The intraoperative modulation of opioids continues to be based on clinical signs. This may result in adverse events such as sympathetic reactivity or opioid-induced hyperalgesia. Recently, the Analgesia/Nociception Index (ANI), a non-invasive 0–100 index derived from heart rate variability analysis, has been proposed for nociception assessment. However, the ability of the ANI to adequately guide intraoperative opioid administration has never been demonstrated. We designed a prospective study to evaluate the ability of the ANI to guide remifentanil administration in vascular surgery.

One hundred and eighty adults presenting for elective surgery were included. All received total intravenous anaesthesia with propofol adjusted to entropy and remifentanil adjusted to the ANI. The primary endpoint was the number of patients without any episode of reactivity defined as a 20% increase in heart rate or arterial pressure or the occurrence of movement. Secondary endpoints included opioid use and maximal pain rate in the first postoperative day.

Anaesthesia was achieved without any episode of reactivity in 160 (89%) patients. Twenty-five episodes of reactivity occurred in 20 (11%) patients. The median remifentanil dose was 0.042 [0.040–0.044]μg.kg^{− 1}.min⁻¹. At 24hours, the maximal NRS pain score was 2 [2,3]. One hundred and fifty-five patients (86%) did not receive any postoperative opioids, whereas 25 (14%) received a median dose of 5[5–10] mg of oxycodone.

This prospective study demonstrated that the ANI can be used to adequately guide intraoperative remifentanil administration during vascular surgery. Such guidance resulted in low remifentanil consumption, low postoperative pain rates and low opioid rescue analgesia.