Nitrous oxide for the treatment of complex regional pain syndrome: a randomized blinded trial

INTRODUCTION

Complex Regional Pain Syndrome (CRPS) is a debilitating neuropathic condition often refractory to conventional treatments. N-methyl-D-aspartate (NMDA) receptor antagonists have a well-established role in the development and modulation of chronic neuropathic pain. Nitrous oxide is widely used and generally safe anesthetic gas with NMDA receptor antagonist activity. We therefore tested the hypothesis that brief periods of nitrous oxide exposure reduce pain in patients with CRPS.

METHODS

Patients with a diagnosis of CRPS were randomized to either 2 hours of nitrous oxide exposure on three alternating days (Nitrous Oxide) versus a placebo air/oxygen mixture (Air-Oxygen). Our primary outcome was patient-reported pain scores at 1 week and 1 month. Secondary and exploratory outcomes were physical and mental health (PRMOIS-29 v2 survey), specific neuropathic pain symptoms (McGill short-form questionnaire), and opioid consumption.

RESULTS

44 patients participated in the study; 20 were randomized to Nitrous Oxide and 24 were assigned to Air-Oxygen. Pain scores did not differ significantly, with the estimated difference in means (Nitrous Oxide-Air-Oxygen) of -0.57 (95% CI: -1.42 to 0.28) points, p=0.19. There were also no differences detected in secondary outcomes, with the estimated difference in mean Z-scores for physical health (Nitrous Oxide-Air-Oxygen) of 0.13 (95% CI: -0.16 to 0.43), mental health 0.087 (95% CI: -0.31 to 0.48), and Patient Global Impression of Change score -0.7 (95% CI: -1.85 to 0.46).

CONCLUSIONS

Compared with air/oxygen, 2 hours of nitrous oxide/oxygen exposure for three sessions did not provide meaningful therapeutic potential for patients with chronic CRPS. Our results do not support using nitrous oxide for the treatment of CRPS.

Effects of Remifentanil Gradual Withdrawal Combined with Postoperative Infusion on Postoperative Hyperalgesia in Patients Undergoing Laparoscopic hysterectomy: A Factorial Design, Double-Blind, Randomized Controlled Trial

Background

Remifentanil-induced hyperalgesia (RIH) increases the risk of persistent postoperative pain, making early postoperative analgesic therapy ineffective and affecting postoperative patient satisfaction. This study aimed to verify the effects of gradual withdrawal of remifentanil combined with postoperative pump infusion of remifentanil on postoperative hyperalgesia and pain in patients undergoing laparoscopic hysterectomy.

Methods

This trial was a factorial design, double-blind, randomized controlled trial. Patients undergoing laparoscopic hysterectomy were randomly allocated to the control group, postoperative pump infusion of remifentanil group, gradual withdrawal of remifentanil group, or gradual withdrawal plus postoperative pump infusion of remifentanil group (n = 35 each). The primary outcome was postoperative mechanical pain thresholds in the medial forearm. The secondary outcomes included postoperative mechanical pain thresholds around the incision, pain numeric rating scale scores, analgesic utilization, awakening agitation or sedation scores, a 15-item quality of recovery survey, and postoperative complications.

Results

Gradual withdrawal of remifentanil significantly increased postoperative pain thresholds versus abrupt discontinuation (P < 0.05), whereas postoperative infusion did not show significant differences compared to the absence of infusion (P > 0.05). The combined gradual withdrawal and postoperative infusion group exhibited the highest thresholds and had the lowest postoperative pain scores and analgesic requirements as well as the highest quality of recovery scores (P < 0.05). No significant differences were observed for agitation scores, sedation scores, or complication rates (P > 0.05).

Conclusion

The novel combined gradual withdrawal and postoperative infusion of remifentanil uniquely attenuates postoperative hyperalgesia, pain severity, analgesic necessity, and improves recovery quality after laparoscopic hysterectomy.

