Relationship between intraoperative requirement for anesthetics and postoperative analgesic consumption in laparoscopic colectomy: a randomized controlled double-blinded study

BACKGROUND

This study investigated the relationship between intraoperative requirement for an inhalational anesthetic (sevoflurane) or an opioid (remifentanil) and postoperative analgesic consumption.

METHODS

The study included 200 adult patients undergoing elective laparoscopic colectomy. In the sevoflurane group, the effect-site concentration of remifentanil was fixed at 1.0 ng/ml, while the inspiratory sevoflurane concentration was adjusted to maintain an appropriate anesthetic depth. In the remifentanil group, the end-expiratory sevoflurane concentration was fixed at 1.0 vol.%, and the remifentanil concentration was adjusted. Pain scores and cumulative postoperative analgesic consumptions were evaluated at 2, 6, 24, and 48 h after surgery.

RESULTS

Average end-tidal concentration of sevoflurane and effect-site concentration of remifentanil were 2.0 ± 0.4 vol.% and 3.9 ± 1.4 ng/ml in the sevoflurane and remifentanil groups, respectively. Cumulative postoperative analgesic consumption at 48 h postoperatively was 55 ± 26 ml in the sevoflurane group and 57 ± 33 ml in the remifentanil group. In the remifentanil group, the postoperative cumulative analgesic consumptions at 2 and 6 h were positively correlated with intraoperative remifentanil requirements (2 h: r = 0.36, P < 0.001; 6 h: r = 0.38, P < 0.001). However, there was no significant correlation in the sevoflurane group (r = 0.04, P = 0.691).

CONCLUSIONS

The amount of intraoperative requirement of short acting opioid, remifentanil, is correlated with postoperative analgesic consumption within postoperative 6 h. It may be contributed by the development of acute opioid tolerance. However, intraoperative sevoflurane requirement had no effect on postoperative analgesic consumption.

NLRs and inflammasome signaling in opioid-induced hyperalgesia and tolerance

We investigated the role that innate immunological signaling pathways, principally nod-like receptors (NLRs) and inflammasomes, in the manifestation of the contradictory outcomes associated with opioids, namely hyperalgesia, and tolerance. The utilization of opioids for pain management is prevalent; nonetheless, it frequently leads to an increased sensitivity to pain (hyperalgesia) and reduced efficacy of the medication (tolerance) over an extended period. This, therefore, represents a major challenge in the area of chronic pain treatment. Recent studies indicate that the aforementioned negative consequences are partially influenced by the stimulation of NLRs, specifically the NLRP3 inflammasome, and the subsequent assembly of the inflammasome. This process ultimately results in the generation of inflammatory cytokines and the occurrence of neuroinflammation and the pathogenesis of hyperalgesia. We also explored the putative downstream signaling cascades activated by NOD-like receptors (NLRs) and inflammasomes in response to opioid stimuli. Furthermore, we probed potential therapeutic targets for modifying opioid-induced hyperalgesia, with explicit emphasis on the activation of the NLRP3 inflammasome. Ultimately, our findings underscore the significance of conducting additional research in this area that includes an examination of the involvement of various NLRs, immune cells, and genetic variables in the development of opioid-induced hyperalgesia and tolerance. The present review provides substantial insight into the possible pathways contributing to the occurrence of hyperalgesia and tolerance in individuals taking opioids.

Opioids and opioid receptors; understanding pharmacological mechanisms as a key to therapeutic advances and mitigation of the misuse crisis

Opioids are a mainstay in acute pain management and produce their effects and side effects (e.g., tolerance, opioid-use disorder and immune suppression) by interaction with opioid receptors. I will discuss opioid pharmacology in some controversial areas of enquiry of anaesthetic relevance. The main opioid target is the µ (mu,MOP) receptor but other members of the opioid receptor family, δ (delta; DOP) and κ (kappa; KOP) opioid receptors also produce analgesic actions. These are naloxone-sensitive. There is important clinical development relating to the Nociceptin/Orphanin FQ (NOP) receptor, an opioid receptor that is not naloxone-sensitive. Better understanding of the drivers for opioid effects and side effects may facilitate separation of side effects and production of safer drugs. Opioids bind to the receptor orthosteric site to produce their effects and can engage monomer or homo-, heterodimer receptors. Some ligands can drive one intracellular pathway over another. This is the basis of biased agonism (or functional selectivity). Opioid actions at the orthosteric site can be modulated allosterically and positive allosteric modulators that enhance opioid action are in development. As well as targeting ligand-receptor interaction and transduction, modulating receptor expression and hence function is also tractable. There is evidence for epigenetic associations with different types of pain and also substance misuse. As long as the opioid narrative is defined by the 'opioid crisis' the drive to remove them could gather pace. This will deny use where they are effective, and access to morphine for pain relief in low income countries.

Balanced Opioid Prescribing via a Clinical Trade-Off: Pain Relief vs. Adverse Effects of Discomfort, Dependence, and Tolerance/Hypersensitivity

In the backdrop of the opioid epidemic, opioid prescribing has distinct medical and social challenges. Overprescribing contributes to the ongoing opioid epidemic, whereas underprescribing yields inadequate pain relief. Moreover, opioids have serious adverse effects including tolerance and increased sensitivity to pain, paradoxically inducing more pain. Prescribing trade-offs are recognized but not modeled in the literature. We study the prescribing decisions for chronic, acute, and persistent pain types to minimize the cumulative pain that incorporates opioid adverse effects (discomfort and dependence) and the risk of tolerance or hypersensitivity (THS) developed with opioid use. After finding closed-form solutions for each pain type, we analytically investigate the sensitivity of acute pain prescriptions and examine policies on incorporation of THS, patient handover, and adaptive treatments. Our analyses show that the role of adverse effects in prescribing decisions is as critical as that of the pain level. Interestingly, we find that the optimal prescription duration is not necessarily increasing with the recovery time. We show that not incorporating THS or information curtailment at patient handovers leads to overprescribing that can be mitigated by adaptive treatments. Last, using real-life pain and opioid use data from two sources, we estimate THS parameters and discuss the proximity of our model to clinical practice. This paper has a pain management framework that leads to tractable models. These models can potentially support balanced opioid prescribing after their validation in a clinical setting. Then, they can be helpful to policy makers in assessment of prescription policies and of the controversy around over- and underprescribing.

