When does acute pain become chronic?

The inhibition of spinal synaptic plasticity mediated by activation of AMP-activated protein kinase signaling alleviates the acute pain induced by oxaliplatin

Our recent findings demonstrated that oxaliplatin entering CNS may directly induce spinal central sensitization, and contribute to the rapid development of CNS-related side effects including acute pain during chemotherapy. However, the mechanism is largely unclear. In the current study, we found that the amplitude of C-fiber-evoked field potentials was significantly increased and the expression of phosphorylated mammalian AMP-activated protein kinase α (AMPKα) was markedly decreased following high frequency stimulation (HFS) or single intraperitoneal injection of oxaliplatin (4mg/kg). Spinal local application of AMPK agonist metformin (25μg) prevented the long term potentiation (LTP) induction and the activation of mTOR/p70S6K signal pathway, and significantly attenuated the acute thermal hyperalgesia and mechanical allodynia following single oxaliplatin treatment. Importantly, we found that incubation of low concentration oxaliplatin at dose of 6.6nM (the detected concentration in CSF following a single intraperitoneal injection of oxaliplatin) also significantly inhibited the AMPKα activation and increased the amplitude of sEPSCs, the number of action potential, and the expression of p-mTOR and p-p70S6K in spinal cord slices. Metformin (25μg) or rapamycin (2μg) inhibited the increased excitability of dorsal horn neurons and the decrease of p-AMPKα expression induced by low concentration oxaliplatin incubation. Furthermore, spinal application of AMPK inhibitor compound C (5μg) induced the spinal LTP, thermal hyperalgesia and mechanical allodynia, and rapamycin attenuated the spinal LTP, the thermal hyperalgesia and mechanical allodynia following oxaliplatin treatment (i.p.). Local application of metformin significantly decreased the mTOR and p70S6K activation induced by tetanus stimulation or oxaliplatin (i.p.). These results suggested that the decreased AMPKα activity via negatively regulating mTOR/p70S6K signal pathway enhanced the synaptic plasticity and contributed to acute pain induced by low concentration of oxaliplatin entering CNS.

Bone pain mechanism in osteoporosis: a narrative review

Bone pain in elderly people dramatically affects their quality of life, with osteoporosis being the leading cause of skeletal related events. Peripheral and central mechanisms are involved in the pathogenesis of the nervous system sensitization. Osteoporosis in the elderly has been associated with increased density of bone sensory nerve fibers and their pathological modifications, together with an over-expression of nociceptors sensitized by the lowering pH due to the osteoclastic activity. The activation of N-methyl-D-aspartate (NMDA) receptors and the microglia, as a response to a range of pathological conditions, represent the leading cause of central sensitization. Unfortunately, osteoporosis is named the "silent thief" because it manifests with painful manifestation only when a fracture occurs. In the management of patients suffering from bone pain, both the nociceptive and the neuropathic component of chronic pain should be considered in the selection of the analgesic treatment.

Immunohistochemical investigation of nerve fiber presence and morphology in elderly cervical spine meniscoids

BACKGROUND CONTEXT

Innervation of anatomical structures is fundamental to their capacity to generate nociceptive impulses. Cervical spine meniscoids are hypothesized to be contributors to neck pain; however, their innervation is not comprehensively understood.

PURPOSE

This study aimed to examine the presence and morphology of nerve fibers within cervical spine meniscoids and adjacent joint capsules.

STUDY DESIGN

This is a cross-sectional study.

PATIENT SAMPLE

The sample consists of cervical hemispines of 12 embalmed cadavers (mean [standard deviation] age 82.9 [6.5] years, six female, six left). Either the right or the left half of the cervical spine (hemispine) of each cadaver was included in the sample. So six left sides and six right sides of the cadaver cervical spines made up the 12 hemispines that formed the sample.

METHODS

Cervical spine meniscoids and adjacent joint capsules were excised from lateral atlantoaxial and cervical zygapophyseal (C2-C3 to C6-C7) joints (n=67), then paraffin embedded. Meniscoids were sectioned sagittally (5 µm), slide mounted, and immunohistochemistry was performed using primary antibodies to neurofilament heavy (NF-H) and pan-neurofilament (Pan-NF) to identify nerve tissue. The study was supported by institutional graduate student funding. The authors have no conflicts of interest to declare.

RESULTS

Seventy-seven meniscoids (23 lateral atlantoaxial, 54 cervical zygapophyseal) were extracted and processed (154 sections in total). Sixty-four individual nerve fiber bundles were identified (26 NF-H positive, 38 Pan-NF positive) from 14 meniscoids. Nerves immunoreactive to both NF-H and Pan-NF were identified in 13 of 77 meniscoids (10 of 14 lateral atlantoaxial joint) from 11 joints (eight cadavers). Nerves were always located in joint capsules except three exclusively Pan-NF immunoreactive nerve fiber bundles from two adipose meniscoids.

CONCLUSIONS

The low nerve prevalence in elderly cervical spine meniscoids, with nerves only found in two adipose type meniscoids, suggests these structures may play a minimal role in cervical nociception generation in this demographic. The joint capsules, which were more frequently innervated, appear to be more likely generators of nociception in the elderly. Joint capsule nerves were mostly NF-H positive, indicating potential Aδ-fiber presence.

