The impact of opioid-induced hyperalgesia for postoperative pain

[Opioid-free anesthesia : Wrong track or meaningful exit from the era of opioid-based analgesia?]

The limitations and disadvantages of opioids in anesthesia are very well known but the advantages combined with a lack of effective alternatives even now still prevents refraining from using opioids as part of an adequate pain therapy. For decades, pain research has had the declared goal of replacing opioids with new substances which have no serious side effects; however, currently this goal seems to be a long way off. Due to the media coverage of the "opioid crisis" in North America, the use of opioids for pain management is also increasingly being questioned by the patients. Measures to contain this crisis are only slowly taking effect in view of the increasing number of deaths, which is why the triggers are still being sought. The perioperative administration of opioids is not only a possible gateway to addiction and abuse but it can also cause outcome-relevant complications, such as respiratory depression, postoperative nausea and vomiting and an increase in postoperative pain. Therefore, these considerations gave rise to the idea of an opioid-free anesthesia (OFA), i.e., opioids are not administered as part of anesthesia to carry out surgical procedures. Although this idea may make sense at first glance, a rapid introduction of this concept appears to be risky as it entails significant changes for the entire anesthesiological management. Based on relatively robust data from clinical studies, this concept can now be evaluated and discussed not only emotionally but also objectively. This review article presents arguments for or against the complete avoidance of intraoperative or even perioperative opioids. The current conditions in Germany are primarily taken into account, so that the perioperative pain therapy is transferable to the established standards. The results from current clinical studies on the implementation of an opioid-free anesthesia are summarized and discussed.

Enhanced Recovery After Surgery (ERAS) Program for Anterior Cervical Discectomy and Fusion (ACDF) in Patients Over 60 Years Old

Background

Enhanced recovery after surgery (ERAS) is currently widely used in many surgical specialties, but there is still a lack of concern about the cervical ERAS program for old patients (>60 years old). We aimed to determine whether our ERAS program significantly improved satisfaction and outcomes in old patients (>60 years old) with anterior cervical discectomy and fusion (ACDF).

Methods

This is a retrospective cohort study. The study enrolled patients if they were over the age of 60 years old underwent ACDF from July 2019 and June 2021 (ERAS group) and from January 2018 and June 2019 (non-ERAS group). Data including demographic, comorbidity, and surgical information were collected. We also evaluated ERAS process compliance, primary outcome, surgical complication, and length of stay (LOS).

Results

There were 135 patients in the ERAS group, and 122 patients in the non-ERAS group were included. A comparison of the demographic data revealed that there were no statistically significant intergroup differences observed between the group. Overall, ERAS pathway compliance was 91.9%. There were no significant differences in the fusion levels, operative time, intraoperative blood loss, postoperative VAS score, and complications between the ERAS and non-ERAS groups. In addition, there was no significant difference in readmission and mortality at 30-day follow-up between the two groups. However, we observed a statistically significant decrease in the LOS in the ERAS group (8.68±2.34 of ERAS group versus 10.43±4.05 in non-ERAS group, p=0.013).

Conclusion

This report describes the first ERAS protocol used in old patients with ACDF. Our ERAS program is safe and associated with incremental benefits with respect to LOS in old patients with ACDF.

Effect of continuous post-operative lidocaine infusion in an enhanced recovery program on opioid use following gynecologic oncology surgery

OBJECTIVE

To determine the effectiveness of implementing an Enhanced Recovery After Surgery (ERAS) program, including continuous intraoperative and postoperative intravenous (IV) lidocaine infusion, on perioperative opioid use.

METHODS

This was a single-institution retrospective pre- post- cohort study. Consecutive patients undergoing planned laparotomy for known or potential gynecologic malignancy were identified after implementation of an ERAS program and compared to a historical cohort. Opioid use was calculated as morphine milligram equivalents (MMEs). Cohorts were compared using bivariate tests.

RESULTS

A total of 215 patients were included in the final analysis, 101 patients received surgery before ERAS implementation and 114 received surgery after. A reduction in total opioid use was observed in ERAS patients compared with historical controls (MME 26.5 [9.6-60.8] versus 194.5 [123.8-266.8], p<0.001). Length of stay (LOS) was reduced by 25% in the ERAS cohort (median 3 days, range 2-26, versus 4 days, range 2-18; p<0.001). Within the ERAS cohort, 64.9% received IV lidocaine for the planned 48 hours, and 5.6% had the infusion discontinued early. Within the ERAS cohort, patients who received IV lidocaine infusion used less opioids compared to those who did not (median 16.9, range 5.6-55.1, versus 46.2, range 23.2-76.1; p<0.002).

CONCLUSION

An ERAS program including a continuous IV lidocaine infusion as the opioid-sparing analgesic strategy was noted to be safe and effective, leading to decreased opioid consumption and LOS compared with a historic cohort. Additionally, lidocaine infusion was noted to decrease opioid consumption even among patients already receiving other ERAS interventions.

Meta-analysis of the efficacy of ketamine in postoperative pain control in adolescent idiopathic scoliosis patients undergoing spinal fusion

PURPOSE

In this meta-analysis, we aim to compare ketamine use versus a control group (saline solution) during induction of anesthesia in adolescent idiopathic scoliosis patients undergoing fusion surgery in terms of postoperative opioid consumption, pain control, and side effects.

METHODS

A PubMed search of studies published over the last 20 years using the descriptor/terms "ketamine AND scoliosis" was performed. Baseline characteristics of each article were obtained and efficacy measures analyzed (morphine equivalent treatment at 24, 48, and 72 h postoperatively, complications (vomiting/nausea and pruritus), length of hospital stay (days); and pain score (VAS)) (Review Manager 5.4 software package).

RESULTS

Five randomized clinical trials were included. Morphine administration showed statistically significant differences at 24 and 48 h (MD - 0.15, 95% CI - 0.18 to - 0.12) and (MD - 0.26, 95% CI - 0.31 to - 0.21) between the ketamine and control (saline solution), respectively. No intergroup differences were found regarding nausea/vomiting and pruritus (OR 0.77, 95% CI 0.35 to 1.67) and (OR 0.71, 95% CI 0.31 to 1.62), respectively, same as for the pain score (MD - 0.75, 95% CI - 1.71 to 0.20).

CONCLUSIONS

The use intraoperative and postoperative continuous low doses of ketamine significantly reduces opioid use throughout the first 48 h in patients with AIS who undergo posterior spinal fusion.