How to Manage Withdrawal of Sedation and Analgesia in Mechanically Ventilated COVID-19 Patients?

COVID-19 patients suffering from severe acute respiratory distress syndrome (ARDS) require mechanical ventilation (MV) for respiratory failure. To achieve these ventilatory goals, it has been observed that COVID-19 patients in particular require high regimens and prolonged use of sedatives, analgesics and neuromuscular blocking agents (NMBA). Withdrawal from analgo-sedation may induce a "drug withdrawal syndrome" (DWS), i.e., clinical symptoms of anxiety, tremor, agitation, hallucinations and vomiting, as a result of adrenergic activation and hyperalgesia. We describe the epidemiology, mechanisms leading to this syndrome and our strategies to prevent and treat it.

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.

A Preliminary Investigation of the Underlying Mechanism Associating Daily Sleep Continuity Disturbance and Prescription Opioid Use Among Individuals With Sickle Cell Disease

BACKGROUND

There are emerging data indicating that sleep disturbance may be linked with an increase in opioid use. The majority of sickle cell disease (SCD) patients experience sleep disturbances, which can elevate pain severity and pain catastrophizing, both of which are important predictors of opioid consumption.

PURPOSE

We conducted a preliminary investigation on the association between previous night sleep disturbance and short-acting opioid use, as well as the potential mediating roles of pain severity and pain catastrophizing. Because sex is associated with sleep disturbance, pain-related experiences, and opioid use, we also explored the potential moderating role of sex.

METHODS

Participants were 45 SCD patients who were prescribed opioids. For 3 months, sleep diaries were collected immediately upon participants' awakening. Daily pain severity, pain catastrophizing, and prescription opioid use measures were collected before bedtime.

RESULTS

Multilevel structural equation modeling revealed that wake time after sleep onset (WASO) during the previous night (Time 1) predicted greater short-acting opioid use during the next day (Time 2). Pain severity and pain catastrophizing measured during the next day (Time 2) also mediated the association between the two. Sex moderation analysis showed that the positive association between WASO and pain severity was largely driven by women.

CONCLUSION

These findings provide some preliminary evidence as to the mechanism linking sleep continuity disturbance and opioid requirement in SCD patients. Future studies should replicate and extend these findings with clearer temporal information and employing more refined measures of sleep continuity and prescription opioid use in a larger sample.

Effects of preoperative opioid education on postoperative opioid use and pain management in orthopaedics: A systematic review

Prescription opioid abuse after surgery is considered a crisis in the United States. The objective of this systematic review was to evaluate use and effectiveness of pre-operative education with respect to post-operative opioid use and management of pain in the orthopaedic setting. Electronic searches were conducted in Ovid/Medline and SCOPUS to identify articles that discuss pre-operative opioid education and its effects on post-operative pain scores and prescription fulfillment. Non-orthopaedic studies were included for comparison. Eleven studies met inclusion criteria, 3 of which were retrospective reviews of large (>1000) post-surgical cohorts, and 8 of which were randomized controlled studies that examined different approaches to opioid education. Best current evidence suggests that incidence of opioid abuse after surgery is 5.9-6.5% and that the internet is the main source of guidance for patients regarding postoperative pain management. Education specifically related to opioid use and pain can be effective in reducing opioid prescription requests and filling. In contrast, education related solely to postoperative expectations does not consistently impact post-operative pain scores and was associated with 44% of total joint arthroplasty patients stating the approach was unhelpful regarding their pain management. This systematic review suggests that it is most effective to give patients verbal information rather than only providing information in written form and that utilizing two forms of education is most effective. The current literature supports this multi-modal approach to preoperative opioid education preoperatively for reducing post-operative opioid use and severity of self-reported pain.

Prolonged Perioperative Use of Pregabalin and Ketamine to Prevent Persistent Pain after Cardiac Surgery

Editor’s Perspective

What We Already Know about This Topic

What This Article Tells Us That Is New

Background

Persistent postsurgical pain is common and affects quality of life. The hypothesis was that use of pregabalin and ketamine would prevent persistent pain after cardiac surgery.

Methods

This randomized, double-blind, placebo-controlled trial was undertaken at two cardiac surgery centers in the United Kingdom. Adults without chronic pain and undergoing any elective cardiac surgery patients via sternotomy were randomly assigned to receive either usual care, pregabalin (150 mg preoperatively and twice daily for 14 postoperative days) alone, or pregabalin in combination with a 48-h postoperative infusion of intravenous ketamine at 0.1 mg · kg−1 · h−1. The primary endpoints were prevalence of clinically significant pain at 3 and 6 months after surgery, defined as a pain score on the numeric rating scale of 4 or higher (out of 10) after a functional assessment of three maximal coughs. The secondary outcomes included acute pain, opioid use, and safety measures, as well as long-term neuropathic pain, analgesic requirement, and quality of life.

Results

In total, 150 patients were randomized, with 17 withdrawals from treatment and 2 losses to follow-up but with data analyzed for all participants on an intention-to-treat basis. The prevalence of pain was lower at 3 postoperative months for pregabalin alone (6% [3 of 50]) and in combination with ketamine (2% [1 of 50]) compared to the control group (34% [17 of 50]; odds ratio = 0.126 [0.022 to 0.5], P = 0.0008; and 0.041 [0.0009 to 0.28], P &lt; 0.0001, respectively) and at 6 months for pregabalin alone (6% [3 of 50]) and in combination with ketamine 0% (0 of 5) compared to the control group (28% [14 of 50]; odds ratio = 0.167 [0.029 to 0.7], P = 0.006; and 0.000 [0 to 0.24], P &lt; 0.0001). Diplopia was more common in both active arms.

Conclusions

Preoperative administration of 150 mg of pregabalin and postoperative continuation twice daily for 14 days significantly lowered the prevalence of persistent pain after cardiac surgery.

