Pathophysiology of postoperative pain

Identification of a novel protein Hq023 of the hard tick Haemaphysalis qinghaiensis and preliminary evaluation of its analgesic effect in mice model

Tick saliva contains a range of critical biological molecules which could inhibit host defenses and guarantee their food supply. Hq023, a novel cDNA sequence, was cloned from a cDNA library constructed from salivary glands of partially-engorged Haemaphysalis qinghaiensis. Hq023 has an open reading frame (ORF) of 408 bp coding a protein containing 135 amino acid residues with a molecular mass of 15 kDa. Database homology showed that Hq023 protein was structurally similar to a natural toxin U33-theraphotoxin-Cg1c from the Chinese tarantula Chilobrachys guangxiensis. A recombinant protein was expressed with the novel cDNA in a prokaryotic system and its analgesic effect was evaluated in mice model. Both tail immersion and hot-plate tests uncovered an antinociceptive activity, while in the acetic acid-induced writhing test this effect was not observed. These results indicated that the novel recombinant protein Hq023 (rHq023) probably possessed a central antinociceptive activity. Finding of the novel protein might pave a new avenue for the development of tick-derived analgesics.

Role of Pregabalin in Pre-Operative and Post-Operative Pain Management of Lower Limb Orthopedic Surgeries

Introduction

Post-operative pain after orthopedic surgery has remained a challenging problem, which prolongs hospital stay and early rehabilitation. Pregabalin comes under the class of gabapentinoids that have been used in postoperative pain in arthroplasty and spine surgeries but studies regarding its role as pre-emptive analgesia in orthopedic limb surgeries are very few.

Aims

To compare the efficacy of pre-operative pregabalin with a placebo drug in early post-operative pain management for lower limb orthopedics surgeries.

Materials and Methods

A randomized double blinded prospective study was undertaken. Sixty patients were enrolled with age between 18 and 70 years and were divided into 2 groups. Group A - received 150 mg of oral pregabalin capsule, and Group B - received matched color empty capsules. Standard spinal anesthesia was given. Breakthrough analgesia was given with an injection of tramadol 50 mg intravenous. Assessment of pain was done with a Visual Analog Scale (VAS) at 6, 12, 24, and 48 h.

Results

In comparison to Group B, Group A had a significantly lower postoperative VAS score and required much less breakthrough analgesia within the 1st 24 h after surgery.

Conclusion

In orthopedic lower limb fracture surgeries, pre-emptive pregabalin of 150 mg provides adequate postoperative analgesia with relatively few unfavorable side effects.

Opioid free analgesia after return home in ambulatory colonic surgery patients: a single-center observational study

BACKGROUND

Because of the adverse effects of morphine and its derivatives, non-opioid analgesia procedures are proposed after outpatient surgery. Without opioids, the ability to provide quality analgesia after the patient returns home may be questioned. We examined whether an opioid-free strategy could ensure satisfactory analgesia after ambulatory laparoscopic colectomy.

METHODS

We performed a retrospective observational single-center study (of prospective collected database) including all patients eligible for scheduled outpatient colectomy. Postoperative analgesia was provided by paracetamol and nefopam. Postoperative follow-up included pain at mobilization (assessed by a numerical rating scale, NRS), hemodynamic variables, temperature, resumption of transit and biological markers of postoperative inflammation. The primary outcome was the proportion of patients with moderate to severe pain (NRS > 4) the day after surgery.

RESULTS

Data from 144 patients were analyzed. The majority were men aged 59 ± 12 years with a mean BMI of 27 [25-30] kg/m2. ASA scores were 1 for 14%, 2 for 59% and 3 for 27% of patients. Forty-seven patients (33%) underwent surgery for cancer, 94 for sigmoiditis (65%) and 3 (2%) for another colonic pathology. Postoperative pain was affected by time since surgery (Q3 = 52.4,p < 0.001) and decreased significantly from day to day. The incidence of moderate to severe pain at mobilization (NRS > 4) on the first day after surgery was (0.19; 95% CI, 0.13-0.27).

CONCLUSION

Non-opioid analgesia after ambulatory laparoscopic colectomy seems efficient to ensure adequate analgesia. This therapeutic strategy makes it possible to avoid the adverse effects of opioids.

TRIAL REGISTRATION

The study was retrospectively registered and approved by the relevant institutional review board (CERAR) reference IRB 00010254-2018 - 188). All patients gave written informed consent for analysis of their data. The anonymous database was declared to the French Data Protection Authority (CNIL) (reference 221 2976 v0 of April 12, 2019).

Adding Ketamine to Epidural Morphine Does Not Prolong Postoperative Analgesia After Lumbar Laminectomy or Discectomy

BACKGROUND

Epidural opioids provide effective postoperative analgesia after lumbar spine surgery. Ketamine has been shown to reduce opioid-induced central sensitization and hyperalgesia. We hypothesized that adding ketamine to epidural opioids would prolong the duration of analgesia and enhance analgesic efficacy after lumbar spine surgery.

METHODS

American Society of Anesthesiologists physical status class I to II patients aged between 18 and 70 years with normal renal function undergoing lumbar laminectomy were recruited into this single-center randomized trial. Patients were randomized to receive either single-dose epidural morphine (group A) or epidural morphine and ketamine (group B) for postoperative analgesia. The primary objective was to compare the duration of analgesia as measured by time to the first postoperative analgesic request. Secondary objectives were the comparison of pain scores at rest and movement, systemic hemodynamics, and the incidence of side effects during the first 24 hours after surgery.

RESULTS

Fifty patients were recruited (25 in each group), of which data from 48 were available for analysis. The mean±SD duration of analgesia was 20±6 and 23±3 hours in group A and group B, respectively ( P =0.07). There were 12/24 (50%) patients in group A and 17/24 (71%) patients in group B who did not receive rescue analgesia during the first 24-hour postoperative period ( P =0.07). Pain scores at rest and movement, systemic hemodynamics, and postoperative complications were comparable between the groups.

CONCLUSIONS

The addition of ketamine to epidural morphine did not prolong the duration of analgesia after lumbar laminectomy.

Surgical incision pain induced an increase in alcohol consumption in mice

INTRODUCTION

Large population-based studies have suggested a link between increased alcohol use and reduced pain. In addition, these studies suggest that higher levels of pain intensity are associated with an increase in alcohol consumption and rates of hazardous drinking which potentiates the risk of developing alcohol use disorders (AUD). The mechanisms and determinants of the alcohol-pain interaction can be studied in preclinical studies.

METHODS

The overall goal of this study is to use animal models to explore the impact of acute postoperative pain on alcohol intake. To achieve this, we characterized the timeline and levels of alcohol intake and preference in mice after laparotomy in the 2-bottle choice paradigm.

RESULTS

Our results show that laparotomy surgery increased alcohol intake and preference in male mice but not females in the 2-bottle choice and 3-bottle choice assays. In addition, ketoprofen administration blocked the increase in alcohol consumption in male mice after laparotomy. We also found that changes in alcohol initial sensitivity and acute functional tolerance, using loss of righting reflex (LORR) response, occur after surgery in mice.

CONCLUSION

Taken together, these findings suggests that sex, pain and alcohol sensitivity-related factors may modulate the relationship between alcohol consumption and pain.

Local Magnesium Sulfate Administration Ameliorates Nociception, Peripheral Inflammation, and Spinal Sensitization in a Rat Model of Incisional Pain

OBJECTIVE

Postoperative pain remains one of the most common complaints after surgery, and appropriate treatments are limited.

METHODS

We therefore investigated the effect of the anti-nociceptive properties of magnesium sulfate (MgSO4), an N-methyl-D-aspartate (NMDA) receptor antagonist, on incision-induced postoperative pain and peripheral and central nervous system inflammation.

RESULTS

We found that local MgSO4 administration dose-dependently increases paw withdrawal latency, indicating reduced peripheral postoperative pain. Furthermore, MgSO4 inhibited the expression of interleukin-1β (IL-1β) and inducible nitric oxide synthase (iNOS) and phosphorylation of the NMDA receptor NR1 subunit in injured paw tissue and significantly attenuated microglial and astrocytic activation in the ipsilateral lumbar spinal cord dorsal horn.

CONCLUSION

Locally administered MgSO4 has potential for development as an adjunctive therapy for preventing central nociceptive sensitization.

Movement-evoked Pain versus Pain at Rest in Postsurgical Clinical Trials and in Meta-analyses: An Updated Systematic Review

BACKGROUND

Given the widespread recognition that postsurgical movement-evoked pain is generally more intense, and more functionally relevant, than pain at rest, the authors conducted an update to a previous 2011 review to re-evaluate the assessment of pain at rest and movement-evoked pain in more recent postsurgical analgesic clinical trials.

METHODS

The authors searched MEDLINE and Embase for postsurgical pain randomized controlled trials and meta-analyses published between 2014 and 2023 in the setting of thoracotomy, knee arthroplasty, and hysterectomy using methods consistent with the original 2011 review. Included trials and meta-analyses were characterized according to whether they acknowledged the distinction between pain at rest and movement-evoked pain and whether they included pain at rest and/or movement-evoked pain as a pain outcome. For trials measuring movement-evoked pain, pain-evoking maneuvers used to assess movement-evoked pain were tabulated.

