The Analgesia Nociception Index (ANI) is one of several nociception monitors currently on the market for recording the sympathico-vagal balance. In the case of the ANI, the measure- ment is based on the analysis of heart rate variability (HRV) in dependence of breathing. The index is given in form of a dimensionless score between 0 and 100, where 0 stands for a lack of parasympathetic activity and 100 for a very strong parasympathetic activity. According to the manufacturer, a value between

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... 0 under anesthesia corresponds to sufficient in- traoperative analgesia. In the present prospective, randomized, single center single-blind study on 110 hysterectomy patients, it was investigated whether the use of the ANI monitor for intraoperative analgesic control has an influence on intraoperative opioid consumption (fentanyl) and whether it has effects on postoperative pain (measured using the numerical rating scale in the post anaes- thesia unit), opioid-induced Side effects (shortness of breath, nausea and vomiting, reduced vigilance) and patient satisfaction with pain therapy. For this purpose, a total of 110 patients with an average age of 48 (± 9) years who underwent a laparoscopic hysterectomy were randomly divided into two homogeneous groups. The par- ticipants were blinded to their group membership. In both groups, the ANI was continuously recorded by the ANI monitor via an additional double electrode placed on the thorax during the entire course of anesthesia. In the intervention group (ANI group), the anesthetist could see the index value at all times and the analgesic therapy was based on this value. In the comparison group (VER group) the index was not visible and the analgesic therapy was car- ried out according to the anesthetist's assessment based on clinical vital parameters (blood pressure, heart rate), but in both cases always within the permissible dose limits according to the specialist information. In addition to the standard monitoring, the depth of anesthesia was also measured using the bispectr [...]