The effects of magnesium sulfate infiltration on perioperative opioid consumption and opioid-induced hyperalgesia in patients undergoing robot-assisted laparoscopic prostatectomy with remifentanil-based anesthesia

Navigating the Postoperative Management of Remifentanil-Induced Hyperalgesia: A Case Report

Opioid induced hyperalgesia in the postoperative setting presents a significant challenge for clinicians managing postoperative pain in opioid tolerant patients. Remifentanil is a fentanyl analog frequently utilized in anesthesia for its favorable pharmacokinetic profile. However, as described in the case report, it may also increase the risk of postoperative hyperalgesia. Management of postoperative pain in the setting of hyperalgesia should be approached in a stepwise fashion, emphasizing therapy options with analgesic effects achieved outside of the opioidergic system while maintaining a neutral opioid balance.

Efficacy and Safety of Magnesium Sulfate as an Adjunct to Ropivacaine Wound Infiltration in Thyroid Surgery: A Prospective, Double-Blind, Randomized Controlled Trial

Background/Objective: Wound infiltration with local anesthetics emerges as a promising modality for postoperative pain alleviation. However, such strategies in neck surgery have not been a well-established practice. To assess wound infiltration with ropivacaine plus magnesium sulfate for pain relief following thyroid surgery. Methods: This prospective, double-blind, randomized study enrolled 68 patients who underwent thyroid surgery. Concerning the solution used for surgical wound infiltration, the study participants were randomly allocated into three groups: (1) 100 mg of ropivacaine (Group R); (2) 100 mg of ropivacaine plus magnesium sulfate 10 mg/kg (Group RMg); and (3) normal saline which served as a placebo (Group P). Pain perception both at rest and at movement, was measured using the Visual Analogue Scale (VAS) at 30 min, as well as at 1, 2, 4, 6, 12, and 24 h postoperatively. The total consumption of analgesics in morphine equivalents was also recorded. Moreover, adverse effects and patient satisfaction were recorded. Cortisol, TNF-α, and IL-6 levels were measured 30 min before infiltration and 6 h and 24 h postoperatively. Results: Demographics and clinical characteristics were similar between the groups. The VAS scores at rest and during movement were significantly lower in the RMg group compared to the saline or ropivacaine groups. Total analgesic consumption was also significantly lower in the RMg group. No operation-, wound-, or infiltration-related adverse effects were recorded in the study groups. Better overall satisfaction was obtained for the RMg group. Conclusions: Ropivacaine plus magnesium sulfate wound infiltration provided better pain control and the analgesic effect was more significant, contributing to effective postoperative analgesia in patients undergoing thyroid surgery.

Feasibility of opioid-free anesthesia in laparoscopic radical prostatectomy: A retrospective, quasi-experimental study

Background and Aims

Opioid-free anesthesia (OFA) provides adequate analgesia minimizing opioids. OFA has not been evaluated in laparoscopic radical prostatectomy (LRP). Our aim was to evaluate OFA feasibility and its effectiveness in LRP.

Material and Methods

A quasi-experimental retrospective study of 55 adult patients undergoing LRP was performed from September 2020 until December 20223. Predefined protocols for either opioid-based anesthesia (OBA; with continuous remifentanil infusion) or OFA (continuous lidocaine, dexmedetomidine, and ketamine infusion) were followed. In both groups, wound infiltration was performed before skin incision. Primary outcome was postoperative pain management (numerical rating scale [NRS]) in the first 24 postoperative hours. Secondary outcomes were opioid consumption, start to sitting and ambulation, postoperative complications, and length of hospital stay.

Results

OFA protocol patients had better median pain scores during movement at 1, 18 and 24 h, that is, 1 (interquartile range [IQR] 0-3) versus 2.5 (IQR 0-4), P = 0.047; 0 (IQR 0-1) versus 1 (IQR 0-2), P = 0.017; and 0 (IQR 0-0.25) versus 1 (IQR 0-2), P = 0.013, respectively. At 6 and 12 h, there were no statistically significant differences, that is, 0.5 (IQR 0-2) versus 1 (IQR 0-2), P = 0.908 and 1 (IQR 0-2) versus 0.5 (IQR 0-2), P = 0.929, respectively. Lower morphine requirements were recorded in the first 18 and 24 postoperative hours, that is, 0 (IQR 0-0) versus 1 (IQR 0-2.75) mg, P = 0.028 and 0 (IQR 0-2) versus 1.5 (IQR 0-3) mg, P = 0.012, respectively. Start to sitting and ambulation occurred earlier in the OFA group (P = 0.030 and P = 0.002, respectively). Linear regression showed that ambulation was independently associated with the analgesic technique (P = 0.034). Only one patient had postoperative nausea and vomiting (PONV) and belonged to the OBA group. There was no difference in total complications or the length of stay.

Conclusion

In this study, OFA strategy was found to be safe, feasible, and provided adequate analgesia, minimizing the use of postoperative opioids, and was independently associated with earlier ambulation.

