Ability of the Nociception Level, a Multiparameter Composite of Autonomic Signals, to Detect Noxious Stimuli during Propofol–Remifentanil Anesthesia

AbstractAbstract A multidimensional index of nociception level was developed using patients under propofol anesthesia receiving remifentanil infusions at a range of rates. The nociception level was found to be a reliable measure of noxious stimulation and outperformed simpler measures. Supplemental Digital Content is available in the text. Background: A novel multidimensional index of nociception, the nociception level (NoL) index, derived from the nonlinear composite of heart rate (HR), HR variability, amplitude of the photoplethysmogram, skin conductance, fluctuations in skin conductance, and their time derivatives, was used to assess nociception during anesthesia. Methods: Seventy-two American Society of Anesthesiologists I to III patients received propofol (target bispectral index, 45) and one of six remifentanil target concentrations in the range of 0 to 5 ng/ml. The NoL, mean arterial pressure (MAP; derived from a beat-to-beat finger cuff measurement), and HR were measured during nonnoxious, moderate noxious (skin incision), and intense noxious (intubation) stimulation. Values are represented as average (95% CI). Results: NoL, HR, and MAP did not change during nonnoxious events. Incision increased HR by 1.3/min (−0.46 to 3.1/min; not significant), MAP by 7.9 mmHg (−1.9 to 13.0 mmHg; not significant), and NoL by 8.0 (0.4 to 16.0; P < 0.001). Intubation increased HR by 7.0/min (1.4 to 12.0/min; P < 0.001), MAP by 13.0 mmHg (3.1 to 20 mmHg; P < 0.001), and NoL by 18.0 (7.8 to 29.0; P < 0.001). The ΔNoL area under the curve (0.95) of the receiver operating characteristic curve was greater compared with ΔHR (0.84, P < 0.001) and ΔMAP (0.78, P < 0.001). Under nonnociceptive conditions, remifentanil had no effect on NoL, in contrast to HR and MAP that showed a dose-dependent decrease. Conclusions: The NoL is a reliable measure of moderate and intense noxious stimulation and outperforms HR and MAP in differentiating noxious from nonnoxious stimuli. In contrast to HR and MAP, the NoL was not affected by hemodynamic effects of remifentanil.