The Emerging Role of Spinal Dynorphin in Chronic Pain: A Therapeutic Perspective

Notable findings point to the significance of the dynorphin peptide neurotransmitter in chronic pain. Spinal dynorphin neuropeptide levels are elevated during development of chronic pain and sustained during persistent chronic pain. Importantly, knockout of the dynorphin gene prevents development of chronic pain in mice, but acute nociception is unaffected. Intrathecal (IT) administration of opioid and nonopioid dynorphin peptides initiates allodynia through a nonopioid receptor mechanism; furthermore, antidynorphin antibodies administered by the IT route attenuate chronic pain. Thus, this review presents the compelling evidence in the field that supports the role of dynorphin in facilitating the development of a persistent pain state. These observations illustrate the importance of elucidating the control mechanisms responsible for the upregulation of spinal dynorphin in chronic pain. Also, spinal dynorphin regulation of downstream signaling molecules may be implicated in hyperpathic states. Therapeutic strategies to block the upregulation of spinal dynorphin may provide a nonaddictive approach to improve the devastating condition of chronic pain that occurs in numerous human diseases.

Stress and pain response after oligofructose induced-lameness in dairy heifers

Lameness is one of the most painful conditions that affects dairy cattle. This study was conducted to evaluate clinical signs and plasma concentration of several pain and stress biomarkers after oligofructose-induced lameness in dairy heifers. Lameness was induced using an oligofructose overload model in 12 non-pregnant heifers. Clinical parameters and blood samples were obtained at 48 and 24 h and at 6, 12, 24, 36 and 48 h after induction of lameness. Clinical parameters included heart rate, respiratory rate, ruminal frequency and lameness score. Plasma biomarkers included cortisol, haptoglobin, norepinephrine, beta-endorphin and substance P. Differences were observed in all parameters between control and treated heifers. The plasma concentration of biomarkers increased significantly in treated animals starting 6 h after induction of lameness, reaching maximum levels at 24 h for cortisol, 48 h for haptoglobin, 6 h for norepinephrine, 12 h for substance P and at 24 h for beta-endorphin. Overall, our results confirm that lameness associated pain induced using the oligofructose model induced changes in clinical parameters and plasma biomarkers of pain and stress in dairy heifers.

A new model of nerve injury in the rat reveals a role of Regulator of G protein Signaling 4 in tactile hypersensitivity

Tactile hypersensitivity is one of the most debilitating symptoms of neuropathic pain syndromes. Clinical studies have suggested that its presence at early postoperative stages may predict chronic (neuropathic) pain after surgery. Currently available animal models are typically associated with consistent tactile hypersensitivity and are therefore limited to distinguish between mechanisms that underlie tactile hypersensitivity as opposed to mechanisms that protect against it. In this study we have modified the rat model of spared nerve injury, restricting the surgical lesion to a single peripheral branch of the sciatic nerve. This modification reduced the prevalence of tactile hypersensitivity from nearly 100% to approximately 50%. With this model, we here also demonstrated that the Regulator of G protein Signaling 4 (RGS4) was specifically up-regulated in the lumbar dorsal root ganglia and dorsal horn of rats developing tactile hypersensitivity. Intrathecal delivery of the RGS4 inhibitor CCG63802 was found to reverse tactile hypersensitivity for a 1h period. Moreover, tactile hypersensitivity after modified spared nerve injury was most frequently persistent for at least four weeks and associated with higher reactivity of glial cells in the lumbar dorsal horn. Based on these data we suggest that this new animal model of nerve injury represents an asset in understanding divergent neuropathic pain outcomes, so far unravelling a role of RGS4 in tactile hypersensitivity. Whether this model also holds promise in the study of the transition from acute to chronic pain will have to be seen in future investigations.

[Pain assessment in the postanaesthesia recovery room]

Pain assessment is an important activity in nursing care. Postanaesthesia recovery rooms are specialised care units. Pain assessment must form part of a global approach, beyond an objective of care. The nurse plays a key role from the reception of the patient through to their transfer to the ward.

Involvement of the dynorphin/KOR system on the nociceptive, emotional and cognitive manifestations of joint pain in mice

Joint pain is a major clinical problem mainly associated to osteoarthritis, and characterized by articular cartilage degradation resulting in a complex chronic pain state that includes nociceptive, emotional and cognitive manifestations. Memory impairment, depressive- and anxiety-like symptoms have been reported to be associated with chronic pain, leading to a decrease of life quality. In this study, we evaluated the involvement of the endogenous dynorphin/kappa opioid receptor (KOR) system on the nociceptive, emotional, cognitive, neurochemical and epigenetic manifestations of joint pain. The murine model of monosodium iodoacetate (MIA) was used to induce joint pain in knockout mice for KOR (KOR-KO), prodynorphin (PDYN-KO) and their wild-type (WT) littermates. KOR-KO and PDYN-KO mice developed mechanical allodynia after intra-articular injection of MIA. This allodynia was significantly increased in both KOR-KO and PDYN-KO when compared to WT mice. Accordingly, both mutants showed increased microglial activation on the lumbar section of the spinal cord after MIA. The emotional responses were evaluated by measuring anxiety-like behaviour in the elevated plus maze and anhedonia as depressive-like behaviour, and cognitive alterations in the object recognition paradigm. Emotional and cognitive impairments after joint pain were differently modified in KOR-KO and PDYN-KO mice. Alterations of corticotropin-releasing factor (CRF) on the amygdala and hippocampus and down regulation of histone 3 acetylation on the amygdala suggest a possible mechanism to explain these emotional and cognitive manifestations. Our results reveal a specific involvement of the dynorphin/KOR system on joint pain manifestations that are usually associated to osteoarthritis.

