Gradual withdrawal of remifentanil infusion may prevent opioid-induced hyperalgesia

Remifentanil-induced hyperalgesia: the current state of affairs

Remifentanil-induced hyperalgesia (RIH) is a part of a general opioid-induced hyperalgesia (OIH) syndrome, seemingly resulting from abrupt cessation of continuous remifentanil infusion at rates equal or exceeding 0.3 mcg/kg/min. The intricate mechanisms of its development are still not completely understood. However, hyperactivation of the N -methyl d -aspartate receptor system, descending spinal facilitation and increased concentration of dynorphin (a κ-opioid ligand) are commonly proposed as possible mechanisms. Several ways of prevention and management have been suggested, such as slow withdrawal of remifentanil infusion, the addition of propofol, pretreatment with or concomitant administration of ketamine, buprenorphine, cyclooxygenase-2 inhibitors (NSAIDs), methadone, dexmedetomidine. In clinical and animal studies, these strategies exhibited varying success, and many are still being investigated.

Remifentanil-induced hyperalgesia in healthy volunteers: a systematic review and meta-analysis of randomized controlled trials

ABSTRACT

Recent literature suggests that the withdrawal of remifentanil (RF) infusion can be associated with hyperalgesia in clinical and nonclinical settings. We performed a systematic review and a meta-analysis of randomized controlled trials with cross-over design, to assess the effect of discontinuing RF infusion on pain intensity and areas of hyperalgesia and allodynia in healthy volunteers. Nine studies were included. The intervention treatment consisted in RF infusion that was compared with placebo (saline solution). The primary outcome was pain intensity assessment at 30 ± 15 minutes after RF or placebo discontinuation, assessed by any pain scale and using any quantitative sensory testing. Moreover, postwithdrawal pain scores were compared with baseline scores in each treatment. Secondary outcomes included the areas (% of basal values) of hyperalgesia and allodynia. Subjects during RF treatment reported higher pain scores after discontinuation than during treatment with placebo [standardized mean difference (SMD): 0.50, 95% confidence interval (CI): 0.03-0.97; P = 0.04, I 2 = 71%]. A significant decrease in pain scores, compared with baseline values, was found in the placebo treatment (SMD: -0.87, 95% CI: -1.61 to -0.13; P = 0.02, I 2 = 87%), but not in the RF treatment (SMD: -0.28, 95% CI: -1.18 to 0.62; P = 0.54, I 2 = 91%). The area of hyperalgesia was larger after RF withdrawal (SMD: 0.55; 95% CI: 0.27-0.84; P = 0.001; I 2 = 0%). The area of allodynia did not vary between treatments. These findings suggest that the withdrawal of RF induces a mild but nonclinically relevant degree of hyperalgesia in HVs, likely linked to a reduced pain threshold.

Microglial Nrf2/HO-1 signaling gates remifentanil-induced hyperalgesia via suppressing TRPV4-mediated M1 polarization

Remifentanil-induced hyperalgesia (RIH) represents a significant clinical challenge due to the widespread use of opioids in pain management. However, the molecular and cellular mechanisms underlying RIH remain elusive. This study aimed to unravel the role of spinal cord microglia, focusing on the Nrf2/HO-1 signaling pathway and TRPV4 channels in the development of RIH. We used both in vivo and in vitro models to investigate the activation state of spinal cord microglia, the expression of TRPV4 channels, and the modulation of the Nrf2/HO-1 pathway under remifentanil exposure. In addition, we evaluated the potential therapeutic effects of dexmedetomidine, a perioperative α2-adrenergic agonist, on RIH and its related molecular pathways. Our results revealed a prominent role of spinal cord microglia in RIH, demonstrating an apparent microglial M1 polarization and increased TRPV4 channel expression. A notable observation was the downregulation of the Nrf2/HO-1 pathway, which was associated with increased neuroinflammation and mechanical allodynia. By upregulating or overexpressing Nrf2, we confirmed its ability to inhibit TRPV4 and thereby attenuate RIH-associated mechanical allodynia, M1 polarization, and neuroinflammation. Encouragingly, dexmedetomidine demonstrated therapeutic potential by positively modulating the Nrf2-TRPV4 nexus, attenuating mechanical allodynia, and reducing microglial inflammation. Our research highlights the critical role of spinal cord microglia in RIH mediated by the Nrf2-TRPV4 axis. The ability of dexmedetomidine to modulate this axis suggests its potential as an adjunctive therapy to remifentanil in mitigating RIH. Further studies are imperative to explore the broader implications and practical applicability of our findings.

Effects of Remifentanil Gradual Withdrawal Combined with Postoperative Infusion on Postoperative Hyperalgesia in Patients Undergoing Laparoscopic hysterectomy: A Factorial Design, Double-Blind, Randomized Controlled Trial

Background

Remifentanil-induced hyperalgesia (RIH) increases the risk of persistent postoperative pain, making early postoperative analgesic therapy ineffective and affecting postoperative patient satisfaction. This study aimed to verify the effects of gradual withdrawal of remifentanil combined with postoperative pump infusion of remifentanil on postoperative hyperalgesia and pain in patients undergoing laparoscopic hysterectomy.

Methods

This trial was a factorial design, double-blind, randomized controlled trial. Patients undergoing laparoscopic hysterectomy were randomly allocated to the control group, postoperative pump infusion of remifentanil group, gradual withdrawal of remifentanil group, or gradual withdrawal plus postoperative pump infusion of remifentanil group (n = 35 each). The primary outcome was postoperative mechanical pain thresholds in the medial forearm. The secondary outcomes included postoperative mechanical pain thresholds around the incision, pain numeric rating scale scores, analgesic utilization, awakening agitation or sedation scores, a 15-item quality of recovery survey, and postoperative complications.

Results

Gradual withdrawal of remifentanil significantly increased postoperative pain thresholds versus abrupt discontinuation (P < 0.05), whereas postoperative infusion did not show significant differences compared to the absence of infusion (P > 0.05). The combined gradual withdrawal and postoperative infusion group exhibited the highest thresholds and had the lowest postoperative pain scores and analgesic requirements as well as the highest quality of recovery scores (P < 0.05). No significant differences were observed for agitation scores, sedation scores, or complication rates (P > 0.05).