Clinical case of postoperative anesthesia of a patient by using subanesthetic dose of ketamine in severe abdominal pathology

Pain is an inevitable consequence of surgical interventions in children, resulting in great stress and discomfort not only for patients but also for their parents. The intensity of the pain depends not only on the level of injury after the operation, but also on the localization and the nature of the procedure. Management of pain in children is best done through a multimodal approach: opioids, auxiliary drugs such as nonsteroidal anti-inflammatory drugs (NSAIDs) and acetaminophen, anti-neuroleptics such as gabapentin, and regional anesthetic methods. Postoperative anesthesia in abdominal surgery at present is a topical problem in anesthetic practice. In this clinical case, we would like to demonstrate the experience of applying post-operative anesthesia using subnormal dosages of ketamine. The patient was given anesthesia with prolonged infusion of a ketamine solution in a submorbid dose of 0.2 mg/kg/h IV. An assessment of the quality of anesthesia by assessing the level of stress markers, such as blood glucose, cortisol levels, and the assessment of the pain level on the NIPS scale was performed. Conclusion: The use of a ketamine solution in a dose of 0.2 mg/kg/h has a positive effect on treating postoperative pain in patients after severe abdominal surgical interventions. Applying a ketamine solution in a dose of 0.2 mg/kg/h reduces tolerance of the patient to opioid analgesics and the development of hyperalgesia and allodynia.

Perioperative intravenous ketamine for acute postoperative pain in adults

BACKGROUND

Inadequate pain management after surgery increases the risk of postoperative complications and may predispose for chronic postsurgical pain. Perioperative ketamine may enhance conventional analgesics in the acute postoperative setting.

OBJECTIVES

To evaluate the efficacy and safety of perioperative intravenous ketamine in adult patients when used for the treatment or prevention of acute pain following general anaesthesia.

SEARCH METHODS

We searched CENTRAL, MEDLINE and Embase to July 2018 and three trials registers (metaRegister of controlled trials, ClinicalTrials.gov and the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP)) together with reference checking, citation searching and contact with study authors to identify additional studies.

SELECTION CRITERIA

We sought randomised, double-blind, controlled trials of adults undergoing surgery under general anaesthesia and being treated with perioperative intravenous ketamine. Studies compared ketamine with placebo, or compared ketamine plus a basic analgesic, such as morphine or non-steroidal anti-inflammatory drug (NSAID), with a basic analgesic alone.

DATA COLLECTION AND ANALYSIS

Two review authors searched for studies, extracted efficacy and adverse event data, examined issues of study quality and potential bias, and performed analyses. Primary outcomes were opioid consumption and pain intensity at rest and during movement at 24 and 48 hours postoperatively. Secondary outcomes were time to first analgesic request, assessment of postoperative hyperalgesia, central nervous system (CNS) adverse effects, and postoperative nausea and vomiting. We assessed the evidence using GRADE and created a 'Summary of findings' table.

MAIN RESULTS

We included 130 studies with 8341 participants. Ketamine was given to 4588 participants and 3753 participants served as controls. Types of surgery included ear, nose or throat surgery, wisdom tooth extraction, thoracotomy, lumbar fusion surgery, microdiscectomy, hip joint replacement surgery, knee joint replacement surgery, anterior cruciate ligament repair, knee arthroscopy, mastectomy, haemorrhoidectomy, abdominal surgery, radical prostatectomy, thyroid surgery, elective caesarean section, and laparoscopic surgery. Racemic ketamine bolus doses were predominantly 0.25 mg to 1 mg, and infusions 2 to 5 µg/kg/minute; 10 studies used only S-ketamine and one only R-ketamine. Risk of bias was generally low or uncertain, except for study size; most had fewer than 50 participants per treatment arm, resulting in high heterogeneity, as expected, for most analyses. We did not stratify the main analysis by type of surgery or any other factor, such as dose or timing of ketamine administration, and used a non-stratified analysis.Perioperative intravenous ketamine reduced postoperative opioid consumption over 24 hours by 8 mg morphine equivalents (95% CI 6 to 9; 19% from 42 mg consumed by participants given placebo, moderate-quality evidence; 65 studies, 4004 participants). Over 48 hours, opioid consumption was 13 mg lower (95% CI 10 to 15; 19% from 67 mg with placebo, moderate-quality evidence; 37 studies, 2449 participants).Perioperative intravenous ketamine reduced pain at rest at 24 hours by 5/100 mm on a visual analogue scale (95% CI 4 to 7; 19% lower from 26/100 mm with placebo, high-quality evidence; 82 studies, 5004 participants), and at 48 hours by 5/100 mm (95% CI 3 to 7; 22% lower from 23/100 mm, high-quality evidence; 49 studies, 2962 participants). Pain during movement was reduced at 24 hours (6/100 mm, 14% lower from 42/100 mm, moderate-quality evidence; 29 studies, 1806 participants), and 48 hours (6/100 mm, 16% lower from 37 mm, low-quality evidence; 23 studies, 1353 participants).Results for primary outcomes were consistent when analysed by pain at rest or on movement, operation type, and timing of administration, or sensitivity to study size and pain intensity. No analysis by dose was possible. There was no difference when nitrous oxide was used. We downgraded the quality of the evidence once if numbers of participants were large but small-study effects were present, or twice if numbers were small and small-study effects likely but testing not possible.Ketamine increased the time for the first postoperative analgesic request by 54 minutes (95% CI 37 to 71 minutes), from a mean of 39 minutes with placebo (moderate-quality evidence; 31 studies, 1678 participants). Ketamine reduced the area of postoperative hyperalgesia by 7 cm² (95% CI -11.9 to -2.2), compared with placebo (very low-quality evidence; 7 studies 333 participants). We downgraded the quality of evidence because of small-study effects or because the number of participants was below 400.CNS adverse events occurred in 52 studies, while 53 studies reported of absence of CNS adverse events. Overall, 187/3614 (5%) participants receiving ketamine and 122/2924 (4%) receiving control treatment experienced an adverse event (RR 1.2, 95% CI 0.95 to 1.4; high-quality evidence; 105 studies, 6538 participants). Ketamine reduced postoperative nausea and vomiting from 27% with placebo to 23% with ketamine (RR 0.88, 95% CI 0.81 to 0.96; the number needed to treat to prevent one episode of postoperative nausea and vomiting with perioperative intravenous ketamine administration was 24 (95% CI 16 to 54; high-quality evidence; 95 studies, 5965 participants).

AUTHORS' CONCLUSIONS

Perioperative intravenous ketamine probably reduces postoperative analgesic consumption and pain intensity. Results were consistent in different operation types or timing of ketamine administration, with larger and smaller studies, and by higher and lower pain intensity. CNS adverse events were little different with ketamine or control. Perioperative intravenous ketamine probably reduces postoperative nausea and vomiting by a small extent, of arguable clinical relevance.