Postoperative pain after different doses of remifentanil infusion during anaesthesia: a meta-analysis

BACKGROUND

This meta-analysis aimed to explore the correlation between the different doses of remifentanil-based anaesthesia and postoperative pain in randomised trials.

METHODS

The electronic databases including PubMed, Cochrane, clinical trial registries, and Google Scholar were searched up to November 2022 for randomised controlled trials (RCTs) that assessed the dose dependent efficacy of remifentanil for postoperative pain intensity and hyperalgesia.

RESULTS

31 studies involving 2019 patients were included for analysis. Compared with the high remifentanil dose administration, patients in low doses showed less postoperative pain intensity at 1-2 h (weighted mean differences (WMD): 0.60, 95% CI, 0.05 to 1.15), 3-8 h (WMD: 0.38, 95% CI, 0.00 to 0.75), 24 h (WMD: 0.26, 95% CI, 0.04 to 0.48) and 48 h (WMD: 0.32, 95% CI, 0.09 to 0.55). Remifentanil-free regimen failed to decrease the pain score at 24 h (WMD: 0.10, 95% CI, -0.10 to 0.30) and 48 h (WMD: 0.15, 95% CI, -0.22 to 0.52) in comparison with remifentanil-based anaesthesia. After excluding trials with high heterogeneity, the dose of the remifentanil regimen was closely correlated with the postoperative pain score (P=0.03). In addition, the dose of the remifentanil regimen was not associated with the incidence of postoperative nausea and vomiting (PONV) (P=0.37).

CONCLUSIONS

Our meta-analysis reveals that the low dose of remifentanil infusion is recommendable for general anaesthesia maintenance. No evidence suggests that remifentanil-free regimen has superiority in reducing postoperative pain. Moreover, remifentanil doesn't have a dose dependent effect in initiating PONV.

TRIAL REGISTRATION

The protocol of present study was registered with PROSPERO (CRD42022378360).

To assess the analgesic efficacy of adjuvant magnesium sulfate added with ropivacaine over ropivacaine alone as a continuous infiltration in total abdominal hysterectomy wound: A randomized controlled trial

Background and Aims

Magnesium sulfate (MgSO4) has been demonstrated to have analgesic property in various clinical settings. This study explores if addition of MgSO4 to ropivacaine increases its analgesic efficacy when infiltrated continuously in the postsurgical wound following total abdominal hysterectomy.

Material and Methods

This randomized controlled trial was conducted at a tertiary care referral hospital in New Delhi, India. Fifty-two patients were randomized into two groups to receive the intervention of which 48 were able to complete the study. The first group (n = 26) received 0.25% ropivacaine infiltration and the second group (n = 26) received 0.25% ropivacaine with 5% MgSO4 at the incision site for 48 h postoperatively. Primary objective was to compare the total postoperative opioid (morphine) consumption by the study participants in both the groups and the secondary objectives were pain scores at rest and at movement, patient satisfaction score, and wound quality of life on the 7th postoperative day among the two groups.

Results

Both the groups were comparable in their demographic characteristics. The median morphine consumed at 48 h postoperatively was 16.5 [0-77] mg in the ropivacaine group and 13[1-45] mg in the ropivacaine with MgSO4 group and the difference was statistically insignificant (P = 0.788). There was no statistical difference between the groups with respect to the pain scores, patient satisfaction, or wound quality of life at 7 days.

Conclusion

The addition of MgSO4 to ropivacaine does not confer any additional postoperative analgesic benefits over ropivacaine alone in continuous wound infiltration following total abdominal hysterectomy.

Comparison of Ropivacaine Plus Dexmedetomidine and Ropivacaine Plus Magnesium Sulfate Infiltration for Postoperative Analgesia in Patients Undergoing Lumbar Spine Surgeries

BACKGROUND

 Acute pain after lumbar spine surgery is due to soft tissue and muscle separation at the operation site. Local anesthetic wound infiltration is a safe and effective method for postoperative analgesia following lumbar spine surgery. In this study, we aimed to investigate and compare the efficacy of ropivacaine plus dexmedetomidine and ropivacaine plus magnesium sulfate for postoperative analgesia in lumbar spine surgeries.

MATERIALS AND METHOD

This prospective randomized study was conducted on 60 patients, aged between 18 and 65 years, either sex, American Society of Anesthesiologists classification I and II patients scheduled for single-level lumbar laminectomy. Patients were randomly allocated into two groups 30 patients each. Twenty to 30 minutes before skin closure and after hemostasis was achieved, the surgeon infiltrated 10 mL of study drugs into paravertebral muscles on each side. Group A received 20 mL of 0.75% ropivacaine plus dexmedetomidine and group B received 20 mL of 0.75% ropivacaine plus magnesium sulfate. Postoperative pain was assessed by the visual analog scale at 0 minute (immediately after extubation), 30 minutes, 1st hour, 2nd hour, and thereafter at 4th hour, 6th hour, 12th hour, and 24th hour. Time to rescue analgesia, total analgesic consumption, hemodynamic variables, and complications if any were recorded. Statistical analysis was done using SPSS version 20.0 (Armonk, NY: IBM Corp.).