RESULTS

Among the 944 included trials, 504 (53%) did not measure movement-evoked pain (vs. 61% in 2011), and 428 (45%) did not distinguish between pain at rest and movement-evoked pain when defining the pain outcome (vs. 52% in 2011). Among the 439 trials that measured movement-evoked pain, selection of pain-evoking maneuver was highly variable and, notably, was not even described in 139 (32%) trials (vs. 38% in 2011). Among the 186 included meta-analyses, 94 (51%) did not distinguish between pain at rest and movement-evoked pain (vs. 71% in 2011).

CONCLUSIONS

This updated review demonstrates a persistent limited proportion of trials including movement-evoked pain as a pain outcome, a substantial proportion of trials failing to distinguish between pain at rest and movement-evoked pain, and a lack of consistency in the use of pain-evoking maneuvers for movement-evoked pain assessment. Future postsurgical trials need to (1) use common terminology surrounding pain at rest and movement-evoked pain, (2) assess movement-evoked pain in virtually every trial if not contraindicated, and (3) standardize movement-evoked pain assessment with common, procedure-specific pain-evoking maneuvers. More widespread knowledge translation and mobilization are required in order to disseminate this message to current and future investigators.

EDITOR’S PERSPECTIVE

β-Caryophyllene Inhibits Monoacylglycerol Lipase Activity and Increases 2-Arachidonoyl Glycerol Levels In Vivo: A New Mechanism of Endocannabinoid-Mediated Analgesia?

The mechanisms of β-caryophyllene (BCP)-induced analgesia are not well studied. Here, we tested the efficacy of BCP in an acute postsurgical pain model and evaluated its effect on the endocannabinoid system. Rats were treated with vehicle and 10, 25, 50, and 75 mg/kg BCP. Paw withdrawal responses to mechanical stimuli were evaluated using an electronic von Frey anesthesiometer. Endocannabinoids, including 2-arachidonoylglycerol (2-AG), were also evaluated in plasma and tissues using high-performance liquid chromatography-tandem mass spectrometry. Monoacylglycerol lipase (MAGL) activity was evaluated in vitro as well as ex vivo. We observed a dose-dependent and time-dependent alleviation of hyperalgesia in incised paws up to 85% of the baseline value at 30 minutes after administration of BCP. We also observed dose-dependent increases in the 2-AG levels of about threefold after administration of BCP as compared with vehicle controls. Incubations of spinal cord tissue homogenates from BCP-treated rats with isotope-labeled 2-arachidonoylglycerol-d8 revealed a reduced formation of the isotope-labeled MAGL product 2-AG-d8 as compared with vehicle controls, indicating MAGL enzyme inhibition. In vitro MAGL enzyme activity assessment using 2-AG as the substrate revealed an IC50 of 15.8 µM for MAGL inhibition using BCP. These data showed that BCP inhibits MAGL activity in vitro and in vivo, causing 2-AG levels to rise. Since the endocannabinoid 2-AG is a CB1 and CB2 receptor agonist, we propose that 2-AG-mediated cannabinoid receptor activation contributes to BCP's mechanism of analgesia. SIGNIFICANCE STATEMENT: β-Caryophyllene (BCP) consumption is relatively safe and is approved by the Food and Drug Administration as a flavoring agent, which can be used in cosmetic and food additives. BCP is a potent anti-inflammatory agent that showed substantial antihyperalgesic properties in this study of acute pain suggesting that BCP might be an alternative to opioids. This study shows an additive mechanism (monoacylglycerol lipase inhibition) by which BCP might indirectly alter CB1 and CB2 receptor activity and exhibit its pharmacological properties.

Prediction of early postoperative pain using sleep quality and heart rate variability

PURPOSE

Accurate predictions of postoperative pain intensity are necessary for customizing analgesia plans. Insomnia is a risk factor for severe postoperative pain. Moreover, heart rate variability (HRV) can provide information on the sympathetic-parasympathetic balance in response to noxious stimuli. We developed a prediction model that uses the insomnia severity index (ISI), HRV, and other demographic factors to predict the odds of higher postoperative pain.

METHODS

We recruited gynecological surgery patients classified as American Society of Anesthesiologists class 1-3. An ISI questionnaire was completed 1 day before surgery. HRV was calculated offline using intraoperative electrocardiogram data. Pain severity at the postanesthesia care unit (PACU) was assessed with the 0-10 numerical rating scale (NRS). The primary outcome was the model's predictive ability for moderate-to-severe postoperative pain. The secondary outcome was the relationship between individual risk factors and opioid consumption in the PACU.

RESULTS

Our study enrolled 169 women. Higher ISI scores (p = 0.001), higher parasympathetic activity (rMSSD, pNN50, HF; p < 0.001, p < 0.001, p < 0.001), loss of fractal dynamics (SD2, alpha 1; p = 0.012, p = 0.039) in HRV analysis before the end of surgery were associated with higher NRS scores, while laparoscopic surgery (p = 0.031) was associated with lower NRS scores. We constructed a multiple logistic model (area under the curve = 0.852) to predict higher NRS scores at PACU arrival. The five selected predictors were age (OR: 0.94; p = 0.020), ISI score (OR: 1.14; p = 0.002), surgery type (laparoscopic or open; OR: 0.12; p < 0.001), total power (OR: 2.02; p < 0.001), and alpha 1 (OR: 0.03; p < 0.001).

CONCLUSION

We employed a multiple logistic regression model to determine the likelihood of moderate-to-severe postoperative pain upon arrival at the PACU. Physicians could personalize analgesic regimens based on a deeper comprehension of the factors that contribute to postoperative pain.

The Role of Neuroactive Steroids in Analgesia and Anesthesia: An Interesting Comeback?

Published evidence over the past few decades suggests that general anesthetics could be neurotoxins especially when administered at the extremes of age. The reported pathology is not only at the morphological level when examined in very young and aged brains, given that, importantly, newly developing evidence suggests a variety of behavioral impairments. Since anesthesia is unavoidable in certain clinical settings, we should consider the development of new anesthetics. A promising and safe solution could be a new family of anesthetics referred to as neuroactive steroids. In this review, we summarize the currently available evidence regarding their anesthetic and analgesic properties.

Neurovascular Compression-Induced Intracranial Allodynia May Be the True Nature of Migraine Headache: an Interpretative Review

PURPOSE OF REVIEW

Surgical deactivation of migraine trigger sites by extracranial neurovascular decompression has produced encouraging results and challenged previous understanding of primary headaches. However, there is a lack of in-depth discussions on the pathophysiological basis of migraine surgery. This narrative review provides interpretation of relevant literature from the perspective of compressive neuropathic etiology, pathogenesis, and pathophysiology of migraine.

RECENT FINDINGS

Vasodilation, which can be asymptomatic in healthy subjects, may produce compression of cranial nerves in migraineurs at both extracranial and intracranial entrapment-prone sites. This may be predetermined by inherited and acquired anatomical factors and may include double crush-type lesions. Neurovascular compression can lead to sensitization of the trigeminal pathways and resultant cephalic hypersensitivity. While descending (central) trigeminal activation is possible, symptomatic intracranial sensitization can probably only occur in subjects who develop neurovascular entrapment of cranial nerves, which can explain why migraine does not invariably afflict everyone. Nerve compression-induced focal neuroinflammation and sensitization of any cranial nerve may neurogenically spread to other cranial nerves, which can explain the clinical complexity of migraine. Trigger dose-dependent alternating intensity of sensitization and its synchrony with cyclic central neural activities, including asymmetric nasal vasomotor oscillations, may explain the laterality and phasic nature of migraine pain. Intracranial allodynia, i.e., pain sensation upon non-painful stimulation, may better explain migraine pain than merely nociceptive mechanisms, because migraine cannot be associated with considerable intracranial structural changes and consequent painful stimuli. Understanding migraine as an intracranial allodynia could stimulate research aimed at elucidating the possible neuropathic compressive etiology of migraine and other primary headaches.

Kidney Donor Perspectives on Acute Postoperative Pain Management

This study employed a qualitative descriptive approach to examine living kidney donor's experience of postoperative pain. Thirteen living kidney donors aged 46.5 (±14.4) years participated in this study. Semi-structured interviews were conducted and transcribed. Transcripts were inductively coded and reviewed for trends, patterns, and insights into donor's experience of postoperative pain. Donors experienced postoperative pain from a variety of sources that hindered recovery and created anxiety and fear in some. Donors managed pain with opioid and non-opioid medications, social support, and ambulation. Donor's past experiences with and expectations about pain, relationships with intended recipients, social support, as well as motivations for and meaning of donation informed their experience of postoperative pain. Prompt pharmacologic intervention for pain, as well as further coaching and education about pain management should be emphasized for nurses caring for living kidney donors. Further study of how donor's motivation might mediate their pain experience is needed.

Is Lidocaine Patch Beneficial for Postoperative Pain?: A Meta-analysis of Randomized Clinical Trials

OBJECTIVES

The aim of this meta-analysis was to evaluate whether a lidocaine patch is beneficial for postoperative pain as an option for multimodal analgesia.