Painful temporomandibular disorders and central sensitization: implications for management-a pilot study

The objective was to investigate the presence of cutaneous allodynia and hyperalgesia in the trigeminal and extra-trigeminal areas, as a surrogate for central sensitization (CS), in women with a painful temporomandibular disorder (TMD) and without other painful conditions. Painful TMDs, depression, and non-specific physical symptoms (NSPS) were classified according to the Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD). The amount of pain in the trigeminal and extra-trigeminal areas was determined using a visual analogue scale (0-100mm) after the application of a vibrotactile stimulus and assessment of the pressure pain threshold (PPT). Statistical tests (Fisher's, χ², and Mann-Whitney) were performed, with a significance level of 5%. The sample comprised 45 women (mean age 37.5 years; 16 with a painful TMD) who were free of any headache, fibromyalgia, or other painful condition. Painful TMD was associated with higher pain sensitivity and lower PPT values in the trigeminal (P<0.01) and extra-trigeminal regions (P<0.01). The presence of depression contributed significantly to increased pain sensitivity. The presence of hyperalgesia and allodynia in both the trigeminal and extra-trigeminal regions among women with a painful TMD indicated the presence of CS. Changes involving the central nervous system should be considered during the evaluation and management of patients with a painful TMD.

Oral non-steroidal anti-inflammatory drugs (single dose) for perineal pain in the early postpartum period

BACKGROUND

Many women experience perineal pain after childbirth, especially after having sustained perineal trauma. Perineal pain-management strategies are thus an important part of postnatal care. Non-steroidal anti-inflammatory drugs (NSAIDs) are a commonly used type of medication in the management of postpartum pain and their effectiveness and safety should be assessed.

OBJECTIVES

To determine the effectiveness of a single dose of an oral NSAID for relief of acute perineal pain in the early postpartum period.

SEARCH METHODS

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (31 March 2016), OpenSIGLE, ProQuest Dissertations and Theses, the ISRCTN Registry and ClinicalTrials.gov (31 March 2016). We also reviewed reference lists of retrieved papers and contacted experts in the field.

SELECTION CRITERIA

Randomised controlled trials (RCTs) assessing a single dose of a NSAID versus a single dose of placebo, paracetamol or another NSAID for women with perineal pain in the early postpartum period. Quasi-RCTs and cross-over trials were excluded.

DATA COLLECTION AND ANALYSIS

Two review authors (FW and VS) independently assessed all identified papers for inclusion and risk of bias. Any discrepancies were resolved through discussion and consensus. Data extraction, including calculations of pain relief scores, was also conducted independently by two review authors and checked for accuracy.

MAIN RESULTS

We included 28 studies that examined 13 different NSAIDs and involved 4181 women (none of whom were breastfeeding). Studies were published between 1967 and 2013, with the majority published in the 1980s. Of the 4181 women involved in the studies, 2642 received a NSAID and 1539 received placebo or paracetamol. Risk of bias was generally unclear due to poor reporting, but in most studies the participants and personnel were blinded, outcome data were complete and the outcomes that were specified in the methods section were reported.None of the included studies reported on any of this review's secondary outcomes: prolonged hospitalisation or re-hospitalisation due to perineal pain; breastfeeding (fully or mixed) at discharge; breastfeeding (fully or mixed) at six weeks; perineal pain at six weeks; maternal views; postpartum depression; instrumental measures of disability due to perineal pain. NSAID versus placeboCompared to women who received a placebo, more women who received a single dose NSAID achieved adequate pain relief at four hours (risk ratio (RR) 1.91, 95% confidence interval (CI) 1.64 to 2.23, 10 studies, 1573 participants (low-quality evidence)) and adequate pain relief at six hours (RR 1.92, 95% CI 1.69 to 2.17, 17 studies, 2079 participants (very low-quality evidence)). Women who received a NSAID were also less likely to need additional analgesia compared to women who received placebo at four hours (RR 0.39, 95% CI 0.26 to 0.58, four studies, 486 participants (low-quality evidence)) and at six hours after initial administration (RR 0.32, 95% CI 0.26 to 0.40, 10 studies, 1012 participants (low-quality evidence)). Fourteen maternal adverse effects were reported in the NSAID group (drowsiness (5), abdominal discomfort (2), weakness (1), dizziness (2), headache (2), moderate epigastralgia (1), not specified (1)) and eight in the placebo group (drowsiness (2), light headed (1), nausea (1), backache (1), dizziness (1), epigastric pain (1), not specified (1)), although not all studies assessed adverse effects. There was no difference in overall maternal adverse effects between NSAIDs and placebo at six hours post-administration (RR 1.38, 95% CI 0.71 to 2.70, 13 studies, 1388 participants (very low-quality evidence)). One small study (with two treatment arms) assessed maternal adverse effects at four hours post-administration, but there were no maternal adverse effects observed (one study, 90 participants (low-quality evidence)). Neonatal adverse effects were not assessed in any of the included studies. NSAID versus paracetamolNSAIDs versus paracetamol were also more effective for adequate pain relief at four hours (RR 1.54, 95% CI 1.07 to 2.22, three studies, 342 participants) but not at six hours post-administration. There was no difference in the need for additional analgesia between the two groups at four hours (RR 0.55, 95% CI 0.27 to 1.13, one study, 73 participants), but women in the NSAID group were less likely to need any additional analgesia at six hours (RR 0.28, 95% CI 0.12 to 0.67, one study, 59 participants). No maternal adverse effects were reported four hours after drug administration (one study). Six hours post-administration, there was no difference between the groups in the number of maternal adverse effects (RR 0.74, 95% CI 0.27 to 2.08, three studies, 300 participants), with one case of pruritis in the NSAID group and one case of sleepiness in the paracetamol group. Neonatal adverse effects were not assessed in any of the included studies.Comparisons of different NSAIDs and different doses of the same NSAID did not demonstrate any differences in their effectiveness on any of the primary outcome measures; however, few data were available on some NSAIDs.