Aminoguanidine Hydrazone Derivatives as Nonpeptide NPFF1 Receptor Antagonists Reverse Opioid Induced Hyperalgesia

Neuropeptide FF receptors (NPFF1R and NPFF2R) and their endogenous ligand neuropeptide FF have been shown previously to display antiopioid properties and to play a critical role in the adverse effects associated with chronic administrations of opiates including the development of opioid-induced hyperalgesia and analgesic tolerance. In this work, we sought to identify novel NPFF receptors ligands by focusing our interest in a series of heterocycles as rigidified nonpeptide NPFF receptor ligands, starting from already described aminoguanidine hydrazones (AGHs). Binding experiments and functional assays highlighted AGH 1n and its rigidified analogue 2-amino-dihydropyrimidine 22e for in vivo experiments. As shown earlier with the prototypical dipeptide antagonist RF9, both 1n and 22e reduced significantly the long lasting fentanyl-induced hyperalgesia in rodents. Altogether these data indicate that AGH rigidification maintains nanomolar affinities for both NPFF receptors, while improving antagonist character toward NPFF1R.

Evidence of opioid-induced hyperalgesia in clinical populations after chronic opioid exposure: a systematic review and meta-analysis

BACKGROUND

Opioid-induced hyperalgesia (OIH) is well documented in preclinical studies, but findings of clinical studies are less consistent. The objective was to undertake a systematic review and meta-analysis of studies examining evidence for OIH in humans after opioid exposure.

METHODS

Systematic electronic searches utilised six research databases (Embase, Medline, PubMed, CINAHL Plus, Web of Science, and OpenGrey). Manual 'grey' literature searches were also undertaken. The Population, Interventions, Comparators, Outcomes, and Study design (PICOS) framework was used to develop search strategies, and findings are reported in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) Statement. Data synthesis and subgroup analyses were undertaken using a random effects model (DerSimonian-Laird method).

RESULTS

A total of 6167 articles were identified. After abstract and full-text reviews, 26 articles (involving 2706 participants) were included in the review. There was evidence of OIH, assessed by pain tolerance, in response to noxious thermal (hot and cold) stimuli, but not electrical stimuli. There was no evidence of OIH when assessing pain detection thresholds. OIH was more evident in patients with opioid use disorder than in patients with pain, and in patient groups treated with N-methyl-d-aspartate receptor antagonists (primarily evidenced in methadone-maintained populations).

CONCLUSIONS

OIH was evident in patients after chronic opioid exposure, but findings were dependent upon pain modality and assessment measures. Further studies should consider evaluating both pain threshold and pain tolerance across a range of modalities to ensure assessment validity. Significant subgroup findings suggest that potential confounders of pain judgements, such as illicit substance use, affective characteristics, or coping styles, should be rigorously controlled in future studies.

Preoperative Reduction of Opioid Use Before Total Joint Arthroplasty

BACKGROUND

The purpose of this study was to assess whether weaning of opioid use in the preoperative period improved total joint arthroplasty (TJA) outcomes.

METHODS

Forty-one patients who regularly used opioids and successfully weaned (defined as a 50% reduction in morphine-equivalent dose) before a primary total knee or hip arthroplasty were matched with a group of TJA patients who did not wean and a matched control group of TJA patients who did not use opioids preoperatively. The difference between preoperative and postoperative (at 6-12 months follow-up) patient-reported outcomes were assessed using the change in University of California, Los Angeles (UCLA) activity score, SF12v2, and The Western Ontario and McMaster Universities Arthritis Index (WOMAC). Paired t tests and 1-way repeated measures analysis of variance were performed to assess differences in TJA outcomes between groups.

RESULTS

Patients using opioids who successfully weaned had greater improvements in both disease-specific and generic measures of health outcomes than patients who did not wean (WOMAC 43.7 vs 17.8, P < .001; SF12v2 Physical Component Score 10.5 vs 1.85, P = .003; UCLA activity score 1.49 vs 0, P < .001). There was no statistical difference between the 2 groups on SF12v2 Mental Component Score 2.48 vs 4.21, P = .409. Patients who successfully weaned from opioids had similar outcomes to control patients who did not use opioids: WOMAC 39.0 vs 43.7, P = .31; SF12v2 Physical Component Score 12.5 vs 10.5, P = .35; SF12v2 Mental Component Score 3.08 vs 2.48, P = .82; UCLA activity 1.90 vs 1.49, P = .23.

CONCLUSION

Patients with a history of chronic opioid use who successfully decreased their use of opioids before surgery had substantially improved clinical outcomes that were comparable to patients who did not use opioids at all.

Comparison of effects of intraoperative nefopam and ketamine infusion on managing postoperative pain after laparoscopic cholecystectomy administered remifentanil

BACKGROUND

Although intraoperative opioids provide more comfortable anesthesia and reduce the use of postoperative analgesics, it may cause opioid induced hyperalgesia (OIH). OIH is an increased pain response to opioids and it may be associated with N-methyl-D-aspartate (NMDA) receptor. This study aimed to determine whether intraoperative nefopam or ketamine, known being related on NMDA receptor, affects postoperative pain and OIH after continuous infusion of intraoperative remifentanil.

METHODS

Fifty-four patients undergoing laparoscopic cholecystectomy were randomized into three groups. In the nefopam group (N group), patients received nefopam 0.3 mg/kg at the induction of anesthesia followed by a continuous infusion of 0.065 mg/kg/h. In the ketamine group (K group), patients received ketamine 0.3 mg/kg at the induction of anesthesia followed by a continuous infusion of 3 µg/kg/min. The control group did not received any other agents except for the standard anesthetic regimen. Postoperative pain score, first time and number of demanding rescue analgesia, OIH and degrees of drowsiness/sedation scale were examined.

RESULTS

Co-administrated nefopam or ketamine significantly reduced the total amount of intraoperative remifentanil and postoperative supplemental morphine. Nefopam group showed superior property over control and ketamine group in the postoperative VAS score and recovery index (alertness and respiratory drive), respectively. Nefopam group showed lower morphine consumption than ketamine group, but not significant.

CONCLUSIONS

Both nefopam and ketamine infusion may be useful in managing in postoperative pain control under concomitant infusion of remifentanil. However, nefopam may be preferred to ketamine in terms of sedation.