Effectiveness of two extended-release buprenorphine formulations during postoperative period in neonatal rats

Information on the effectiveness of a new long-lasting buprenorphine formulation, extended-release buprenorphine, in the neonatal rat is very limited. This study compares whether a high dose of extended-release buprenorphine (XR-Hi) attenuates thermal hypersensitivity for a longer period than a low dose of extended-release buprenorphine (XR-Lo) in a neonatal rat incisional pain model. Two experiments were performed. Experiment one: Male and female postnatal day-5 rat pups (n = 38) were randomly assigned to 1 of 4 treatment groups and received a subcutaneous administration of one of the following: 1) 0.9%NaCl (Saline), 0.1 mL; 2) sustained release buprenorphine (Bup-SR), 1 mg/kg; 3) XR-Lo, 0.65 mg/kg; and 4) XR-Hi, 1.3 mg/kg. Pups were anesthetized with sevoflurane in 100% O₂ and a 5 mm long skin incision was made over the left lateral thigh and underlying muscle dissected. The skin was closed with surgical tissue glue. Thermal hypersensitivity testing (using a laser diode) and clinical observations were conducted 1 hour (h) prior to surgery and subsequently after 1, 4, 8, 24, 48, 72 h of treatment. Experiment two: The plasma buprenorphine concentration level was evaluated at 1, 4, 8, 24, 48, 72 h on five-day-old rat pups. Plasma buprenorphine concentration for all treatment groups remained above the clinically effective concentration of 1 ng/mL for at least 4 h in the Bup-SR group, 8 h in XR-Lo and 24 h in XR-Hi group with no abnormal clinical observations. This study demonstrates that XR-Hi did not attenuate postoperative thermal hypersensitivity for a longer period than XR-Lo in 5-day-old rats; XR-Hi attenuated postoperative thermal hypersensitivity for up to 4 h while Bup-SR and XR-Lo for at least 8 h in this model.

Effect of Sufentanil Combined with Gabapentin on Acute Postoperative Pain in Patients Undergoing Intraspinal Tumor Resection: Study Protocol for a Randomized Controlled Trial

Purpose

Patients undergoing intraspinal tumor resection usually experience severe postoperative pain. Inadequate postoperative analgesia usually leads to severe postsurgical pain, which could cause patients to suffer from many other related complications. Recently, an increasing number of studies have found that gabapentin can relieve hyperalgesia, postoperative pain, and postoperative inflammation. However, there have been no reports on the use of gabapentin combined with sufentanil preoperatively for acute pain following intraspinal tumor resection.

Study Design and Methods

This is a protocol for a randomized, placebo-controlled, and double-blinded trial. One-hundred and sixty-eight participants with chronic pain related to the intraspinal tumor will be randomized into the gabapentin and placebo groups in a 1:1 ratio. In the gabapentin group, patients will be given 300 mg gabapentin orally 36 h, 24 h, and 12 h before surgery; the placebo group will receive a placebo orally at the same time points preoperatively. To estimate the efficacy and safety endpoints, all the researchers and patients will be blinded until the completion of this study. The primary outcome will be the consumption of sufentanil within 48 h postoperatively. The secondary outcomes include the visual analog scale pain score and Von Frey mechanical pain threshold 36 h and 24 h before and 24 h and 48 h after surgery, the incidence of postoperative nausea, vomiting, and drowsiness, the length of hospital stay and medical expenses.

Discussion

This trial is to evaluate the efficacy and safety of gabapentin combined with sufentanil for postoperative analgesia in patients who complain of pain before intraspinal tumor resection. The findings will provide a new strategy for multimode perioperative analgesia management in these patients.

Effects of Lidocaine on Motor-Evoked Potentials and Somatosensory-Evoked Potentials in Patients Undergoing Intraspinal Tumour Resection: Study Protocol for a Prospective Randomized Controlled Trial

Purpose

Study Design and Methods

Discussion

Medicaid Payer Status Is a Predictor of Early Postoperative Pain Following Upper Extremity Procedures

Background: The purpose of this study was to investigate the relationship between insurance status and patient-reported pain both before and after upper extremity surgical procedures. We hypothesized that patients with Medicaid payer status would report higher levels of pre- and postoperative pain and report less postoperative pain relief. Methods: In all, 376 patients who underwent upper extremity procedures by a single surgeon at an academic ambulatory surgery center were identified. Patient information, including insurance status and Visual Analog Scale pain score (VAS-pain) at baseline, 2 weeks, and 1, 3, and 6 months, were collected. VAS-pain scores were compared with t-tests and linear regression. Results: Preoperatively and at 2-week, 1-month, and 3-month follow-up, Medicaid patients reported statistically significant higher pain levels than patients with Private insurance, finding a mean adjusted increase of 0.51 preoperatively, 0.39 at 1 month, and 0.79 at 3 months. Preoperatively and at 3-month follow-up, Medicaid patients reported statistically significant higher pain than patients with Medicare, finding increases in VAS-pain of 0.99 preoperatively and 0.94 at 3 months. There was no difference in pain improvement between any insurance types at any time point (all P values > .05). Conclusions: Patients with Medicaid report higher levels of preoperative pain and early postoperative pain, but reported the same improvement in pain as patients with other types of insurance. As healthcare systems are becoming increasingly dependent on patient-reported outcomes, including pain, it is important to consider that differences may exist in subjective pain depending on insurance status.

Combination of inhaled nitrous oxide and oral opioids induces long-lasting analgesic effects in patients with neuropathic pain: ProtoTOP study post hoc exploratory analyses

ABSTRACT

Experimental studies have suggested that nitrous oxide-induced analgesia depends on interactions with opioids. On the basis of these results, we hypothesized that the effects of inhaled nitrous oxide/oxygen (N2O/O2) 50%-50% equimolar mixture (EMONO) on patients with neuropathic pain would be higher in those receiving concomitant opioids. To test this hypothesis, we did exploratory post hoc analyses of our recently published ProtoTOP study to compare the effects of EMONO and placebo in patients with or without concomitant opioid treatment. A total of 92 patients of the 221 (ie, 41.6%) included in the ProtoTOP study were concomitantly treated with opioids. In contrast with our previous analyses, average pain intensity was significantly decreased in comparison with placebo one week after the last treatment administration in patients treated with opioids, but not in those treated without opioid, and this effect was maintained over the 4-week follow-up period. Neuropathic pain symptom inventory (NPSI total and subscores) was also significantly more decreased after inhalation of EMONO in comparison with placebo only in patients receiving opioids. The proportion of patients with at least 30% pain reduction and of those reporting an overall improvement with the Patient Global Impression of Change were significantly higher only in this population of patients. In conclusion, these results complement our previous analyses with the identification of a specific population of responders to EMONO inhalation in patients with neuropathic pain. As suggested by experimental studies, we hypothesized that these long-lasting analgesic effects could depend on the anti-N-methyl-D-aspartate properties of N2O.

P2Y1 purinergic receptor inhibition attenuated remifentanil-induced postoperative hyperalgesia via decreasing NMDA receptor phosphorylation in dorsal root ganglion

BACKGROUND

Remifentanil-induced postoperative hyperalgesia is an intractable side effect of the clinical use of remifentanil, the mechanism of which remains obscure, especially in the peripheral nervous system. N-methyl-D-aspartate receptor (NMDAR) phosphorylation in dorsal root ganglion (DRG) plays a pronociceptive role in neuropathic pain. The contribution of the P2Y1 purinergic receptor (P2Y1R) in DRG to pain hypersensitivity derived from various origins and P2Y1R upregulation-induced NMDAR activation in neurons have also been uncovered. This study aimed to investigate whether P2Y1R participates in nociceptive processing in the DRG and spinal cord in remifentanil-induced postoperative hyperalgesia.

METHODS

Rats with remifentanil-induced postoperative hyperalgesia were intrathecally injected with NMDAR antagonist MK801 or P2Y1R antagonist MRS2179 at 10 min prior to remifentanil infusion. Mechanical allodynia, heat hyperalgesia, and cold hyperalgesia were measured at -24 h, 2 h, 6 h, 24 h, and 48 h following remifentanil infusion. The P2Y1R expression and NMDAR expression and phosphorylation in DRG ipsilateral to the incision were detected by Western blot and immunofluorescence.