AUTHORS' CONCLUSIONS

In women who are not breastfeeding and who sustained perineal trauma, NSAIDs (compared to placebo) provide greater pain relief for acute postpartum perineal pain and fewer women need additional analgesia when treated with a NSAID. However, the risk of bias was unclear for many of the included studies, adverse effects were often not assessed and breastfeeding women were not included in the studies. The overall quality of the evidence (GRADE) was low with the evidence for all outcomes rated as low or very low. The main reasons for downgrading were inclusion of studies with high risk of bias and inconsistency of findings of individual studies.NSAIDs also appear to be more effective in providing relief for perineal pain than paracetamol, but few studies were included in this analysis.Future studies should examine NSAIDs' adverse effects profile including neonatal adverse effects and the compatibility of NSAIDs with breastfeeding, and assess other important secondary outcomes of this review. Moreover, studies mostly included women who had episiotomies. Future research should consider women with and without perineal trauma, including perineal tears. High-quality studies should be conducted to further assess the efficacy of NSAIDs versus paracetamol and the efficacy of multimodal treatments.

Pattern recognition receptors in chronic pain: Mechanisms and therapeutic implications

For the individual, it is vital to promptly detect and recognize a danger that threatens the integrity of the body. Pattern recognition receptors (PRRs) are several classes of protein families originally classified as receptors detecting exogenous pathogens. PRRs are also capable of recognizing molecules released from damaged tissues (damage-associated molecular pattern molecules; DAMPs) and thereby contribute to danger recognition. Importantly, it is now evident that PRRs, such as toll-like receptors (TLRs) and receptors for advanced glycation end products (RAGE), are not only expressed in peripheral immune cells but also present in neurons and glial cells in the nervous system. These PRR-expressing cells work in concert, enabling highly sensitive danger recognition. However, this sensitiveness can act as a double-edged sword. Accumulated evidence has led to the hypothesis that aberrant activation of PRRs may play a crucial role in the pathogenesis of pathological pain. Indeed, numerous studies employing gene deletion or pharmacological inhibition of PRRs successfully reversed or prevented pathological pain in experimental animal models. Furthermore, a number of preclinical studies have shown the therapeutic potential of targeting PRRs for chronic pain. Here, we review the current knowledge regarding the role of PRRs in chronic pain and discuss the promise and challenges of targeting PRRs as a novel therapeutic approach for chronic pain.

The Effect of Intravenous Magnesium Sulfate on Post-Operative Analgesia During Laminectomy

Background and Objectives:

Post-operative pain control is an important concern for both patients and physicians. Magnesium is being used as an adjuvant for anesthesia and analgesia during and after various surgeries. We aimed to investigate the effects of intravenous magnesium sulfate on post-operative analgesia after laminectomy.

Methods Materials:

In this randomized double-blind controlled clinical trial, we enrolled 40 adult patients aged 18-60 with American Society of Anesthesiologists (ASA)  Class I-II who were candidates for elective laminectomy. The patients were randomly assigned in two control groups and were similarly anesthetized. In the case group, after the induction of anesthesia, a loading dose of magnesium sulfate (30 mg/kg) was administered within five to 10 minutes followed by a maintenance dose of 10 mg/kg/hr up to the end of the surgery; while, the patients in the control group received the same volume of saline. After the surgery, all patients received a patient-controlled intravenous analgesia (PCA) pump containing morphine. The first time of using PCA, the amount of consumed morphine during the first 24 hours, and pain score were recorded at 6,12,18 and 24 hours in the post-operative period.

Results:

There was no significant difference between the two groups with respect to the amount of morphine consumed in 24 hours after the surgery (P value =0.23), the first time of using of PCA pump (P value =0.79) and pain intensity (P value=0.52).

Conclusion:

The infusion of Magnesium Sulfate during laminectomy had no effect on patients’ pain and opioid requirement during the first 24 hours after the surgery.

Morphine paradoxically prolongs neuropathic pain in rats by amplifying spinal NLRP3 inflammasome activation

Opioid use for pain management has dramatically increased, with little assessment of potential pathophysiological consequences for the primary pain condition. Here, a short course of morphine, starting 10 d after injury in male rats, paradoxically and remarkably doubled the duration of chronic constriction injury (CCI)-allodynia, months after morphine ceased. No such effect of opioids on neuropathic pain has previously been reported. Using pharmacologic and genetic approaches, we discovered that the initiation and maintenance of this multimonth prolongation of neuropathic pain was mediated by a previously unidentified mechanism for spinal cord and pain-namely, morphine-induced spinal NOD-like receptor protein 3 (NLRP3) inflammasomes and associated release of interleukin-1β (IL-1β). As spinal dorsal horn microglia expressed this signaling platform, these cells were selectively inhibited in vivo after transfection with a novel Designer Receptor Exclusively Activated by Designer Drugs (DREADD). Multiday treatment with the DREADD-specific ligand clozapine-N-oxide prevented and enduringly reversed morphine-induced persistent sensitization for weeks to months after cessation of clozapine-N-oxide. These data demonstrate both the critical importance of microglia and that maintenance of chronic pain created by early exposure to opioids can be disrupted, resetting pain to normal. These data also provide strong support for the recent "two-hit hypothesis" of microglial priming, leading to exaggerated reactivity after the second challenge, documented here in the context of nerve injury followed by morphine. This study predicts that prolonged pain is an unrealized and clinically concerning consequence of the abundant use of opioids in chronic pain.