Conclusion

The novel combined gradual withdrawal and postoperative infusion of remifentanil uniquely attenuates postoperative hyperalgesia, pain severity, analgesic necessity, and improves recovery quality after laparoscopic hysterectomy.

Epigenetic regulation in opioid induced hyperalgesia

About 25 million American adults experience pain daily and one of the most commonly prescribed drugs to treat pain are opioids. Prolonged opioid usage and dose escalations can cause a paradoxical response where patients experience enhanced pain sensitivity. This opioid induced hyperalgesia (OIH) is a major hurdle when treating pain in the clinic because its underlying mechanisms are still not fully understood. OIH is also commonly overlooked and lacks guidelines to prevent its onset. Research on pain disorders and opioid usage have recognized potential epigenetic drivers of disease including DNA methylation, histone modifications, miRNA regulation, but their involvement in OIH has not been well studied. This article discusses epigenetic changes that may contribute to pathogenesis, with an emphasis on miRNA alterations in OIH. There is a crucial gap in knowledge including how multiple epigenetic modulators contribute to OIH. Elucidating the epigenetic changes underlying OIH and the crosstalk among these mechanisms could lead to the development of novel targets for the prevention and treatment of this painful phenomena.

Pharmacological interventions for preventing opioid-induced hyperalgesia in adults after opioid-based anesthesia: a systematic review and network meta-analysis

Background: Opioid-induced hyperalgesia (OIH) is an adverse event of prolonged opioid use that increases pain intensity. The optimal drug to prevent these adverse effects is still unknown. We aimed to conduct a network meta-analysis to compare different pharmacological interventions for preventing the increase in postoperative pain intensity caused by OIH. Methods: Several databases were searched independently for randomized controlled trials (RCTs) comparing various pharmacological interventions to prevent OIH. The primary outcomes were postoperative pain intensity at rest after 24 h and the incidence of postoperative nausea and vomiting (PONV). Secondary outcomes included pain threshold at 24 h after surgery, total morphine consumption over 24 h, time to first postoperative analgesic requirement, and shivering incidence. Results: In total, 33 RCTs with 1711 patients were identified. In terms of postoperative pain intensity, amantadine, magnesium sulphate, pregabalin, dexmedetomidine, ibuprofen, flurbiprofen plus dexmedetomidine, parecoxib, parecoxib plus dexmedetomidine, and S (+)-ketamine plus methadone were all associated with milder pain intensity than placebo, with amantadine being the most effective (SUCRA values = 96.2). Regarding PONV incidence, intervention with dexmedetomidine or flurbiprofen plus dexmedetomidine resulted in a lower incidence than placebo, with dexmedetomidine showing the best result (SUCRA values = 90.3). Conclusion: Amantadine was identified as the best in controlling postoperative pain intensity and non-inferior to placebo in the incidence of PONV. Dexmedetomidine was the only intervention that outperformed placebo in all indicators. Clinical Trial Registration: https://www.crd.york.ac. uk/prospero/display_record.php?, CRD42021225361.

Perioperative opioids: a narrative review contextualising new avenues to improve prescribing

Opioids have dominated the management of perioperative pain in recent decades with higher doses than ever before used in some circumstances. Through the expanding use of opioids, growing research has highlighted their associated side-effects and the intertwined phenomena of acute withdrawal syndrome, opioid tolerance, and opioid-induced hyperalgesia. With multiple clinical guidelines now endorsing multimodal analgesia, a diverse array of opioid-sparing agents emerges and has been studied to variable degrees, including techniques of opioid-free anaesthesia. It remains unclear to what extent such methods should be adopted, yet current evidence does suggest dependence on opioids as the primary perioperative analgesic might not meet the principles of 'rational prescribing' as described by Maxwell. In this narrative review we describe how, using current evidence, a patient-centred rational-prescribing approach can be applied to opioids in the perioperative period. To contextualise this approach, we discuss the historical adoption of opioids in anaesthesia, our growing understanding of associated side-effects and emerging strategies of opioid-sparing and opioid-free anaesthesia. We discuss avenues and challenges for improving opioid prescribing to limit persistent postoperative opioid use and how these may be incorporated into a rational-prescribing approach.

Remifentanil does not affect human microglial immune activation in response to pro-inflammatory cytokines

Remifentanil is a potent ultra-short acting μ-opioid analgesic drug, frequently used in anaesthesia due to its favorable pharmacodynamic and pharmacokinetic profile. It may be associated with the occurrence of hyperalgesia. Preclinical studies suggest a potential role of microglia, although the molecular mechanisms have not been fully elucidated. Considering the role of microglia in brain inflammation and the relevant differences among species, the effects of remifentanil were studied on the human microglial C20 cells. The drug was tested at clinically relevant concentrations under basal and inflammatory conditions. In the C20 cells, the expression and secretion of interleukin 6, interleukin 8 and the monocyte chemotactic protein 1 were rapidly induced by a mixture of pro-inflammatory cytokines. This stimulatory effect was sustained up to 24 h. Remifentanil did not exert any toxic effect nor modify the production of these inflammatory mediators, thus suggesting the lack of direct immune modulatory actions on human microglia.

Comparison of Single Target-Controlled Infusion Pump-Delivered Mixed Propofol and Remifentanil with Two Target-Controlled Infusion Pumps-Delivered Propofol and Remifentanil in Patients Undergoing Breast Cancer Surgery-A Prospective Study

Total intravenous anesthesia (TIVA) with remifentanil and propofol (RP) is considered to be an ideal type of general anesthesia (GA) for pediatric and adult patients undergoing medical procedures. However, delivery of an RP mixture by target-controlled infusion (TCI) for GA in surgical procedures has not been described. We investigated the merit of this approach for breast cancer surgery. Eighty-four patients (n = 42 per group) were randomly allocated to propofol and remifentanil either delivered by separate TCI pumps (S group) or in an RP mixture by a single TCI pump (M group). Dosages were adjusted based on the bispectral index (BIS) and the analgesia nociception index (ANI). The primary outcomes were adequate anesthesia (BIS 40-60 and ANI 50-70, respectively), acceptable hemodynamic fluctuations (<30% of baseline) with less frequent TCI pump adjustments, bolus injections of anesthetics, and total consumption of anesthetics during the procedure. The secondary endpoints included time of emergence from anesthesia, patient satisfaction, postoperative pain, rescue with opioids, and adverse events. The characteristics of patients, hemodynamic parameters, BIS and ANI scores, duration of surgery, anesthesia, and emergence were not significantly different between groups. The adjustment frequency of TCI was significantly higher in the S group (3 (range 0-6) vs. 2 (0-6) times; p = 0.005). The total dosage of anesthetics, pain rating, patient satisfaction, need for opioids postoperatively, and incidence of adverse events were not significantly different. We have demonstrated that this RP mixture provided adequate hypnotic and analgesic effects under BIS and ANI monitoring in patients undergoing breast cancer surgery within 1 h.