Pre-procedural Preparation and Sedation for Gastrointestinal Endoscopy in Patients with Advanced Liver Disease

Gastrointestinal endoscopy in patients with advanced liver disease poses various challenges, a major one being procedural sedation and its associated considerations. While sedation during endoscopy can improve patient comfort, decrease anxiety, and facilitate procedural completion, in patients with advanced liver disease, it is also associated with substantial and unique risks due to alterations in drug metabolism and other factors. As such, the choice of sedative agent(s) and related logistics may require careful inter-disciplinary planning and individualized considerations. Furthermore, a large proportion of agents require dose reductions and particular monitoring of the vital signs, level of consciousness, and other indices. In the present review, we provide a contemporary overview of procedural sedation considerations, commonly used intravenous sedatives, and second-line as well as novel sedatives for gastrointestinal endoscopy in patients with advanced liver disease.

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

ABSTRACT

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

Evaluation of antihyperalgesic and analgesic effects of 35% nitrous oxide when combined with remifentanil: A randomised phase 1 trial in volunteers

BACKGROUND

Remifentanil is an effective drug in peri-operative pain therapy, but it can also induce and aggravate hyperalgesia. Supplemental administration of N2O may help to reduce remifentanil-induced hyperalgesia.

OBJECTIVE

To evaluate the effect of 35 and 50% N2O on hyperalgesia and pain after remifentanil infusion.

DESIGN

Single site, phase 1, double-blind, placebo-controlled, randomised crossover study.

SETTING

University Hospital, Germany from January 2012 to April 2012.

PARTICIPANTS

Twenty-one healthy male volunteers.

INTERVENTIONS

Transcutaneous electrical stimulation induced spontaneous acute pain and stable areas of hyperalgesia. Each volunteer underwent the following four sessions in a randomised order: 50 to 50% N2-O2 and intravenous (i.v.) 0.9% saline infusion (placebo); 50 to 50% N2-O2 and i.v. remifentanil infusion at 0.1 μg kg-1 min-1 (remifentanil); 35 to 15 to 50% N2O-N2-O2 and i.v. remifentanil infusion at 0.1 μg kg-1 min-1 (tested drug) and 50 to 50% N2O-O2 and i.v. remifentanil infusion at 0.1 μg kg-1 min-1 (gas active control). Gas mixtures were inhaled for 60 min; i.v. drugs were administered for 30 min.

MAIN OUTCOME MEASURES

Areas of pin-prick hyperalgesia, areas of touch-evoked allodynia and pain intensity on a visual analogue scale were assessed repeatedly for 160 min.

RESULTS

Data from 20 volunteers were analysed. There were significant treatment and treatment-by-time effects regarding areas of hyperalgesia (P < 0.001). After the treatment period, the area of hyperalgesia was significantly reduced (P < 0.001) in the tested drug and in the gas active control (30.6 ± 9.25 and 24.4 ± 7.3 cm2, respectively) compared with remifentanil (51.0 ± 17.0 cm2). There was also a significant difference between the gas active control and the tested drug sessions (P < 0.001). For the area of allodynia and pain rating, results were consistent with the results for hyperalgesia.

CONCLUSIONS

Administration of 35% N2O significantly reduced hyperalgesia, allodynia and pain intensity induced after remifentanil. It might therefore be suitable in peri-operative pain relief characterised by hyperalgesia and allodynia, such as postoperative pain, and may help to reduce opioid demand.

TRIAL REGISTRATION

EudraCT-No.: 2011-000966-37.

Postoperative Drip-Infusion of Remifentanil Reduces Postoperative Pain-A Retrospective Observative Study