Dependence of Nociceptive Detection Thresholds on Physiological Parameters and Capsaicin-Induced Neuroplasticity: A Computational Study

Physiological properties of peripheral and central nociceptive subsystems can be altered over time due to medical interventions. The effective change for the whole nociceptive system can be reflected in changes of psychophysical characteristics, e.g., detection thresholds. However, it is challenging to separate contributions of distinct altered mechanisms with measurements of thresholds only. Here, we aim to understand how these alterations affect Aδ-fiber-mediated nociceptive detection of electrocutaneous stimuli. First, with a neurophysiology-based model, we study the effects of single-model parameters on detection thresholds. Second, we derive an expression of model parameters determining the functional relationship between detection thresholds and the interpulse interval for double-pulse stimuli. Third, in a case study with topical capsaicin treatment, we translate neuroplasticity into plausible changes of model parameters. Model simulations qualitatively agree with changes in experimental detection thresholds. The simulations with individual forms of neuroplasticity confirm that nerve degeneration is the dominant mechanism for capsaicin-induced increases in detection thresholds. In addition, our study suggests that capsaicin-induced central plasticity may last at least 1 month.

Intravenous Ibuprofen for Treatment of Post-Operative Pain: A Multicenter, Double Blind, Placebo-Controlled, Randomized Clinical Trial

BACKGROUND

Non-steroidal anti-inflammatory drugs are often used as components of multimodal therapy for postoperative pain management, but their use is currently limited by its side effects. The specific objective of this study was to evaluate the efficacy and safety of a new formulation of intravenous (IV) ibuprofen for the management of postoperative pain in a European population.

METHODS AND FINDINGS

A total of 206 patients from both abdominal and orthopedic surgery, were randomly assigned in 1:1 ratio to receive 800 mg IV-ibuprofen or placebo every 6 hours; all patients had morphine access through a patient controlled analgesia pump. The primary outcome measure was median morphine consumption within the first 24 hours following surgery. The mean±SEM of morphine requirements was reduced from 29,8±5,25 mg to 14,22±3,23 mg (p = 0,015) and resulted in a decrease in pain at rest (p = 0,02) measured by Visual Analog Scale (VAS) from mean±SEM 3.34±0,35 to 0.86±0.24, and also in pain during movement (p = 0,02) from 4.32±0,36 to 1.90±0,30 in the ibuprofen treatment arm; while in the placebo group VAS score at rest ranged from 4.68±0,40 to 2.12±0,42 and during movement from 5.66±0,42 to 3.38±0,44. Similar treatment-emergent adverse events occurred across both study groups and there was no difference in the overall incidence of these events.

CONCLUSIONS

Perioperative administration of IV-Ibuprofen 800 mg every 6 hours in abdominal surgery patient's decreases morphine requirements and pain score. Furthermore IV-Ibuprofen was safe and well tolerate. Consequently we consider appropriate that protocols for management of postoperative pain include IV-Ibuprofen 800 mg every 6 hours as an option to offer patients an analgesic benefit while reducing the potentially risks associated with morphine consumption.

TRIAL REGISTRATION

EU Clinical Trials Register 2011-005007-33.

The use of pupillometry as monitoring of intraoperative analgesia in the consumption of analgesics during the first 12 hours after surgery

INTRODUCTION

Intraoperative evaluation of analgesia remains today often based on heart rate and arterial pressure fluctuations. None of these parameters is specific. Incorrect handling during this process may increase surgical morbi-mortality of the patients and their acute postoperative pain. The aim of this study was to evaluate the impact of intraoperative analgesia controlled by pupillometry on postoperative analgesic consumption and the pain intensity in the first 12h in the hospital room, after major gynecological surgery.

PATIENTS AND METHODS

A prospective, cohort study with allocation of groups of sequentially according to programming of operating room was designed. ASA I-III patients scheduled for elective surgery of abdominal hysterectomy by laparotomy or laparoscopy through intravenous general anesthesia were included. Patients were divided into 2 groups: pupillometry group (P-1), in which intraoperative analgesia was guided by pupillometry, and hemodynamic group (H-2) according to values of blood pressure and heart rate. In the hospitalization room the values of visual analogue scale (VAS) were routinely registered with 3 courts for the study: 3, 8 and 12h of the postoperative period. Postoperative analgesia was standardized as follows: NSAIDs was administered if VAS was ≥ 3 or if the patient expressly requested an analgesic. After this, the efficacy of treatment was assessed. If the patient had pain, the next scheduled drug was given up to an VAS<3. Data for total analgesic consumption administered in the hospital room, VAS and adverse effects were collected within 12h postoperatively.

RESULTS

A total of 59 patients, 30 group P-1 and 29 group H-2, were included. Group P-1 experienced less pain than group H-2, with statistical significance in each phase (VAS 3h, VAS 8h and VAS 12h). These data are consistent with the consumption of analgesics for patients. There was a statistically significant reduction (p<0.001) in the group P-1 (1.80 [DE 0.99]; medium 2, 95% confidence interval 1.43-2.17) compared with group H-2 (5.66 [1.58]; medium 6, 95% confidence interval 5.05-6.26).

CONCLUSIONS

Monitoring of the intraoperative analgesia by pupillometry was able to reduce the intensity of the acute postoperative pain and analgesic consumption in the first 12h in the hospital room after major gynecological surgery.

Acute to chronic pain transition in extremity trauma: A narrative review for future preventive interventions (part 2)

BACKGROUND

The first part of this series of 2 articles revealed that chronic pain is an important issue post extremity trauma (ET) involving permanent biological transformations. Interventions aimed at preventing chronic pain in ET patients are therefore required.

OBJECTIVE

To conduct a comprehensive analysis of literature on risk and protective factors for chronic pain post-ET to guide the development of relevant preventive interventions.

METHODS

A narrative review of the literature was undertaken. Databases were searched to identify studies on chronic pain prognostic factors in ET patients.