Pharmacological Interventions for Opioid-Induced Hyperalgesia: A Scoping Review of Preclinical Trials

BACKGROUND

Opioid analgesics are the most effective pharmacological agents for moderate and severe pain. However, opioid use has several limitations such as opioid-induced hyperalgesia (OIH), which refers to the increased pain sensitivity that occurs once analgesia wears off after opioid administration. Several pharmacological interventions have been suggested for OIH, but the current literature does not provide guidelines on which interventions are the most effective and whether they differ depending on the opioid that induces hyperalgesia. This scoping review aimed to identify and describe all the preclinical trials investigating pharmacological interventions for OIH caused by remifentanil, fentanyl, or morphine as the first step towards evaluating whether the most effective OIH interventions are different for different opioids.

METHODS

Electronic database searches were carried out in Embase, PubMed, and Web of Science. Detailed data extraction was conducted on the eligible trials.

RESULTS

72 trials were eligible for the review. Of these, 27 trials investigated remifentanil, 14 trials investigated fentanyl, and 31 trials investigated morphine. A total of 82 interventions were identified. The most studied interventions were ketamine (eight trials) and gabapentin (four trials). The majority of the interventions were studied in only one trial. The most common mechanism suggested for the interventions was inhibition of N-methyl-D-aspartate (NMDA) receptors.

CONCLUSION

This scoping review identified plenty of preclinical trials investigating pharmacological interventions for OIH. Using the current literature, it is not possible to directly compare the effectiveness of the interventions. Hence, to identify the most effective interventions for each opioid, the interventions must be indirectly compared in a meta-analysis.

Opioid-induced analgesia among persons with opioid use disorder receiving methadone or buprenorphine: A systematic review of experimental pain studies

BACKGROUND

Treating acute pain among persons with opioid use disorder (OUD) on opioid agonist therapy (OAT) is complex, and the therapeutic benefits of opioids remain unclear when weighted against their abuse potential and respiratory depressant effects.

METHODS

We conducted a systematic review of experimental pain studies examining opioid-induced analgesia among persons with OUD on OAT. We searched multiple databases from inception to July 30, 2021. Study quality was assessed by previously established validity measures.

RESULTS

Nine studies were identified, with a total of 225 participants, of whom 63% were male, and 37% were female. Six studies included methadone-maintained persons with OUD; four studies included buprenorphine-maintained persons with OUD; and three studies included healthy persons as comparison groups. Either additional doses of OAT or other opioids - morphine, oxycodone, hydromorphone, or remifentanil - were administered. In seven studies, persons with OUD on OAT did not experience analgesia, despite receiving opioid doses up to 20 times greater than those clinically used to treat severe pain among the opioid naïve. Conversely, in two studies, high-potency opioids did produce analgesia, albeit with greater abuse potential. Notably, persons with OUD on OAT remained vulnerable to respiratory depression.

CONCLUSIONS

Although persons with OUD on OAT can derive analgesic effects from opioids, high-potency compounds may be required to achieve clinically significant pain relief. Further, persons with OUD on OAT may remain vulnerable to opioid-induced abuse potential and respiratory depression. Together, these finding have clinical, methodological, and mechanistic implications for the treatment of acute pain in the context of OAT.

Store-Operated Calcium Channels Contribute to Remifentanil-Induced Postoperative Hyperalgesia via Phosphorylation of CaMKIIα in Rats

Purpose

The mechanisms of remifentanil-induced postoperative hyperalgesia (RIPH) remain unclear. Store-operated calcium channels (SOCCs) are mainly comprised of stromal interaction molecules 1 (STIM1) and pore-forming subunits (Orai1). They were found to take a pivotal part in Ca²⁺-dependent procedures and involved in the development of central sensitization and pain. Ca²⁺/calmodulin-dependent protein kinase IIα (CaMKIIα), regulated by Ca²⁺/calmodulin complex, has been shown to have a crucial role in RIPH. This study aims to determine whether SOCCs contribute to RIPH via activating CaMKIIα.

Materials and Methods

Intra-operative infusion of remifentanil (1.0 µg kg⁻¹ min⁻¹, 60 min) was used to establish a RIPH rat model. The SOCCs blocker (YM-58483) was applied intrathecally to confirm the results. Animal behavioral tests including paw withdrawal thermal latency (PWTL) and paw withdrawal mechanical threshold (PWMT) were performed at −24, 2, 6, 24, 48 h after incision and remifentanil treatments. The protein expression of STIM1, Orai1, CaMKIIα, and p-CaMKIIα was assayed with Western blot, and the number of STIM1 and Orai1 positive cells was shown by immunofluorescence.

Results

Remifentanil administration significantly induced postoperative mechanical and thermal hyperalgesia, as well as increased STIM1 and Orai1 protein expression in the spinal dorsal horn. Furthermore, the intrathecal administration of YM-58483 effectively alleviated remifentanil-induced postoperative mechanical and thermal hyperalgesia according to the behavioral tests. In addition, YM-58483 suppressed the phosphorylation of CaMKIIα but had no effect on the expression of STIM1 and Orai1.

Conclusion

Our study demonstrated that SOCCs are involved in RIPH. The over-expressed STIM1 and Orai1 in the spinal cord contribute to RIPH via mediating the phosphorylation of CaMKIIα. Blockade of SOCCs may provide an effective therapeutic approach for RIPH.