METHODS

Information was obtained from PubMed, Embase, and the Cochrane Central Register of Controlled Trials for clinical randomized controlled trials of lidocaine patches for postoperative pain (as of March 2022). Two researchers independently completed study screening, risk bias assessment, and data extraction. Review Manager (version 5.4, Cochrane Collaboration) was used to conduct the meta-analysis. The evaluation metrics were postoperative pain scores, opioid consumption, and patient satisfaction.

RESULTS

Sixteen randomized controlled trials were included, and data from 918 patients were available. Pain scores differed between the 2 groups at 12, 24, and 48 hours postoperatively, and the pain scores of the lidocaine patch group were significantly lower (mean difference [MD]=-1.32 [95% CI, -1.96 to -0.68], P <0.0001; I2 =92%) at 12 hours after the operation; (MD=-1.23 [95% CI, -1.72 to -0.75], P <0.00001; I2 =92%) at 24 hours after the operation; and (MD=-0.25 [95% CI,-0.29 to -0.21], P <0.00001; I2 =98%) at 48 hours after the operation. In addition, the lidocaine patch group had decreased opioid requirements (MD=-3.57 [95% CI, -5.06 to -2.09], P <0.00001; I2 =96%). The lidocaine patch group seemed to be more satisfied, but there was no statistically significant difference (risk ratio, 1.50 [95% CI, 0.74 to 3.05], P =0.26) between the groups.

DISCUSSION

Lidocaine patches are beneficial for postoperative pain and can be used in multimodal analgesia to reduce opioid use, but there is no significant increase in patient satisfaction with pain control. More data are needed to support this conclusion due to the large heterogeneity in the present study.

Comparison between supra-inguinal fascia iliaca and pericapsular nerve group blocks on postoperative pain and functional recovery after total hip arthroplasty: A noninferiority randomised clinical trial

BACKGROUND

Pain after a posterolateral approach for total hip arthroplasty (THA) may affect early functional recovery. Supra-inguinal fascia iliaca (SFIB) and pericapsular nerve group (PENG) blocks have been proposed as promising analgesia techniques.

OBJECTIVES

This trial was conducted to compare a PENG with a SFIB for controlling postoperative pain and for providing functional recovery.

DESIGN

Noninferiority monocentric randomised controlled study.

SETTING

One hundred and two patients scheduled for a total hip arthroplasty via the posterolateral approach under spinal anaesthesia were prospectively allocated to two groups. Data acquisition occurred between October 2021 and July 2022 at the University Hospital of Liege.

PATIENTS

One hundred and two patients completed the trial.

INTERVENTIONS

Group SFIB received supra-inguinal fascia iliaca block (SFIB) (40 ml ropivacaine 0.375%), whereas group PENG received a PENG block (20 ml ropivacaine 0.75%).

MAIN OUTCOME MEASURES

Rest and mobilisation pain on a 0 to 10 numeric rating scale at fixed time points: 1 and 6 h after surgery, on day-1 and day-2 at 8 a.m.,1 p.m. and 6 p.m. On day-1 and day-2, evolution of quality-of-recovery-15 score was assessed, and timed-up-and-go, 2 and 6 min-walking tests. The noninferiority margin was set as 1 numeric rating scale point 6 h after surgery.

RESULTS

Six hours after surgery, pain scores in group PENG were noninferior to those of group SFIB, with a difference between medians at 0 (95% CI -0.93 to 0.93). There were no significant differences between the groups regarding rest and dynamic pain trajectories during the first 48 postoperative hours, with no significant effects of group (rest P  = 0.800; dynamic P  = 0.708) or interaction between group and time (rest P  = 0.803; dynamic P  = 0.187). Similarly, no significant differences were observed regarding motor and functional recovery as assessed by timed-up-and-go ( P  = 0.197), 2 min ( P  = 0.364), and 6 min walking ( P  = 0.347) tests and quality-of-recovery-15 ( P  = 0.417) score.

CONCLUSION

Following a total hip arthroplasty via the posterolateral approach, a PENG block is noninferior to SFIB regarding postoperative pain control 6 h after surgery, and functional recovery.

TRIAL REGISTRATION

European Clinical Trial Register under EudraCT-number 2020-005126-28 ( https://www.clinicaltrialsregister.eu/ctr-search/trial/2020-005126-28/BE ).

The mechanisms and management of persistent postsurgical pain

An estimated 10%-50% of patients undergoing a surgical intervention will develop persistent postsurgical pain (PPP) lasting more than 3 months despite adequate acute pain management and the availability of minimally invasive procedures. The link between early and late pain outcomes for surgical procedures remains unclear-some patients improve while others develop persistent pain. The elective nature of a surgical procedure offers a unique opportunity for prophylactic or early intervention to prevent the development of PPP and improve our understanding of its associated risk factors, such as pre-operative anxiety and the duration of severe acute postoperative pain. Current perioperative pain management strategies often include opioids, but long-term consumption can lead to tolerance, addiction, opioid-induced hyperalgesia, and death. Pre-clinical models provide the opportunity to dissect mechanisms underpinning the transition from acute to chronic, or persistent, postsurgical pain. This review highlights putative mechanisms of PPP, including sensitisation of peripheral sensory neurons, neuroplasticity in the central nervous system and nociceptive signalling along the neuro-immune axis.

The waiting game: investigating the neurobiological transition from acute to persistent pain in adolescent rats

Persistent postsurgical pain affects 20% of youth undergoing a surgical procedure, with females exhibiting increased prevalence of chronic pain compared with males. This study sought to examine the sexually-dimorphic neurobiological changes underlying the transition from acute to persistent pain following surgery in adolescence. Male and female Sprague Dawley rats were randomly allocated to a sham or injury (plantar-incision surgery) condition and assessed for pain sensitivity while also undergoing magnetic resonance imaging at both an acute and chronic timepoint within adolescence. We found that injury resulted in persistent pain in both sexes, with females displaying most significant sensitivity. Injury resulted in significant gray matter density increases in brain areas including the cerebellum, caudate putamen/insula, and amygdala and decreases in the hippocampus, hypothalamus, nucleus accumbens, and lateral septal nucleus. Gray matter density changes in the hippocampus and lateral septal nucleus were driven by male rats whereas changes in the amygdala and caudate putamen/insula were driven by female rats. Overall, our results indicate persistent behavioral and neurobiological changes following surgery in adolescence, with sexually-dimorphic and age-specific outcomes, highlighting the importance of studying both sexes and adolescents, rather than extrapolating from male adult literature.

Effects of Physical Exercise and Motor Activity on Oxidative Stress and Inflammation in Post-Mastectomy Pain Syndrome

It is estimated that 10–50% of interventions can generate persistent post-surgical pain. Chronic post-mastectomy pain is a condition persisting for at least three months after surgery. It has been shown that physical activity in the cancer patient allows the improvement of the pain symptom. The aim of this study was to evaluate the effects of physical activity on the intensity and interference of chronic pain in the quality of life of women underwent mastectomy needed for breast cancer removal. The secondary objective was to measure the effects of physical activity on inflammatory and oxidative markers in the same population. A Numeric Rating Scale (NRS) was used to assess pain intensity, and Brief Inventory Pain (BIP) was used for assessing interference of pain in quality of life. Physical activity was measured with the International Physical Activity Questionnaire (IPAQ). Inflammatory mediators such as interleukin (IL)-6, IL-8, tumor necrosis factor (TNF)-α, c-reactive protein (CRP), and biomarkers of oxidative stress malondialdehyde (MDA), superoxide dismutase (SOD), and catalase (CAT) were evaluated in the blood of patients. All the evaluations were performed after three and six months after surgery. Results showed that adequate physical activity can diminish intensity and interference of pain and that these effects are associated with a reduction of blood biomarkers of inflammation.

Buprenorphine for acute post-surgical pain: A systematic review and meta-analysis

Our study was designed to evaluate the efficacy of buprenorphine for the management of acute post-surgical pain reported in published studies in the years 2015-2022. Comprehensive research was performed by using online resources like PUBMED and the Wiley Library database to gather the relevant literature. Two authors were assigned to independently collect the information. Cochran's Q-test and I square statistic were used to determine the heterogeneity across the studies. Publication bias was estimated by using the Egger regression analysis and found to be significantly present once the P value <0.05. In this review, 15 studies were included. The pooled ratio of pain reduction after 12 hours of surgery was reported as 11.2% with 97% heterogeneity. Day one shows 5.9 reductions in pain with 98% heterogeneity. The 3% more pain was reduced on day 2. The day 3 pooled pain reduction score was observed as 1.9%. The overall pool prevalence of pain reduction was noted as 6.2% at different time duration with significant heterogeneity of 100%. Buprenorphine transdermal and sublingual both have significant pain relief scores. The analgesic drug consumption was reduced at the end of the follow-up duration.

