Perioperative ketamine does not prevent chronic pain after thoracotomy

Rationale and design of a multicenter randomized clinical trial with memantine and dextromethorphan in ketamine-responder patients

The N-methyl-D-aspartate receptor plays an important role in central sensitization of neuropathic pain and N-methyl-D-aspartate receptor antagonists, such as ketamine, memantine and dextromethorphan may be used for persistent pain. However, ketamine cannot be repeated too often because of its adverse events. A drug relay would be helpful in the outpatient to postpone or even cancel the next ketamine infusion. This clinical trial evaluates if memantine and/or dextromethorphan given as a relay to ketamine responders may maintain or induce a decrease of pain intensity and have a beneficial impact on cognition and quality of life. This trial is a multi-center, randomized, controlled and single-blind clinical study (NCT01602185). It includes 60 ketamine responder patients suffering from neuropathic pain. They are randomly allocated to memantine, dextromethorphan or placebo. After ketamine infusion, 60 patients received either memantine (maximal dose 20 mg/day), or dextromethorphan (maximal dose 90 mg/day), or placebo for 12 weeks. The primary endpoint is pain measured on a (0-10) Numeric Rating Scale 1 month after inclusion. Secondary outcomes include assessment of neuropathic pain, sleep, quality of life, anxiety/depression and cognitive function at 2 and 3 months. Data analysis is performed using mixed models and the tests are two-sided, with a type I error set at α=0.05. This study will explore if oral memantine and/or dextromethorphan may be a beneficial relay in ketamine responders and may diminish ketamine infusion frequency. Preservation of cognitive function and quality of life is also a central issue that will be analyzed in these vulnerable patients.

Pain Management Strategies for Thoracotomy and Thoracic Pain Syndromes

Pain after thoracic surgery can be severe and, in the acute phase, contribute to perioperative morbidity and mortality. Unfortunately, patients also incur a significant risk of chronic pain. Although there are guidelines for postoperative pain management in these patients, there is no widespread surgical or anesthetic “best practice.” Here, we review the recent literature on techniques specific to perioperative pain control for thoracic patients, including medical management, neuraxial blockade, and other regional techniques, and suggest an algorithm for developing a multimodal pain management strategy.

Neuropathic aspects of persistent postsurgical pain: a French multicenter survey with a 6-month prospective follow-up

To investigate the role of peripheral neuropathy in the development of neuropathic postsurgical persistent pain (N-PSPP) after surgery, this French multicentric prospective cohort study recruited 3,112 patients prior to elective cesarean, inguinal herniorrhaphy (open mesh/laparoscopic), breast cancer surgery, cholecystectomy, saphenectomy, sternotomy, thoracotomy, or knee arthroscopy. Besides perioperative data collection, postoperative postal questionnaires built to assess the existence, intensity, and neuropathic features (with the Douleur Neuropathique 4 Questions [DN4]) of pain at the site of surgery were sent at the third and sixth months after surgery. In the 2,397 patients who completed follow-up, the cumulative risk of N-PSPP within the 6 months ranged from 3.2% (laparoscopic herniorrhaphy) to 37.1% (breast cancer surgery). Pain intensity was greater if DN4 was positive and decreased with time since surgery; it depended on the type of surgery. In pain-reporting patients, the response to the DN4 changed from time to time in about 1:4 of the cases. Older age and a low anxiety score were independent protective factors of N-PSPP, whereas a recent negative event, a low preoperative quality of life, and previous history of peripheral neuropathy were risk factors. The type of anesthesia had no influence on the occurrence of N-PSPP.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT00812734.

PERSPECTIVE

This prospective observational study provides the incidence rate of N-PSPP occurring within the 6 months after 9 types of elective surgical procedures. It highlights the possible consequences of nerve aggression during some common surgeries. Finally, some preoperative predispositions to the development of N-PSPP have been identified.

Pharmacotherapy for the prevention of chronic pain after surgery in adults

BACKGROUND

Chronic pain can often occur after surgery, substantially impairing patients' health and quality of life. It is caused by complex mechanisms that are not yet well understood. The predictable nature of most surgical procedures has allowed for the conduct of randomized controlled trials of pharmacological interventions aimed at preventing chronic postsurgical pain.

OBJECTIVES

The primary objective was to evaluate the efficacy of systemic drugs for the prevention of chronic pain after surgery by examining the proportion of patients reporting pain three months or more after surgery. The secondary objective was to evaluate the safety of drugs administered for the prevention of chronic pain after surgery.

SEARCH METHODS

We identified randomized controlled trials (RCTs) of various systemically administered drugs for the prevention of chronic pain after surgery from CENTRAL, MEDLINE, EMBASE and handsearches of other reviews and trial registries. The most recent search was performed on 17 July 2013.  