Development of remifentanil-induced hyperalgesia (RIH) postoperatively is an unpleasant experience that requires further treatment. This study assessed the effects of gradual withdrawal combined with drip infusion of remifentanil on postoperative pain and the requirement for rescue analgesics. A total of 559 patients receiving total intravenous anesthesia with propofol and remifentanil were enrolled. All patients either underwent gradual withdrawal of remifentanil (GWR) or gradual withdrawal combined with drip infusion (GWDR) with a dose of 1 mcg·kg⁻¹ for 30 min after extubation. The numeric rating scale (NRS) and the requirement of rescue analgesics were assessed. The requirement for rescue analgesics was significantly lower in the GWDR group than in the GWR group (13.2% vs. 35.7%; p < 0.001). At the post-anesthetic care unit (PACU), patients in the GWDR group had a lower NRS pain score (p < 0.001). In addition, in the postoperative 2nd hour, patients in the GWDR group had a significantly lower NRS than the GWR group (beta, −0.31; p = 0.003). No remifentanil-related adverse effects were observed. We found that gradual withdrawal combined with drip infusion of remifentanil required less rescue analgesics and reduced pain scores. The new way of remifentanil administration may be effective to prevent RIH.

Assessing the antinociceptive effect of nitrous oxide to tetanic stimulation in anaesthetised patients with new intra-operative nociception monitors: An observational study

BACKGROUND

Nitrous oxide (N2O) has been used since the 19th century for its analgesic, antinociceptive and anxiolytic effects during surgical procedures in awake and anaesthetised patients. However, quantification of noxious stimuli that occur under general anaesthesia is a constant challenge for anaesthesiologists, and recently two new indices have been developed to assess intra-operative nociception.

OBJECTIVE

The aim of this study was to quantify with new indices as well as with more classical clinical parameters the antinociceptive effect of N2O during general anaesthesia.

DESIGN

Prospective, open label, patient-blinded, observational and descriptive trial.

SETTING

Single-centre academic hospital.

PARTICIPANTS

Forty American Society of Anesthesiologists' physical status 1 to 3 patients undergoing general anaesthesia for elective abdominal surgery via laparotomy were recruited.

MAIN OUTCOMES MEASURES

Intra-operative pain was assessed using a standardised electrical stimulation of the forearm (tetanic stimulation at 70 mA, 100 Hz for 30 s), at 0, 25 and 50% inhaled N2O/O2. Heart rate (HR), mean arterial blood pressure, bispectral index, the analgesia nociception index and the nociception level (NOL) index were used to evaluate intra-operative nociception before and after each standardised tetanic stimulation.

RESULTS

There was a 16% reduction of the analgesia nociception index reaction, a 31% reduction of the NOL reaction and a 51% reduction of the HR reaction to a standardised electrical tetanic nociceptive stimulation during administration of 50% N2O. Administration of 50 or 25% inhaled N2O produced the same quality of antinociception based on HR and NOL index analyses. HR and the NOL index were the best parameters to identify the antinociceptive effect of intra-operatively administered N2O.

CONCLUSION

In anaesthetised patients, our study demonstrated clinically significant antinociceptive properties of N2O. Our results showed that low concentrations of N2O (25%) are as effective as higher concentrations (50%) to achieve a significant antinociceptive effect. These findings may help decrease negative effects of using higher concentrations of N2O, including its side effects and its environmental pollution.

TRIAL REGISTRATION

ClinicalTrials.gov registration identifier: NCT02701478.

Opioid-free anesthesia for adenotonsillectomy in children

INTRODUCTION

Opioids are administered during the intraoperative and postoperative periods in pediatric adenotonsillectomy and tonsillectomy. Non-opioid analgesics are often used as an analgesic during pediatric adenotonsillectomy and tonsillectomy. In this hypothesis generating study, we are evaluating safety and efficacy of stand-alone opioid analgesia for adenotonsillectomy and tonsillectomy.

METHODS

This is a single-center retrospective chart review of patients ages 2 to 13 who underwent elective adenotonsillectomy and tonsillectomy. We used a convenience sampling method to select patients who received intraoperative intravenous fentanyl, acetaminophen, ibuprofen, or any combination thereof. The following outcomes were analyzed in this study: (i) the length of Post Anesthesia Care Unit stay, (ii) administration of postoperative opioids; (iii) postoperative opioid equivalents required; (iv) administration of postoperative non-opioid analgesics; and (v) inpatient admission from ED within 30 days. We used univariate analysis to compare the data points.