RESULTS

Demographic, injury-related and psychological factors were shown to either contribute to or limit acute to chronic pain transition. High-intensity acute pain hasconsistently been identified as an important chronic pain risk factor. Other significant documented risk factors include: female gender, older age, less than college education, lower limb injury, symptoms of anxiety and depression and pain catastrophizing. Pain self-efficacy and pain acceptance have been shown to protect individuals against chronic pain.

CONCLUSIONS

This narrative review highlights factors placing ET patients at higher risk of chronic pain or protecting them against this problem. Determining how these factors could be addressed in preventive interventions is the next step before undertaking their development.

Pain in an era of armed conflicts: Prevention and treatment for warfighters and civilian casualties

Chronic pain is a common squealae of military- and terror-related injuries. While its pathophysiology has not yet been fully elucidated, it may be potentially related to premorbid neuropsychobiological status, as well as to the type of injury and to the neural alterations that it may evoke. Accordingly, optimized approaches for wounded individuals should integrate primary, secondary and tertiary prevention in the form of thorough evaluation of risk factors along with specific interventions to contravene and mitigate the ensuing chronicity. Thus, Premorbid Events phase may encompass assessments of psychological and neurobiological vulnerability factors in conjunction with fostering preparedness and resilience in both military and civilian populations at risk. Injuries per se phase calls for immediate treatment of acute pain in the field by pharmacological agents that spare and even enhance coping and adaptive capabilities. The key objective of the Post Injury Events is to prevent and/or reverse maladaptive peripheral- and central neural system's processes that mediate transformation of acute to chronic pain and to incorporate timely interventions for concomitant mental health problems including post-traumatic stress disorder and addiction We suggest that the proposed continuum of care may avert more disability and suffering than the currently employed less integrated strategies. While the requirements of the armed forces present a pressing need for this integrated continuum and a framework in which it can be most readily implemented, this approach may be also instrumental for the care of civilian casualties.

Managing Neuropathic Pain in Dogs

Disorders of the somatosensory system such as neuropathic pain are common in people with chronic neurologic and musculoskeletal diseases, yet these conditions remain an underappreciated morbidity in veterinary patients. This is likely because assessment of neuropathic pain in people relies heavily on self-reporting, something our veterinary patients are not able to do. The development of neuropathic pain is a complex phenomenon, and concepts related to it are frequently not addressed in the standard veterinary medical curriculum such that veterinarians may not recognize this as a potential problem in patients. The goals of this review are to discuss basic concepts in the pathophysiology of neuropathic pain, provide definitions for common clinical terms used in association with the condition, and discuss pharmacological treatment options for dogs with neuropathic pain. The development of neuropathic pain involves key mechanisms such as ectopic afferent nerve activity, peripheral sensitization, central sensitization, impaired inhibitory modulation, and pathologic activation of microglia. Treatments aimed at reducing neuropathic pain are targeted at one or more of these mechanisms. Several drugs are commonly used in the veterinary clinical setting to treat neuropathic pain. These include gabapentin, pregabalin, amantadine, and amitriptyline. Proposed mechanisms of action for each drug, and known pharmacokinetic profiles in dogs are discussed. Strong evidence exists in the human literature for the utility of most of these treatments, but clinical veterinary-specific literature is currently limited. Future studies should focus on objective methods to document neuropathic pain and monitor response to therapy in veterinary patients.

The Acute to Chronic Pain Transition: Can Chronic Pain Be Prevented?

Chronic postsurgical pain (CPSP) is a distressing disease process that can lead to long-term disability, reduced quality of life, and increased health care spending. Although the exact mechanism of development of CPSP is unknown, nerve injury and inflammation may lead to peripheral and central sensitization. Given the complexity of the disease process, no novel treatment has been identified. The preoperative use of multimodal analgesia has been shown to decrease acute postoperative pain, but it has no proven efficacy in preventing development of CPSP.

Acute pain: a multifaceted challenge - the role of nimesulide

BACKGROUND

This article summarizes the outcome from an international consensus meeting, which took place in Vienna on 4 November 2014.

SCOPE

The aim of the meeting was to provide the state of the art on the pathophysiology and treatment of acute pain with special emphasis on nimesulide, a non-steroidal anti-inflammatory drug (NSAID) indicated for the treatment of acute pain and primary dysmenorrhea. Besides the data on the mechanisms of acute inflammatory pain and on the efficacy and safety of nimesulide in patients affected by different forms of acute pain, the clinical experience of attending experts was discussed based on selected case reports.

RESULTS

The members of this consensus group recognized that nimesulide is a NSAID highly effective in the treatment of several painful situations with an acute inflammatory component including primary dysmenorrhea. Although safety concerns regarding nimesulide have emerged in recent years, both robust new epidemiological data and clinical experience confirm a positive benefit/risk profile of nimesulide in the treatment of several forms of acute pain.

CONCLUSIONS

The members of this international consensus group concluded that nimesulide, when used appropriately, remains a particularly valuable and safe option for the treatment of several conditions characterized by the presence of acute inflammatory pain because of the rapid onset of the analgesic action, and the positive evidence-based benefit/risk profile.

The in vitro mechanisms and in vivo efficacy of intravenous lidocaine on the neuroinflammatory response in acute and chronic pain

INTRODUCTION

The neuroinflammatory response plays a key role in several pain syndromes. Intravenous (iv) lidocaine is beneficial in acute and chronic pain. This review delineates the current literature concerning in vitro mechanisms and in vivo efficacy of iv lidocaine on the neuroinflammatory response in acute and chronic pain.

DATABASES AND DATA TREATMENT

We searched PUBMED and the Cochrane Library for in vitro and in vivo studies from July 1975 to August 2014. In vitro articles providing an explanation for the mechanisms of action of lidocaine on the neuroinflammatory response in pain were included. Animal or clinical studies were included concerning iv lidocaine for acute or chronic pain or during inflammation.