Hyperalgesia induced by low-dose opioid treatment before orthopaedic surgery: An observational case-control study

BACKGROUND

Chronic pain and opioid consumption may trigger diffuse hyperalgesia, but their relative contributions to pain vulnerability remain unclear.

OBJECTIVES

To assess preoperative opioid-induced hyperalgesia and its postoperative clinical consequences in patients with chronic pain scheduled for orthopaedic surgery.

DESIGN

A prospective observational study.

SETTINGS

Raymond Poincare teaching hospital.

PATIENTS

Adults with or without long-term opioid treatment, scheduled for orthopaedic surgery.

PRIMARY OUTCOME MEASURE

Preoperative hyperalgesia was assessed with eight quantitative sensory tests, in a pain-free zone.

SECONDARY OUTCOME MEASURES

Postoperative morphine consumption and pain intensity were evaluated using a numerical rating scale (NRS) in the recovery room and during the first 72 h.

RESULTS

We analysed results from 68 patients (28 opioid-treated patients and 40 controls). Mean daily opioid consumption was 42 ± 25 mg of morphine equivalent. The opioid-treated group displayed significantly higher levels of preoperative hyperalgesia in three tests: heat tolerance threshold (47.1°C vs. 48.4°C; P = 0.045), duration of tolerance to a 47°C stimulus (40.2 vs. 51.1 s; P = 0.03) and mechanical temporal summation [1.79 vs. 1.02 (ΔNRS10-1); P = 0.036]. Patients in the opioid-treated group consumed more morphine (19.1 vs. 9.38 mg; P = 0.001), had a higher pain intensity (7.6 vs. 5.5; P = 0.001) in the recovery room and a higher cumulative morphine dose at 72 h (39.8 vs. 25.6 mg; P = 0.02).

CONCLUSION

Chronic pain patients treated with low doses of opioid had hyperalgesia before surgery. These results highlight the need to personalise the management of patients treated with opioids before surgery.

TRIAL REGISTRATION

ID-RCB 2011-A00304-37.

Gradual withdrawal of remifentanil infusion may prevent opioid-induced hyperalgesia

BACKGROUND

The aim of this study was to examine if gradual withdrawal of remifentanil infusion prevented opioid-induced hyperalgesia (OIH) as opposed to abrupt withdrawal. OIH duration was also evaluated.

METHODS

Nineteen volunteers were enrolled in this randomized, double-blinded, placebo-controlled, crossover study. All went through three sessions: abrupt or gradual withdrawal of remifentanil infusion and placebo. Remifentanil was administered at 2.5 ng ml(-1) for 30 min before abrupt withdrawal or gradual withdrawal by 0.6 ng ml(-1) every five min. Pain was assessed at baseline, during infusion, 45-50 min and 105-110 min after end of infusions using the heat pain test (HPT) and the cold pressor test (CPT).

RESULTS

The HPT 45 min after infusion indicated OIH development in the abrupt withdrawal session with higher pain scores compared with the gradual withdrawal and placebo sessions (both P<0.01. Marginal mean scores: placebo 2.90; abrupt 3.39; gradual 2.88), but no OIH after gradual withdrawal compared with placebo (P=0.93). In the CPT 50 min after end of infusion there was OIH in both remifentanil sessions compared with placebo (gradual P=0.01, abrupt P<0.01. Marginal mean scores: placebo 4.56; abrupt 5.25; gradual 5.04). There were no differences between the three sessions 105-110 min after infusion.

CONCLUSIONS

We found no development of OIH after gradual withdrawal of remifentanil infusion in the HPT. After abrupt withdrawal OIH was present in the HPT. In the CPT there was OIH after both gradual and abrupt withdrawal of infusion. The duration of OIH was less than 105 min for both pain modalities.

CLINICAL TRIAL REGISTRATION

NCT 01702389. EudraCT number 2011-002734-39.

Changes in Pain Sensitivity and Pain Modulation During Oral Opioid Treatment: The Impact of Negative Affect

OBJECTIVE

Opioids are frequently prescribed for chronic low back pain (CLBP), but there are broad individual differences in the benefits and risks of opioid therapy, including the development opioid-induced hyperalgesia. This study examined quantitative sensory testing (QST) data among a group of CLBP patients undergoing sustained oral opioid treatment. We investigated whether individual differences in psychological characteristics were related to opioid-induced changes in pain perception and pain modulation.

DESIGN

The six-month, open-label trial evaluated patients with low to high levels of negative affect (e.g., symptoms of distress, depression and anxiety); participants underwent QST at baseline (prior to initiating treatment) and during oral opioid treatment.

SETTING

A chronic pain management center.

PATIENTS

The 31 study participants had chronic discogenic back pain, with a pain intensity rating >3/10. Participants were divided into groups with high vs. low levels of Negative Affect (NA).

RESULTS

In the previously-published manuscript describing the clinical outcomes of the trial, high NA patients achieved only about half of the analgesic effect observed in the low NA group (Wasan AD, Michna E, Edwards RR, et al. Psychiatric comorbidity is associated prospectively with diminished opioid analgesia and increased opioid misuse in patients with chronic low back pain. Anesthesiology 2015;123:861-72). The QST findings reported here suggested that tolerance to experimental (cold pressor) pain and conditioned pain modulation tended to decrease in the high NA group over the course of opioid treatment, while temporal summation of mechanical pain declined in the low NA group.

CONCLUSIONS

These results reveal that while the low NA group seemed to exhibit a generally adaptive, analgesic pattern of changes during opioid management, the high NA group showed a pattern more consistent with opioid-induced hyperalgesic processes. A greater susceptibility to hyperalgesia-promoting changes in pain modulation among patients with high levels of distress may contribute to a lower degree of benefit from opioid treatment in high NA patients.