RESULTS

We analyzed data from 323 patients who underwent adenotonsillectomy and tonsillectomy. The Post Anesthesia Care Unit length stay was similar for the intraoperative opioid-free and intraoperative opioid groups, 146.68 (±67.35) and 143.18 (±37.85) minutes, respectively (p = 0.586). Additionally, 102 patients (73.4%) in the intraoperative opioid-free group and 184 patients (83.2%) in the intraoperative opioid group did not receive any postoperative opioids (p = 0.033). The incidence of adverse events was similar between the intraoperative opioid-free and intraoperative opioid groups 3 (2.2%) and 5 (2.7%) respectively, p-value 0.749. A subgroup analysis comparing extracapsular 235 (72.8%) versus intracapsular 88 (27.2%) tonsillectomy yielded similar results.

CONCLUSION

In this study, our data indicates that American Society of Anesthesiologists I- II pediatric patients undergoing adenotonsillectomy and tonsillectomy can be efficiently and safely managed with an opioid-free intraoperative and postoperative analgesic regimen. Due to the explained limitations, our study results should be interpreted cautiously.

Postoperative Pain Management in Pediatric Spinal Fusion Surgery for Idiopathic Scoliosis

This article reviews and summarizes current evidence and knowledge gaps regarding postoperative analgesia after pediatric posterior spine fusion for adolescent idiopathic scoliosis, a common procedure that results in severe acute postoperative pain. Inadequate analgesia may delay recovery, cause patient dissatisfaction, and increase chronic pain risk. Despite significant adverse effects, opioids are the analgesic mainstay after scoliosis surgery. However, growing emphasis on opioid minimization and enhanced recovery has increased adoption of multimodal analgesia (MMA) regimens. While opioid adverse effects remain a concern, MMA protocols must also consider risks and benefits of adjunct medications. We discuss use of opioids via different administration routes and elaborate on the effect of MMA components on opioid/pain and recovery outcomes including upcoming regional analgesia. We also discuss risk for prolonged opioid use after surgery and chronic post-surgical pain risk in this population. Evidence supports use of neuraxial opioids at safe doses, low-dose ketorolac, and methadone for postoperative analgesia. There may be a role for low-dose ketamine in those who are opioid-tolerant or have chronic pain, but the evidence for preoperative gabapentinoids and intravenous lidocaine is currently insufficient. There is a need for further studies to evaluate pediatric-specific optimal MMA dosing regimens after scoliosis surgery. Questions remain regarding how best to prevent acute opioid tolerance, opioid-induced hyperalgesia, and chronic postsurgical pain. We anticipate that this timely update will enable clinicians to develop efficient pain regimens and provide impetus for future research to optimize recovery outcomes after spine fusion.

Remifentanil-Induced Secondary Hyperalgesia Is Not Prevented By Preoperative Acetazolamide Administration In Patients Undergoing Total Thyroidectomy: A Randomized Controlled Trial

Purpose

Acute administration of remifentanil may lead to opioid-induced hyperalgesia (OIH). Studies in mice suggest that OIH is mediated by impaired anionic homeostasis in spinal lamina I neurons due to a down-regulation of the K⁺-Cl⁻ co-transporter KCC2, which was reverted using acetazolamide (ACTZ), a carbonic anhydrase inhibitor. We propose that ACTZ prevents remifentanil-mediated OIH in humans.

Patients and methods

We conducted a randomized, double-blind, placebo-controlled clinical trial between December 2016 and September 2018. Patients were randomly allocated to receive ACTZ (250 mg of ACTZ 2 h before surgery) or placebo. To detect hyperalgesia, mechanical pain threshold (MPT) were measured before and after surgery using hand-held von Frey filaments in the forearm. Anesthesia was maintained with remifentanil at a target effect site of 4.5 ± 0.5 ng/mL, and sevoflurane at an end-tidal concentration of 0.8 MAC corrected for age.

Results

In total, 47 patients completed the study. Both groups were comparable in the baseline characteristics and intraoperative variables. Baseline MPT were similar in both groups. However, MPT in the forearm significantly diminished in the time in both groups. Finally, postoperative pain and morphine consumption were similar between groups.

