = 2 or 4 ng ml(-1). Upon incision and during surgery, circulatory response was assessed using beat-by-beat measurements of minor hypertension and tachycardia to give a cardiovascular index, CARDEAN, scaled between 0 and 100. Upon skin incision, CARDEAN increased in the remifentanil Ce = 2 ng ml(-1) group (n = 7, P < 0.05), while it did not increase in the remifentanil Ce = 4 ng ml(-1) group (n = 7, P = 0.18). During surgery, retrospectively, CARDEAN > 60 was associated with tachycardia and hypertension (P (k) = 0.81 ± 0.10). Changes in CARDEAN appeared linked to adequacy of anti-nociception.