Chronic pain and local pain in usually painless conditions including neuroma may be due to compressive proximal neural lesion

It has been unexplained why chronic pain does not invariably accompany chronic pain-prone disorders. This question-driven, hypothesis-based article suggests that the reason may be varying occurrence of concomitant peripheral compressive proximal neural lesion (cPNL), e.g., radiculopathy and entrapment plexopathies. Transition of acute to chronic pain may involve development or aggravation of cPNL. Nociceptive hypersensitivity induced and/or maintained by cPNL may be responsible for all types of general chronic pain as well as for pain in isolated tissue conditions that are usually painless, e.g., neuroma, scar, and Dupuytren's fibromatosis. Compressive PNL induces focal neuroinflammation, which can maintain dorsal root ganglion neuron (DRGn) hyperexcitability (i.e., peripheral sensitization) and thus fuel central sensitization (i.e., hyperexcitability of central nociceptive pathways) and a vicious cycle of chronic pain. DRGn hyperexcitability and cPNL may reciprocally maintain each other, because cPNL can result from reflexive myospasm-induced myofascial tension, muscle weakness, and consequent muscle imbalance- and/or pain-provoked compensatory overuse. Because of pain and motor fiber damage, cPNL can worsen the causative musculoskeletal dysfunction, which further accounts for the reciprocity between the latter two factors. Sensitization increases nerve vulnerability and thus catalyzes this cycle. Because of these mechanisms and relatively greater number of neurons involved, cPNL is more likely to maintain DRGn hyperexcitability in comparison to distal neural and non-neural lesions. Compressive PNL is associated with restricted neural mobility. Intermittent (dynamic) nature of cPNL may be essential in chronic pain, because healed (i.e., fibrotic) lesions are physiologically silent and, consequently, cannot provide nociceptive input. Not all patients may be equally susceptible to develop cPNL, because occurrence of cPNL may vary as vary patients' predisposition to musculoskeletal impairment. Sensitization is accompanied by pressure pain threshold decrease and consequent mechanical allodynia and hyperalgesia, which can cause unusual local pain via natural pressure exerted by space occupying lesions or by their examination. Worsening of local pain is similarly explainable. Neuroma pain may be due to cPNL-induced axonal mechanical sensitivity and hypersensitivity of the nociceptive nervi nervorum of the nerve trunk and its stump. Intermittence and symptomatic complexity of cPNL may be the cause of frequent misdiagnosis of chronic pain.

Ultrasound-Guided Transversus Abdominis Plane Block Versus Single-Shot Epidural Block for Postoperative Analgesia in Patients Undergoing Inguinal Hernia Surgery

Background Transversus abdominis plane (TAP) block and epidural analgesia are two frequently used regional anaesthesia techniques that attenuate postoperative pain after inguinal hernia repair.  Aim To compare the analgesic efficacy between the single-shot epidural block and TAP block for postoperative analgesia in patients undergoing inguinal hernia repair surgery.  Methods Forty patients of either gender undergoing elective inguinal hernia surgery of American Society of Anesthesiologists (ASA) class Ⅰ and Ⅱ were randomly allocated into two groups. Group E received a single-shot epidural with 20 ml of 0.25% bupivacaine. Group T received a TAP block with 20 ml of 0.25% bupivacaine under ultrasound guidance. Postoperative pain was evaluated by the visual analog scale (VAS). Rescue analgesia was given on VAS score ≥ 4 or on-demand in the postoperative period. The primary outcome included VAS score at 15 min, 1st h, 2nd h, 6th h, 12th h, and 24th h after the block. The secondary outcome was the analgesia duration, the total rescue analgesia dose required, and the patient satisfaction level. Results The VAS pain scores were significantly lower in the epidural group compared to the TAP group at the 2nd, 6th, 12th, and 24th h postoperatively (p<0.0001). The mean duration of analgesia was significantly more in Group E (576.75±96.64 min) compared to Group T (276.75±105.56 min). The total analgesic consumption was seen significantly more in 24 h in Group T than in Group E. Patient satisfaction score was significantly higher with a mean value of 5.55±0.6 in group E compared to 4.75±0.72 in group T. Conclusion A single-shot epidural provides better postoperative pain control than a TAP block. The duration of the first analgesic demand was prolonged, with less analgesic consumption in the epidural group.

Intraoperative abobotulinumtoxinA alleviates pain after surgery and improves general wellness in a translational animal model

Pain after surgery remains a significant healthcare challenge. Here, abobotulinumtoxinA (aboBoNT-A, DYSPORT) was assessed in a post-surgical pain model in pigs. Full-skin-muscle incision and retraction surgery on the lower back was followed by intradermal injections of either aboBoNT-A (100, 200, or 400 U/pig), vehicle (saline), or wound infiltration of extended-release bupivacaine. We assessed mechanical sensitivity, distress behaviors, latency to approach the investigator, and wound inflammation/healing for 5-6 days post-surgery. We followed with immunohistochemical analyses of total and cleaved synaptosomal-associated protein 25 kD (SNAP25), glial fibrillary acidic protein (GFAP), ionized calcium-binding adaptor protein-1(Iba1), calcitonin gene-related peptide (CGRP) and substance P (SP) in the skin, dorsal root ganglia (DRG) and the spinal cord of 400 U aboBoNT-A- and saline-treated animals. At Day 1, partial reversal of mechanical allodynia in aboBoNT-A groups was followed by a full reversal from Day 3. Reduced distress and normalized approaching responses were observed with aboBoNT-A from 6 h post-surgery. Bupivacaine reversed mechanical allodynia for 24 h after surgery but did not affect distress or approaching responses. In aboBoNT-A-treated animals cleaved SNAP25 was absent in the skin and DRG, but present in the ipsilateral dorsal horn of the spinal cord. In aboBoNT-A- versus saline-treated animals there were significant reductions in GFAP and Iba1 in the spinal cord, but no changes in CGRP and SP. Analgesic efficacy of aboBoNT-A appears to be mediated by its activity on spinal neurons, microglia and astrocytes. Clinical investigation to support the use of aboBoNT-A as an analgesic drug for post-surgical pain, is warranted.

Anti-nociceptive effects of magnolol via inhibition of TRPV1/P2Y and TLR4/NF-κB signaling in a postoperative pain model

AIMS

The current study explored the anti-nociceptive activity of magnolol in post-incisional inflammatory nociceptive pain.

MAIN METHODS

Preliminary, the anti-inflammatory, antioxidant, and cytoprotective potential of magnolol were confirmed against hydrogen peroxide (H₂O₂)-induced PC12 cells. Next, an in-vivo model of planter incision surgery was established in BALB/c mice. Tramadol 50 mg/kg intraperitoneal (i.p.) and magnolol (0.1, 1, 10 mg/kg i.p. + 10 mg/kg intra planter) were administered after plantar incision surgery and behavior parameters were measured.

KEY FINDINGS

The results indicate that magnolol significantly suppressed post-incision-induced mechanical allodynia, thermal hyperalgesia, and paw edema. Magnolol promisingly inhibited post-incision induces nitric oxide (NO), malondialdehyde (MDA), eosinophil peroxidase (EPO), and neutrophil infiltration. Magnolol strongly attenuated post-incision inducing the release of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β) and inhibited deoxyribonucleic acid (DNA) fragmentation. Magnolol markedly reverses post-incisional histopathological changes and biochemical composition of the incised paw. Magnolol markedly down-regulated post-incisional increase expression of transient receptor potential vanilloid 1 (TRPV1), purinergic (P2Y) nociceptors as well as toll-like receptor 4 (TLR4), nuclear factor kappa light chain enhancer of activated B cell (NF-κB), cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) while upregulating the expression of inhibitor of nuclear kappa B alpha (IκB-α).

SIGNIFICANCE

The present study strongly suggests that magnolol significantly suppressed post-incisional inflammatory nociceptive pain by targeting TRPV1/P2Y and TLR4/NF-κB signaling.

A Novel Rat Model to Study Postsurgical Pain After Joint Replacement Surgery

Purpose

The mechanisms underlying chronic postsurgical pain after joint replacement (JR) are complex, and it has been suggested that chronic postsurgical pain can develop as a result of inadequate acute pain management. Few studies have addressed acute pain after JR using specific animal models. This study aimed to develop a novel JR model focused on postsurgical pain assessment and the time course of pain recovery.

Materials and Methods

Rats were allocated to the following three groups: sham (joint exposure), joint destruction (JD; resection of the femoral head), and JR (femoral head replacement using an originally developed implant). The time course of postsurgical pain behavior was measured using a dynamic weight-bearing apparatus, along with radiological assessments. The expression of calcitonin gene-related peptide-immunoreactive (CGRP-IR) neurons in the dorsal root ganglion (DRG) was evaluated by immunohistochemistry on days 28 and 42.

Results

The ratio of weight-bearing distribution in the JR group gradually recovered from day 14 and reached the same level as that in the sham group on day 42, which was significantly greater than that in the JD group after day 7 (p<0.05). Radiologically, no significant issues were found, except for transient central migration of the implant in the JR group. The percentage of CGRP-IR DRG neurons in the JR group was significantly lower than that in the JD group on day 28 (mean, 37.4 vs 58.1%, p<0.05) and day 42 (mean, 32.3 vs 50.0%, p<0.05).