RESULTS

Incision and remifentanil induced mechanical allodynia, heat hyperalgesia, and cold hyperalgesia accompanied by upregulated P2Y1R expression, increased NMDAR subunit NR1 expression and phosphorylation at Ser896, and NR2B expression and phosphorylation at Tyr1472 in DRG. Inhibition of NMDAR phosphorylation by MK801 effectively attenuated remifentanil-induced postoperative hyperalgesia. Furthermore, P2Y1R blockade by MRS2179 not only lessened remifentanil-evoked postoperative hypersensitivity to mechanical, heat, and cold stimuli, but also suppressed the increases in NR1 and NR2B expression and phosphorylation in DRG induced by incision and remifentanil.

CONCLUSION

The process by which P2Y1R mediates NMDAR expression and phosphorylation represents a mechanism of remifentanil-induced postoperative hyperalgesia in the DRG and/or spinal cord.

Impact of Intraoperative Ketamine on Postoperative Analgesic Requirement Following Bariatric Surgery: a Meta-analysis of Randomized Controlled Trials

This meta-analysis aimed at exploring the impact of intravenous ketamine on pain relief and analgesic consumption in patients undergoing bariatric surgery (BS). Literature searches identified nine eligible trials with 458 participants. Forest plot revealed a significantly lower pain score [mean difference (MD) =  - 1.06, p = 0.005; 390 patients) and morphine consumption (MD =  - 3.85 mg, p = 0.01; 212 patients) immediately after BS in patients with intravenous ketamine than in those without. In contrast, pooled analysis showed comparable pain score (p = 0.28), morphine consumption (p = 0.45) within 24 h, and risk of postoperative nausea/vomiting (p = 0.67) between the two groups. In conclusion, the meta-analysis demonstrated improvements in pain outcomes immediately after surgery through perioperative intravenous ketamine administration despite the absence of analgesic benefit in the late postoperative period and a positive impact on postoperative nausea/vomiting.

Serotonin Plays a Key Role in the Development of Opioid-Induced Hyperalgesia in Mice

Opioid usage for pain therapy is limited by its undesirable clinical effects, including paradoxical hyperalgesia, also known as opioid-induced hyperalgesia (OIH). However, the mechanisms associated with the development and maintenance of OIH remain unclear. Here, we investigated the effect of serotonin inhibition by the 5-HT3 receptor antagonist, ondansetron (OND), as well as serotonin deprivation via its synthesis inhibitor para-chlorophenylalanine, on mouse OIH models, with particular focus on astrocyte activation. Co-administering of OND and morphine, in combination with serotonin depletion, inhibited mechanical hyperalgesia and astrocyte activation in the spinal dorsal horn of mouse OIH models. Although previous studies have suggested that activation of astrocytes in the spinal dorsal horn is essential for the development and maintenance of OIH, herein, treatment with carbenoxolone (CBX), a gap junction inhibitor that suppresses astrocyte activation, did not ameliorate mechanical hyperalgesia in mouse OIH models. These results indicate that serotonin in the spinal dorsal horn, and activation of the 5-HT3 receptor play essential roles in OIH induced by chronic morphine, while astrocyte activation in the spinal dorsal horn serves as a secondary effect of OIH. Our findings further suggest that serotonergic regulation in the spinal dorsal horn may be a therapeutic target of OIH. PERSPECTIVE: The current study revealed that the descending serotonergic pain-facilitatory system in the spinal dorsal horn is crucial in OIH, and that activation of astrocytes is a secondary phenotype of OIH. Our study offers new therapeutic targets for OIH and may help reduce inappropriate opioid use.

Effects of Curcumin and Its Different Formulations in Preclinical and Clinical Studies of Peripheral Neuropathic and Postoperative Pain: A Comprehensive Review

Lesion or disease of the somatosensory system leads to the development of neuropathic pain. Peripheral neuropathic pain encompasses damage or injury of the peripheral nervous system. On the other hand, 10–15% of individuals suffer from acute postoperative pain followed by persistent pain after undergoing surgeries. Antidepressants, anticonvulsants, baclofen, and clonidine are used to treat peripheral neuropathy, whereas opioids are used to treat postoperative pain. The negative effects associated with these drugs emphasize the search for alternative therapeutics with better efficacy and fewer side effects. Curcumin, a polyphenol isolated from the roots of Curcuma longa, possesses antibacterial, antioxidant, and anti-inflammatory properties. Furthermore, the low bioavailability and fast metabolism of curcumin have led to the advent of various curcumin formulations. The present review provides a comprehensive analysis on the effects of curcumin and its formulations in preclinical and clinical studies of neuropathic and postoperative pain. Based on the positive outcomes from both preclinical and clinical studies, curcumin holds the promise of mitigating or preventing neuropathic and postoperative pain conditions. However, more clinical studies with improved curcumin formulations are required to involve its use as adjuvant to neuropathic and postoperative drugs.

Opioids and Sickle Cell Disease: From Opium to the Opioid Epidemic

Sickle cell disease (SCD) is an inherited disorder of hemoglobin structure. The clinical effects of the sickle gene are pleiotropic in nature causing multiple phenotypic expressions associated with the various complications of the disease. The hallmark of the disease is pain that could be acute, chronic, nociceptive, or neuropathic that could occur singly or in various combinations. The acute vaso-occlusive painful crisis (VOC) is the most common cause of admissions to the Emergency Department and/or the hospital. Although progress has been made in understanding the pathophysiology of SCD as well as in developing preventive and curative therapies, effective pain management continues to lag behind and depend mostly on the use of opioids. This review describes the history of opioids from the ancient times of opium to the current use of the many controversial opioids. In addition, the major cause of death of patients with SCD is the complications of the disease itself and not the use of opioids. The use of opioids by patients with SCD has been stable over the years. Judicious use of opioids to treat sickle cell pain according to available guidelines could minimize the unnecessary suffering experienced by patients with SCD.

Chronic cancer and non-cancer pain and opioid-induced hyperalgesia share common mechanisms: neuroinflammation and central sensitization

Neuroinflammation, a peculiar form of inflammation that occurs in response to noxious stimuli in peripheral and central nervous system (CNS), consists in altered vascular permeability followed by leukocyte recruitment and activation in the inflamed tissue, release of inflammatory mediators including cytokines and chemokines, and finally in the activation of microglia and astrocytes in the spinal cord and CNS. This phenomenon mediates and even worsen the inflammatory pain in many painful states and is responsible for central sensitization leading to pain chronicity. We describe the major neuroinflammatory mechanisms shared by cancer and non-cancer pain. Particular attention is given to two different chronic inflammatory painful diseases such as the complex regional pain syndrome and the rheumatoid arthritis as prototypes of neuroinflammatory diseases (gliopathies). In addition, we describe the complexity of tumor microenvironment, their main cellular components (tumor cells, tumor infiltrating leukocytes and sensory neurons) and their reciprocal interactions that characterize different forms and intensity of cancer pain. We also hypothesize that one type of cancer pain, the breakthrough pain, can be attributable to receptor-mediated interaction of opioids with tumor cells and intratumoral leukocytes. Surprisingly, long-term opioid treatment shares the same neuroinflammatory potential responsible for the chronicity of both cancer and non-cancer pain; thus, resulting in paradoxical worsening rather than relieving pain. This paradox has upset the world of pain therapy, with neuroinflammation now being a main target of emerging therapies.