Postoperative Drip-Infusion of Remifentanil Reduces Postoperative Pain-A Retrospective Observative Study

Development of remifentanil-induced hyperalgesia (RIH) postoperatively is an unpleasant experience that requires further treatment. This study assessed the effects of gradual withdrawal combined with drip infusion of remifentanil on postoperative pain and the requirement for rescue analgesics. A total of 559 patients receiving total intravenous anesthesia with propofol and remifentanil were enrolled. All patients either underwent gradual withdrawal of remifentanil (GWR) or gradual withdrawal combined with drip infusion (GWDR) with a dose of 1 mcg·kg⁻¹ for 30 min after extubation. The numeric rating scale (NRS) and the requirement of rescue analgesics were assessed. The requirement for rescue analgesics was significantly lower in the GWDR group than in the GWR group (13.2% vs. 35.7%; p < 0.001). At the post-anesthetic care unit (PACU), patients in the GWDR group had a lower NRS pain score (p < 0.001). In addition, in the postoperative 2nd hour, patients in the GWDR group had a significantly lower NRS than the GWR group (beta, −0.31; p = 0.003). No remifentanil-related adverse effects were observed. We found that gradual withdrawal combined with drip infusion of remifentanil required less rescue analgesics and reduced pain scores. The new way of remifentanil administration may be effective to prevent RIH.

Mechanisms, diagnosis, prevention and management of perioperative opioid-induced hyperalgesia

Opioid-induced hyperalgesia (OIH) occurs when opioids paradoxically enhance the pain they are prescribed to ameliorate. To address a lack of perioperative awareness, we present an educational review of clinically relevant aspects of the disorder. Although the mechanisms of OIH are thought to primarily involve medullary descending pathways, it is likely multifactorial with several relevant therapeutic targets. We provide a suggested clinical definition and directions for clinical differentiation of OIH from other diagnoses, as this may be confusing but is germane to appropriate management. Finally, we discuss prevention including patient education and analgesic management choices. As prevention may serve as the best treatment, patient risk factors, opioid mitigation, and both pharmacologic and non-pharmacologic strategies are discussed.

Safety and Efficacy of Ultrasound-Guided Retrolaminar Block of Multiple Injections in Retroperitoneal Laparoscopic Nephrectomy: A Prospective Randomized Controlled Study

Purpose

Ultrasound-guided retrolaminar block (RLB) has the potential to provide postoperative analgesia in retroperitoneal laparoscopic surgery. This study was conducted to evaluate the effects of RLB when compared with local infiltration analgesia (LIA) in retroperitoneal laparoscopic nephrectomy.

Patients and Methods

One hundred and fifteen patients scheduled for laparoscopic nephrectomy were divided into two groups: the RLB group (n = 57) received an ultrasound-guided RLB, while the LIA group (n = 58) received LIA. At 2, 4, 6, 24, and 48 hours after operation, the maximal visual analog score (VAS), sufentanil and rescue analgesia consumption, and the utilization of patient-controlled intravenous analgesia (PCIA) were assessed. The incidence rates of postoperative nausea and vomiting (PONV); time of leaving bed (at the first instance); and the levels of plasma β-Endorphin (β-EP), Interleukin-1β (IL-1β), and prostaglandin E2 (PEG2) 30 min after extubation were noted.

Results

Patients in the RLB group had significantly lower VAS scores; lower sufentanil cumulative consumption; lower manual addition frequency of PCIA; lower proportion of using rescue analgesia within 48 hours after operation; lower incidence rate of PONV; shorter resuscitation times; earlier time of leaving the bed; and lower β-EP, IL-1 β, and PEG2 levels.

Conclusion

Ultrasound-guided RLB of multiple injections is both safe and controllable for postoperative analgesia after retroperitoneal laparoscopic nephrectomy. When compared with LIA, RLB has better and longer-lasting analgesic effect, lower incidence rates of PONV, and the potential to reduce the level of postoperative inflammatory factors.

Trial Registration

China Clinical Trials Registration Center (http://www.chictr.org.cn, No. ChiCTR1800017526, Date of registration: 2018-08-02).

Procedure-specific and patient-specific pain management for ambulatory surgery with emphasis on the opioid crisis

PURPOSE OF REVIEW

Postoperative pain is frequent while, on the other hand, there is a grooving general concern on using effective opioid pain killers in view of the opioid crisis and significant incidence of opioid abuse. The present review aims at describing nonopioid measures in order to optimize and tailor perioperative pain management in ambulatory surgery.

RECENT FINDINGS

Postoperative pain should be addressed both preoperatively, intraoperatively and postoperatively. The management should basically be multimodal, nonopioid and procedure-specific. Opioids should only be used when needed on top of multimodal nonopioid prophylaxis, and then limited to a few days at maximum, unless strict control is applied. The individual patient should be screened preoperatively for any risk factors for severe postoperative pain and/or any abuse potential.

SUMMARY

Basic multimodal analgesia should start preoperatively or peroperatively and include paracetamol, cyclo-oxygenase (COX)-2 specific inhibitor or conventional nonsteroidal anti-inflammatory drug (NSAID) and in most cases dexamethasone and local anaesthetic wound infiltration. If any of these basic analgesics are contraindicated or there is an extra risk of severe postoperative pain, further measures may be considered: nerve-blocks or interfascial plane blocks, gabapentinnoids, clonidine, intravenous lidocaine infusion or ketamine infusion. In the abuse-prone patient, a preferably nonopioid perioperative approach should be aimed at.

Opioid-Induced Hyperalgesia in the Nonsurgical Setting: A Systematic Review

BACKGROUND

Opioid-induced hyperalgesia (OIH) is a phenomenon that causes an increased pain sensitization and perception of pain to noxious stimuli secondary to opioid exposure. While this clinical effect has been described in the surgical setting, it is unclear if OIH occurs in the nonsurgical setting.

STUDY QUESTION

To review the available literature which evaluated OIH in nonsurgical settings.

DATA SOURCES

A comprehensive literature search was performed using PubMed (January 1946-July 2017) using a variety of keywords for OIH. This review included randomized controlled trials with objectives to identify OIH in the nonsurgical setting. The clinical outcomes of interest were identification of OIH, adverse events, and impact of OIH on opioid consumption.