Dezocine Prevents Postoperative Hyperalgesia in Patients Undergoing Open Abdominal Surgery

Objective. Postoperative hyperalgesia is very frequent and hard to treat. Dezocine is widely used and has a modulatory effect for thermal hyperalgesia in animal models. So, this study was designed to investigate the potential role of dezocine in decreasing postoperative hyperalgesia for patients undergoing open abdominal surgery. Methods. This is a randomized, double-blinded, and placebo-controlled trial. 50 patients for elective open gastrectomy were randomly allocated to either a true treatment group (0.15 mg/kg intravenous dezocine at the end of surgery) or a sham treatment group (equivalent volume of saline) in a 1 : 1 ratio. Patients were followed up for 48 hours postoperatively and pain threshold to Von Frey filaments, pain scores, PCIA consumption, rescue analgesics use, sedation score, and occurrence of postoperative nausea and vomiting were recorded. Results. Patients in the true treatment group experienced statistically significantly higher pain threshold on forearm and smaller extent of peri-incisional hyperalgesia than the sham treatment group. Rescue analgesic use, cumulative PCIA consumption, and pain scores were statistically significantly decreased in the true treatment group compared to the sham treatment group. Conclusions. Dezocine offers a significant antihyperalgesic and analgesic effect in patients undergoing elective open gastrectomy for up to 48 hours postoperatively.

Opioid-induced hyperalgesia in chronic pain patients and the mitigating effects of gabapentin

Chronic pain patients receiving opioid drugs are at risk for opioid-induced hyperalgesia (OIH), wherein opioid pain medication leads to a paradoxical pain state. OIH involves central sensitization of primary and secondary afferent neurons in the dorsal horn and dorsal root ganglion, similar to neuropathic pain. Gabapentin, a gamma-aminobutyric acid (GABA) analog anticonvulsant used to treat neuropathic pain, has been shown in animal models to reduce fentanyl hyperalgesia without compromising analgesic effect. Chronic pain patients have also exhibited lower opioid consumption and improved pain response when given gabapentin. However, few human studies investigating gabapentin use in OIH have been performed in recent years. In this review, we discuss the potential mechanisms that underlie OIH and provide a critical overview of interventional therapeutic strategies, especially the clinically-successful drug gabapentin, which may reduce OIH.

Stepwise tapering of remifentanil at the end of surgery decreased postoperative pain and the need of rescue analgesics after thyroidectomy

BACKGROUND

This study was designed to investigate whether stepwise tapering of remifentanil at the end of surgery could decrease postoperative pain scores and requirements of rescue analgesics after remifentanil-desflurane anesthesia in patients with thyroidectomy.

METHODS

Sixty two patients undergoing thyroidectomy under general anesthesia were randomly allocated into two groups. All patients were anesthetised with desflurane and high-dose remifentanil. Remifentnail was infused at the rate of 0.3 μg/kg/min until the end of surgery in patients of the control group (group A) whereas remifentanil was tapered gradually from 0.3 to 0.1 μg/kg/min until the end of surgery for at least 30 minutes in patients with group B. Pain scores (0-100 numerical rating scale, NRS), rescue analgesic requirements and adverse events were assessed at 30 min, 2 h, 6 h, 12 h, and 24 h after operation.

RESULTS

There was a significant decrease in pain scores at 30 min (20 [0-80] vs. 50 [0-100], P = 0.002) and 2 h (30 [10-60] vs. 40 [20-80], P = 0.018) after surgery in group B compared with group A. In addition, rescue analgesics are less required in group B than in group A postoperatively (2 [1-3] vs. 3 [2,3], P = 0.039). There were no significant differences in adverse events between the two groups.

CONCLUSIONS

Tapering of remifentanil at the end of surgery decreased postoperative pain scores immediately after thyroidectomy with desflurane and high-dose remifentanil anesthesia.

TRIAL REGISTRATION

Clinical Research information Service (CRiS, registration number KCT0000589).

Optimal analgesia during major open and laparoscopic abdominal surgery

Optimal analgesia is a key element of enhanced recovery after surgery (ERAS), not only for humanitarian reasons but also because poorly relieved surgical pain contributes to surgical stress and impairs recovery. A multimodal analgesic approach is advised in order to provide adequate analgesia, reduce opioid consumption, reduce side effects and facilitate the achievement of ERAS milestones. For open surgery, a thoracic epidural for 48 to 72 hours, with regular acetaminophen and antiinflammatories is probably the treatment of choice. For laparoscopic surgery, intrathecal or local anesthesia in the wound combined with regular acetaminophen and antiinflammatory drugs is effective.

A systematic review and meta-analysis of ketamine for the prevention of persistent post-surgical pain

While post-operative pain routinely resolves, persistent post-surgical pain (PPSP) is common in certain surgeries; it causes disability, lowers quality of life and has economic consequences. The objectives of this systematic review and meta-analysis were to evaluate the effectiveness of ketamine in reducing the prevalence and severity of PPSP and to assess safety associated with its use. We searched the Cochrane Central Register of Controlled Trials, MEDLINE and EMBASE through December 2012 for articles in any language. We included randomized, controlled trials in adults in which ketamine was administered perioperatively via any route. Seventeen studies, the majority of which administered ketamine intravenously, met all inclusion criteria. The overall risk of developing PPSP was not significantly reduced at any time point in the ketamine group vs. placebo, nor did comparisons of pain severity scores reach statistical significance. Sensitivity analysis of exclusively intravenous ketamine studies included in this meta-analysis demonstrated statistically significant reductions in risk of developing PPSP at 3 and 6 months (P = 0.01 and P = 0.04, respectively). Adverse event rates were similar between ketamine and placebo groups. The study data from our review are heterogeneous and demonstrate efficacy of intravenously administered ketamine only in comparison with placebo. Highly variable timing and dosing of ketamine in these studies suggest that no unifying effective regimen has emerged. Future research should focus on clinically relevant outcomes, should stratify patients with pre-existing pain and possible central sensitization and should enroll sufficiently large numbers to account for loss to follow-up in long-term studies.

Regional anesthesia in neonates and infants

Optimal pain management can significantly impact the surgical outcome and length of stay in the neonatal intensive care unit (NICU). Regional anesthesia is an effective alternative that can be used in both term and preterm neonates. A variety of neuraxial and peripheral nerve blocks have been used for specific surgical and NICU procedures. Ultrasound guidance has increased the feasibility of using these techniques in neonates. Education and training staff in the use of continuous epidural infusions are important prerequisites for successful implementation of regional anesthesia in NICU management protocols.

Acquired pharmaco-dynamic opioid tolerance: a concept analysis

AIM

To report an analysis of the concept of acquired pharmaco-dynamic opioid tolerance.

