SPI-directed Analgesia for Lumbar Discectomy

Monitoring depth of anaesthesia using spectral entropy (SE) and quality of neuromuscular block are routine in modern anaesthesia, whereas monitoring of analgesia still requires further studies. Recently, the Surgical Pleth Index (SPI) was added as a surrogate variable showing the nociception-antinociception balance into abovementioned parametres constituting a novel approach in monitoring patients intraoperatively, known as adequacy of anaesthesia (AoA) or tailor-made anaesthesia. This study aims at evaluating utility of SPI-directed analgesia in patients undergoing general anaesthesia (GA) where analgesia intraoperatively will be achieved either with regional preemptive wound infiltration using 0,2 % ropivacaine with fentanyl or 0,2 % bupivacaine with fentanyl or intravenous analgesia using continuous infusion of metamizole with tramadol for lumbar discectomy. Intraoperatively, SPI value will be recorded with sampling frequency of 1 minute. When SPI value reaches a level higher than 15 SPI points above basic level, a rescue dose of 1mg/kg body weight of fentanyl will be administered intravenously every 5 minutes until SPI value decreases to basic level calculated previously before operation started. Additionally, the investigators will compare Numerical Rating Scale (NRS) with Surgical Pleth Index (SPI) values for monitoring the efficacy of analgesia postoperatively. After emergence from GA patients will be questioned in terms of their pain intensity in a scale 0-10. In the case of pain perception above 3, a bolus of 2mg of morphine will be administered intravenously every 10 minutes until pain perception will be lower than 4. SPI values will be recorded every 1 minute and analysed for aute pain (NRS 7-10), average (4-6) and mild pain perception intervals to assess if there exists a correlation between NRS and SPI. In addition, some patients develop Failed Back Surgery Syndrome (FBSS) following lumbar surgeries so the investigators will aim to analyze if SPI-directed analgesia intra- and post-operatively reduces rate of FBSS. After 5 months after operation patient will be surveyed using melzack protocol to assess the rate of FBSS as well as symptoms of chronic pain.