Conclusion

Our novel JR model presented acute postsurgical pain behavior that was successfully recovered to the baseline level at day 42 after surgery. Difference of the pain manifestation between the JR and JD groups could be supported by the expression of CGRP-IR in DRG neurons. This model is the first step toward understanding detailed mechanisms of post-JR pain.

Objective and Quantitative Evaluation of Spontaneous Pain-Like Behaviors Using Dynamic Weight-Bearing System in Mouse Models of Postsurgical Pain

Background

The paucity of objective and reliable measurements of pain-like behaviors has impeded the translatability of mouse models of postsurgical pain. The advanced dynamic weight-bearing (DWB) system enables evaluation of spontaneous pain-like behaviors in pain models. This study investigated the suitability and efficiency of the DWB system for assessing spontaneous pain-like behaviors and analgesic therapies in murine models of postsurgical pain.

Methods

Male adult C57BL/6JJcl mice were subjected to multiple surgical pain models with distinct levels of invasiveness, including a superficial incisional pain model involving only hind paw skin incision, deep incisional pain model that also involved incision and elevation of the underlying hind paw muscles, and orthopedic pain model involving tibial bone fracture and fixation with a pin (fracture and pinning [F/P] model). Spontaneous pain-like behaviors post-surgery were evaluated using weight distribution, pawprint area of the operated paw in the DWB system, and guarding pain score. Mechanical hypersensitivity was assessed using the von Frey test. The therapeutic effects of analgesics (diclofenac and buprenorphine for the deep incision model and diclofenac for the F/P model) were evaluated using the DWB system and von Frey test.

Results

The von Frey test demonstrated contradictory results between superficial and deep incisional pain models. The DWB system captured weight distribution changes in the operated hind paw, in accordance with the invasiveness and time course of wound healing in these surgical pain models. The reduction in weight-bearing on the operated paw correlated with guarding score, degree of paw swelling, and local expression of inflammatory mediators. DWB enabled accurate evaluation of the pharmacological effects of analgesics for detecting attenuation of surgery-induced weight-bearing changes in these models.

Conclusion

The DWB system serves as an objective and reliable method for quantifying pain-like behaviors and evaluating the therapeutic effects of analgesics in mouse models of postsurgical pain models.

Local effects of natural alkylamides from Acmella oleracea and synthetic isobutylalkyl amide on neuropathic and postoperative pain models in mice

Neuropathic and postoperative pain are clinical conditions that impair the patient's quality of life. The current pharmacotherapy of both painful states is ineffective and accompanied by several side effects. In order to develop new therapeutics targets, the secondary metabolites of plants have been extensively studied. Acmella oleracea ("jambu") is a native plant from the Amazon region and rich in alkylamides, bioactive compounds responsible for inducing anesthetic and chemesthetic sensations. We previously demonstrated that the intraplantar administration of an hexanic fraction (HF) rich in alkylamides from jambu and the synthetic isobutylalkyl amide (IBA) at 0.1 μg/20 μL can promote antinociceptive and anti-inflammatory effects. Thus, this study aimed to evaluate the local effect of HF and IBA (0.1 μg/20 μL) on neuropathic (partial sciatic nerve ligation, PSNL) and postoperative pain (plantar incision surgery, PIS) models in mice. Seven days after the PSNL, the mechanical (von Frey test) and cold (acetone-evoked evaporative cooling) allodynia, and digital gait parameters were analyzed. The intraplantar HF and IBA treatments attenuated the mechanical and cold allodynia as well as the static (max. Contact and print area) and dynamic (stand duration) parameters of digital gait analyses. On the day after PIS, the mechanical allodynia, heat hyperalgesia (hot plate, 52 ± 0.1°C), and spontaneous nociception scores were evaluated. Topical treatment with HF reduced the mechanical allodynia, heat hyperalgesia, and spontaneous nociception scores. In contrast, IBA treatment only partially reduced the mechanical allodynia. In summary, the local treatment with HF was effective on both neuropathic and postoperative pain, as opposed to IBA, which only had an effect on neuropathic pain.

Genetic and epigenetic mechanisms influencing acute to chronic postsurgical pain transitions in pediatrics: Preclinical to clinical evidence

Background

Chronic postsurgical pain (CPSP) in children remains an important problem with no effective preventive or therapeutic strategies. Recently, genomic underpinnings explaining additional interindividual risk beyond psychological factors have been proposed.

Aims

We present a comprehensive review of current preclinical and clinical evidence for genetic and epigenetic mechanisms relevant to pediatric CPSP.

Methods

Narrative review.

Results

Animal models are relevant to translational research for unraveling genomic mechanisms. For example, Cacng2, p2rx7, and bdnf mutant mice show altered mechanical hypersensitivity to injury, and variants of the same genes have been associated with CPSP susceptibility in humans; similarly, differential DNA methylation (H1SP) and miRNAs (miR-96/7a) have shown translational implications. Animal studies also suggest that crosstalk between neurons and immune cells may be involved in nociceptive priming observed in neonates. In children, differential DNA methylation in regulatory genomic regions enriching GABAergic, dopaminergic, and immune pathways, as well as polygenic risk scores for enhanced prediction of CPSP, have been described. Genome-wide studies in pediatric CPSP are scarce, but pathways identified by adult gene association studies point to potential common mechanisms.

Conclusions

Bench-to-bedside genomics research in pediatric CPSP is currently limited. Reverse translational approaches, use of other -omics, and inclusion of pediatric/CPSP endophenotypes in large-scale biobanks may be potential solutions. Time of developmental vulnerability and longitudinal genomic changes after surgery warrant further investigation. Emergence of promising precision pain management strategies based on gene editing and epigenetic programing emphasize need for further research in pediatric CPSP-related genomics.

Alpha lipoic acid attenuates evoked and spontaneous pain following surgical skin incision in rats

Our previous studies have implicated CaV3.2 isoform of T-type Ca2+ channels (T-channels) in the development of postsurgical pain. We have also previously established that different T-channel antagonists can alleviate in vivo postsurgical pain. Here we investigated the analgesic potential of another T-channel blocker and endogenous antioxidant molecule, α-lipoic acid (ALA), in a postsurgical pain model in rats. Our in vivo results suggest that single and repetitive intraperitoneal injections of ALA after surgery or preemptively, significantly reduced evoked mechanical hyperalgesia following surgical paw incision. Furthermore, repeated preemptive systemic injections of ALA effectively alleviated spontaneous postsurgical pain as determined by dynamic weight-bearing testing. We expect that our preclinical study may lead to further investigation of analgesic properties and mechanisms of analgesic action of ALA in patients undergoing surgery.

Mechanism of Incisional Pain: Novel Finding on Long Noncoding RNA XIST/miR-340-5p/RAB1A Axis

The objective of this study is to investigate the effect of long noncoding RNA (lncRNA) XIST on postoperative pain and inflammation of plantar incision pain (PIP) in rats and its underlying mechanisms.

PIP rat models were established by plantar incision. Rats in the sham group were subjected to povidone-iodine scrubbing, and no incision was made. To explore the role of XIST/miR-340-5p/RAB1A in postoperative pain and inflammation, PIP rats were separately or simultaneously injected with lentivirus containing sh-NC, sh-XIST, mimic NC, miR-340-5p mimic, inhibitor NC, miR-340-5p inhibitor, pcDNA3.1, or pcDNA3.1-RAB1A through an intrathecal catheter. The paw withdrawal threshold (PWT) and paw withdrawal latency (PWL) values of rats in each group were assessed to evaluate the pain behavior. RT-qPCR and Western blot were utilized to determine the levels of XIST, miR-340-5p, RAB1A, and NF-κB pathway-related proteins (p-IκBα, IκBα, p-p65, and p65). The concentrations of inflammatory cytokines (TNF-α, IL-1β, and IL-6) in rat spinal dorsal horn tissues were inspected by ELISA. H and E staining was applied to observe the pathological changes of neurons in the spinal dorsal horn, TUNEL staining to detect neuronal apoptosis, and immunohistochemistry to measure RAB1A level.

Plantar incision surgery caused decreased PWT and PWL values, enhanced levels of XIST, RAB1A, and inflammatory cytokines, along with an increased proportion of apoptotic neurons. The pain sensitivity and inflammation of rats were motivated after plantar incision surgery. Intrathecal injection of sh-XIST or miR-340-5p mimic ameliorated the pain and inflammation of PIP rats, while silencing of miR-340-5p or overexpression of RAB1A partly reversed the effect of sh-XIST on PIP rats. XIST targeted miR-340-5p and miR-340-5p negatively regulated RAB1A. The XIST/miR-340-5p/RAB1A axis activated the NF-κB signaling pathway.

LncRNA XIST aggravates inflammatory response and postoperative pain of PIP rats by activating the NF-κB pathway via the miR-340-5p/RAB1A axis.