RESULTS

Eighty-eight articles regarding iv lidocaine were included: 36 in vitro studies evaluating the effect on ion channels and receptors; 31 animal studies concerning acute and chronic pain and inflammatory models; 21 clinical studies concerning acute and chronic pain. Low-dose lidocaine inhibits in vitro voltage-gated sodium channels, the glycinergic system, some potassium channels and Gαq-coupled protein receptors. Higher lidocaine concentrations block potassium and calcium channels, and NMDA receptors. Animal studies demonstrate lidocaine to have analgesic effects in acute and neuropathic pain syndromes and anti-inflammatory effects early in the inflammatory response. Clinical studies demonstrate lidocaine to have advantage in abdominal surgery and in some neuropathic pain syndromes.

CONCLUSIONS

Intravenous lidocaine has analgesic, anti-inflammatory and antihyperalgesic properties mediated by an inhibitory effect on ion channels and receptors. It attenuates the neuroinflammatory response in perioperative pain and chronic neuropathic pain.

The Prevalence and Characteristics of Pain in Critically Ill Cancer Patients: A Prospective Nonrandomized Observational Study

Context:

Pain is a distressing symptom common to all stages and ubiquitous at all levels of care in cancer patients. However, there is a lack of scientific literature on prevalence, severity, predictors, and the quality of pain in cancer patients admitted to an Intensive Care Unit (ICU).

Objectives:

To elucidate the prevalence of pain, moderate to severe pain, neuropathic pain, chronic pain, and pain as the most distressing symptom in critically ill-cancer patients at the time of ICU admission.

Methods:

We prospectively interviewed 126 patients within first 24 h of admission to a medical ICU. The patients were assessed for the presence of pain, its severity, sites, duration, nature, and its impact as a distressing symptom. Numerical Rating Scale and self-report version of Leeds Assessment of Neuropathic Signs and Symptoms were used to elucidate intensity of pain and neuropathic pain, respectively. Demographic characteristics such as age and sex, primary site, and stage of cancer were considered for a possible correlation with the prevalence of pain.

Results:

Of 126 patients included in the study 95 (75.40%), 79 (62.70%), 34 (26.98%), and 17 (13.49%) patients had pain, moderate-severe, chronic, and neuropathic pain, respectively. The average duration of pain was 171.16 ± 716.50 days. Totally, 58 (46.03%) and 42 (42.01%) patients had at least one and more than equal to 2 neuropathic pain symptoms, respectively. The primary malignancies associated with the highest prevalence of pain were genitourinary, hematological, and head and neck whereas breast and lung cancers were associated with the highest prevalence of neuropathic and chronic pain, respectively.

Conclusion:

The prevalence of pain among critically ill-cancer patients is high. Assessment for pain at the time of ICU admission would ensure appropriate assessment for the presence, type, severity, and the significance imparted to it.

The anti-nociceptive potential of tilmicosin against chemical-induced but not thermal-induced pain in mice

The aim of the present study was to assess the analgesic activity of the macrolide antibiotic tilmicosin at dose levels of 20 and 40 mg/kg of body weight, subcutaneously, against chemical- and thermal-induced acute pains, using acetic acid-induced writhing, formalin-induced pain, hot-plate, and tail-flick models in mice. Tilmicosin showed a dose-dependent significant decrease in the number of writhes in the acetic acid-induced writhing test and significant decrease in hind paw-licking time in the late phase of the formalin test. However, it did not cause any significant changes in the reaction times to heat stimuli in the hot-plate and tail-flick models. In chemically-induced pains, both dose levels of tilmicosin showed significant effects compared to those of the corresponding standard peripheral analgesic, acetylsalicylic acid (200 mg/kg of body weight, subcutaneously) being 26.37±2.88 and 43.64±3.85% vs. 73.35±1.44% in acetic acid test; and 19.23±3.85 and 44.90±1.80% vs. 73.63±2.39% in the late phase of formalin test, respectively. These results may indicate that tilmicosin possesses a significant peripheral but not central analgesic potential that may be beneficial in symptomatic relief of pain when it is used in therapy, in addition to its well-established antibacterial effect.

Perioperative low-dose ketamine improves postoperative analgesia following Cesarean delivery with general anesthesia

OBJECTIVE

In this study, the effect of perioperative uses of low dose ketamine on post-operative wound pain and analgesic consumption in patients undergoing elective Cesarean section was evaluated.

METHODS

In randomized, double blind clinical trial, 52 women with American Society of Anesthesiologists (ASA) class I-II identification undergoing elective Cesarean section in general anesthesia were enrolled. In the ketamine group (group K), a ketamine bolus of 0.5 mg kg(-1) IV was administered at the time of induction of general anesthesia. After induction, a ketamine infusion of 0.25 mg kg(-1) h(-1) was started and discontinued at the end of surgery. Patients allocated to the control group (group C) were given identical volumes of saline. The cumulative dose of morphine consumption after surgery was measured as the primary outcome of this study. Secondary outcomes were pain control assessed by numeric rating scale (NRS) and need for rescue analgesia and incidence of side effects.

RESULTS

The mean 24-h morphine consumption was lower in group K (p = 0,001). At 15 min postoperatively, NRS values were lower in group K than group C (p = 0,001). There was no difference among groups regarding the need for supplemental analgesia (rescue diclofenac doses) (p > 0.05).

CONCLUSIONS

Perioperative uses of low dose ketamine decreased post-operative opioid requirements, which was observed long after the normal expected duration of ketamine.