RESULTS

The time to first requirement of analgesia in postoperative period was significantly longer in group A (10.05 ± 1.62 hours) than in group B (8.07 ± 1.83 hours) (p < 0.001). Total analgesic consumption was significantly higher in group B (197.50 ± 36.76 mL) compared to group A (142.50 ± 22.88 mL) (p < 0.001). Heart rate and mean arterial pressure were significantly lower in group A compared to group B (p < 0.05).

CONCLUSION

Local infiltration of surgical site with ropivacaine plus dexmedetomidine provided better pain control than ropivacaine plus magnesium sulphate infiltration and is safe and effective analgesia for patients undergoing lumbar spine surgeries in postoperative period.

Updates in Enhanced Recovery Pathways for Gynecologic Surgery

Gynecologic surgery encompasses over a quarter of inpatient surgical procedures for US women, and current projections estimate an increase of the US female population by nearly 50% in 2050. Over the last decade, US hospitals have embraced enhanced recovery pathways in many specialties. They have increasingly been used in multiple institutions worldwide, becoming the standard of care for patient optimization. According to the last updated enhanced recovery after surgery (ERAS) guideline published in 2019, there are several new considerations behind each practice in ERAS protocols. This article discusses the most updated evidence regarding ERAS programs for gynecologic surgery.

PROSPECT guidelines update for evidence-based pain management after prostatectomy for cancer

The aim of this review was to update the recommendations for optimal pain management after open and laparoscopic or robotic prostatectomy. Optimal pain management is known to influence postoperative recovery, but patients undergoing open radical prostatectomy typically experience moderate dynamic pain in the immediate postoperative day. Robot-assisted and laparoscopic surgery may be associated with decreased pain levels as opposed to open surgery. We performed a systematic review using Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) with PROcedure SPECific Postoperative Pain ManagemenT (PROSPECT) methodology. Randomised controlled trials (RCTs) published in English language, from January 2015 until March 2020, assessing postoperative pain, using analgesic, anaesthetic and surgical interventions, were identified from MEDLINE, EMBASE and Cochrane Databases. Of the 1797 studies identified, 35 RCTs and 3 meta-analyses met our inclusion criteria. NSAIDs and COX-2 selective inhibitors proved to lower postoperative pain scores. Continuous intravenous lidocaine reduced postoperative pain scores during open surgery. Local wound infiltration showed positive results in open surgery. Bilateral transversus abdominis plane (TAP) block was performed at the end of surgery and lowered pain scores in robot-assisted procedures, but results were conflicting for open procedures. Basic analgesia for prostatic surgery should include paracetamol and NSAIDs or COX-2 selective inhibitors. TAP block should be recommended as the first-choice regional analgesic technique for laparoscopic/robotic radical prostatectomy. Intravenous lidocaine should be considered for open surgeries.

Anaesthetic management for robotic-assisted laparoscopic prostatectomy: the first UK national survey of current practice

Robotic-assisted laparoscopic prostatectomy (RALP) is the most common robotic surgical procedure, but there are little published data to inform anaesthetic practice. We aimed to characterise the range of anaesthetic practice for RALP in the United Kingdom through a national survey. We conducted an online national survey to determine current anaesthetic practice for RALP. The survey was distributed to all NHS hospitals within the UK that perform RALP. Thirty-four (79%) of 43 hospitals responded to the survey. Fourteen (41%) centres routinely provide spinal anaesthesia and 79% of these use diamorphine as their intrathecal opioid of choice. Thirty-one (91%) centres administer intravenous strong opioids intraoperatively, and a wide range of non-opioid analgesic agents are also administered. Five (15%) centres reported that they discharge a minority of patients on the day of surgery. High-volume centres are more likely to have a formalised enhanced recovery after surgery (ERAS) pathway and to provide ambulatory surgery for selected patients. This represents the first UK national survey of anaesthetic practice for RALP. The results of the survey revealed significant variation in anaesthetic practice implying a lack of consensus on best perioperative management.

Adjuncts to local anesthetic wound infiltration for postoperative analgesia: a systematic review

Local anesthetics (LAs) are commonly infiltrated into surgical wounds for postsurgical analgesia. While many adjuncts to LA agents have been studied, it is unclear which adjuncts are most effective for co-infiltration to improve and prolong analgesia. We performed a systematic review on adjuncts (excluding epinephrine) to local infiltrative anesthesia to determine their analgesic efficacy and opioid-sparing properties. Multiple databases were searched up to December 2019 for randomized controlled trials (RCTs) and two reviewers independently performed title/abstract screening and full-text review. Inclusion criteria were (1) adult surgical patients and (2) adjunct and LA agents infiltration into the surgical wound or subcutaneous tissue for postoperative analgesia. To focus on wound infiltration, studies on intra-articular, peri-tonsillar, or fascial plane infiltration were excluded. The primary outcome was reduction in postoperative opioid requirement. Secondary outcomes were time-to-first analgesic use, postoperative pain score, and any reported adverse effects. We screened 6670 citations, reviewed 126 full-text articles, and included 89 RCTs. Adjuncts included opioids, non-steroidal anti-inflammatory drugs, steroids, alpha-2 agonists, ketamine, magnesium, neosaxitoxin, and methylene blue. Alpha-2 agonists have the most evidence to support their use as adjuncts to LA infiltration. Fentanyl, ketorolac, dexamethasone, magnesium and several other agents show potential as adjuncts but require more evidence. Most studies support the safety of these agents. Our findings suggest benefits of several adjuncts to local infiltrative anesthesia for postoperative analgesia. Further well-powered RCTs are needed to compare various infiltration regimens and agents.

