Anaesthesia is often performed using a balanced technique by administering both opioids and anaesthetics agents. Intraoperative opioid administration is still relying on simple parameters such as heart rate and blood pressure variations. However, many studies in both adults and children have shown the poor accuracy of those parameters in predicting pain because of their sensibility to other intraoperative events such as depth of anaesthesia and volaemic variations. Consequently, intraoperative analgesia is still inadequately managed with periods of under dosage or over dosage of opioid agents. This has been hypothesized to cause postoperative hyperalgesia related to both intraoperative pain (in case of under dosage) or to opioid agents (in case of over dosage). The main resulting effect is an increase of postoperative opioid consumption and the inadequate postoperative rehabilitation because of adverse effects of opioids. During the last decade, many pain-monitors have been investigated. Most of these devices are relying on the determination of the sympathetic-to the parasympathetic systems balance. Among those monitors, the Analgesia Nociceptive Index (ANI) quantifies the parasympathetic system. The ANI device can produce two parameters the instantaneous ANI (ANIi), derived from 60 seconds analysis and the mean ANI (ANIm) derived from 4 minutes analysis. Studies have shown the accuracy of ANIi to detect both experimental and clinical pain in various populations. Moreover, a recent randomized controlled trial during spine surgery in adults has found ANIi to decrease the intraoperative and postoperative opioid consumption when used intraoperatively for guiding the administration of opioid agents
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to evaluate the cumulative dose (in mg) of morphine during the first postoperative 24 hours according to the use or not of the ANI monitor (ANIi parameter) for guiding intraoperative opioid administration.
Timeframe: 24 hours