SELECTION CRITERIA

Included studies were double-blind, placebo-controlled, randomized trials involving adults and evaluating one or more drugs administered systemically before, during or after surgery, or both, which measured pain three months or more after surgery.

DATA COLLECTION AND ANALYSIS

Data collected from each study included the study drug name, dose, route, timing and duration of dosing; surgical procedure; proportion of patients reporting any pain three months or more after surgery, reporting at least 4/10 or moderate to severe pain three months or more after surgery; and proportion of participants dropping out of the study due to treatment-emergent adverse effects.

MAIN RESULTS

We identified 40 RCTs of various pharmacological interventions including intravenous ketamine (14 RCTs), oral gabapentin (10 RCTs), oral pregabalin (5 RCTs), non-steroidal anti-inflammatories (3 RCTs), intravenous steroids (3 RCTs), oral N-methyl-D-aspartate (NMDA) blockers (3 RCTs), oral mexiletine (2 RCTs), intravenous fentanyl (1 RCT), intravenous lidocaine (1 RCT), oral venlafaxine (1 RCT) and inhaled nitrous oxide (1 RCT). Meta-analysis suggested a modest but statistically significant reduction in the incidence of chronic pain after surgery following treatment with ketamine but not gabapentin or pregabalin. Results with ketamine should be viewed with caution since most of the included trials were small (that is < 100 participants per treatment arm), which could lead to the overestimation of treatment effect.

AUTHORS' CONCLUSIONS

Additional evidence from better, well designed, large-scale trials is needed in order to more rigorously evaluate pharmacological interventions for the prevention of chronic pain after surgery. Furthermore, available evidence does not support the efficacy of gabapentin, pregabalin, non-steroidal anti-inflammatories, intravenous steroids, oral NMDA blockers, oral mexiletine, intravenous fentanyl, intravenous lidocaine, oral venlafaxine or inhaled nitrous oxide for the prevention of chronic postoperative pain.

Nefopam after total hip arthroplasty: role in multimodal analgesia

BACKGROUND

Multimodal analgesia combining several non-opioid analgesics is recommended for pain control after surgery. In one study of total hip arthroplasty (THA), pain relief achieved by adding ketamine to the paracetamol-ketoprofen combination was statistically significant but remained inadequate in most patients. In two other studies, the analgesic effect of nefopam was synergistic with that of ketoprofen and additive with that of paracetamol. Adding nefopam to the paracetamol-ketoprofen-ketamine combination has not been evaluated.

HYPOTHESIS

Adding nefopam to the paracetamol-ketoprofen-ketamine combination significantly improves analgesia after THA.

MATERIAL AND METHODS

A prospective single-centre comparative non-randomised study (control group then nefopam group) was conducted in patients undergoing THA under general anaesthesia. All patients received paracetamol-ketoprofen-ketamine and morphine/droperidol patient-controlled analgesia. The nefopam group also received a continuous infusion of nefopam (120 mg/d for 48 h). Pain was evaluated daily for 7 days. The main evaluation criteria were morphine consumption, and pain intensity evaluated using a numerical rating scale and a validated questionnaire. To detect a 40% morphine-sparing effect by H24 (α=0.05 and β=0.2), 85 patients were needed in each group.

RESULTS

The two groups (90 patients/group) had no significant differences for perioperative characteristics, pain scores, morphine consumption at H24 (nefopam, 13 ± 12 mg and control, 14 ± 13 mg, P=0.39), or functional recovery. Compared to the control group, the nefopam group had lower rates of nausea/vomiting (P<0.0001), pruritus (P=0.002), and visual disturbances (P=0.02).

DISCUSSION

Nefopam failed to improve pain relief when added to a multimodal analgesia regimen but alleviated several morphine-induced side effects. Redundancy between nefopam and ketamine may explain the absence of greater pain relief. This study emphasises the need for clinical evaluations of every analgesic regimen, as the available data were not sufficient to predict these results.

LEVEL OF EVIDENCE

Level III, case-control study.

Chronic postsurgical pain: still a neglected topic?

Background

Surgical injury can frequently lead to chronic pain. Despite the obvious importance of this problem, the first publications on chronic pain after surgery as a general topic appeared only a decade ago. This study tests the hypothesis that chronic postsurgical pain was, and still is, represented insufficiently.

Methods

We analyzed the presentation of this topic in journal articles covered by PubMed and in surgical textbooks. The following signs of insufficient representation in journal articles were used: (1) the lack of journal editorials on chronic pain after surgery, (2) the lack of journal articles with titles clearly indicating that they are devoted to chronic postsurgical pain, and (3) the insufficient representation of chronic postsurgical pain in the top surgical journals.

