The Effect of Remifentanil on the Objectively Measured Pressure Pain Threshold

Upon arrival in the operating room, the patient will undergo standard monitoring, including non-invasive blood pressure, electrocardiography (ECG), pulse oximetry (SpO₂), bispectral index (BIS™), and train-of-four (TOF) monitoring. An intravenous (IV) line will be placed, and crystalloid infusion will be initiated. Mechanical pain threshold will then be assessed using a Medoc algometer. Measurements will be performed on the dorsum of the non-dominant hand. Four measurements will be obtained at different target plasma concentrations of remifentanil(Ultiva®): 0, 1, 2, and 3 ng/mL. Remifentanil will be administered using a target-controlled infusion (TCI) system based on the Minto pharmacokinetic model. Following completion of these measurements, standardized intravenous anesthesia will be induced and maintained using propofol (propolipid®), remifentanil, and rocuronium (B.Braun®). Total perioperative consumption of remifentanil and propofol will be recorded.

At the end of the surgical procedure, intravenous acetaminophen 1 g and a 4 mg morphine bolus will be administered. Upon arrival in the post-anesthesia care unit (PACU), pain will be assessed using the visual analogue scale (VAS). During the first 24 postoperative hours, analgesia will be provided via a patient-controlled analgesia (PCA) pump delivering 2 mg intravenous HCL morphine (Sterop®) boluses on demand. The PCA settings will follow a 2/10/20 regimen: 2 mg morphine per demand dose, a 10-minute lockout interval, and a maximum dose of 20 mg over 4 hours. The use of acetaminophen as adjunct analgesia is permitted; however, corticosteroids, nonsteroidal anti-inflammatory drugs (NSAIDs), piritramide, and magnesium are prohibited. Pain scores (VAS) will be reassessed at 12 and 24 hours postoperatively. All adverse events (e.g., nausea, delirium) will be monitored and recorded during the 24-hour postoperative period.