Molecular Biology of Opioid Analgesia and Its Clinical Considerations

Understanding the molecular biology of opioid analgesia is essential for its proper implementation and mechanistic approach to its modulation in order to maximize analgesia and minimize undesired effects. By appreciating the molecular mechanisms intrinsic to opioid analgesia, one can manipulate a molecular target to augment or diminish a specific effect using adjuvant drugs, select an appropriate opioid for opioid rotation or define a molecular target for new opioid drug development. In this review, we present the cellular and molecular mechanisms of opioid analgesia and that of the associated phenomena of tolerance, dependence, and hyperalgesia. The specific mechanisms highlighted are those that presently can be clinically addressed.

Reduced postoperative pain using Nociception Level-guided fentanyl dosing during sevoflurane anaesthesia: a randomised controlled trial

Background

The majority of postoperative patients report moderate to severe pain, possibly related to opioid underdosing or overdosing during surgery. Objective guidance of opioid dosing using the Nociception Level (NOL) index, a multiparameter artificial intelligence-driven index designed to monitor nociception during surgery, may lead to a more appropriate analgesic regimen, with effects beyond surgery. We tested whether NOL-guided opioid dosing during general anaesthesia results in less postoperative pain.

Methods

In this two-centre RCT, 50 patients undergoing abdominal surgery under fentanyl/sevoflurane anaesthesia were randomised to NOL-guided fentanyl dosing or standard care in which fentanyl dosing was based on haemodynamics. The primary endpoint of the study was postoperative pain assessed in the PACU.

Results

Median postoperative pain scores were 3.2 (inter-quartile range 1.3–4.3) and 4.8 (3.0–5.3) in NOL-guided and standard care groups, respectively (P=0.006). Postoperative morphine consumption (standard deviation) was 0.06 (0.07) mg kg⁻¹ (NOL-guided group) and 0.09 (0.09) mg kg⁻¹ (control group; P=0.204). During surgery, fentanyl dosing was not different between groups (NOL-guided group: 6.4 [4.2] μg kg⁻¹vs standard care: 6.0 [2.2] μg kg⁻¹, P=0.749), although the variation between patients was greater in the NOL-guided group (% coefficient of variation 66% in the NOL-guided group vs 37% in the standard care group).

Conclusions

Despite absence of differences in fentanyl and morphine consumption during and after surgery, a 1.6-point improvement in postoperative pain scores was observed in the NOL-guided group. We attribute this to NOL-driven rather than BP- and HR-driven fentanyl dosing during anaesthesia.

Clinical trial registration

www.trialregister.nl under identifier NL7845.

Post-Thoracotomy Pain: Current Strategies for Prevention and Treatment

Treating acute pain after thoracotomy surgery and preventing the development of chronic post-thoracotomy pain syndrome (PTPS) remain significant challenges in this surgical population. While appropriately treated acute thoracotomy pain often resolves, a significant number of patients develop PTPS, with up to 65% of patients experiencing some pain and 10% suffering life-altering, debilitating pain. Currently, there is very little known about specific molecular targets or novel therapeutic combinations that effectively prevent PTPS. Identifying modifiable clinical risk factors (procedure, physical and mental health, preoperative pain in the surgical area and another regions) seems to the most pragmatic approach for prevention for now. Effective acute pain management adopting a multimodal approach can result in a decreased incidence of PTPS. Interventional techniques such as paraverterbral blocks, intercostal blocks, and erector spinae blocks show some promise as well. Future research should be focused on minimally invasive surgeries and also the effect of ERAS protocols, including early mobilization, nutrition, and early removal of drains, on the development of PTPS.

How I Treat Acute and Persistent Sickle Cell Pain

Sickle pain is the hallmark of sickle cell disease (SCD). It could be acute, persistent/relapsing, chronic, or neuropathic. Although there is a general consensus that pain is a major manifestation of SCD, there is a controversy as to the types of pain and their interrelationship between acute, chronic, relapsing, persistent, etc. This report first reviews the general approach to the management of acute vaso-occlusive crisis (VOC) pain, including education, counseling, pharmacotherapy, non-pharmacotherapy, and fluid therapy. This is followed by the presentation of five patients that represent typical issues that are commonly encountered in the management of patients with SCD. These issues are: individualized treatment of pain, bilaterality of pain, use of illicit drugs, tolerance to opioids, opioid-induced hyperalgesia, and withdrawal syndrome. The clinical aspects and management of each of these issues are described. Moreover, such complications as tolerance and withdrawal may persist after discharge and may be mistaken as chronic pain rather than resolving, persistent or relapsing pain.

Unintentional Epidural Anesthesia Mimicking Cauda Equina Syndrome from Suprafascial Injection of Liposomal Bupivacaine After Lumbar Foraminotomy: A Case Report

CASE

This case report describes a 46-year-old woman undergoing right-sided L5 to S1 decompression who received liposomal bupivacaine (LB) for postoperative analgesia and developed unintentional epidural anesthesia with symptoms mimicking cauda equina syndrome. The patient's symptoms resolved 72 hours postoperatively, approximately the length that LB typically lasts. At the 16-month follow-up, the patient demonstrated complete neurological function with no lower extremity strength or sensation deficits.

CONCLUSIONS

Tracking of LB into the epidural space after lumbar surgery may cause transient epidural anesthesia with symptoms that mimic cauda equina syndrome.

Effect of Intravenous Lidocaine on Postoperative Pain in Patients Undergoing Intraspinal Tumor Resection: Study Protocol for a Prospective Randomized Controlled Trial

Purpose

Patients undergoing intraspinal tumor resection usually experience severe acute pain, delaying postoperative rehabilitation, and increasing incidence of chronic pain. Recently, an increasing number of studies have found that low-dose intravenous lidocaine infusion during and/or after surgery can reduce opioid usage and the incidence of related side effects, inhibit hyperalgesia and promote recovery. Thus far, no studies have evaluated the analgesic effect and safety of perioperative intravenous lidocaine infusion for intraspinal tumor resection, especially the long-term analgesic effects of patient-controlled analgesia (PCA) with lidocaine during the first postoperative 48 hours. This study tests the hypothesis that intra- and postoperative systemic lidocaine infusion for patients undergoing intraspinal tumor resection can relieve postoperative acute or chronic pain and reduce the opioid dosage and incidence of related side effects without other problems.

Study Design and Methods

This is a prospective, randomized, placebo-controlled, and double-blinded study. In total, 180 participants scheduled for intraspinal tumor resection will be randomly divided into lidocaine and placebo groups. The lidocaine group will be administered lidocaine intravenously during anesthesia and postoperative pain management during the first 48 postoperative hours; the placebo group will be administered normal saline at the same volume, infusion rate, and timing. The primary outcome will be the postoperative visual analog scale (VAS) score. Secondary outcomes will be postoperative cumulative sufentanil consumption, indicators of postoperative recovery, and the incidence of perioperative adverse events.

Discussion

This study investigates the effect of continuous intravenous lidocaine infusion on postoperative sufentanil consumption and VAS scores. The findings will provide a new strategy of anesthesia and analgesia management for intraspinal tumor resection.