Results

It was demonstrated that insufficient representation of this topic existed in 1981–2000, especially in surgical journals and textbooks. Interest in this topic began to increase, however, mostly regarding one specific surgery: herniorrhaphy. It is important that the change in the attitude toward chronic postsurgical pain spreads to other groups of surgeries.

Conclusion

Chronic postsurgical pain is still a neglected topic, except for pain after herniorrhaphy. The change in the attitude toward chronic postsurgical pain is the important first step in the approach to this problem.

Effects of nefopam on early postoperative hyperalgesia after cardiac surgery

OBJECTIVE

The purpose of this randomized, double-blind placebo-controlled study was to evaluate the effect of nefopam, a centrally acting antinociceptive compound, on the development of hyperalgesia after sternotomy. Preventive strategy giving nefopam from the early stage of anesthesia was compared with a postoperative strategy only and placebo.

DESIGN

This study was double-blinded and randomized.

SETTING

It was conducted in a single university hospital.

PARTICIPANTS

Ninety American Society of Anesthesiologists II to III patients scheduled for elective cardiac surgery.

INTERVENTIONS

Patients were assigned randomly to receive a 0.3-mg/kg bolus of nefopam at the induction of anesthesia followed by a continuous infusion of 0.065 mg/kg/h for 48 hours (G1), a 0.3-mg/kg bolus of nefopam at the end of surgery followed by a continuous infusion of 0.065 mg/kg/h for 48 hours (G2), or a placebo (G3). Postoperative analgesia was based on morphine patient-controlled analgesia and rescue analgesia when necessary. Postoperative hyperalgesia, pain scores, morphine consumption, and postoperative cognitive dysfunction were assessed for the first 48 hours and thereafter on postoperative days 4 and 7.

MEASUREMENTS AND MAIN RESULTS

The postoperative extent of dynamic hyperalgesia and the decrease of the nociceptive threshold evaluated by von Frey filaments at the sternal midline were smaller in group 1 and group 2 compared with the placebo group at the 24th hour. The primary objective was the extent of hyperalgesia at the midline given as the mean (standard deviation [SD]) (4.4 [2.5] cm for G1, 4.1 [2.7] for G2, and 6.1 [2.7] cm for G3. The punctuate is given as mean (SD) (64 [43] g for G1, 68 [40.8] g for G2, and 32 [27] g for G3; with p < 0.05 for the comparisons of extent and punctuate hyperalgesia between G1 and G3 and G2 and G3). The extent of hyperalgesia was not significantly different among the 3 groups on days 2, 4, and 7 after surgery. There were no significant differences in pain scores, morphine consumption, or postoperative cognitive dysfunctions.

CONCLUSIONS

Nefopam administered during the perioperative period slightly reduced acute hyperalgesia after cardiac surgery, but this was not associated with improved analgesic efficacy.

Room for improvement: unmet needs in postoperative pain management

Postoperative pain treatment is an important healthcare issue. However, the management of pain in patients after surgery remains insufficient. In the present review, several key areas important for postoperative pain management are discussed. New findings about efficacy and side effects of nonopioid analgesics, such as paracetamol, NSAIDs and COX-2 inhibitors, are presented and discussed in light of acute, short-term application in the perioperative period. Second, new findings about postoperative pain management in patients with preoperative pain and chronic opioid consumption are reported. Third, feasibility of the transversus abdominal plane block as a new and promising regional anesthesia technique is discussed. Finally, potential predictors, mechanisms and preventive treatment strategies of persistent chronic pain after surgery are presented.

Targeting N-methyl-D-aspartate receptors for treatment of neuropathic pain

Neuropathic pain remains a major clinical problem and a therapeutic challenge because existing analgesics are often ineffective and can cause serious side effects. Increased N-methyl-d-aspartate receptor (NMDAR) activity contributes to central sensitization in certain types of neuropathic pain. NMDAR antagonists can reduce hyperalgesia and allodynia in animal models of neuropathic pain induced by nerve injury and diabetic neuropathy. Clinically used NMDAR antagonists, such as ketamine and dextromethorphan, are generally effective in patients with neuropathic pain, such as complex regional pain syndrome and painful diabetic neuropathy. However, patients with postherpetic neuralgia respond poorly to NMDAR antagonists. Recent studies on identifying NMDAR-interacting proteins and molecular mechanisms of increased NMDAR activity in neuropathic pain could facilitate the development of new drugs to attenuate abnormal NMDAR activity with minimal impairment of the physiological function of NMDARs. Combining NMDAR antagonists with other analgesics could also lead to better management of neuropathic pain without causing serious side effects.