Conclusion

Both groups developed remifentanil-mediated OIH at 12–18 h after surgery. However, ACTZ did not prevent the MPT reduction in patients undergoing total thyroidectomy.

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.

Effect of remifentanil on the recovery profile after head and neck surgeries: A prospective study

Background and Aims:

Development of opioid tolerance in the perioperative period due to remifentanil remains controversial. We evaluated occurrence of opioid tolerance and other adverse effects due to remifentanil in patients undergoing head and neck surgery.

Material and Methods:

We recruited adult participants with ASA status I to III who received general anesthesia for approximately 2 h for elective head and neck procedures. Remifentanil infusion was used in one group and intermittent boluses of morphine or fentanyl were administered in another group. Postoperative pain was treated with intermittent boluses of morphine and fentanyl in post-anaesthesia care unit (PACU) to achieve a numerical rating scale score of 3. Opioid requirement was assessed as an indicator of opioid tolerance. Patients were also evaluated for time to discharge from PACU.

Results:

We studied 222 adults aged between 21 and 80 years. One hundred and eleven patients received a combination of remifentanil infusion and morphine boluses, and another 111 patients received only fentanyl and/or morphine boluses intraoperatively. Fifty-one patients in the remifentanil group and 25 in the fentanyl/morphine group required opioids in the PACU. Opioid requirement were significantly more (mean ± SD, 44.98 ± 59.7 Vs 20.23 ± 46.66 mcg.kg⁻¹; P = 0.001) and required longer time to discharge from PACU in the remifentanil group compared to the fentanyl/morphine group (Mean ± SD, 88.6 ± 39.5 min Vs 73.1 ± 38.4 min; P < 0.001). No difference in the incidence of adverse effects in two groups was noted.

Conclusion:

At clinically relevant doses, intraoperative remifentanil infusion appears to increase opioid consumption in the immediate postoperative period. This can result in delayed discharge from PACU for patients undergoing elective head and neck procedures.

Effects of propofol/remifentanil-based total intravenous anesthesia versus sevoflurane-based inhalational anesthesia on the release of VEGF-C and TGF-β and prognosis after breast cancer surgery: a prospective, randomized and controlled study

Background

Vascular endothelial growth factor (VEGF) and transforming growth factor-β (TGF-β) have been involved in tumor growth and metastasis. Sevoflurane may promote angiogenesis, whereas propofol can present an anti-angiogenic effect. In this study, we compared the effects of propofol/remifentanil-based total intravenous anesthesia (TIVA) and sevoflurane-based inhalational anesthesia on the release of VEGF-C and TGF-β, as well as recurrence- free survival (RFS) rates in the patients undergoing breast cancer surgery.

Methods

Eighty female patients undergoing breast cancer resection were enrolled and randomized to receive either sevoflurane-based inhalational anesthesia (SEV group) or propofol/remifentanil-based TIVA (TIVA group). The serum concentrations of VEGF-C and TGF-β before and 24 h after surgery were measured and RFS rates over a two-year follow-up were analyzed in both groups. The postoperative pain scores assessed using a visual analogue scale (VAS) and the use of perioperative opioids were also evaluated.

Results

Although VAS scores at 2 h and 24 h after surgery were comparable between the two groups, there were more patients receiving postoperative fentanyl in the TIVA group (16[40%]) compared with the SEV group (6[15%], p = 0.023). VEGF-C serum concentrations increased after surgery from 105 (87–193) pg/ml to174 (111–281) pg/ml in the SEV group (P = 0.009), but remained almost unchanged in the TIVA group with 134 (80–205) pg/ml vs.140(92–250) pg/ml(P = 0.402). The preoperative to postoperative change for VEGF-C of the SEV group (50 pg/ml) was significantly higher than that of the TIVA group (12 pg/ml) with a difference of 46 (− 11–113) pg/ml (P = 0.008). There were also no significant differences in the preoperative and postoperative TGF-β concentrations between the two groups. The two-year RFS rates were 78% and 95% in the SEV and TIVA groups (P = 0.221), respectively.