Pain Intensity in the First 96 Hours After Abdominal Surgery: A Prospective Cohort Study

OBJECTIVE

Multimodal pain management strategies aim to improve postoperative pain control. The purpose of this study was to analyze pain scores and risk factors for acute postoperative pain after various abdominal surgery procedures.

METHODS

Data on 11 different abdominal surgery procedures were prospectively recorded. Pain intensity (rest, mobilization) and patient satisfaction at discharge were assessed using a visual analog scale (VAS; 0-10), and analgesic consumption was recorded until 96 hours postoperation. Demographic, surgery-related, and pain management-related univariate risk factors for insufficient pain control (VAS ≥ 4) were entered in a multivariate logistic regression model.

RESULTS

A total of 1,278 patients were included. Overall, mean VAS scores were <3 at all time points, and scores at mobilization were consistently higher than at rest (P < 0.05). Thirty percent of patients presented a prolonged VAS score ≥4 at mobilization at 24 hours, significantly higher than at rest (14%, P < 0.05). High pain scores correlated with high opioid consumption, whereas a variability of pain scores was observed in patients with low opioid consumption. The only independent risk factor for moderate and severe pain (VAS ≥ 4) was younger age (<70 years, P = 0.001). The mean satisfaction score was 8.18 ± 1.29.

CONCLUSIONS

Among 1,278 patients, pain was controlled adequately during the first four postoperative days, resulting in high levels of patient satisfaction. Pain levels were higher at mobilization. Younger age was the only independent risk factor for insufficient pain control. Preventive treatment in patients <70 years old and before mobilization could be evaluated for potential improvement.

Evolution of Analgesic Tolerance and Opioid-Induced Hyperalgesia Over 6 Months: Double-Blind Randomized Trial Incorporating Experimental Pain Models

Contributors to the ongoing epidemic of prescription opioid abuse, addiction, and death include opioid tolerance, withdrawal symptoms, and possibly opioid-induced hyperalgesia (OIH). Thirty stable chronic nonmalignant pain patients entered a 6-month long, randomized, double-blind, dose-response, 2-center trial of the potent opioid levorphanol, conducted over a decade ago during an era of permissive opioid prescribing. Eleven were taking no opioids at study entry and eleven were taking between 35 and 122 morphine equivalents. Five weeks titration preceded twenty weeks stable dosing. Tolerance and OIH were inferred individually based on chronic pain ratings, brief pain inventory scores, and results of the brief thermal sensitization model at 5 opioid dosing sessions. Seventeen patients completed. The average final daily opioid dose was 132; range 14 to 300; average addition 105 morphine equivalents. After observed dosing, the brief thermal sensitization area of hyperalgesia changed minimally but the painfulness of skin heating was reduced. Weekly 0 to 100 visual analog scale pain ratings (average 64 at study entry, 48 at end titration, 45 at end stable dosing) decreased a median 19%, but 8 completed with higher visual analog scale ratings. Three completers had evidence of both tolerance and hyperalgesia. A fully-powered trial similar to this feasibility study is ethically questionable. A large-scale pragmatic trial is more realistic. TRIAL REGISTRATION: NCT00275249 Evolution of Analgesic Tolerance With Opioids PERSPECTIVE: A double-blind, 6-month, high-dose opioid feasibility trial, completed years ago, provides critically important data for clinically defining analgesic tolerance and OIH. Overall benefit was small, and 18% of patients had evidence of both tolerance and OIH. Future work requires a different approach than a classic randomized controlled trial design.

Achieving Opioid-Free Major Colorectal Surgery: Is It Possible?

INTRODUCTION

Opioid analgesia remains the mainstay of postoperative pain management strategies despite being associated with many adverse effects. A specific opioid-free protocol was designed to limit opioid usage.

OBJECTIVE

The aim of the study was to audit the opioid-free rate within this protocol and to identify factors that might contribute to opioid-free surgery.

METHODS

A retrospective study of all elective patients receiving abdominal colorectal surgery at the Center for Colon and Rectal Surgery at AdventHealth over 6 months was performed. Data on demographics, indications, perioperative management, outcomes, and inpatient and outpatient analgesic requirements were collected with subsequent analysis.

RESULTS

A total of 303 consecutive patient records were analyzed. Approximately two-thirds (67.7%) of patients did not receive narcotics once they left the postanesthesia care unit as an inpatient. One-third of patients (32.0%) did not receive narcotic analgesia within 30 days of surgery as an outpatient. Patients in the opioid-free cohort were significantly older and had a malignant indication, less perioperative morbidity, and a shorter length of stay.

CONCLUSIONS

Our study demonstrates that opioid-free analgesia is indeed possible in major colorectal surgery. Study limitations include its retrospective nature and that it is from a single institution. Despite these limitations, this study provides proof of concept that opioid-free colorectal surgery is possible within a specific protocol.

Morphine in Plasma and Cerebrospinal Fluid of Patients Addicted to Opiates Undergoing Surgery: High-performance Liquid Chromatography Method

Background

The prevalence of opium addiction among Iranians is considerable. Since endogenous opioid systems may be altered as a consequence of addiction, it is very important to determine the plasma and cerebrospinal fluid (CSF) levels of morphine in Iranian patients addicted to opiates who will undergo surgery.

Methods

We obtained CSF and plasma samples from 50 volunteers with an established opioid addiction pattern. Samples were analyzed using high-performance liquid chromatography (HPLC). Additionally, frequency of nausea and vomiting, baseline heart rate (BHR), and systolic blood pressure (SBP) were recorded within the surgery and postoperatively during a 10-min interval.

Findings

84% of participants were men with a median age of 39.08 years. Mean score of body mass index (BMI) was 23.30 and most of the participants (46%) used opium in its traditional inhaled form. A higher concentration of morphine in blood was found in comparison with CSF (P < 0.001) in relation to the way of use. However, no statistically significant differences were found in relation to the type of addictive substance. No other association was found between the levels of morphine and the clinical characteristics of the patients. Moreover, results revealed no difference between hemodynamic-related data with blood and CSF level in opium-dependent patients.

Conclusion

Quantification of plasma and CSF morphine, both immediately before initiation of surgery and subsequently on recovery room, showed that although clinical efficacy of systemic morphine was poor in addicted patients, it had no effect on patients' hemodynamic variable and following complications after surgery.

Acceptance and Commitment Therapy for Prevention of Chronic Postsurgical Pain and Opioid Use in At-Risk Veterans: A Pilot Randomized Controlled Study

High levels of pain, significant anxiety, or depressive symptoms before surgery put patients at elevated risk for chronic pain and prolonged opioid use following surgery. The purpose of this preliminary study was to assess the efficacy of a 1-day Acceptance and Commitment Therapy (ACT) workshop in "at-risk" veterans for the prevention of chronic pain and opioid use following orthopedic surgery. In a randomized controlled trial, 88 at-risk veterans undergoing orthopedic surgery were assigned to treatment as usual (TAU; n = 44) or TAU plus a 1-day ACT workshop (n = 44). Pain levels and opioid use were assessed up to 3 months following surgery. Pain acceptance and values-based behavior were assessed at baseline and 3-month follow-up. Participants who completed the ACT workshop reached pain and opioid cessation sooner than those in TAU. Postoperative complications exhibited a moderating effect on these outcomes, such that the effects of ACT were greater in patients without complications. Increases in pain acceptance and values-based behavior, processes targeted in ACT, were related to better outcomes. These promising results merit further investigation in a larger clinical trial. Providing an intervention before surgery for at-risk veterans has the potential to change clinical practice from a focus on management of postoperative pain to prevention of chronic pain in at-risk individuals.

