General anesthesia is a combination of hypnotic drugs and opioid analgesics. Modern general anesthesia aims to treat nociception induced by surgical stimulation while avoiding an overdose of opioid analgesics and reducing side-effects of opioid administration. Underdosing of opioids during surgery can lead to nociception with increased sympathetic tone, elevated levels of stress hormones, unintended patient movement due to nociception as well as increased postoperative pain. On the other hand, overdosing of opioids can lead to negative side effects such as nausea and vomiting, arterial hypotension, immunosuppression, prolonged recovery times, postoperative delirium and an increase in postoperative pain by opioid-induced-hyperalgesia. Anesthesiologists aim for a long-lasting perioperative anesthesia while at the same time trying to reduce the intraoperative and postoperative opioid administration.

An alternative approach to the intraoperative administration of high potency opioids in order to achieve antinociception during surgery is combining a general anesthesia with a regional anesthesia. However, the quality of regional anesthesia cannot be assessed during general anesthesia by the anesthesiologist and patients cannot express pain themselves. Therefore, anesthesiologists tend to administer a certain calculated opioid dose during the operation. If this calculated opioid administration is essential for a sufficient anesthesia or an unnecessary overdose cannot be assessed by the anesthesiologist. Until now there has been no measurement tool that could estimate the effectiveness of regional anesthesia and the absence of nociception during general anesthesia combined with a regional anesthesia.

In recent years, different monitoring devices estimating the effect of nociception during unconsciousness have become commercially available. Such monitoring devices should help physicians to choose the right dose of opioid analgesics during general anesthesia. Among those, the Surgical Pleth Index (SPI) was one of the first commercially available nociception monitoring devices. The SPI is derived by the CARESCAPE™B650 patient monitor (GE Healthcare) and calculates an index value from normalized heart rate and pulse wave amplitude derived by photoplethysmography. The index is presented on a scale from 0 (low sympathetic tone) to 100 (high sympathetic tone). Nevertheless, current literature is inconclusive about the impact of nociception-monitor-guided opioid administration. So far, there is no definitive evidence on anesthesia related outcome parameters like the administered amount of opioid, postoperative short-term recovery, and long-term outcome. Besides, there has been no study evaluating the assessment of the effectiveness of regional anesthesia during general anesthesia by monitoring the intraoperative nociception with the SPI. If the SPI was able to assess nociception, SPI guided opioid administration would prevent unnecessary opioid administration during the operation and reduce the total dose of opioids. Reduction of the intraoperative opioid dose would mean a clinically important benefit for patients against the background of potential risks of opioid administration. Nevertheless, it remains unknown whether guiding sufentanil administration by SPI monitoring effects the administered amount of intraoperative and postoperative opioid, immediate postoperative pain in the postanesthesia care unit (PACU) and the quality of postoperative recovery in patients with a combination of general and regional anesthesia.

This prospective, randomized controlled trial aims to investigate whether guiding sufentanil administration by SPI monitoring - compared to routine care - reduces intraoperative sufentanil consumption in patients having trauma and orthopaedic surgery with a combination of general and regional anesthesia. The hypothesis tested in the present study is that in patients having trauma and orthopaedic surgery with a combination of general and regional anesthesia guiding sufentanil administration of sufentanil guided by SPI monitoring reduces intraoperative sufentanil consumption compared to routine care.