Protocol registration

PROSPERO (CRD42018103851) (https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=103851)

Effectiveness of Magnesium in Preventing Shivering in Surgical Patients: A Systematic Review and Meta-analysis

BACKGROUND

Clinical trials regarding the antishivering effect of perioperative magnesium have produced inconsistent results. We conducted a systematic review and meta-analysis with Trial Sequential Analysis to evaluate the effect of perioperative magnesium on prevention of shivering.

METHODS

We searched PubMed, EMBASE, Web of Science, Cochrane Central Register of Controlled Trials, and 2 registry sites for randomized clinical trials that compared the administration of magnesium to a placebo or no treatment in patients undergoing surgeries. The primary outcome of this meta-analysis was the incidence of shivering. The incidence of shivering was combined as a risk ratio with 95% CI using a random-effect model. The effect of the route of administration was evaluated in a subgroup analysis, and Trial Sequential Analysis with a risk of type 1 error of 5% and power of 90% was performed. The quality of each included trial was evaluated, and the quality of evidence was assessed using the Grading of Recommendation Assessment, Development, and Evaluation approach. We also assessed adverse events.

RESULTS

Sixty-four trials and 4303 patients (2300 and 2003 patients in magnesium and control groups, respectively) were included. The overall incidence of shivering was 9.9% in the magnesium group and 23.0% in the control group (risk ratio, 0.42; 95% CI, 0.33-0.52). Subgroup analysis revealed that the incidence of shivering was lower with IV (risk ratio, 0.29; 95% CI, 0.29-0.54; Grading of Recommendation Assessment, Development, and Evaluation, moderate), epidural (risk ratio, 0.24; 95% CI, 0.13-0.43; Grading of Recommendation Assessment, Development, and Evaluation, low), and intrathecal administration (risk ratio, 0.64; 95% CI, 0.43-0.96; Grading of Recommendation Assessment, Development, and Evaluation, moderate). Only trials with low risk of bias were included for Trial Sequential Analysis. The Z-cumulative curve for IV magnesium crossed the Trial Sequential Analysis monitoring boundary for benefit even though only 34.9% of the target sample size had been reached. The Z-cumulative curve for epidural or intrathecal administration did not cross the Trial Sequential Analysis monitoring boundary for benefit. No increase in adverse events was reported.

CONCLUSIONS

Perioperative IV administration of magnesium effectively reduced shivering and Trial Sequential Analysis suggested that no more trials are required to confirm that IV magnesium effectively reduces shivering.

Effects of low-dose ketamine infusion on remifentanil-induced acute opioid tolerance and the inflammatory response in patients undergoing orthognathic surgery

Purpose

Remifentanil is associated with acute opioid tolerance that can lead to increased postoperative consumption of opioid analgesics. The purpose of this study was to determine whether a low dose of ketamine prevents remifentanil-induced acute opioid tolerance and affects the neutrophil–lymphocyte ratio (NLR), a newly recognized biomarker of inflammation.

Materials and methods

Forty patients undergoing orthognathic surgery were enrolled in this prospective, randomized, double-blind study and randomly assigned to intraoperative administration of one of the following anesthetic regimens: high-dose remifentanil (0.6 µg/kg/minute); low-dose remifentanil (0.2 µg/kg/minute); or high-dose remifentanil with ketamine (remifentanil 0.6 µg/kg/minute with 0.5 mg/kg ketamine just after induction followed by an intraoperative infusion of ketamine 5 µg/kg/minute until wound closure). Fentanyl by intravenous patient-controlled analgesia was used for postoperative pain control. Visual Analog Scale pain scores and fentanyl consumption were recorded in the first 24 hours postoperatively. Perioperative serum C-reactive protein level and NLR were also determined.

Results

Baseline characteristics were similar in the three study groups. There were no between-group differences in Visual Analog Scale pain scores during the study period. The high-dose remifentanil group had a significantly higher requirement for fentanyl than the other two groups. Addition of ketamine did not affect the C-reactive protein level but increased the NLR; this increase was associated with decreased fentanyl consumption.

Conclusion

High-dose intraoperative remifentanil induced postoperative acute opioid tolerance that was prevented by infusion of low-dose ketamine. Ketamine increased the postoperative NLR associated with decreased fentanyl requirement for postoperative pain control.

Why mu-opioid agonists have less analgesic efficacy in neuropathic pain?