PERSPECTIVE

This pilot study compared the effects of a 1-day preventive behavioral intervention (ACT) to TAU in at-risk veterans undergoing orthopedic surgery. Three months following the intervention, veterans receiving ACT exhibited quicker cessation of pain and opioid use. Focusing on preoperative pain management may help prevent chronic postsurgical pain.

Perioperative Surgical Home for the Patient with Chronic Pain

The management of acute pain for the phenotypically different patient who suffers from chronic pain is challenging. The care of these patients is expensive and siloed. The physician-led, multidisciplinary, patient-centric, care coordination framework of the perioperative surgical home is an optimal vehicle for the management of these patients. The engagement of physician anesthesiologists in the optimization, in-hospital management, and postdischarge care of the patient with chronic pain will lead to improved outcomes, reduced health care expenditures, and improve the health of this challenging population.

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.

Δ-opioid receptor inhibition prevents remifentanil-induced post-operative hyperalgesia via regulating GluR1 trafficking and AMPA receptor function

The interaction of remifentanil with glutamate systems has an important role in remifentanil-induced thermal and mechanical hyperalgesia. A previous study by our group suggested that the trafficking and function of glutamate receptor 1 (GluR1) subunits contributes to remifentanil-induced hyperalgesia by regulating the phosphorylation of GluR1 in dorsal horn neurons. The present study demonstrated that δ opioid receptor (DOR) inhibition prevented thermal and mechanical hyperalgesia, which was induced by remifentanil infusion via attenuating GluR1 subunit trafficking and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) function in dorsal horn neurons. Sprague Dawley rats received a plantar incision and remifentanil infusion to induce a model of postoperative hyperalgesia. Thermal and mechanical pain was tested at 8 different time-points. Expression of AMPAR subunits GluR1 and DOR, as well as the phosphorylation status of GluR1 were evaluated by western blot analysis. Furthermore, the function of AMPAR in the spinal dorsal horn was measured by whole-cell patch-clamp recording. Remifentanil-induced thermal and mechanical hyperalgesia appeared after the 60-min infusions, reaching a peak level on day 2 and persisting for 5 days. Remifentanil infusion led to upregulation of membrane expression of the AMPAR subunit GluR1 and DOR (P=0.003 and 0.001, respectively) no change in total GluR1 and DOR expression levels (P=0.244 and 0.531, respectively). Selective DOR inhibitor naltrindole caused a reduction of remifentanil-induced hyperalgesia, which was accompanied by downregulation of membrane levels of GluR1 in the spinal cord (P=0.0013). In addition, DOR inhibition led to downregulation of GluR1 phosphorylated at Ser845. Furthermore, the AMPAR-mediated miniature excitatory post-synaptic current was increased in frequency and in amplitude in dorsal horn neurons (P=0.002 and 0.0011, respectively), which was decreased by incubation with naltrindole. Combined behavioral, western blot and electrophysiological evidence indicated that remifentanil-induced hyperalgesia was mediated by DOR activation, followed by phosphorylation-dependent GluR1 trafficking and AMPAR function enhancement in the spinal cord. DOR appears to be required for remifentanil and incision-induced hyperalgesia development and to be a potential biochemical target for treating opioid-induced postoperative hyperalgesia.

Essential Elements of Multimodal Analgesia in Enhanced Recovery After Surgery (ERAS) Guidelines

Perioperative multimodal analgesia uses combinations of analgesic medications that act on different sites and pathways in an additive or synergistic manner to achieve pain relief with minimal or no opiate consumption. Although all medications have side effects, opiates have particularly concerning, multisystemic, long-term, and short-term side effects, which increase morbidity and prolong admissions. Enhanced recovery is a systematic process addressing each aspect affecting recovery. This article outlines the evidence base forming the current multimodal analgesia recommendations made by the Enhanced Recovery After Surgery Society (ERAS). We describe current evidence and important future directions for effective perioperative multimodal analgesia in enhanced recovery pathways.

Chronic post-amputation pain: peri-operative management - Review

Study design

Narrative review.

Method

Eight bibliographic databases were searched for studies published in the (last five years up until Feb 2017). For the two database searches (Cochrane and DARE), the time frame was unlimited. The review involved keyword searches of the term 'Amputation' AND 'chronic pain'. Studies selected were interrogated for any association between peri-operative factors and the occurrence of chronic post amputation pain (CPAP).

Results

Heterogeneity of study populations and outcome measures prevented a systematic review and hence a narrative synthesis of results was undertaken. The presence of variation in two gene alleles (GCH1 and KCNS1) may be relevant for development of CPAP. There was little evidence to draw conclusions on the association between age, gender and CPAP. Pre-operative anxiety and depression influenced pain intensity post operatively and long-term post amputation pain (CPAP). The presence of pre-amputation pain is correlated to the development of acute and chronic post amputation pain while evidence for the association of post-operative pain with CPAP is modest. Regional anaesthesia and peri-neural catheters improve acute postoperative pain relief but evidence on their efficacy to prevent CPAP is limited. A suggested whole system pathway based on current evidence to optimize peri-operative amputation pain is described.

Conclusion

The current evidence suggests that optimized peri-operative analgesia reduces the incidence of acute peri-operative pain but no firm conclusion can be drawn on reducing risk for CPAP.

Factors associated with high pain intensity during wound care procedures: A model

The most common wound care procedures (WPCs) performed on open wounds are dressing changes and wound cleansing. Dressing changes cause moderate to severe pain in 74% of patients, nearly half (36%) of whom experience severe pain (rated as 8-10 on a 10-point numeric rating scale). The purpose of this paper is to propose a model of clinically accessible factors that can be tested in order to develop a clinical tool to identify which patients are likely to experience high intensity pain during nonoperative WCPs, such as dressing changes. Although multiple factors are known to be associated with pain, the factors selected for this model were limited to those that (1) are supported based on evidence and/or pain mechanisms and (2) are readily accessible to clinicians/practitioners and can be tested as a prediction tool to be used prior to WCPs. This model may be helpful to identify those likely to experience high intensity pain during WCPs. In this way, use of aggressive pain management strategies, including specialty dressings, pharmacologic analgesics, and/or non-pharmacological strategies, such as high intensity transcutaneous electrical stimulation.

Chronic postsurgical pain: is there a possible genetic link?