RESULTS

The search identified 8 studies that fulfilled the criteria. Six studies enrolled healthy male volunteers, 1 study used chronic low-back patients, and another used heroin-dependent treatment-seeking adults. Studies used various opioids and dosages, including remifentanil, alfentanil, fentanyl, morphine, methadone, and buprenorphine. Three primary experimental pain induction models were used to evaluate for OIH. Measured outcomes included hyperalgesia area, pain threshold, and pain tolerance. All 5 studies that used the electrical stimulation model identified OIH as a significant outcome. However, only 2 of 5 studies using the cold pressor model and 1 of 3 studies using the heat pressor model identified OIH. None of the trials explored clinical outcomes, such as effects on opioid consumption.

CONCLUSIONS

Most included studies identified OIH as a significant outcome within the nonsurgical setting. However, due to conflicting conclusions and various limitations, the clinical impact of OIH could not be assessed. Clinicians should monitor for effects of OIH in the nonoperative setting because there is insufficient evidence from the available literature to conclude that OIH is consistently observed in this setting.

Determination of acute tolerance and hyperalgesia to remifentanil constant rate infusion in dogs undergoing sevoflurane anaesthesia

OBJECTIVE

To determine if acute opioid tolerance (AOT) or opioid-induced hyperalgesia (OIH) could develop and limit the remifentanil-induced reduction in the sevoflurane minimum alveolar concentration (MAC). The response to mechanical nociceptive threshold (MNT) was evaluated and related to OIH.

STUDY DESIGN

A crossover, randomized, experimental animal study.

ANIMALS

A total of nine Beagle dogs.

METHODS

The dogs were anaesthetized with sevoflurane in 50% oxygen. Baseline sevoflurane MAC was measured (MACb1). Remifentanil (0.3 μg kg^-1 minute^-1) or 0.9% saline constant rate infusion (CRI) was administered intravenously (IV). Sevoflurane MAC was determined 20 minutes after CRI was initiated (MACpostdrug1), 30 minutes after MACpostdrug1 determination (MACpostdrug2) and after 1 week (MACb2). The MNT was determined at baseline (before anaesthesia), 3 and 7 days after anaesthesia. An increase of MACpostdrug2 ≥0.25% compared to MACpostdrug1 was considered evidence of AOT. A decrease in MNT at 3 and 7 days or an increase in MACb2 or both with respect to MACb1 were considered evidence of OIH.

RESULTS

Remifentanil CRI reduced sevoflurane MACpostdrug1 by 43.7% with respect to MACb1. MACpostdrug2 was no different from MACpostdrug1 with the saline (p = 0.62) or remifentanil (p = 0.78) treatments. No significant differences were observed in the saline (p = 0.99) or remifentanil (p = 0.99) treatments between MACb1 and MACb2, or for MNT values between baseline, 3 and 7 days.

CONCLUSION AND CLINICAL RELEVANCE

In dogs, under the study conditions, remifentanil efficacy in reducing sevoflurane MAC did not diminish in the short term, suggesting remifentanil did not induce AOT. Hyperalgesia was not detected 3 or 7 days after the administration of remifentanil. Contrary to data from humans and rodents, development of AOT or OIH in dogs is not supported by the findings of this study.

Ketamine Enhances Visual Sensory Evoked Potential Long-term Potentiation in Patients With Major Depressive Disorder

BACKGROUND

The rapid-acting clinical effects of ketamine as a novel treatment for depression along with its complex pharmacology have made it a growing research area. One of the key mechanistic hypotheses for how ketamine works to alleviate depression is by enhancing long-term potentiation (LTP)-mediated neural plasticity.

METHODS

The objective of this study was to investigate the plasticity hypothesis in 30 patients with depression noninvasively using visual LTP as an index of neural plasticity. In a double-blind, active placebo-controlled crossover trial, electroencephalography-based LTP was recorded approximately 3 to 4 hours following a single 0.44-mg/kg intravenous dose of ketamine or active placebo (1.7 ng/mL remifentanil) in 30 patients. Montgomery-Åsberg Depression Rating Scale scores were used to measure clinical symptoms. Visual LTP was measured as a change in the visually evoked potential following high-frequency visual stimulation. Dynamic causal modeling investigated the underlying neural architecture of visual LTP and the contribution of ketamine.

RESULTS

Montgomery-Åsberg Depression Rating Scale scores revealed that 70% of participants experienced 50% or greater reduction in their depression symptoms within 1 day of receiving ketamine. LTP was demonstrated in the N1 (p = .00002) and P2 (p = 2.31 × 10^-11) visually evoked components. Ketamine specifically enhanced P2 potentiation compared with placebo (p = .017). Dynamic causal modeling replicated the recruitment of forward and intrinsic connections for visual LTP and showed complementary effects of ketamine indicative of downstream and proplasticity modulation.

CONCLUSIONS

This study provides evidence that LTP-based neural plasticity increases within the time frame of the antidepressant effects of ketamine in humans and supports the hypothesis that changes to neural plasticity may be key to the antidepressant properties of ketamine.

Effects of propofol combined with remifentanil anesthesia on the NO, endothelin and inflammatory cytokines in the plasma of patients with liver cirrhosis during the perioperative period

The effects of propofol combined with remifentanil on the nitric oxide (NO), endothelin (ET-1) and inflammatory cytokines in the plasma of patients with liver cirrhosis were investigated. A retrospective analysis of 68 patients with liver cirrhosis who underwent hepatectomy in the Hunan Provincial People's Hospital from March 2016 to July 2018 was made. According to different anesthesia methods, 30 patients anesthetized with propofol were enrolled into Group A. The other 38 patients anesthetized with propofol combined with remifentanil were enrolled into Group B, and the operation time, amount of bleeding during operation and postoperative awake time of the two groups were recorded. At three separate time-points T₁ (30 min before the anesthesia), T₂ (after the portal triad clamping), T₃ (3 days after the operation), aspartate transaminase (AST) and alanine transaminase (ALT) levels in the plasma were measured by rate method, and the levels of NO, ET-1, interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF-α) in plasma were detected by enzyme-linked immunosorbent assay (ELISA). The plasma NO levels at the T₂ time-point were significantly lower than those at the T₁ and T₃ time-points (P<0.05); at the T₂ time-point, the concentrations of AST, ALT, ET-1, IL-6 and TNF-α in the plasma in Group A were significantly higher than those of Group B (P<0.05), while the levels of plasma NO in Group A were the opposite (P<0.05). The anesthesia of propofol combined with remifentanil could contribute to the balance of NO/ET-1 and the inhibition of inflammatory factors during the hepatectomy operation in patients with liver cirrhosis, and help to protect the liver function of patients, reducing the incidence of liver ischemia-reperfusion injury in patients.