Injury to peripheral nerves often leads to abnormal pain states (hyperalgesia, allodynia and spontaneous pain), which can remain long after the injury heals. Although opioid agonists remain the gold standard for the treatment of moderate to severe pain, they show reduced efficacy against neuropathic pain. In addition to analgesia, opioid use is also associated with hyperalgesia and analgesia tolerance, whose underlying mechanisms share some commonalities with nerve injury-induced hypersensitivity. Here, we reviewed up-to-day research exploring the contribution of mu-opioid receptor (MOR) on the pathophysiology of neuropathic pain and on analgesic opioid actions under these conditions. We focused on the specific contributions of MOR populations at peripheral, spinal and supraspinal level. Moreover, evidences of neuroplastic changes that may underlie the low efficacy of MOR agonists under neuropathic pain conditions are reviewed and discussed. Sensitization processes leading to pain hypersensitivity, molecular changes in signalling pathways triggered by MOR and glial activation are some of these mechanisms elicited by both nerve injury and opioid exposure. Nerve injury-induced pain hypersensitivity might be masking the initial analgesic effects of opioid agonists, and alternatively, sustained opioid treatment to individuals already suffering from neuropathic pain could aggravate their pathophysiological state. Finally, some combined therapies that can increase opioid analgesic effectiveness in neuropathic pain treatment are highlighted. SIGNIFICANCE: This review provides evidence of the low benefit of opioid monotherapy in neuropathic pain and analyses the reasons of this reduced effectiveness. Opioid agonists along with drugs targeted to block the sensitization processes induced by MOR stimulation might result in a better management of neuropathic pain.

Remifentanil-induced postoperative hyperalgesia: current perspectives on mechanisms and therapeutic strategies

The use of remifentanil in clinical practice offers several advantages and it is used for a wide range of procedures, ranging from day-surgery anesthesia to more complex procedures. Nonetheless, remifentanil has been consistently linked with development of opioid-induced hyperalgesia (OIH), which is described as a paradoxical increase in sensitivity to painful stimuli that develops after exposure to opioid treatment. The development of OIH may cause several issues, delaying recovery after surgery and preventing timely patient's discharge. Moreover, it causes patient's discomfort with higher pain scores, greater use of analgesics, and associated side effects. Remifentanil is the opioid most convincingly associated with OIH, and hereby we provide a review of remifentanil-induced hyperalgesia, describing both the underlying mechanisms involved and the available studies investigating experimental and clinical pharmacologic approaches aiming at reducing its incidence and degree.

Comparison of Bupivacaine Plus Magnesium Sulfate and Ropivacaine Plus Magnesium Sulfate Infiltration for Postoperative Analgesia in Patients Undergoing Lumbar Laminectomy: A Randomized Double-blinded Study

Aim:

The objective of this study was to assess and compare the analgesic duration of local infiltration of bupivacaine plus magnesium sulfate and ropivacaine plus magnesium sulfate for postoperative analgesia in patients undergoing lumbar laminectomy.

Study Design:

A randomized, prospective, double-blinded single hospital, comparative study.

Methods:

Sixty adult patients of the American Society of Anesthesiologists physical Status I and II were randomly allocated into two Groups BM and RM, comprising 30 and 31 patients. Postlumbar laminectomy, the study drug was locally infiltrated into the paravertebral muscles on either side before skin closure. Group BM was given 20 ml of 0.25% bupivacaine combined with 500 mg of magnesium sulfate (constituted with normal saline [NS]), and Group RM was given 20 ml of 0.25% ropivacaine combined with 500 mg of magnesium sulfate (constituted with NS). Postoperative visual analog scale pain score was assessed hourly for the first 24 h postoperatively. Duration of postoperative analgesia, rescue analgesia consumption and side effects were also recorded.

Statistical Analysis:

Comparison of data between the groups was done with SPSS 21.0© using independent t-test, Chi-square test, and Mann–Whitney U-test accordingly. P<0.05 was considered statistically significant.

Results:

Time to first analgesic consumption was significantly longer in Group BM (7.3 ± 0.46 h) compared to Group RM (6.6 ± 0.69 h) (P < 0.05). The consumption of nalbuphine rescue analgesic was significantly higher in Group RM (15.33 ± 5.07 mg) compared to Group BM (12 ± 4.07 mg) (P < 0.05).

Conclusion:

Wound infiltration with bupivacaine and magnesium sulfate compared to ropivacaine and magnesium sulfate provided longer duration of postoperative analgesia and significantly reduced postoperative opioid consumption in patients undergoing lumbar laminectomy.

Preemptive, preventive, multimodal analgesia: what do they really mean?

