Analgesia nociception index for intra‐operative remifentanil dose and pain after gynaecological laparotomy

We read with interest the article by Yoon et al. [1]. The authors found no difference in their primary outcome (postoperative pain scores), or their secondary outcomes, compared with remifentanil titrated to the patients' systolic blood pressure. We have several questions for the authors regarding the analgesic strategy utilised in both of their study groups. According to the study protocol, the patient's intra-operative analgesia consisted of titrated remifentanil, paracetamol 1 g and a one-off 50 μg bolus of fentanyl. Due to the rapid offset of action of remifentanil, we are surprised that patients received no other analgesic intervention before emergence from anaesthesia [2]. The authors note during their discussion that they “did not use regional analgesic techniques”. We wonder whether any local analgesic drug was administered by the surgeons as part of the surgical technique and, as such, was not considered part of the anaesthetist's analgesic regimen? If no form of regional or local analgesia were administered, we are interested in the rationale for this approach. Is this analgesic protocol standard in their centre or was this regimen used solely for the purposes of this study? In the postoperative period, no non-opioid medication appears to have been administered regularly. Instead, first-line analgesia consisted of patient-controlled 20 μg fentanyl boluses with a 10-min lock-out time. Alternative analgesics, such as non-steroidal anti-inflammatories, paracetamol and tramadol, were administered on an as-required basis to patients with pain scores ≥ 4. This approach differs to recommendations from many pain societies worldwide, where analgesic regimens aim to reduce opioid use in the peri-operative period [3]. The intra-operative analgesia recommendations from the UK advocate the use of multimodal analgesia and opioid-sparing analgesic techniques. What was the rationale for using a primarily opioid-based analgesic regimen without the automatic inclusion of regular non-opioid adjuncts? Can it be recommended in a climate where opioid misuse has, for example, contributed to a reversal in the year-on-year reduction in general mortality in the USA and appears to be a growing problem in South Korea [4, 5]? We do, however, acknowledge the addition of non-opioid-based analgesic drugs in response to pain scores ≥ 4 on the postoperative ward. Our final question revolves around the use of an analgesic nociceptive device based on heart rate variability in a setting where ephedrine is used. Did the authors account for the effect of ephedrine on heart rate variability when reading the average analgesia nociceptive indices? We commend the authors in their efforts to reduce postoperative opioid consumption and hyperalgesia by avoiding excessive intra-operative remifentanil. However, we would appreciate clarification on the points raised above, as they deviate significantly from our standard practice.