Gradual withdrawal of remifentanil delays initial post-operative analgesic demand after thyroid surgery; double-blinded, randomized controlled trial

Background

Mismanagement of remifentanil leads to severe side effects such as opioid-induced tolerance and hyperalgesia. Recently studies revealed an alternative withdrawal method to limit these side effects. A gradual withdrawal of remifentanil seems to be associated with less pain. The hypothesis of this double-blinded, randomized controlled trial was that a gradual withdrawal of remifentanil would be associated with less immediate post-operative pain compared to after an abrupt discontinuation of remifentanil in patients who underwent thyroid surgery.

Methods

This double-blinded, randomized controlled trial was conducted in a tertiary level hospital in Brussels (Belgium) from April until August 2017. 34 patients undergoing thyroid surgery were randomized and 29 patients completed the study. After randomization, patients undergoing thyroid surgery were allocated to two groups: one with an abrupt discontinuation of remifentanil after surgery and one with a gradual withdrawal of remifentanil after surgery. The primary outcome was the initial post-operative demand of analgesic medication.

Results

Gradual withdrawal of remifentanil was associated with a delayed initial post-operative demand of analgesic medication (P = 0.006). The first morphine bolus was given after 76.3 +/− 89.0 min in the group with a gradual withdrawal of remifentanil versus after 9.0 +/− 13.5 min in the group with an abrupt discontinuation of remifentanil.

However, overall morphine consumption, numeric rating scale scores, Ramsay Sedation Scale scores, and quality of recovery scores (QoR-40) were similar in both groups (P > 0.05).

Conclusion

Though overall morphine consumption, numeric rating scale scores, Ramsay Sedation Scale scores, and quality of recovery scores (QoR-40) are not altered, a gradual withdrawal of remifentanil after thyroid surgery is safe and associated with a delayed initial post-operative demand of analgesic drugs. The withdrawal process does, however, require vigilance and training.

Trial registration

Clinicaltrials.gov NCT03110653 (PI: Luc Barvais; date of registration: 03/31/2017).

Perioperative opioid analgesia-when is enough too much? A review of opioid-induced tolerance and hyperalgesia

Opioids are a mainstay of acute pain management but can have many adverse effects, contributing to problematic long-term use. Opioid tolerance (increased dose needed for analgesia) and opioid-induced hyperalgesia (paradoxical increase in pain with opioid administration) can contribute to both poorly controlled pain and dose escalation. Hyperalgesia is particularly problematic as further opioid prescribing is largely futile. The mechanisms of opioid tolerance and hyperalgesia are complex, involving μ opioid receptor signalling pathways that offer opportunities for novel analgesic alternatives. The intracellular scaffold protein β-arrestin-2 is implicated in tolerance, hyperalgesia, and other opioid side-effects. Development of agonists biased against recruitment of β-arrestin-2 could provide analgesic efficacy with fewer side-effects. Alternative approaches include inhibition of peripheral μ opioid receptors and blockade of downstream signalling mechanisms, such as the non-receptor tyrosine kinase Src or N-methyl-D-aspartate receptors. Furthermore, it is prudent to use multimodal analgesic regimens to reduce reliance on opioids during the perioperative period. In the third paper in this Series we focus on clinical and mechanism-based understanding of tolerance and opioid-induced hyperalgesia, and discuss current and future strategies for pain management.

Immediate extubation after heart transplantation in a child by remifentanil-based ultra-fast anesthesia: A case report

RATIONALE

Ventilator-associated complications comprise important fatal aetiologies during heart transplantation. Ultra-fast anesthesia might provide the most effective measure to prevent this type of complication. Immediate extubation after heart transplantation (IEAHT) has recently been reported in adult patients. However, IEAHT in children is much more challenging due to limitations in anesthesia protocols. Recently, we managed to perform an ultra-fast anesthesia protocol combined with IEAHT during a heart transplant operation in a child, who had an excellent postoperative outcome.

PATIENT CONCERNS

A 13-year-old girl had been diagnosed with dilated cardiomyopathy 5 years before this case, due to intractable dyspnoea and cough. She received multiple medical treatments after diagnosis, with minimal effects. Physical examination findings included a bulge in her left chest and pitting edema over both legs. Moist rales could be heard in the lung. Echocardiography revealed very large heart chambers, with an ejection fraction of 17%.

DIAGNOSIS

The patient was diagnosed with dilated cardiomyopathy and scheduled to undergo an emergent operation for heart transplantation.

INTERVENTIONS

The patient underwent an ultra-fast anesthesia protocol and ultra-fast reversal during heart transplantation. General anesthesia was induced with etomidate, fentanyl, and vecuronium; it was then maintained with remifentanil-based total intravenous anesthesia.

OUTCOMES

Immediately after the end of the operation, the patient was brought to consciousness with stable breathing and haemodynamics. The patient was successfully extubated on the operating table and transferred to the intensive care unit with spontaneous breathing, without postoperative mechanical ventilation. The recovery period was uneventful and the patient was discharged 1 month later without complications.

LESSONS

Our experience, in this case, revealed that IEAHT in children is achievable if the ultra-fast protocol is performed properly and carefully, in order to prevent ventilator-associated complications.

New concepts in opioid analgesia

INTRODUCTION

Opioids are the oldest and most potent drugs for the treatment of severe pain, but they are burdened by detrimental side effects such as respiratory depression, addiction, sedation, nausea, and constipation. Their clinical application is undisputed in acute (e.g. perioperative) and cancer pain, but their long-term use in chronic pain has met increasing scrutiny and has contributed to the current 'opioid crisis.'

