• Ruth Edry, Vasile Recea, Yuri Dikust, and Daniel I Sessler.
• From the Department of Anesthesiology, Rambam Medical Centre, The Ruth and Bruce Rappaport Faculty of Medicine, Technion Institute of Technology, Haifa, Israel (R.E.); Department of Anesthesiology, Rambam Medical Centre, Haifa, Israel (V.R., Y.D.); and Department of Outcomes Research, Cleveland Clinic, Cleveland, Ohio (D.I.S.).
• Anesthesiology. 2016 Jul 1; 125 (1): 193-203.

BackgroundThe nociception level (NoL) index is an index of nociception based on nonlinear combination of heart rate, heart rate variability, photoplethysmograph wave amplitude, skin conductance, skin conductance fluctuations, and their time derivatives. The authors evaluated the abilities of the NoL index and other measures of nociception to discriminate between noxious and nonnoxious stimuli, to progressively respond to graded stimuli, and to respond to opioid administration.MethodsIntraoperative NoL was compared to heart rate, pulse plethysmograph amplitude, noninvasive blood pressure, and the surgical pleth index around five specific stimuli: tetanic stimulation with and without fentanyl analgesia, intubation, first incision/trocar insertion, and a nonnoxious period. The response around first incision was analyzed at two target plasma concentrations of remifentanil.ResultsIn 58 patients, the NoL index responded progressively to increased stimulus intensity and remained unchanged in response to nonnoxious stimuli. Compared to other accepted measures of nociception, the NoL index better discriminated noxious from nonnoxious stimuli with an area under the curve of 0.93 (95% CI, 0.89 to 0.97) and a sensitivity of 87% at a specificity of 84%. The NoL index was the only measure that reliably reflected two different analgesic concentrations of remifentanil during initial skin incision or trocar insertion.ConclusionsThe NoL index changes proportionately with patients' response to various clinical and experimental noxious stimuli and discriminates noxious from nonnoxious stimuli with high sensitivity and specificity. The NoL index also responds progressively to increasing stimuli intensity and is appropriately blunted by analgesic administration. The NoL index was superior to other compared measures and appears to accurately characterize nociception during general anesthesia.

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