Nociception and role of immune system in pain

Both pain and inflammation are protective responses. However, these self-limiting conditions (with well-established negative feedback loops) become pathological if left uncontrolled. Both pain and inflammation can interact with each other in a multi-dimensional manner. These interactions are known to create an array of 'difficult to manage' pathologies. This review explains in detail the role of immune system and the related cells in peripheral sensitization and neurogenic inflammation. Various neuro-immune interactions are analyzed at peripheral, sensory and central nervous system levels. Innate immunity plays a critical role in central sensitization and in establishing acute pain as chronic condition. Moreover, inflammatory mediators also exhibit psychological effects, thus contributing towards the emotional elements associated with pain. However, there is also a considerable anti-inflammatory and analgesic role of immune system. This review also attempts to enlist various novel pharmacological approaches that exhibit their actions through modification of neuro-immune interface.

Clinically meaningful reduction in pain severity in children treated by paramedics: a retrospective cohort study

INTRODUCTION

Pediatric pain is a common presenting symptom in the prehospital setting; however, there is a lack of data identifying factors associated with effective pain management in this population. We sought to identify the factors associated with clinically meaningful pain reduction in children.

METHODS

An analysis of electronic patient care records of all patients younger than 15 years presenting with pain to the emergency medical service of Victoria, Australia, over a 4-year period (2008-2011). Data were analyzed using descriptive statistics and multivariate regression to assess predictors of clinically meaningful pain reduction. Clinically meaningful pain reduction was defined as a reduction of 2 or more points on an 11-point scale.

RESULTS

A total of 92378 children were transported, of whom 15016 (16.3%) met the inclusion criteria. The median age was 11 (interquartile range, 9-13) years, and 59.2% were male. Patients older than 9 years were less likely (adjusted odds ratio [AOR], 0.5; 95% confidence interval [CI], 0.4-0.6) and boys were more likely (adjusted odds ratio, 1.1; 95% CI, 1.0-1.3) to have a clinically meaningful reduction in pain. Patients with pain classified as musculoskeletal were more likely to achieve a reduction in pain score of 2 or more when compared with pain due to other medical causes (AOR, 1.7; 95% CI, 1.5-1.9).

CONCLUSIONS

Factors other than the type of analgesia are important determinants of prehospital pain relief and are likely to impact on clinical care and research. Clinical audit and research projects should stratify patients according to patient as well as management factors to maximize service improvement.

Acute Pain Medicine in the United States: A Status Report

BACKGROUND

Consensus indicates that a comprehensive,multimodal, holistic approach is foundational to the practice of acute pain medicine (APM),but lack of uniform, evidence-based clinical pathways leads to undesirable variability throughout U. S. healthcare systems. Acute pain studies are inconsistently synthesized to guide educational programs. Advanced practice techniques involving regional anesthesia assume the presence of a physician-led, multidisciplinary acute pain service,which is often unavailable or inconsistently applied.This heterogeneity of educational and organizational standards may result in unnecessary patient pain and escalation of healthcare costs.

METHODS

A multidisciplinary panel was nominated through the APM Shared Interest Group of the American Academy of Pain Medicine. The panel met in Chicago, IL, in July 2014, to identify gaps and set priorities in APM research and education.

RESULTS

The panel identified three areas of critical need: 1) an open-source acute pain data registry and clinical support tool to inform clinical decision making and resource allocation and to enhance research efforts; 2) a strong professional APM identity as an accredited subspecialty; and 3) educational goals targeted toward third-party payers,hospital administrators, and other key stake holders to convey the importance of APM.

CONCLUSION

This report is the first step in a 3-year initiative aimed at creating conditions and incentives for the optimal provision of APM services to facilitate and enhance the quality of patient recovery after surgery, illness, or trauma. The ultimate goal is to reduce the conversion of acute pain to the debilitating disease of chronic pain.

Spinorphin inhibits membrane depolarization- and capsaicin-induced intracellular calcium signals in rat primary nociceptive dorsal root ganglion neurons in culture

OBJECTIVE

Spinorphin is a potential endogenous antinociceptive agent although the mechanism(s) of its analgesic effect remain unknown. We conducted this study to investigate, by considering intracellular calcium concentrations as a key signal for nociceptive transmission, the effects of spinorphin on cytoplasmic Ca(2+) ([Ca(2+)]i) transients, evoked by high-K(+) (30 mM) depolariasation or capsaicin, and to determine whether there were any differences in the effects of spinorphin among subpopulation of cultured rat dorsal root ganglion (DRG) neurons.

METHODS

DRG neurons were cultured on glass coverslips following enzymatic digestion and mechanical agitation, and loaded with the calcium sensitive dye fura-2 AM (1 µM). Intracellular calcium responses in individual DRG neurons were quantified using standard fura-2 based ratiometric calcium imaging technique. All data were analyzed by using unpaired t test, p < 0.05 defining statistical significance.

RESULTS

Here we found that spinorphin inhibited cytoplasmic Ca(2+) ([Ca(2+)]i) transients, evoked by depolarization and capsaicin selectively in medium and small cultured rat DRG neurons. Spinorphin (10-300 µM) inhibited the Ca(2+) signals in concentration dependant manner in small- and medium diameter DRG neurons. Capsaicin produced [Ca(2+)]i responses only in small- and medium-sized DRG neurons, and pre-treatment with spinorphin significantly attenuated these [Ca(2+)]i responses.

CONCLUSION

Results from this study indicates that spinorphin significantly inhibits [Ca(2+)]i signaling, which are key for the modulation of cell membrane excitability and neurotransmitter release, preferably in nociceptive subtypes of this primary sensory neurons suggesting that peripheral site is involved in the pain modulating effect of this endogenous agent.