IGF1-driven induction of GPCR kinase 2 in the primary afferent neuron promotes resolution of acute hyperalgesia

Dynamic regulation of G-protein-coupled receptor (GPCR) kinase 2 (GRK2) expression restores cellular function by protecting from overstimulation via GPCR and non-GPCR signaling. In the primary afferent neurons, GRK2 negatively regulates nociceptive tone. The present study tested the hypothesis that induction of GRK2 in the primary afferent neurons contributes to the resolution of acute pain after tissue injury. GRK2 expression in the dorsal root ganglion (DRG) was analyzed at 1 and 7 days after the incision. Intraperitoneal administration of a GRK2 inhibitor was performed 7 days post-incision in male Sprague-Dawley rats who underwent plantar incisions to analyze the pain-related behavioral effect of the GRK2 inhibitor. Separately, GRK2 expression was analyzed after injecting insulin-like growth factor 1 (IGF1) into the rat hind paw. In addition, an IGF1 receptor (IGF1R) inhibitor was administered in the plantar incision rats to determine its effect on the incision-induced hyperalgesia and GRK2 expression. Plantar incision induced an increase in GRK2 in the DRG at 7 days, but not at 1 day post-incision. Acute hyperalgesia after the plantar incision disappeared by 7 days post-incision. Intraperitoneal injection of the GRK2 inhibitor at this time reinstated mechanical hyperalgesia, although the GRK2 inhibitor did not produce hyperalgesia in naive rats. After the incision, IGF1 expression increased in the paw, but not in the DRG. Intraplantar injection of IGF1 increased GRK2 expression in the ipsilateral DRG. IGF1R inhibitor administration prevented both the induction of GRK2 and resolution of hyperalgesia after the plantar incision. These findings demonstrate that induction of GRK2 expression driven by tissue IGF1 has potent analgesic effects and produces resolution of hyperalgesia after tissue injury. Dysregulation of IGF1-GRK2 signaling could potentially lead to failure of the spontaneous resolution of acute pain and, hence, development of chronic pain after surgery.

The Effect of Continuous Field Block through Intercostal Muscles after Atrial Septal Defect Closure via a Mini-Right Thoracotomy in Pediatric Patients

BACKGROUND

Postoperative pain management in thoracotomy patients often is difficult. Furthermore, pediatric patients present more challenges because of their inability to effectively communicate their pain intensity. The purpose of this study was to evaluate the use of continuous field block through intercostal muscles as postoperative pain management in pediatric thoracotomy.

METHODS

Between 2014 and 2018, 11 patients underwent an ASD closure using a cardiopulmonary bypass via a mini-right thoracotomy through the fourth intercostal space. At the time of chest closure, a single-shot field block via the fourth intercostal muscles was performed with levobupivacaine (0.6 mg/kg). The first five patients were only given the single-shot field block (Single group). The remaining six patients were given levobupivacaine continuously (0.1 mg/kg/hr) through an indwelling catheter until the chest tube removal (Continuous group). The groups' vital signs, total amounts of acetaminophen used, postoperative courses were compared.

RESULTS

Although the heart rate did not differ between the groups, the respiratory rate was significantly higher in the Single group versus the Continuous group at 16 and 32 hr post-surgery (35.6 ± 9.7/min vs. 18.5 ± 4.7/min; p=0.007, 43.0 ± 10.4 vs. 25.3 ± 3.1; p=0.042, respectively). The accumulated dosage of acetaminophen given by postoperative day 2 was significantly higher in the Single group versus the Continuous group (55.3 ± 22.1 mg/kg vs. 7.8 ± 17.4 mg/kg; p=0.012).

CONCLUSIONS

Continuous field block via intercostal muscles after ASD closure via a mini-right thoracotomy in children was effective to stabilize the vital signs and reduce the analgesic medication use.

Intrathecal Injection of GRIP-siRNA Reduces Postoperative Synaptic Abundance of Kainate Receptor GluK2 Subunits in Rat Dorsal Horns and Pain Hypersensitivity

The mechanisms underlying postoperative pain differ from the inflammatory or neuropathic pain. Previous studies have demonstrated that intrathecal α-amino-3-hydroxy-5-methy-4-isoxazole propionate (AMPA) -kainate (KA) receptor antagonist inhibits the guarding pain behavior and mechanical hyperalgesia, indicating a critical role of spinal KA receptors in postoperative pain hypersensitivity. However, how the functional regulations of spinal KA receptor subunits are involved in the postoperative pain hypersensitivity remains elusive. Therefore, in the current study, we investigated the synaptic delivery of spinal KA receptor subunits and the interaction between KA receptor subunits and glutamate receptor-interacting protein (GRIP) during the postoperative pain. Our data indicated that plantar incision induced the synaptic delivery of GluK2, but not GluK1 or GluK3 in ipsilateral spinal cord dorsal horns. The co-immunoprecipitation showed an increased GluK2 -GRIP interaction in ipsilateral dorsal horn neurons at 6 h post-incision. Interestingly, Intrathecal pretreatment of GRIP siRNA increased the paw withdrawal thresholds to mechanical stimuli and decreased the cumulative pain scores in the paws ipsilateral to the incision at 6 h post-incision. Additionally, Intrathecal pretreatment of GRIP siRNA reduced the synaptic abundance of GluK2 in ipsilateral spinal dorsal horn at 6 h after plantar incision. In general, our data have demonstrated that the GluK2- GRIP interaction-mediated synaptic abundance of GluK2 in dorsal horn neurons plays an important role in the postoperative pain hypersensitivity. Disrupting the GluK2- GRIP interaction may provide a new approach for relieving postoperative pain.

Epigallocatechin-3-Gallate Modulates Postoperative Pain by Regulating Biochemical and Molecular Pathways

Treating postoperative (PO) pain is a clinical challenge. Inadequate PO pain management can lead to worse outcomes, for example chronic post-surgical pain. Therefore, acquiring new information on the PO pain mechanism would increase the therapeutic options available. In this paper, we evaluated the role of a natural substance, epigallocatechin-3-gallate (EGCG), on pain and neuroinflammation induced by a surgical procedure in an animal model of PO pain. We performed an incision of the hind paw and EGCG was administered for five days. Mechanical allodynia, thermal hyperalgesia, and motor dysfunction were assessed 24 h, and three and five days after surgery. At the same time points, animals were sacrificed, and sera and lumbar spinal cord tissues were harvested for molecular analysis. EGCG administration significantly alleviated hyperalgesia and allodynia, and reduced motor disfunction. From the molecular point of view, EGCG reduced the activation of the WNT pathway, reducing WNT3a, cysteine-rich domain frizzled (FZ)1 and FZ8 expressions, and both cytosolic and nuclear β-catenin expression, and the noncanonical β-catenin–independent signaling pathways, reducing the activation of the NMDA receptor subtype NR2B (pNR2B), pPKC and cAMP response element-binding protein (pCREB) expressions at all time points. Additionally, EGCG reduced spinal astrocytes and microglia activation, cytokines overexpression and nuclear factor kappa-light-chain-enhancer of activated B cells (NFkB) pathway, downregulating inducible nitric oxide synthase (iNOS) activation, cyclooxygenase 2 (COX-2) expression, and prostaglandin E2 (PGE2) levels. Thus, EGCG administration managing the WNT/β-catenin signaling pathways modulates PO pain related neurochemical and inflammatory alterations.

Effect of applying cold gel pack on reduction of postoperative pain in cesarean section, low midline skin incision: A randomized controlled trial

AIM

The present study aims to investigate the efficacy of cryotherapy in pain reduction following low midline cesarean section.

METHODS

This randomized controlled trial was conducted at the Department of Obstetrics and Gynecology, Thammasat University Hospital, Thailand from December 2019 to February 2020. Participants were term pregnant women who were indicated for low midline cesarean section. The control group received standard postoperative care while cold pack was applied to the intervention group for 6 h after the operation. The primary outcome was the postoperative visual analog scale (VAS) score in both the control and intervention groups. The secondary outcomes consisted of the amount of intravenous pain reliever each participant required and the length of hospital stay.

RESULTS

All 100 pregnant women were recruited into the study. They were equally allocated into intervention or control groups. Both groups underwent cesarean section under spinal anesthesia. The demographic characteristics of both groups were comparable. VAS of intervention and control group were 3.2 ± 2.4 versus 5.3 ± 2.2, 3.0 ± 2.4 versus 5.6 ± 2.0, 2.0 ± 2.3 versus 5.3 ± 2.2, and 1.1 ± 1.7 versus 4.8 ± 2.4 at 6, 8, 12, and 24 h postoperatively (p-value <0.05), respectively. Moreover, the intervention group showed a statistically significantly lower number of participants who needed intravenous meperidine or tramadol (14% vs. 24%, p-value <0.05) and lower intravenous meperidine or tramadol usage than in control group (13.2 ± 0.9 vs. 19.9 ± 4.0 mg, p-value <0.05).

CONCLUSIONS

Cryotherapy could reduce postoperative pain from 6 h to within 24 h of the postoperative period, as well as lower overall opioid requirement.