SUMMARY

To improve postoperative pain management, several concepts have been developed, including preemptive analgesia, preventive analgesia, and multimodal analgesia. This article will discuss the role of these concepts in improving perioperative pain management. Preemptive analgesia refers to the administration of an analgesic treatment before the surgical insult or tissue injury. Several randomized clinical trials have, however, provided equivocal evidence regarding the benefits of preincisional compared with postincisional analgesic administration. Current general consensus, therefore, indicates that use of preemptive analgesia does not translate into consistent clinical benefits after surgery. Preventive analgesia is a wider concept where the timing of analgesic administration in relation to the surgical incision is not critical. The aim of preventive analgesia is to minimize sensitization induced by noxious stimuli arising throughout the perioperative period. Multimodal analgesia consists of the administration of 2 or more drugs that act by different mechanisms for providing analgesia. These drugs may be administered via the same route or by different routes. Thus, the aim of multimodal analgesia is to improve pain relief while reducing opioid requirements and opioid-related adverse effects. Analgesic modalities currently available for postoperative pain control include opioids, local anesthetic techniques [local anesthetic infiltration, peripheral nerve blocks, and neuraxial blocks (epidural and paravertebral)], acetaminophen, nonsteroidal anti-inflammatory drugs, and cyclooxygenase-2-specific inhibitors as well as analgesic adjuncts such as steroids, ketamine, α-2 agonists, and anticonvulsants.

Optimal pain management for radical prostatectomy surgery: what is the evidence?

BACKGROUND

Increase in the diagnosis of prostate cancer has increased the incidence of radical prostatectomy. However, the literature assessing pain therapy for this procedure has not been systematically evaluated. Thus, optimal pain therapy for patients undergoing radical prostatectomy remains controversial.

METHODS

Medline, Embase, and Cochrane Central Register of Controlled Trials were searched for studies assessing the effects of analgesic and anesthetic interventions on pain after radical prostatectomy. All searches were conducted in October 2012 and updated in June 2015.

RESULTS

Most treatments studied improved pain relief and/or reduced opioid requirements. However, there were significant differences in the study designs and the variables evaluated, precluding quantitative analysis and consensus recommendations.

CONCLUSIONS

This systematic review reveals that there is a lack of evidence to develop an optimal pain management protocol in patients undergoing radical prostatectomy. Most studies assessed unimodal analgesic approaches rather than a multimodal technique. There is a need for more procedure-specific studies comparing pain and analgesic requirements for open and minimally invasive surgical procedures. Finally, while we wait for appropriate procedure specific evidence from publication of adequate studies assessing optimal pain management after radical prostatectomy, we propose a basic analgesic guideline.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

TRIAL REGISTRATION

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

The analgesic effect of nefopam combined with low dose remifentanil in patients undergoing middle ear surgery under desflurane anesthesia: a randomized controlled trial

BACKGROUND

We investigated the effects of the combined administration of nefopam, a N-methyl-D-aspartate receptor antagonist and low dose remifentanil, on early postoperative pain and analgesic requirement.

METHODS

Fifty patients scheduled to undergo mastoidectomy and tympanoplasty were randomized to be given either nefopam 40 mg mixed with normal saline 100 ml (Group N) or an equal amount of normal saline (Group C) before anesthesia induction. Anesthesia was maintained with 5-6 vol% desflurane and remifentanil 0.05-0.15 µg/kg/min during the surgery. Postoperative pain was controlled by titration of ketorolac in the postanesthesia care unit (PACU) and ward. We evaluated the intraoperative remifentanil dose, recovery profiles, ketorolac demand in the PACU and ward, numeric rating scale (NRS) for pain at time intervals of every 10 min for 1 h in the PACU, 6, 12, 18 and 24 h in a ward, as well as the time to first analgesic requirement in the PACU and ward.

RESULTS

Ketorolac demand and NRS in the PACU were significantly lower in Group N than Group C (P = 0.002, P = 0.005, respectively). The time to first analgesic requirement in the PACU in Group N were significantly longer than Group C (P = 0.046). There were no significant differences in intraoperative remifentanil dose, ketorolac demand, NRS, and the time to first analgesic requirement in the ward between the groups.

CONCLUSIONS

Nefopam administration combined with low dose remifentanil infusion reduces pain and analgesic consumption during the immediate postoperative period in patients undergoing middle ear surgery under desflurane anesthesia.

Total intravenous anaesthesia with high-dose remifentanil does not aggravate postoperative nausea and vomiting and pain, compared with low-dose remifentanil: a double-blind and randomized trial

The study was designed to investigate postoperative nausea and vomiting (PONV) in low- and high-dose remifentanil regimens for total intravenous anaesthesia (TIVA) in adult female patients with American Society of Anaesthesiologists physical status classification I undergoing local breast excision. Propofol and remifentanil 5 ng·mL⁻¹ (L group) or 10 ng·mL⁻¹ (H group) were administered for anaesthesia induction and maintenance. Propofol was titrated within range of 0.1 μg·mL⁻¹ to maintain bispectral index (BIS) values between 40 and 60. Haemodynamic parameters during the intra- and postoperative periods and 24 h postoperative visual analogue scale (VAS) and PONV were evaluated. Each group with 63 patients was analyzed. The H group showed higher use of remifentanil and lower use of propofol, with similar recovery time. Mean systemic arterial blood pressure (MBP), heart rate, and BIS did not differ significantly before and after endotracheal intubation in the H group. However, significant increases in MBP and BIS were apparent in the L group. Postoperative VAS, PONV incidence and scale, and Rhodes index did not differ significantly between the two groups. In conclusion, TIVA with high-dose remifentanil did not aggravate PONV with similar postoperative pain, compared with low-dose remifentanil. Furthermore, high-dose remifentanil showed more haemodynamic stability after endotracheal intubation. This trial is registered with KCT0000185.