AREAS COVERED

This article reviews pharmacological principles and research strategies aiming at novel opioids with reduced side effects. Basic mechanisms underlying pain, opioid analgesia, and other opioid actions are outlined. To illustrate the clinical situation and medical needs, plasticity of opioid receptors, intracellular signaling pathways, endogenous and exogenous opioid receptor ligands, central and peripheral sites of analgesic, and side effects are discussed.

EXPERT OPINION

The epidemic of opioid misuse has taught us that there is a lack of fundamental knowledge about the characteristics and management of chronic pain, that conflicts of interest and validity of models must be considered in the context of drug development, and that novel analgesics with less abuse liability are badly needed. Currently, the most promising perspectives appear to be augmenting endogenous opioid actions and selectively targeting pathological conformations of peripheral opioid receptors.

The influence of dexmedetomidine on remifentanil-induced hyperalgesia and the sex differences

In the clinical settings, patients often develop opioid-induced hyperalgesia (OIH) after utilization of high dose intra-operative remifentanil. Systemic α2 agonists, including dexmedetomidine, are believed to reduce pain and opioid requirements after surgery, thus decreasing the incidence of hyperalgesia. The present study aimed to investigate the effect of dexmedetomidine on remifentanil-induced hyperalgesia and explored the sex differences. A total of 48 patients (24 male, 24 female) with an American Society of Anesthesiologists physical status of I-II that were undergoing thyroidectomy were randomly assigned to one of the following six groups: Male controlled group (MC) and female controlled group (FC) (group MC, n=8 and group FC, n=8), which received a preoperative placebo of 0.2 µg.kg^-1 normal saline and intraoperative remifentanil 0.2 µg.kg^-1.min^-1; male and female group with low-dose dexmedetomidine (group MD1, n=8 and group FD1, n=8), which received preoperative dexmedetomidine 0.2 µg.kg^-1 and intraoperative remifentanil 0.2 µg.kg^-1.min^-1; and male and female groups with high-dose dexmedetomidine (group MD2, n=8 and group FD2, n=8), which received dexmedetomidine 0.6 µg.kg^-1 and intraoperative remifentanil 0.2 µg.kg^-1.min^-1. Result indicated that the visual analog scale (VAS) scores and morphine dosing frequency were significantly higher in MC and FC groups compared with the other same sex groups. Furthermore, the mechanical hyperalgesia threshold and patients' analgesia satisfaction score after surgery were significantly lower in MC and FC groups. Notably, the frequency of post-operative chills, nausea and vomiting were significantly lower in groups MD1, MD2, FD1 and FD2. The present findings indicated that low- and high-dose dexmedetomidine injection significantly decreased the patient's risk of enhanced pain intensity and increased postoperative morphine dosing caused by remifentanil-induced hyperalgesia. These findings suggest that the influence of dexmedetomidine displayed minimal significant differences between sex. Trial registration no., IRB2018-YX-001 (Name of registry: Institutional Medical Ethics Committee of Tianjin Medical University General Hospital; date of registration: February 1, 2016).

The increased release of amino acid neurotransmitters of the primary somatosensory cortical area in rats contributes to remifentanil-induced hyperalgesia and its inhibition by lidocaine

Background

Studies have confirmed that activation of the neurons of primary somatosensory cortex (S1) is involved in the process of remifentanil (Remi)-induced hyperalgesia (RIH), which can be suppressed by lidocaine (Lido). A total intravenous anesthesia model of rats mimicking clinical Remi-based anesthesia was set up to explore the release of amino acid neurotransmitters of S1 cortex in RIH and its inhibition by Lido in this study.

Materials and methods

Sprague Dawley rats were randomly divided into the following four groups: propofol (Pro), Remi, Remi combined Lido, and Lido groups. Mechanical hyperalgesia was evaluated by von Frey test; the amino acid neurotransmitters in the microdialysates of S1 area were detected by high-performance liquid chromatography (HPLC)-fluorescence, and conventional protein kinase C (cPKC)γ levels in the whole-cell lysates and membrane lipid rafts (MLRs) were determined by Western blotting.

Results

The von Frey test showed that co-administration of Lido significantly inhibited a Remi-induced decrease in the threshold of the paw withdrawal response in Remi group at 2 h postinfusion. Meanwhile, the Remi-induced increases in both the excitatory and inhibitory amino acid releases in S1 were suppressed by co-administrating Lido within 5 h postinfusion. Western blotting showed that the increased cPKCγ level in the membrane lipid rafts (MLR) induced by Remi was also inhibited by Lido.

Conclusion

The increased release of amino acid neurotransmitters and the translocation of cPKCγ in MLR suggest the activation of S1 neurons, which may be one of the mechanisms underlying RIH. Lido reduces the release of amino acid neurotransmitters in S1 neurons and the translocation of cPKCγ in MLRs after stopping Remi, which may be one of its antihyperalgesic mechanisms.

Opioid-induced hyperalgesia in clinical anesthesia practice: what has remained from theoretical concepts and experimental studies?

PURPOSE OF REVIEW

This article reviews the phenomenon of opioid-induced hyperalgesia (OIH) and its implications for clinical anesthesia. The goal of this review is to give an update on perioperative prevention and treatment strategies, based on findings in preclinical and clinical research.

RECENT FINDINGS

Several systems have been suggested to be involved in the pathophysiology of OIH with a focus on the glutaminergic system. Very recently preclinical data revealed that peripheral μ-opioid receptors (MORs) are key players in the development of OIH and acute opioid tolerance (AOT). Peripheral MOR antagonists could, thus, become a new prevention/treatment option of OIH in the perioperative setting. Although the impact of OIH on postoperative pain seems to be moderate, recent evidence suggests that increased hyperalgesia following opioid treatment correlates with the risk of developing persistent pain after surgery. In clinical practice, distinction among OIH, AOT and acute opioid withdrawal remains difficult, especially because a specific quantitative sensory test to diagnose OIH has not been validated yet.

SUMMARY

Since the immediate postoperative period is not ideal to initiate long-term treatment for OIH, the best strategy is to prevent its occurrence. A multimodal approach, including choice of opioid, dose limitations and addition of nonopioid analgesics, is recommended.