Sleep Well and Recover Faster with Less Pain-A Narrative Review on Sleep in the Perioperative Period

Sleep disturbance, pain, and having a surgical procedure of some kind are all very likely to occur during the average lifespan. Postoperative pain continues to be a prevalent problem and growing evidence supports the association between pain and sleep disturbances. The bidirectional nature of sleep and pain is widely acknowledged. A decline in sleep quality adds a risk for the onset of pain and also exacerbates existing pain. The risk factors for developing insomnia and experiencing severe pain after surgery are quite similar. The main aim of this narrative review is to discuss why it is important to be aware of sleep disturbances both before and after surgery, to know how sleep disturbances should be assessed and monitored, and to understand how better sleep can be supported by both pharmacological and non-pharmacological interventions.

Perioperative Opioid Administration

Opioids form an important component of general anesthesia and perioperative analgesia. Discharge opioid prescriptions are identified as a contributor for persistent opioid use and diversion. In parallel, there is increased enthusiasm to advocate opioid-free strategies, which include a combination of known analgesics and adjuvants, many of which are in the form of continuous infusions. This article critically reviews perioperative opioid use, especially in view of opioid-sparing versus opioid-free strategies. The data indicate that opioid-free strategies, however noble in their cause, do not fully acknowledge the limitations and gaps within the existing evidence and clinical practice considerations. Moreover, they do not allow analgesic titration based on patient needs; are unclear about optimal components and their role in different surgical settings and perioperative phases; and do not serve to decrease the risk of persistent opioid use, thereby distracting us from optimizing pain and minimizing realistic long-term harms.

Effect of transcutaneous electrical nerve stimulation on quality of recovery and pain after abdominal hysterectomy

Background and Aims:

Transcutaneous electrical nerve stimulation (TENS) is a noninvasive complementary therapy for postoperative pain management. The effect of TENS on quality of recovery (QoR) and pain treatment in the early postoperative period is not well documented. The aim of this study was to evaluate the effect of TENS on postoperative QoR and pain in patients who had undergone a total abdominal hysterectomy with bilateral salpingo-oophorectomy (TAH + BSO).

Material and Methods:

Fifty-two patients were randomized into two groups: control (sham TENS treatment) and TENS (TENS treatment). QoR, dynamic pain, and static pain were evaluated after surgery.

Results:

The QoR score was significantly higher in the TENS group as compared with that in the control group (P = 0.029). Pain scores during coughing (dynamic pain) were significantly less in TENS group compared to control group (P <0.001). However, there was no between-group difference in pain scores at rest (static pain) or total analgesic consumption (P = 0.63 or P = 0.83, respectively).

Conclusion:

TENS may be a valuable tool to improve patients' QoR and dynamic pain scores after TAH + BSO.

Plantar incision with severe muscle injury can be a cause of long-lasting postsurgical pain in the skin

AIMS

Although chronic local inflammation in deeper tissues after skin wound healing might produce chronification of acute postsurgical pain, its mechanisms have not been fully elucidated. We hypothesized that muscle injury and severe inflammation would prolong acute postsurgical pain by its central nervous system mechanisms.

MAIN METHODS

After approval of the Animal Care Committee, experiments were performed in Male Sprague-Dawley rats weighing 250-300 g. Plantar incision and plantar incision combined with cryoinjury of the plantar flexor digitorum brevis muscle were made in the plantar incision group and muscle injury group, respectively. Pain-related behaviors were assessed, and inflammatory cells were isolated from injured muscle and analyzed by flow cytometry. Spinal microglial activation was assessed with Iba-1 staining.

KEY FINDINGS

Mechanical hyperalgesia from day 5 to day 8 and spontaneous pain-related behavior from day 3 to day 7 were significantly greater in the muscle injury group than in the plantar incision group (P < 0.05), whereas there was no significant difference between the two groups in thermal hyperalgesia. In the muscle injury group, the number of inflammatory cells on day 4 was significantly larger and spinal Iba-1 expression levels on days 4 and 7 were significantly higher than those in the plantar incision group (P < 0.05).

SIGNIFICANCE

Surgical injury in deep tissues accompanying severe muscle inflammation induced prolonged postsurgical pain in the healing wound of the skin not by the persistence of muscle inflammation but by a central mechanism involving microglial activation at the level of the spinal cord.

Nociceptive Sensitization by Activation of Protease-Activated Receptor 2 in a Rat Model of Incisional Pain

Postoperative pain and consequent inflammatory responses after tissue incision adversely affects many surgical patients due to complicated mechanisms. In this study, we examined whether activation of protease-activated receptor 2 (PAR-2), which is stimulated by tryptase from mast cells, elicits nociception and whether the PAR-2 antagonist could reduce incisional nociceptive responses in vivo and in vitro. The effects of a selective PAR-2 antagonist, N3-methylbutyryl-N-6-aminohexanoyl-piperazine (ENMD-1068), pretreatment on pain behaviors were assessed after plantar incision in rats. The effects of a PAR-2 agonist, SLIGRL-NH₂, on nociception was assessed after the injection into the hind paw. Furthermore, the responses of C-mechanosensitive nociceptors to the PAR-2 agonist were observed using an in vitro skin–nerve preparation as well. Intraplantar injection of SLIGRL-NH₂ elicited spontaneous nociceptive behavior and hyperalgesia. Local administration of ENMD-1068 suppressed guarding behaviors, mechanical and heat hyperalgesia only within the first few hours after incision. SLIGRL-NH₂ caused ongoing activity in 47% of C-mechanonociceptors in vitro. This study suggests that PAR-2 may support early nociception after incision by direct or indirect sensitization of C-fibers in rats. Moreover, PAR-2 may play a regulatory role in the early period of postoperative pain together with other co-factors to that contribute to postoperative pain.

Use of human fibrin glue (Tisseel) versus suture during transvaginal natural orifice ovarian cystectomy of benign and non-endometriotic ovarian tumor: a retrospective comparative study

Background

To evaluate the use of a human fibrin glue (Tisseel) for minor bleeding control and approximation of ovarian defect during transvaginal natural orifice ovarian cystectomy (TNOOC) of benign and non-endometriotic ovarian tumors.

Methods

A total of 125 women with benign and non-endometriotic ovarian tumors who underwent TNOOC between May 2011 and January 2020: 54 with the aid of Tisseel and 71 with traditional suture for hemostasis and approximation of ovarian defect. Surgical outcomes such as length of surgery, operative blood loss, postoperative pain score, and postoperative hospital stay were recorded. Before and immediately (10 days) and at 6 months after the procedure, serum anti-Müllerian hormone (AMH) levels were also determined.

Results

Complete hemostasis and approximation of ovarian defect were achieved in all cases. No significant difference was noted in the operating time, operative blood loss, postoperative pain scores after 12, 24 and 48 h, length of postoperative stay, and baseline AMH levels between the two groups. The operation did not have a negative effect on the immediate and 6-month postoperative AMH levels in the suture group. However, the decline in the AMH levels was significant immediately after surgery in the Tisseel group, nevertheless, no significant difference was noted in the AMH levels at 6 months (3.3 vs. 1.7 mg/mL; p = 0.042, adjusted p = 0.210).

Conclusion

The use of Tisseel in TNOOC of benign and non-endometriotic ovarian tumors without suturing the ovarian tissue is clinically safe and feasible.

Preemptive Analgesic Effect of Intrathecal Applications of Neuroactive Steroids in a Rodent Model of Post-Surgical Pain: Evidence for the Role of T-Type Calcium Channels

Preemptive management of post-incisional pain remains challenging. Here, we examined the role of preemptive use of neuroactive steroids with activity on low-voltage activated T-type Ca²⁺ channels (T-channels) and γ-aminobutyric acid A (GABA_A) receptors in the development and maintenance of post-incisional pain. We use neuroactive steroids with distinct effects on GABA_A receptors and/or T-channels: Alphaxalone (combined GABAergic agent and T-channel inhibitor), ECN (T-channel inhibitor), CDNC24 (GABAergic agent), and compared them with an established analgesic, morphine (an opioid agonist without known effect on either T-channels or GABA_A receptors). Adult female rats sustained the skin and muscle incision on the plantar surface of the right paw. We injected the agents of choice intrathecally either before or after the development of post-incisional pain. The pain development was monitored by studying mechanical hypersensitivity. Alphaxalone and ECN, but not morphine, are effective in alleviating mechanical hyperalgesia when administered preemptively whereas morphine provides dose-dependent pain relief only when administered once the pain had developed. CDNC24 on the other hand did not offer any analgesic benefit. Neuroactive steroids that inhibit T-currents—Alphaxalone and ECN—unlike morphine, are effective preemptive analgesics that may offer a promising therapeutic approach to the treatment of post-incisional pain, especially mechanical hypersensitivity.

The Impact of Music on Nociceptive Processing

OBJECTIVE

Music has been shown to modulate pain, although the impact of music on specific aspects of nociceptive processing is less well understood. Using quantitative sensory testing (QST), we assessed the impact of a novel music app on specific aspects of nociceptive processing.

DESIGN

Within-subjects paired comparison of pain processing in control vs music condition.

SETTING

Human psychophysical laboratory.

SUBJECTS

Sixty healthy adult volunteers.