Interaction between postoperative shivering and hyperalgesia caused by high-dose remifentanil

BACKGROUND

High-dose remifentanil-based anesthesia is associated with opioid-induced hyperalgesia (OIH) and postanesthetic shivering (PAS). These effects can be prevented by N-methyl-d-aspartate (NMDA) receptor antagonists. This study aimed to investigate correlations between OIH and PAS caused by high-dose remifentanil and the effects of low-dose ketamine on OIH and PAS.

METHODS

Seventy-five patients scheduled for single-port laparoscopic gynecologic surgery were randomly allocated into three groups, each of which received intraoperative remifentanil: group L at 0.1 µg/kg/min; group H at 0.3 µg/kg/min; and group HK at 0.3 µg/kg/min plus 0.25 mg/kg ketamine just before incision, followed by a continuous infusion of 5 µg/kg/min ketamine until skin closure.

RESULTS

PAS, postoperative tactile pain threshold, and the extent of hyperalgesia in group H were significantly different (P < 0.05) than in the other two groups. PAS was significantly correlated with OIH, including mechanically evoked pain such as postoperative tactile pain threshold (r = -0.529, P = 0.01) (r = -0.458, P = 0.021) and the extent of hyperalgesia (r = 0.537, P = 0.002) (r = 0.384, P = 0.031), respectively, in group H and group HK. Notably, both groups were treated with high-dose remifentanil. Tympanic membrane temperature, time to first postoperative analgesic requirement, postoperative pain scores, analgesic consumption, and cumulative patient-controlled analgesia volume containing morphine were comparable in all three groups.

CONCLUSIONS

OIH, including the enhanced perception of pain, and PAS were both associated with high-dose remifentanil, were significantly correlated and were attenuated by a low dose of ketamine. This suggests that a common mechanism in part mediated through activation of the central glutamatergic system (e.g., NMDA receptors), underlies the two effects caused by high doses of remifentanil.

Antihyperalgesic effects of dexmedetomidine on high-dose remifentanil-induced hyperalgesia

Background

Dexmedetomidine is a highly selective α2 adrenergic agonist that has been shown to decrease the intensity of opioid-induced hyperalgesia (OIH). We aimed to investigate the antihyperalgesic effects of dexmedetomidine on high-dose remifentanil-induced hyperalgesia.

Methods

Ninety American Society of Anesthesiologists physical status I-II patients undergoing laparoscopically assisted vaginal hysterectomy (LAVH) were randomly assigned to one of the following three groups, each of which received either dexmedetomidine (an initial dose of 1.0 µg/kg for 10 min, followed by a continuous infusion of 0.7 µg/kg/hr) or placebo saline 15 min before the induction of anesthesia and intraoperative remifentanil infusion: group C received a placebo and 0.05 µg/kg/min remifentanil; group RH received a placebo and 0.3 µg/kg/min remifentanil; and group DRH received dexmedetomidine and 0.3 µg/kg/min remifentanil.

Results

The mechanical hyperalgesia threshold 24 hr after surgery was significantly lower in group RH than in the other two groups. Postoperative pain intensity using visual analog scale (VAS) and cumulative volume of a patient-controlled analgesia (PCA) containing morphine over 24 hr were significantly greater in group RH than in group DRH. The time to the first postoperative analgesic requirement was significantly shorter in group RH than in the other two groups. The desflurane requirement was significantly greater in group C than in the other groups. The frequency of hypotension and bradycardia was significantly higher, but shivering and postoperative nausea and vomiting were significantly lower in group DRH than in the other two groups.

Conclusions

High-doses of remifentanil induced hyperalgesia, which presented a decreased mechanical hyperalgesia threshold, enhanced pain intensity, a shorter time to first postoperative analgesic requirement, and greater morphine consumption, but dexmedetomidine efficiently alleviated those symptoms. Dexmedetomidine may be a novel and effective treatment option for preventing or attenuating OIH.

