Prediction of blood pressure change during surgical incision under opioid analgesia using sympathetic response evoking threshold

Opioid inhibition of nociceptive stimuli varies in individuals and is difficult to titrate. We have reported the vascular stiffness value (K) as a standard monitor to quantify sympathetic response with high accuracy. On the contrary, among individuals, a considerable variation in the rate of change in K for constant pain has been observed. In this study, we proposed a new index, the minimum stimulus intensity value that evoked the response on K (MEC(K): Minimum Evoked Current of K), and evaluated its accuracy in predicting sympathetic response to nociceptive stimuli under constant opioid administration. Thirty patients undergoing open surgery under general anesthesia were included. After anesthetic induction, remifentanil was administered at a constant concentration of 2 ng/ml at the effect site followed by tetanus stimulation. MEC(K) was defined as the minimal current needed to produce a change in K. MEC(K) significantly (P < 0.001) correlated with the rate of change of systolic blood pressure during skin incision (ROC(BP)). Bland–Altman plot analysis using the predicted ROC(BP) calculated from MEC(K) and the measured ROC(BP) showed that the prediction equation for ROC(BP) was highly accurate. This study showed the potential of MEC(K) to predict blood pressure change during surgical incision under opioid analgesia. Clinical trial registration Registry: University hospital medical information network; Registration number: UMIN000041816; Principal investigator's name: Satoshi Kamiya; Date of registration: July 9th, 2019.