Persistent or chronic postsurgical pain (CPSP) has been defined as 'pain persisting beyond 2 months'. The cut-off limit of 2 months has been controversial, and some researchers argue for a 3-month period for the definition of CPSP. Multiple mechanisms, including both patient and surgical, have been shown to influence this transition. Patient factors include age, gender, anxiety, depression, somatisation, catastrophising, pre-existing pain anywhere and pain at the site of surgery. The various surgical factors include site and nature of surgery, infection, inflammation and repeat surgery. There is evidence that pre- or post-op chemotherapy and radiotherapy can also contribute towards the chronification of pain after surgery. The question of why pain following surgery or trauma persists long after the normal healing time is not yet fully explained by current evidence. This is frustrating to healthcare providers and intensely disappointing to the patients, many of whom suffer in silence for years. Genetics is now being shown to influence both the onset and the perpetuation of chronic pain in the susceptible patient. The main mechanisms are believed to be 'single nucleotide polymorphisms' (SNPs) and 'epigenetics', both of which will be discussed, with current and ongoing research and evidence, in this review. The influence of SNPs has not been replicated in recent studies and researchers advise caution in interpreting past studies. More research is needed to demonstrate the involvement of epigenetics as well as linking SNPs to the susceptible patient's journey.

Prolonged Perioperative Low-Dose Ketamine Does Not Improve Short and Long-term Outcomes After Pediatric Idiopathic Scoliosis Surgery

STUDY DESIGN

A randomized, double-blind, placebo-controlled study, with a six-month follow-up period.

OBJECTIVES

The aim of this study was to test the hypothesis that a 72-hour dose of subanesthetic ketamine in this surgical procedure reduces postoperative morphine use and to assess whether there are fewer adverse effects, if postoperative recovery is faster, if there is less peri-incisional hyperalgesia, or if there is lower incidence of persistent postsurgical pain.

SUMMARY OF BACKGROUND DATA

Tissue injury and high opioid requirements following posterior spinal fusion surgery produce central sensitization, which can in turn be associated with hyperalgesia and chronic pain. Clinical trials involving this type of procedure using subanesthetic ketamine doses have assessed pain and morphine requirements with contradictory results. The effects of prolonged subanesthetic ketamine doses on postoperative recovery, mechanical hyperalgesia, and the incidence of chronic pain are unknown.

METHODS

A total of 48 pediatric patients between 10 and 18 years diagnosed with idiopathic scoliosis were randomized to receive perioperative low-dose ketamine or placebo for 72 hours. They received general anesthesia, intraoperative remifentanil, and morphine postoperatively (patient-controlled analgesia). We measured morphine consumption, pain at rest and during movement (coughing), undesirable effects, and sedation during morphine treatment. The onset of oral intake, ambulation, and hospital stay were recorded. The extent of the peri-incisional hyperalgesia was measured at 72 hours and pain controls were conducted postsurgery.

RESULTS

Primary endpoint results (total cumulative morphine consumption while admitted) were obtained in 44 patients. Results were 2.72 (SD 1.13) in the placebo group and 3.13 (SD 1.13) in the study group (P = 0.2903), with no significant differences. Moreover, differences were not found between the experimental group and the placebo group in the secondary endpoints analyzed.

CONCLUSION

Our findings do not support the routine combining of prolonged subanesthetic ketamine doses with opioids in posterior fusion surgery in children with idiopathic scoliosis.

LEVEL OF EVIDENCE

2.

Randomised, double-blind, parallel group, placebo-controlled study to evaluate the analgesic efficacy and safety of VVZ-149 injections for postoperative pain following laparoscopic colorectal surgery

INTRODUCTION

In spite of advances in understanding and technology, postoperative pain remains poorly treated for a significant number of patients. In colorectal surgery, the need for developing novel analgesics is especially important. Patients after bowel surgery are assessed for rapid return of bowel function and opioids worsen ileus, nausea and constipation. We describe a prospective, double-blind, parallel group, placebo-controlled randomised controlled trial testing the hypothesis that a novel analgesic drug, VVZ -149, is safe and effective in improving pain compared with providing opioid analgesia alone among adults undergoing laparoscopic colorectal surgery.

METHODS AND ANALYSIS

Based on sample size calculations for primary outcome, we plan to enrol 120 participants. Adult patients without significant medical comorbidities or ongoing opioid use and who are undergoing laparoscopic colorectal surgery will be enrolled. Participants are randomly assigned to receive either VVZ-149 with intravenous (IV) hydromorphone patient-controlled analgesia (PCA) or the control intervention (IV PCA alone) in the postoperative period. The primary outcome is the Sum of Pain Intensity Difference over 8 hours (SPID-8 postdose). Participants receive VVZ-149 for 8 hours postoperatively to the primary study end point, after which they continue to be assessed for up to 24 hours. We measure opioid consumption, record pain intensity and pain relief, and evaluate the number of rescue doses and requests for opioid. To assess safety, we record sedation, nausea and vomiting, respiratory depression, laboratory tests and ECG readings after study drug administration. We evaluate for possible confounders of analgesic response, such as anxiety, depression and catastrophising behaviours. The study will also collect blood sample data and evaluate for pharmacokinetic and pharmacodynamic relationships.

ETHICS AND DISSEMINATION

Ethical approval of the study protocol has been obtained from Institutional Review Boards at the participating institutions. Trial results will be disseminated through scientific conference presentations and by publication in scientific journals.

TRIAL REGISTRATION NUMBER

NCT02489526; pre-results.

Prevention of Remifentanil Induced Postoperative Hyperalgesia by Dexmedetomidine via Regulating the Trafficking and Function of Spinal NMDA Receptors as well as PKC and CaMKII Level In Vivo and In Vitro

Remifentanil-induced secondary hyperalgesia has been demonstrated in both animal experiments and clinical trials. Enhancement of N-methyl-D-aspartate (NMDA) receptor trafficking as well as protein kinase C (PKC) and calmodulin-dependent protein kinase II (CaMKII) have been reported to be involved in the induction and maintenance of central sensitization. In the current study, it was demonstrated that dexmedetomidine could prevent remifentanil-induced hyperalgesia (RIH) via regulating spinal NMDAR-PKC-Ca2+/ CaMKII pathway in vivo and in vitro. We firstly investigated the effect of dexmedetomidine, a highly selective α2-adrenergic receptor agonist, on mechanical and thermal hyperalgesia using a rat model of RIH. NMDA receptor subunits (NR1, NR2A and NR2B) expression and membrane trafficking as well as PKC and CaMKII expression in spinal cord L4-L5 segments were measured by Western blot analysis. The expression of NMDA receptor subunits (NR1, NR2A and NR2B) were also detected by immunohistochemistry. Further more, the effect of dexmedetomidine on NMDA receptor current amplitude and frequency in spinal cord slices were investigated by whole-cell patch-clamp recording. We found that remifentail infusion at 1.2 μg.kg-1.min-1 for 90 min caused mechanical and thermal hyperalgesia, up-regulated NMDA receptor subunits NR1 and NR2B expression in both membrane fraction and total lysate as well as increased PKC and CaMKII expression in spinal cord dorsal horn. Subcutaneously injection of dexmedetomidine at the dose of 50 μg/kg at 30 min before plantar incision significantly attenuated remifentanil-induced mechanical and thermal hyperalgesia from 2 h to 48 h after infusion, and this was associated with reversal of up-regulated NR1 and NR2B subunits in both membrane fraction and total lysate as well as increased PKC and CaMKII expression in spinal cord dorsal horn. Furthermore, remifentanil incubation increased amplitude and frequency of NMDA receptor-induced current in dorsal horn neurons, which was dose-dependently attenuated by dexmedetomidine. These results suggest that dexmedetomidine can significantly ameliorate RIH via modulating the expression, membrane trafficking and function of NMDA receptors as well as PKC and CaMKII level in spinal dorsal horn, which present useful insights into the mechanistic action of dexmedetomidine as a potential anti-hyperalgesic agents for treating RIH.

