Thу goal of this study was to learn whether intraoperative analgesia nociception monitoring (ANI) could be beneficial during intraoperative monitoring for patients undergoing living donor liver resections. The main questions it aims to answer are:

• Could it impact the average dose of intraoperative fentanyl used?
• Could it impact the occurrence of postoperative nausea and vomiting?

Patients who were included in this study underwent living liver donor resections with fentanyl infusion and thoracic epidural analgesia. Two groups of patients were analysed - the ANI group (n = 24), in which fentanyl dose was adjusted with ANI monitoring, and the retrospective control group (n = 25) with a standard practice without ANI monitoring.

Monitoring nociception accurately during general anaesthesia has presented a long-standing difficulty. Typically, anaesthesiologists rely on changes in the autonomic nervous system, such as heart rate, blood pressure, and sweating, to help determine the need for pain relief medication. Analgesia nociception index (ANI) is a noninvasive tool for monitoring the intraoperative state of the autonomic nervous system, particularly the parasympathetic nervous system.

During the long-lasting high nociceptive surgery, the infusion of fentanyl was used at our institution. Opioids can lead to postoperative nausea, vomiting, and other complications when an overdose occurs. Fentanyl dosage changes significantly after hours of infusion due to context-sensitive halftime. It is practically impossible to adjust an infusion dose with the subjective evaluation of standard monitoring, such as heart rate and blood pressure. Doses of opioids that we use in our daily practice, e.g. mcg.kg-1, are unpredictable and vary between individuals due to pharmacogenetics and pharmacokinetic reasons. The best method to exclude pharmacokinetic peculiarities and predict the subsequent dose is to directly measure analgesic agents' concentration in the blood, though it is practically impossible. This study aimed to assess whether intraoperative analgesia nociception monitoring (ANI) could have an impact on the average intraoperative dose of fentanyl and on the occurrence of postoperative nausea and vomiting.

Inclusion Criteria:

• Female and male patients, 18 - 60 years old, undergoing living donor liver resections with general anaesthesia with sevoflurane, thoracic epidural analgesia and fentanyl on infusion. ASA I, II

Exclusion Criteria:

• patients with cardiac arrhythmia (atrial fibrillation, frequent extrasystoles - more than one extrasystole in 30 seconds), total intravenous anaesthesia with propofol

Due to the institutional policy, the IPD will not be shared.