Common trace elements alleviate pain in an experimental mouse model

Trace elements represent a group of essential metals or metaloids necessary for life, present in minute amounts. Analgesic adjuvants can enhance the effect of other pain drugs or be used for pain control themselves. Previous studies on the effects of trace elements on nociception and their potential use as analgesic adjuvants have yielded conflicting results. In this study, we tested the hypothesis that three vital trace elements (Zn²⁺, Mg²⁺, Cu²⁺) have direct antinociceptive effects. Groups of eight Swiss mice were intraperitoneally (i.p) injected with incremental concentrations of Zn²⁺ sulfate (0.5, 2.0 mg/kg), Zn²⁺ citrate (0.125, 0.5 mg/kg), Mg²⁺ chloride (37.5, 75, 150 mg/kg), Cu²⁺ chloride (0.5, 1.0, 2.0 mg/kg), and Cu²⁺ sulfate (0.5, 1.0 mg/kg) or saline (control). Evaluations were made by hot plate (HP) and tail flick (TF) tests for central antinociceptive effect, writhing test (WT) for visceral antinociceptive effect, and activity cage (AC) test for spontaneous behavior. Zn²⁺ induced pain inhibition in HP/TF tests (up to 17%) and WT (up to 25%), with no significant differences among the salts used. Mg²⁺ salts induced pain inhibition for all performed tests (up to 85% in WT). Cu²⁺ salts showed antinociceptive effects for HP/TF (up to 28.6%) and WT (57.28%). Only Mg²⁺ and Cu²⁺ salts have displayed significant effects in AC (Mg²⁺ anxiolytic/depressant effect; Cu²⁺ anxiolytic effect). We interpret these data to mean that all tested trace elements induced antinociceptive effects in central and visceral pain tests. Our data indicate the potential use of these cheap adjuvants in pain therapy.

Effect of oral pregabalin on opioid-induced hyperalgesia in patients undergoing laparo-endoscopic single-site urologic surgery

Background

Pregabalin is an antiepileptic drug that is effective for treating postoperative pain, neuropathic pain, anxiety, and hemodynamic instability. The aim of this study was to investigate the effect of a single preoperative dose of pregabalin in patients with opioid-induced hyperalgesia (OIH).

Methods

Ninety ASA I-II patients undergoing laparoendoscopic single-site urologic surgery were randomly assigned to one of the following three groups that received either pregabalin or placebo 1 h before anesthesia and an intraoperative remifentanil infusion. Group plL received placebo and 0.05 µg/kg/min remifentanil, group plH received placebo and 0.3 µg/kg/min remifentanil, and group prH received 300 mg pregabalin plus 0.3 µg/kg/min remifentanil. The primary endpoint was pain intensity upon movement 1, 6, 12, and 24 h after surgery. Secondary endpoints were the area of hyperalgesia and mechanical hyperalgesia threshold 24 h after surgery, time to first postoperative analgesic requirement, and cumulative postoperative volume of morphine administered via a patient-controlled analgesia (PCA) pump over 24 h.

Results

The time to first postoperative analgesic requirement in group plH was significantly shorter than that in group plL. The injected PCA volume was significantly greater in group plH than that in the other two groups. Postoperative pain intensity in group plH was significantly greater than that in the other two groups at 6, 12, and 24 h after surgery. The mechanical hyperalgesia threshold and the area of hyperalgesia around the surgical incision 24 h after surgery in group plH differed significantly from those in the other two groups, which were not significantly different. Adverse effects were comparable among groups.

Conclusions

High-dose remifentanil induced hyperalgesia, including increased pain intensity, increased area of hyperalgesia, and decreased mechanical hyperalgesia threshold. These effects were attenuated by oral administration of a single preoperative dose of pregabalin (300 mg) in patients undergoing laparo-endoscopic single-site urologic surgery.

Endogenous opiates and behavior: 2011

This paper is the thirty-fourth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2011 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration (Section 16); and immunological responses (Section 17).

A review of a family of ultra-rapid-acting insulins: formulation development

This review summarizes the clinical development of a family of ultra-rapid-acting recombinant human insulin formulations. These formulations use ethylenediaminetetraacetic acid (EDTA) to chelate zinc and thereby destabilize insulin hexamers. In addition, insulin monomer surface charges are chemically masked with citrate to prevent reaggregation. The first phase 1 trials were performed using BIOD-090, an acidic 25 unit U/ml insulin formulation, which contained disodium-EDTA (NaEDTA). When compared with regular human insulin (RHI) and/or insulin lispro in multiple phase 1 studies, BIOD-090 consistently showed more rapid absorption and/or onset of action. A standard meal challenge study also demonstrated improved postprandial glucose profiles associated with BIOD-090. However, increased patient exposure in larger phase 3 trials showed that this formulation was associated with an increased incidence of local injection site reactions, most commonly pain. A next generation formulation, BIOD-100, contained the same excipients as a standard insulin concentration of 100 U/ml. BIOD-100 maintained an ultra-rapid action profile and was associated with modest but significantly improved toleration when compared with BIOD-090. In order to further improve toleration, the hypothesis that NaEDTA contributed to discomfort by chelating endogenous calcium was tested by either substituting calcium-EDTA for NaEDTA or by adding calcium chloride to the NaEDTA formulation. These calcium formulations essentially eliminated the excess discomfort associated with BIOD-090 but were associated with less optimal pharmacokinetic profiles in humans. Recent efforts have succeeded in developing ultra-rapid-acting human insulin formulations with acceptable injection site toleration by optimizing concentrations of calcium (BIOD-125) and with the use of magnesium sulfate to mitigate discomfort (BIOD-123). Similar formulation technology has also been shown to accelerate absorption of insulin analogs in animal models.