BACKGROUND

Acquired pharmaco-dynamic opioid tolerance is a complex and poorly understood phenomenon associated with strong opioid therapy for managing pain. Critical review of the concept provides greater clarification of the attributes, assisting healthcare professionals in addressing pain and functional management of patients, particularly those with non-malignant pain.

DESIGN

Concept analysis.

DATA SOURCES

A systematic literature search was undertaken using electronic data bases: CINAHL, British Nursing Index, EMBase, Medline, Pubmed and AMED. All literature reviewed was in English and published between 1976 and 2012. The key search terms were 'chronic non-malignant pain', 'strong opioid therapy' and 'development of acquired pharmaco-dynamic opioid tolerance'; all possible variant terms were also searched.

METHOD

The Walker and Avant approach was used to guide the concept analysis.

RESULTS

The concept analysis revealed four empirical referents: plasticity, drug administration, reduced analgesic efficacy and increased drug dosing. Tachyphylexia was identified as a borderline case, opioid induced hyperalgesia as a related case and pseudo-tolerance as a contrary case. The antecedent is administration of an opioid analgesic drug and the consequences, increasing opioid drug dose to maintain analgesic effect.

CONCLUSION

Untangling the antecedents, empirical referents and consequences of tolerance help healthcare professionals understand its complexities. Improved knowledge may ultimately influence patient outcomes through the construction of better monitoring systems. This concept analysis may also provide insights for policy change and give empirical direction for future research.

Phosphorylated CaMKII levels increase in rat central nervous system after large-dose intravenous remifentanil

Background

Postoperative remifentanil-induced pain sensitization is common, but its molecular mechanism remains unclear. Calcium/calmodulin-dependent protein kinase II (CaMKII) has been shown to have a critical role in morphine-induced hyperalgesia. This study was designed to determine how CaMKII phosphorylation and protein expression levels change in the central nervous system of rats with remifentanil-induced hyperalgesia.

Material/Methods

Male Sprague-Dawley^® rats were exposed to large-dose (bolus of 6.0 μg/kg and 2.5 μg/kg/min for 2 hours) intravenous remifentanil to induce post-transfusion hyperalgesia. Levels of phosphorylated CaMKII (P-CaMKII) and total protein of CaMKII (T-CaMKII) were determined at different post-transfusion times by Western blot and immunostaining and were compared with controls.

Results

P-CaMKII increased significantly (P<0.05) at 0, 0.5, and 2 hours. However, P-CaMKII at 5 to 24 hours and T-CaMKII at 0 to 24 hours post-transfusion did not change significantly in rats’ spinal dorsal horn, hippocampus, or primary somatosensory (S1) cortex (n=6 per group). Similarly, immunostaining showed stronger P-CaMKII immunoreactants (P<0.05) and more P-CaMKII- positive cells (P<0.05) in the spinal dorsal horn, CA1 region of the hippocampus, and S1 cortex of rats 0.5 hours post-transfusion compared with the control group treated with 0.9% sodium chloride (n=3 per group).

Conclusions

These results suggest that a temporary rise in the P-CaMKII level in the central nervous system may correlate with remifentanil-induced pain sensitization in the postoperative period.

Effects of different doses of sufentanil and remifentanil combined with propofol in target-controlled infusion on stress reaction in elderly patients

The current study aimed to observe the effects of sufentanil and remifentanil combined with propofol in target-controlled infusion (TCI) on perioperative stress reaction in elderly patients. A total of 80 elderly patients requiring general anesthesia were recruited. They were divided into four groups (each n=20) according to different target concentrations of remifentanil and sufentanil. These target concentrations were: 4 ng/ml remifentanil + 0.2 ng/ml sufentanil for group I; 3 ng/ml remifentanil + 0.3 ng/ml sufentanil for group II; 2 ng/ml remifentanil + 0.5 ng/ml sufentanil for anesthesia induction and post-intubation 3 ng/ml remifentanil + 0.2 ng/ml sufentanil for anesthesia maintenance for group III; and 5 ng/ml remifentanil for anesthesia induction and post-intubation 4 ng/ml remifentanil for anesthesia maintenance for group IV. Norepinephrine (NE), epinephrine (E) and angiotensin II (Ang II) levels in plasma were measured prior to the induction of anesthesia, as well as at several different time-points following surgery. The numbers of intraoperative severe hemodynamic fluctuation, postoperative eye-opening and extubation time, and post-extubation restlessness and pain scores were recorded. Group IV had a larger circulation fluctuation control number and higher levels of NE, E and Ang II at 3 h after surgery than any other group (P<0.01). Although group IV had shorter postoperative eye-opening and extubation times compared with the other groups (P<0.05), it also had higher restlessness and pain scores (P<0.01). The combined use of sufentanil and remifentanil stabilizes perioperative hemodynamics and reduces stress hormone levels.

Medical and psychological risks and consequences of long-term opioid therapy in women

BACKGROUND

Long-term opioid use has increased substantially over the past decade for U.S. women. Women are more likely than men to have a chronic pain condition, to be treated with opioids, and may receive higher doses. Prescribing trends persist despite limited evidence to support the long-term benefit of this pain treatment approach.

PURPOSE

To review the medical and psychological risks and consequences of long-term opioid therapy in women.

METHOD

Scientific literature containing relevant keywords and content were reviewed.

RESULTS AND CONCLUSIONS

Long-term opioid use exposes women to unique risks, including endocrinopathy, reduced fertility, neonatal risks, as well as greater risk for polypharmacy, cardiac risks, poisoning and unintentional overdose, among other risks. Risks for women appear to vary by age and psychosocial factors may be bidirectionally related to opioid use. Gaps in understanding and priorities for future research are highlighted.

Perioperative management of the child on long-term opioids

The strategies used to manage children exposed to long-term opioids are extrapolated from adult literature. Opioid consumption during the perioperative period is more than three times that observed in patients not taking chronic opioids. A sparing use of opioids in the perioperative period results in both poor pain management and withdrawal phenomena. The child's pre-existing opioid requirement should be maintained, and acute pain associated with operative procedures should be managed with additional analgesia. This usually comprises short-acting opioids, regional or local anesthesia, and adjuvant therapies. Long-acting opioids, transdermal opioid patches, and implantable pumps can be used to maintain the regular opioid requirement. Intravenous infusion, nurse controlled analgesia, patient-controlled analgesia, or oral formulations are invaluable for supplemental requirements postoperatively. Effective management requires more than simply increasing opioid dose during this time. Collaboration of the child, family, and all teams involved is necessary. While chronic pain or palliative care teams and other staff experienced with the care of children suffering chronic pain may have helpful input, many pediatric hospitals do not have chronic pain teams, and many patients receiving long-term opioids are not palliative. Acute pain services are appropriate to deal with those on long-term opioids in the perioperative setting and do so successfully in many centers. Staff caring for such children in the perioperative period should be aware of the challenges these children face and be educated before surgery about strategies for postoperative management and discharge planning.

