[Intraoperative guidance of anesthesia: Analgesie Nociception Index (ANI) vs. standard care for hysterectomy under anesthesia with sevoflurane : A randomized controlled simple blinded study on intraoperative opioid consumption, postoperative pain and patient satisfaction].

backgroundGeneral anesthesia leads to different effects depending on the drugs used (hypnosis, analgesia, muscle relaxation). While there are validated methods for clinical monitoring and control of hypnosis and muscle relaxation in routine anesthesia, the assessment of analgesia is still mainly based on the interpretation of clinical vital parameters, such as heart rate, blood pressure, perspiration or intraoperative movements of the patient. The present clinical study investigated whether the use of a so-called nociception monitor to record the intraoperative need for analgesics is superior to the previous analysis of vital parameters. The analgesia nociception index (ANI; MDoloris, Lille, France) was used, which is one of several nociception monitors currently on the market for recording the sympathicovagal balance. In the case of the ANI, the measurement is based on the analysis of the heart rate variability (HRV) as a function of breathing. The index is given in the 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 50-70 under anesthesia corresponds to sufficient intraoperative analgesia.

methodsThis was a clinical prospective randomized study in which 110 patients who underwent laparoscopic hysterectomy under balanced anesthesia using propofol, fentanyl and atracurium for induction and sevoflurane and fentanyl for anesthesia maintenance, were divided into two groups. In the intervention group (ANI group), during the operation analgesics were administered with the aid of the ANI monitor (bolus of 0.1 mg fentanyl if the ANI was < 50), whereas in the comparison group analgesics were administered according to previous clinical parameters (vital parameters, intraoperative defensive movements). The groups were then compared with respect to intraoperative fentanyl consumption (primary outcome), postoperative pain and opioid-induced side effects (measured by the numeric rating scale [NRS]) as well as patient satisfaction on postoperative day 3 (secondary outcome).

resultsThe observations showed a higher total intraoperative consumption of fentanyl in the intervention group, due to a significantly higher number of individual doses (0.54 vs. 0.44 mg, p < 0.001). With respect to the other observation points, there were hardly any differences between the groups, neither with respect to the pain score nor the side effects in the recovery room. At most there was a trend towards a slightly lower pain score at the first measurement point in the recovery room (NRS at 15 min). In the patient survey on the postoperative day 3, there was a difference with respect to the subjectively described reduction in vigilance in the ANI group, but not other side effects or overall satisfaction with the pain therapy.

conclusionIn this group of patients the additional use of the ANI monitor for intraoperative control of analgesia led to an increased consumption of fentanyl compared to the comparison group, without having an impact on the postoperative pain score, opioid-induced side effects or patient satisfaction. An optimization of pain therapy through intraoperative use of the ANI monitoring in hysterectomy patients under balanced anesthesia with sevoflurane and fentanyl could therefore not be proven. Transferability of the results to a much older and/or sicker patient collective remains questionable.