An expert opinion on postoperative pain management, with special reference to new developments

IMPORTANCE OF THE FIELD

Recently, much attention has been directed towards the effect of opioid-sparing strategies on postoperative morbidity and hospitalization, and on different nociceptive mechanisms involved in various postoperative pain states and surgical procedures. This has resulted in an increased interest in secondary, or adjunct, analgesics and procedure-specific analgesic methods.

AREAS COVERED IN THIS REVIEW

The present paper aims to review and discuss recent developments within the field of various adjunct, systemic analgesics and local/regional anesthetic methods for management of postoperative pain, based on evidence from randomized, clinical trials published within the last 5 years.

WHAT THE READER WILL GAIN

The reader will gain insight into the current role of pregabalin, glucocorticoids and systemic lidocaine for the management of postoperative pain. In addition, the current status of local infiltration analgesia for hip and knee arthroplasty, transversus abdominis plane block for abdominal operations, and the analgesic effect of wound instillation of capsaicin are reviewed.

TAKE HOME MESSAGE

The evidence of a substantial analgesic effect of pregabalin on acute postoperative pain is questionable, and more convincing evidence of the role of glucocorticoids and systemic lidocaine is needed before they should be recommended as analgesics in daily clinical practice. Local infiltration analgesia after hip and knee arthroplasty, transversus abdominis plane block after abdominal operations and local application of capsaicin lend some promise, but there is still a lack of well-performed RCTs to draw any firm conclusions. Procedure-specific analgesic combinations within well-defined rehabilitation paradigms should be explored further to reduce adverse effects associated with the use of conventional analgesic treatment protocols, and to improve postoperative outcome.

Central sensitization: implications for the diagnosis and treatment of pain

Nociceptor inputs can trigger a prolonged but reversible increase in the excitability and synaptic efficacy of neurons in central nociceptive pathways, the phenomenon of central sensitization. Central sensitization manifests as pain hypersensitivity, particularly dynamic tactile allodynia, secondary punctate or pressure hyperalgesia, aftersensations, and enhanced temporal summation. It can be readily and rapidly elicited in human volunteers by diverse experimental noxious conditioning stimuli to skin, muscles or viscera, and in addition to producing pain hypersensitivity, results in secondary changes in brain activity that can be detected by electrophysiological or imaging techniques. Studies in clinical cohorts reveal changes in pain sensitivity that have been interpreted as revealing an important contribution of central sensitization to the pain phenotype in patients with fibromyalgia, osteoarthritis, musculoskeletal disorders with generalized pain hypersensitivity, headache, temporomandibular joint disorders, dental pain, neuropathic pain, visceral pain hypersensitivity disorders and post-surgical pain. The comorbidity of those pain hypersensitivity syndromes that present in the absence of inflammation or a neural lesion, their similar pattern of clinical presentation and response to centrally acting analgesics, may reflect a commonality of central sensitization to their pathophysiology. An important question that still needs to be determined is whether there are individuals with a higher inherited propensity for developing central sensitization than others, and if so, whether this conveys an increased risk in both developing conditions with pain hypersensitivity, and their chronification. Diagnostic criteria to establish the presence of central sensitization in patients will greatly assist the phenotyping of patients for choosing treatments that produce analgesia by normalizing hyperexcitable central neural activity. We have certainly come a long way since the first discovery of activity-dependent synaptic plasticity in the spinal cord and the revelation that it occurs and produces pain hypersensitivity in patients. Nevertheless, discovering the genetic and environmental contributors to and objective biomarkers of central sensitization will be highly beneficial, as will additional treatment options to prevent or reduce this prevalent and promiscuous form of pain plasticity.

Role of N-methyl-D-aspartate receptor antagonists in postoperative pain management

PURPOSE OF REVIEW

In recent years, hundreds of studies have examined the clinical efficacy of N-methyl-D-aspartate (NMDA) receptor antagonists such as ketamine and dextromethorphan as an adjunct to routine postoperative pain management. The purpose of this review is to describe the detail of the study that successfully demonstrated the efficacy of NMDA receptor antagonists.

RECENT FINDINGS

The effect of perioperative ketamine infusion, dextromethorphan, and memantine on postoperative opioid-induced analgesia and prevention of long-term persistent pain is described.

SUMMARY

The co-administration of ketamine and morphine as a mixture is not recommended for postoperative pain relief. As an adjunct in multimodal analgesia, low-dose ketamine infusion and the administration of dextromethorphan may be able to improve postoperative pain status. Memantine exhibits the greatest potency among NMDA receptor antagonists. In future, research should consider the perioperative infusion of ketamine followed by long-term administration of memantine for the prevention of persistent pain.