METHODS

Subjects were assessed for baseline anxiety, depression, and catastrophizing using validated questionnaires. QSTs measured included 1) pain threshold and tolerance to deep muscle pressure, 2) pain with mechanical pinprick, 3) temporal summation of pain (TSP) with a repeated pain stimulus, and 4) conditioned pain modulation (CPM) with a second painful stimulus. QSTs were performed in the absence and presence of music delivered through a music app.

RESULTS

We found an increase in pressure pain thresholds in both the forearm (P = 0.007) and trapezius (P = 0.002) with music, as well as a decrease in the amount of pinprick pain (P < 0.001) and TSP (P = 0.01) with music. Interestingly, CPM was also significantly diminished (P < 0.001) in the music condition. No significant difference in cold pain, anxiety, or situational catastrophizing was observed with music. Higher baseline pain catastrophizing scores were associated with less music-induced pressure pain reduction.

CONCLUSIONS

Several measures of mechanical pain sensitivity were reduced with music. TSP, a measure of central sensitization, also decreased with music, but CPM, a measure of descending modulation of pain, was not further augmented by music.

The Protective Effects of Pre- and Post-Administration of Micronized Palmitoylethanolamide Formulation on Postoperative Pain in Rats

Background: Postoperative pain (PO) is a common form of acute pain. Inadequate PO treatment is an important health problem, as it leads to worse outcomes, such as chronic post-surgical pain. Therefore, it is necessary to acquire new knowledge on PO mechanisms to develop therapeutic options with greater efficacy than those available today and to lower the risk of adverse effects. For this reason, we evaluated the ability of micronized palmitoylethanolamide (PEA-m) to resolve the pain and inflammatory processes activated after incision of the hind paw in an animal model of PO. Methods: The animals were subjected to surgical paw incision and randomized into different groups. PEA-m was administered orally at 10 mg/kg at different time points before or after incision. Results: Our research demonstrated that the pre- and post-treatment with PEA-m reduced the activation of mast cells at the incision site and the expression of its algogenic mediator nerve growth factor (NGF) in the lumbar spinal cord. Furthermore, again at the spinal level, it was able to decrease the activation of phospho-extracellular signal-regulated kinases (p-ERK), ionized calcium binding adaptor molecule 1 (Iba1), glial fibrillary acidic protein (GFAP), and the expression of brain-derived neurotrophic factor (BDNF). PEA-m also reduced the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) spinal pathway, showing a protective effect in a rat model of PO. Conclusion: The results obtained reinforce the idea that PEA-m may be a potential treatment for the control of pain and inflammatory processes associated with PO. In addition, pre- and post-treatment with PEA-m is more effective than treatment alone after the surgery and this limits the time of taking the compound and the abuse of analgesics.

Implementation and evaluation of a pain management core competency education program for surgical nurses

Objective

To investigate the effect of a pain management core competency education program on surgical nurses’ pain knowledge and pain management nursing practice behaviors.

Methods

An 8-h education program focused on pain management core competency was provided twice in two weeks including the multidimensional nature of pain, pain assessment, pharmacological and non-pharmacological management, and knowledge application was developed and implemented for surgical nurses by a multidisciplinary team. Multimodal teaching approaches such as didactic teaching and vignettes of cases for nurses to discuss were used. The Clinical Pain Knowledge Test (CPKT) was completed by 135 and 107 nurses from 17 surgical wards pre and post-program, respectively. Two hundred and three patients’ medical records were randomly sampled according to the number of operations in each ward one week before and in the fifth week after the intervention, respectively. Documentation of patients’ postoperative pain management nursing practice behaviors and pain intensity scores were collected.

Results

After the intervention, the CPKT scores of nurses significantly increased from 45.6% ± 12.3% to 54.2% ± 10.2% (t = 5.786, P < 0.001). Nurses’ postoperative pain management nursing practice improved, with proportion of pain assessment documentation increased from 59.6% (121/203) to 74.9% (152/203) (χ² = 10.746, P = 0.001), those using pain intensity assessment tools increased from 81.8% (99/121) to 95.4% (145/152) (χ² = 13.079, P < 0.001), and intramuscular injection of nonopioids decreased from 12.6% (13/103) to 2.7% (3/111) (χ² = 7.598, P = 0.006). Patients’ average worst pain score on the operation day significantly decreased (Z = −2.486, P = 0.013), and scores from the first to the third postoperative day also decreased (Z = −2.172, P = 0.030).

Conclusions

Implementation of a pain management core competency education program for surgical nurses can increase their knowledge of core competencies of pain management, improve selected pain management practices, and decrease patients’ postoperative pain intensity.

Intrathecal Oxytocin Improves Spontaneous Behavior and Reduces Mechanical Hypersensitivity in a Rat Model of Postoperative Pain

The first few days post-surgery, patients experience intense pain, hypersensitivity and consequently tend to have minor locomotor activity to avoid pain. Certainly, injury to peripheral tissues produces pain and increases sensitivity to painful (hyperalgesia) and non-painful (allodynia) stimuli. In this regard, preemptive pharmacological treatments to avoid or diminish pain after surgery are relevant. Recent data suggest that the neuropeptide oxytocin when given at spinal cord level could be a molecule with potential preemptive analgesic effects, but this hypothesis has not been properly tested. Using a validated postoperative pain model (i.e. plantar incision), we evaluated in male Wistar rats the potential preemptive antinociceptive effects of intrathecal oxytocin administration measuring tactile hypersensitivity (across 8 days) and spontaneous motor activity (across 3 days). Hypersensitivity was evaluated using von Frey filaments, whereas spontaneous activity (total distance, vertical activity episodes, and time spent in the center of the box) was assessed in real time using a semiautomated open-field system. Under these conditions, we found that animals pretreated with spinal oxytocin before plantar incision showed a diminution of hypersensitivity and an improvement of spontaneous behavior (particularly total distance and vertical activity episodes). This report provides a basis for addressing the therapeutic relevance of oxytocin as a potential preemptive analgesic molecule.

[Transdermal buprenorphine for acute postoperative pain: a systematic review]

BACKGROUND AND OBJECTIVES

Postoperative pain is still a major concern in several surgical procedures. Multimodal analgesia is best for postoperative pain management; however, opioid therapy is still the main treatment for pain after surgical procedures. Transdermal buprenorphine is a partial μ agonist opioid widely used for chronic pain syndromes, with limited evidence for acute postoperative pain. A systematic review of studies examining transdermal buprenorphine for acute pain management after surgery was conducted.

CONTENTS

Data from PubMed, Embase, The Cochrane Central Register of Controlled Trials (CENTRAL), CINAHL via EBSCOhost, and LILACS were reviewed, including randomized clinical trials that evaluated total postoperative pain, postoperative analgesic consumption, drug-related side effects and patient satisfaction with analgesia regimen. Data from nine studies (615 patients) were included in this review. Most studies initiated transdermal buprenorphine use 6 to 48 hours before surgery, maintaining use from 1 to 8 days after the procedure. Most studies showed lower or similar postoperative pain scores, postoperative analgesic consumption and patient satisfaction comparing buprenorphine to placebo, tramadol, celecoxib, flurbiprofen and parecoxib. The incidence of side effects varied between studies, with most showing no increase in drug-related side effects with buprenorphine use, except one study, which compared buprenorphine to oral tramadol, and one to transdermal fentanyl. However, most results were derived from evidence with an overall high or unclear risk of bias.

CONCLUSIONS

Although more studies are necessary, initial results show that transdermal buprenorphine seems to be an effective and safe opioid choice for management of acute postoperative pain.

Intravenous, Perioperatively Administered Lidocaine Regulates Serum Pain Modulators’ Concentrations in Children Undergoing Spinal Surgery

Objectives

We analyzed the influence of perioperative, intravenous (i.v.) lidocaine infusion as a part of multimodal anesthesia on concentrations of selected pain modulators.

Design

An observational study.

Setting

University Children’s Hospital in Cracow, Poland, from May 2015 to May 2018.

Subjects

Forty-four children undergoing extensive spinal surgery, divided into two groups after surgery: the study group (N = 23), anesthetized generally with lidocaine as a co-analgesic, and the control group (N = 22), anesthetized generally without lidocaine.

Methods

We assessed proinflammatory mediators like neuron growth factor (NGF), high mobility group box 1 (HMGB1), interleukin 6 (IL-6), and FOS protein before, immediately after, six hours and 12–15 hours after surgery. We evaluated pain intensity at corresponding time points using a 10-point numerical/graphical scale.

Results

We observed that children in the lidocaine group had reduced pain intensity in the resting state and during movement until six hours after surgery when compared with controls. We found lower NGF concentrations in the lidocaine group vs controls only at six hours after surgery. Mean HMGB1 concentrations during the postoperative period in the study group were relatively stable, whereas we observed significant increases at six hours after surgery and a slight decrease at 12–15 hours after surgery in the control group. IL-6 concentrations at six hours were lower in lidocaine patients when compared with controls. We noted a negative correlation between HMGB1, NGF, Il-6, and lidocaine concentrations after surgery. We did not find any differences in FOS protein concentrations between the groups.

Conclusions

Our findings suggest that intraoperative and postoperative i.v. lidocaine administration as a part of multimodal anesthesia may reduce inflammatory-dependent postoperative pain intensity.