BackgroundRoutine hemodynamic monitoring parameters under general anesthesia, such as heart rate (HR), systolic blood pressure (SBP), and perfusion index (PI), do not solely reflect intraoperative nociceptive levels. We developed a hemodynamic model combining these 3 parameters for nociceptive responses during general anesthesia, and evaluated nociceptive responses to surgical skin incision.Material/MethodsWe first retrospectively performed discriminant analysis using 3 values – HR, SBP, and PI – to assess response to skin incision during tympanoplasty, laparoscopic cholecystectomy, and open gastrectomy to determine if combined use of these parameters differentiates nociceptive levels among these 3 surgeries. Secondly, ordinal logistic regression analysis was applied using the 3 parameters to develop an equation representing nociceptive response during general anesthesia, and then evaluated its utility to discern nociceptive responses to skin incision.ResultsWe developed the following hemodynamic model as calculated nociceptive response= −1+2/(1+ exp(−0.01 HR −0.02 SBP +0.17 PI)), and prospectively determined that calculated nociceptive responses to small skin incision for laparoscopic surgery were significantly lower than responses to large skin incision for laparotomy.ConclusionsOur hemodynamic model using HR, SBP, and PI likely reflects nociceptive levels at skin incision during general anesthesia, and quantitatively discerned the difference in nociceptive responses to skin incision between laparoscopy and laparotomy. This model could be applicable to assess either real-time nociceptive responses or averaged nociceptive responses throughout surgery without using special equipment.

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Acute postsurgical pain, probably including acute neuropathic pain (ANeP), starts at the early postoperative period, and chronic postsurgical pain including chronic neuropathic pain (CNeP) persists at least 3 months after surgery. Although it must be important for prevention and treatment of acute and chronic postoperative pain to reveal the time course of postoperative neuropathic characteristics, a neuropathic pain profile after surgery has not been evaluated. Pain status at the surgical site in adult patients who underwent video-assisted thoracic surgery (VATS) for lung cancer was prospectively assessed until 12 months after surgery. Neuropathic characteristics were assessed using the Douleur Neuropathique 4 (DN4) questionnaire until 6 days after surgery and the DN2 questionnaire throughout the study. Twenty-seven patients were enrolled in this study. Pain intensity at surgical sites were significantly higher at 1 and 6 days after surgery during resting state, and were also significantly higher at 3, 6, and 12 months after surgery during movement than those before surgery. The incidence of ANeP was 33.3% at 1 day, and 18.5% at 6 days after surgery. The incidence of CNeP decreased to 12.5% at 3 months, 5.0% at 6 months, and 0.0% at 12 months after surgery. The number of neuropathic characteristics, assessed by DN2 scores, significantly increased at 1 and 6 days after surgery, compared to those before surgery. DN2 scores at 3, 6, and 12 months after surgery, however, showed no significant differences compared to those before surgery. In patients with acute postsurgical pain, 20% to 30% of patients show ANeP characteristics, and the incidence of CNeP gradually decreases after VATS in patients with chronic postsurgical pain.

Surgical invasion activates nociception, while anesthesia suppresses it. Under general anesthesia, stimulation, which is the balance between nociception and anti-nociception, induces responses, including activation of the autonomic nervous system. To evaluate the associations between stimulation (S) and the resultant responses (R), we examined R values, which were calculated using mathematical models of Stevens’ power law, Gompertz function and logistic function. The previously developed Nociceptive Response (NR) formula was applied as a modified logistic model. S values were calculated using a linear function in the NR formula. In a retrospective study, we developed an exponential model of Stevens’ power law and a sigmoidal model of Gompertz function using differential equations, by adjusting R values to correspond to NR values, in consecutive patients undergoing surgery under general anesthesia (n = 4,395). In a subsequent prospective study, we validated the superiority of R values of Gompertz function and the NR formula in an exponential model in adult patients undergoing tympanoplasty (n = 141) and laparoscopic cholecystectomy (n = 86). In conclusion, both modified logistic function and Gompertz function are likely appropriate mathematical models for representing responses to stimulation resulting from the balance between nociception/anti-nociception during surgical procedures under general anesthesia.

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