Pro con debate: the use of regional vs systemic analgesia for neonatal surgery

In recent years the inclusion of regional techniques to pediatric anesthesia has transformed practice. Simple procedures such as caudal anesthesia with local anaesthetics can reduce the amounts of general anesthesia required and provide complete analgesia in the postoperative period while avoiding large amounts of opioid analgesia with potential side effects that can impair recovery. However, the application of central blocks (epidural and spinal local anesthesia) via catheters in the younger infant, neonate and even preterm neonate remains more controversial. The potential for such invasive maneuvers themselves to augment risk, can be argued to outweigh the benefits, others would argue that epidural analgesia can reduce the need for postoperative ventilation and that this not only facilitates surgery when intensive care facilities are limited, but also reduces cost in terms of PICU stay and recovery profile. Currently, opinions are divided and strongly held with some major units adopting this approach widely and others maintaining a more conservative stance to anesthesia for major neonatal surgery. In this pro-con debate the evidence base is examined, supplemented with expert opinion to try to provide a balanced overall view.

Suspected opioid-induced hyperalgesia in an infant

One explanation for diminished opioid analgesic efficacy is opioid-induced hyperalgesia (OIH). We report a case of OIH in an infant with gastroschisis, requiring multiple surgical interventions and prolonged sedation for ventilation. This is the first report of OIH in an infant. On day 41 of life after nine separate surgical interventions, the patient's pain scores increased and remained elevated, despite increasing opioid administration. The patient also developed hyperalgesia, allodynia, and photophobia and became extremely irritable upon handling. Other possible causes were excluded, including interruption to opioid delivery, sepsis, acid-base and electrolyte disturbance, and ongoing surgical pathology. An opioid rotation to hydromorphone was initiated and ketamine was commenced. Sedation for ventilation was achieved with dexmedetomidine and midazolam infusions. Over a period of 24 h after opioid de-escalation, pain scores reduced rapidly and the patient became significantly less irritable with handling. All infusions were gradually weaned and eventually ceased.

A systematic review of combination step III opioid therapy in cancer pain: an EPCRC opioid guideline project

BACKGROUND

The use of combinations of opioids is a common clinical practice; however, this is not advocated by the World Health Organization (WHO) analgesic ladder. As opioid combination therapy becomes used increasingly, a review of the evidence on this practice was conducted.

AIMS

To carry out a systematic review of the use of strong opioids in combination in cancer pain.

METHODS

The following databases were searched electronically: Embase (1980-2010 week 2), Medline (1950-2010 week 1) and the Cochrane Database of Systematic Reviews (fourth quarter 2009). Only strong opioids as defined by the WHO ladder and full opioid agonists were examined. Only studies conducted in human, adult patients with chronic cancer pain were eligible. Studies must have contained data on efficacy and/or side effects in the key point. Appraisal was conducted using predetermined criteria set by the EAPC guideline development group. All potential papers were reviewed independently by both authors.

RESULTS

In total 596 articles were retrieved resulting in only two eligible studies, which were rated as grade C and grade D evidence. These examined morphine in combination with oxycodone or fentanyl/methadone.

CONCLUSION

Only a weak recommendation can be used to support combination opioid therapy. This recommendation is also based on the caveat that the desirable effects of combination opioid therapy is outweighed by any disadvantages that this would confer. Prospective randomized trials are needed to clarify the benefits and safety of combination opioid therapy.

Elevated pain sensitivity in chronic pain patients at risk for opioid misuse

This study employed quantitative sensory testing (QST) to evaluate pain responses in chronic spinal pain patients at low risk and high risk for opioid misuse, with risk classification based on scores on the Screener and Opioid Assessment for Patients with Pain-Revised (SOAPP-R). Patients were further subgrouped according to current use of prescription opioids. Of the 276 chronic pain patients tested, approximately 65% were taking opioids; a median split was used to further categorize these patients as being on lower or higher doses of opioids. The high-risk group (n = 161) reported higher levels of clinical pain, had lower pressure and thermal pain thresholds at multiple body sites, had lower heat pain tolerance, and rated repetitive mechanical stimuli as more painful relative to the low-risk group (n = 115; P's < .01). In contrast, QST measures did not differ across opioid groups. Multiple linear regression analysis suggested that indices of pain-related distress (ie, anxiety and catastrophizing about pain) were also predictive of hyperalgesia, particularly in patients taking opioids. Collectively, regardless of opioid status, the high-risk group was hyperalgesic relative to the low-risk group; future opioid treatment studies may benefit from the classification of opioid risk, and the examination of pain sensitivity and other factors that differentiate high- and low-risk groups.

PERSPECTIVE

This study demonstrates that chronic spinal pain patients at high risk for misuse of prescription opioids are more pain-sensitive than low-risk patients, whether or not they are currently taking opioids. Indices of pain-related distress were important predictors of pain sensitivity, particularly among those patients taking opioids for pain.

Opioid-induced hyperalgesia: clinically relevant or extraneous research phenomenon?

Opioids have become the unequivocal therapy of choice in treating many varieties of chronic pain. With the increased prescription of opioids, some unintended consequences have occurred. After prolonged opioid exposure, opioid-induced hyperalgesia (OIH), the paradoxical effect that opioid therapy may in fact enhance or aggravate preexisting pain, may occur. Over the past several decades, an increasing number of laboratory and clinical reports have suggested lowered pain thresholds and heightened atypical pain unrelated to the original perceived pain sensations as hallmarks of OIH. However, not all evidence supports the clinical importance of OIH, and some question whether the phenomenon exists at all. Here, we present a nonexhaustive, brief review of the recent literature. OIH will be reviewed in terms of preclinical and clinical evidence for and against its existence; recommendations for clinical evaluation and intervention also will be discussed.