Remifentanil-induced postoperative hyperalgesia: current perspectives on mechanisms and therapeutic strategies

The use of remifentanil in clinical practice offers several advantages and it is used for a wide range of procedures, ranging from day-surgery anesthesia to more complex procedures. Nonetheless, remifentanil has been consistently linked with development of opioid-induced hyperalgesia (OIH), which is described as a paradoxical increase in sensitivity to painful stimuli that develops after exposure to opioid treatment. The development of OIH may cause several issues, delaying recovery after surgery and preventing timely patient's discharge. Moreover, it causes patient's discomfort with higher pain scores, greater use of analgesics, and associated side effects. Remifentanil is the opioid most convincingly associated with OIH, and hereby we provide a review of remifentanil-induced hyperalgesia, describing both the underlying mechanisms involved and the available studies investigating experimental and clinical pharmacologic approaches aiming at reducing its incidence and degree.

Pharmacokinetics and -dynamics of intramuscular and intranasal naloxone: an explorative study in healthy volunteers

PURPOSE

This study aimed to develop a model for pharmacodynamic and pharmacokinetic studies of naloxone antagonism under steady-state opioid agonism and to compare a high-concentration/low-volume intranasal naloxone formulation 8 mg/ml to intramuscular 0.8 mg.

METHODS

Two-way crossover in 12 healthy volunteers receiving naloxone while receiving remifentanil by a target-controlled infusion for 102 min. The group were subdivided into three different doses of remifentanil. Blood samples for serum naloxone concentrations, pupillometry and heat pain threshold were measured.

RESULTS

The relative bioavailability of intranasal to intramuscular naloxone was 0.75. Pupillometry showed difference in antagonism; the effect was significant in the data set as a whole (p < 0.001) and in all three subgroups (p < 0.02-p < 0.001). Heat pain threshold showed no statistical difference.

CONCLUSIONS

A target-controlled infusion of remifentanil provides good conditions for studying the pharmacodynamics of naloxone, and pupillometry was a better modality than heat pain threshold. Intranasal naloxone 0.8 mg is inferior for a similar dose intramuscular. Our design may help to bridge the gap between studies in healthy volunteers and the patient population in need of naloxone for opioid overdose.

TRIAL REGISTRATION

clinicaltrials.gov : NCT02307721.

Intraoperative neurophysiologic monitoring: utility and anesthetic implications

PURPOSE OF REVIEW

Intraoperative neurophysiologic monitoring (IONM) has been rapidly adopted as a standard monitoring technique for a growing number of surgical procedures. This article offers a basic review of IONM and discusses some of its latest applications and anesthetic techniques that optimize monitoring conditions.

RECENT FINDINGS

IONM has been demonstrated to alert the surgical team to potential injury and can also be used to detect impending positioning injuries. Upper extremity somatosensory evoked potential monitoring is particularly helpful in preventing ulnar neuropathy that is more common in patients who are positioned prone and with severe arm abduction. Somatosensory evoked potential monitoring has a high specificity for vascular compromise and neurologic ischemia that may occur during neurovascular procedures. Electroencephalography is also helpful in alerting the surgical and anesthesia teams to an impending ischemic event. Although a total intravenous anesthesia technique offers better monitoring conditions, propofol may prolong emergence.

SUMMARY

IONM is commonly used in a growing number and variety of surgical procedures, and has been shown to improve outcomes. IONM poses challenges for the anesthesiologist, but tailoring the anesthetic to be compatible with the monitoring techniques in use can help to prevent surgical complications.

Rationale for and approach to preoperative opioid weaning: a preoperative optimization protocol

The practice of chronic opioid prescription for chronic non-cancer pain has come under considerable scrutiny within the past several years as mounting evidence reveals a generally unfavorable risk to benefit ratio and the nation reels from the grim mortality statistics associated with the opioid epidemic. Patients struggling with chronic pain tend to use opioids and also seek out operative intervention for their complaints, which combination may be leading to increased postoperative "acute-on-chronic" pain and fueling worsened chronic pain and opioid dependence. Besides worsened postoperative pain, a growing body of literature, reviewed herein, indicates that preoperative opioid use is associated with significantly worsened surgical outcomes, and severely increased financial drain on an already severely overburdened healthcare budget. Conversely, there is evidence that preoperative opioid reduction may result in substantial improvements in outcome. In the era of accountable care, efforts such as the Enhanced Recovery After Surgery (ERAS) protocol have been introduced in an attempt to standardize and facilitate evidence-based perioperative interventions to optimize surgical outcomes. We propose that addressing preoperative opioid reduction as part of a targeted optimization approach for chronic pain patients seeking surgery is not only logical but mandatory given the stakes involved. Simple opioid reduction/abstinence however is not likely to occur in the absence of provision of viable and palatable alternatives to managing pain, which will require a strong focus upon reducing pain catastrophization and bolstering self-efficacy and resilience. In response to a call from our surgical community toward that end, we have developed a simple and easy-to-implement outpatient preoperative optimization program focusing on gentle opioid weaning/elimination as well as a few other high-yield areas of intervention, requiring a minimum of resources.

Pharmacological sedation management in the paediatric intensive care unit

Objective

This review addresses sedation management on paediatric intensive care units and possible gaps in the knowledge of optimal sedation strategies. We present an overview of the commonly used sedatives and their pharmacokinetic and pharmacodynamic considerations in children, as well as the ongoing studies in this field. Also, sedation guidelines and current sedation strategies and assessment methods are addressed.

Key findings

This review shows that evidence and pharmacokinetic data are scarce, but fortunately, there is an active research scene with promising new PK and PD data of sedatives in children using new study designs with application of advanced laboratory methods and modelling. The lack of evidence is increasingly being recognized by authorities and legislative offices such as the US Food and Drug Administration (FDA) and European Medicines Agency (EMA).

Conclusion

The population in question is very heterogeneous and this overview can aid clinicians and researchers in moving from practice-based sedation management towards more evidence- or model-based practice. Still, paediatric sedation management can be improved in other ways than pharmacology only, so future research should aim on sedation assessment and implementation strategies of protocolized sedation as well.