The role of p38MAPK activation in spinal dorsal horn in remifentanil-induced postoperative hyperalgesia in rats

OBJECTIVES

Remifentanil may induce hyperalgesia. Recent studies implicate a close relationship between post-surgical hyperalgesia and phosphorylation and activation of p38 mitogen-activated protein kinase (p38MAPK) in the spinal microglia. This study aimed to investigate whether the combination of post-surgical and remifentanil-induced hyperalgesia worsens post-operative pain and whether phosphorylated p38MAPK (phospho-p38MAPK) in the spinal dorsal horn in rats is involved in remifentanil-induced postoperative hyperalgesia.

METHODS

Sprague-Dawley rats were randomly divided into six groups: control, incision only, remifentanil only, remifentanil + incision, remifentanil + incision + SB203580, and remifentanil + incision + DMSO. The p38MAPK inhibitor SB203580 and DMSO were injected intrathecally. A right plantar surgical incision was performed in the incision groups, and remifentanil was infused for 60 min in the remifentanil groups. Mechanical paw withdrawal threshold (PWT) and thermal paw withdrawal latency (PWL) of the bilateral hind paws were measured and the number of phospho-p38MAPK-positive cells in rat spinal dorsal horn sections was counted.

RESULTS

Intravenous remifentanil infusion decreased bilateral plantar PWL values from 1 h to 3 days after surgery, however there was no additive effect with incision-induced values. There was a significant increase in the number of dorsal horn phospho-p38MAPK-positive cells in the remifentanil + incision group compared to the incision group, but no increase in the number of these cells when remifentanil was given alone. Intrathecal pretreatment with SB203580 attenuated remifentanil + incision-induced postoperative hyperalgesia and significantly reduced activation of phospho-p38MAPK in spinal dorsal horn.

CONCLUSIONS

Incision-induced and remifentanil-induced increases in hyperalgesia were not additive when incision and remifentanil were used together. Data on phospho-38MAPK activation in remifenanil-induced hyperalgesia were contradictory and need further clarification.

Parecoxib increases muscle pain threshold and relieves shoulder pain after gynecologic laparoscopy: a randomized controlled trial

Objectives

Postlaparoscopic shoulder pain (PLSP) remains a common problem after laparoscopies. The aim of this study was to investigate the correlation between pressure pain threshold (PPT) of different muscles and PLSP after gynecologic laparoscopy, and to explore the effect of parecoxib, a cyclooxygenase-2 inhibitor, on the changes of PPT.

Materials and methods

The patients were randomly allocated into two groups; group P and group C. In group P, parecoxib 40 mg was intravenously infused at 30 minutes before surgery and 8 and 20 hours after surgery. In group C, normal saline was infused at the corresponding time point. PPT assessment was performed 1 day before surgery and at postoperative 24 hours by using a pressure algometer at bilateral shoulder muscles (levator scapulae and supraspinatus) and forearm (flexor carpi ulnaris). Meanwhile, bilateral shoulder pain was evaluated through visual analog scale score at 24 hours after surgery.

Results

Preoperative PPT level of the shoulder, but not of the forearm, was significantly and negatively correlated with the intensity of ipsilateral PLSP. In group C, PPT levels of shoulder muscles, but not of forearm muscles, decreased after laparoscopy at postoperative 24 hours. The use of parecoxib significantly improved the decline of PPT levels of bilateral shoulder muscles (all P<0.01). Meanwhile, parecoxib reduced the incidence of PLSP (group P: 45% vs group C: 83.3%; odds ratio: 0.164; 95% confidence interval: 0.07–0.382; P<0.001) and the intensity of bilateral shoulder pain (both P<0.01).

Conclusion

Preoperative PPT levels of shoulder muscles are closely associated with the severity of shoulder pain after gynecologic laparoscopy. PPT levels of shoulder muscles, but not of forearm muscles, significantly decreased after surgery. Parecoxib improved the decrease of PPT and relieved PLSP.

Involvement of Spinal PKMζ Expression and Phosphorylation in Remifentanil-Induced Long-Term Hyperalgesia in Rats

Up-regulation of GluN2B-containing N-methyl-D-aspartate receptors (NMDARs) expression and trafficking is the key mechanism for remifentanil-induced hyperalgesia (RIH), nevertheless, the signaling pathway and pivotal proteins involved in RIH remain equivocal. PKMζ, an isoform of protein kinase C (PKC), maintains pain memory storage in neuropathic pain and inflammatory pain, which plays a parallel role regulated by NMDARs in long-term memory trace. In the present study, Zeta Inhibitory Peptide (ZIP), a PKMζ inhibitor, and a selective GluN2B antagonist Ro-256981 are injected intrathecally before remifentanil infusion (1 μg kg^-1 min^-1 for 1 h, iv) in order to detect whether GluN2B contributes to RIH through affecting synthesis and activity of PKMζ in spinal dorsal horn. Nociceptive tests are measured by Paw withdrawal mechanical threshold (PWT) and paw withdrawal thermal latency (PWL). The L₄-L₆ segments of dorsal horn taken from rats with RIH are for determining expression of PKMζ and pPKMζ by Western blot and immunohistochemistry. Our data suggest that remifentanil infusion causes an increase of PKMζ in expression and phosphorylation in rats with nociceptive sensitization, beginning at 2 h, peaked at 2 days, and returned to basal level at 7 days. ZIP (10 ng) could block behavioral sensitization induced by remifentanil. Ro25-6981 dosage-dependently attenuated mechanical and thermal hyperalgesia and reversed expression of PKMζ and pPKMζ, indicating that GluN2B-containing NMDA receptor facilitates development of RIH through mediating expression and activity of spinal PKMζ in rats. Although detailed mechanisms require further comprehensive study, the preventive role of Ro25-6981 and ZIP provide novel options for the effective precaution of RIH in clinics.

Fentanyl-induced hyperalgesia in acute pain management

There are safety concerns with the use of fentanyl, including respiratory depression, nausea, constipation, and possibly opioid-induced hyperalgesia (OIH). The purpose of this review is to evaluate the occurrence and significance of opioid-induced hyperalgesia (OIH) after acute fentanyl exposure. A literature search was conducted from October 1995 through January 2015 using MEDLINE, Embase, and Scopus with the terms hyperalgesia, fentanyl, pronociceptive, acute tolerance, and acute. Published articles evaluating the adverse effects of fentanyl during acute pain management (≤96 hours) in humans were included. Opioid-induced hyperalgesia is a phenomenon defined by increasing pain after opioid exposure with the worsening of pain occurring when opioid doses are increased. Hyperalgesia has been described following remifentanil and morphine use, but the question remains about the associated risk with acute fentanyl exposure. Six randomized, controlled trials evaluating the effect of fentanyl on pain in the acute setting have been conducted. Two trials oppose whereas four trials support the occurrence of fentanyl-induced hyperalgesia. The data on OIH after acute fentanyl exposure are limited and conflicting. Hyperalgesia should be considered in patients with uncontrolled pain despite escalating fentanyl doses, since the possibility of fentanyl-induced OIH exists in the acute setting. Well-designed trials are needed to determine the clinical significance of this phenomenon.