Conclusion

In comparison with sevoflurane-based inhalational anesthesia, propofol/remifentanil -based total intravenous anesthesia can effectively inhibit the release of VEGF-C induced by breast surgery, but didn’t seem to be beneficial in the short-term recurrence rate of breast cancer.

Trial registration

Chictr.org.cn ChiCTR1800017910. Retrospectively Registered (Date of registration: August 20, 2018).

Persistent Postsurgical Pain

The development of chronic pain is considered a major complication after surgery. Basic science research in animal models helps us understand the transition from acute to chronic pain by identifying the numerous molecular and cellular changes that occur in the peripheral and central nervous systems. It is now well recognized that inflammation and nerve injury lead to long-term synaptic plasticity that amplifies and also maintains pain signaling, a phenomenon referred to as pain sensitization. In the context of surgery in humans, pain sensitization is both responsible for an increase in postoperative pain via the expression of wound hyperalgesia and considered a critical factor for the development of persistent postsurgical pain. Using specific drugs that block the processes of pain sensitization reduces postoperative pain and prevents the development of persistent postoperative pain. This narrative review of the literature describes clinical investigations evaluating different preventative pharmacologic strategies that are routinely used by anesthesiologists in their daily clinical practices for preventing persistent postoperative pain. Nevertheless, further efforts are needed in both basic and clinical science research to identify preclinical models and novel therapeutics targets. There remains a need for more patient numbers in clinical research, for more reliable data, and for the development of the safest and the most effective strategies to limit the incidence of persistent postoperative pain.

Electro-acupuncture stimulation prevents remifentanil-induced postoperative hyperalgesia by suppressing spinal microglia in rats

The aim of the present study was to assess the effect of electro-acupuncture (EA) stimulation on remifentanil-induced postoperative hyperalgesia (RIPH) and the possible involvement of spinal microglia suppression. A model of RIPH was established using adult male Sprague-Dawley rats by administration of remifentanil at 0.08 mg/kg intravenously for 60 min. The Huantiao and Yanglingquan acupoints were stimulated continuously by EA (2 Hz, ~1 mA) for 90 min from before paw incision to the end of remifentanil administration. Sham acupoints were stimulated by EA in the sham group. Paw withdrawal threshold (PWT) and paw thermal withdrawal latency (PWL) were determined. Cluster of differentiation (CD)11b, tumor necrosis factor (TNF)-α, interleukin (IL)-1β and IL-6 levels in spinal cord samples were measured using immunohistochemistry and ELISA. PWT and PWL values were decreased following the administration of remifentanill; however, following EA, PWT and PWL values increased compared with the sham group (P<0.05), indicating that EA alleviates remifentanil-induced RIPH. CD11b, TNF-α, IL-1β and IL-6 levels were increased following remifentanil administration and these effects were counteracted by EA (all P<0.05). In the sham group, no significant differences were observed in PWT and PWL values or CD11b, TNF-α, IL-1β and IL-6 levels compared with the control group, suggesting that EA was responsible for the reduction in CD11b and pro-inflammatory cytokine expression following remifentanil administration. The results of the present study demonstrated that EA at the Huantiao and Yanglingquan acupoints may reduce remifentanil-induced postoperative hyperalgesia, likely by inhibiting spinal microglia via reduction of CD11b and pro-inflammatory cytokine expression. However, these results are preliminary and require further validation.

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.

Preoperative But Not Postoperative Flurbiprofen Axetil Alleviates Remifentanil-induced Hyperalgesia After Laparoscopic Gynecological Surgery: A Prospective, Randomized, Double-blinded, Trial

BACKGROUND

Acute remifentanil exposure during intraoperative analgesia might enhance sensitivity to noxious stimuli and nociceptive responses to innocuous irritation. Cyclooxygenase inhibition was demonstrated to attenuate experimental remifentanil-induced hyperalgesia (RIH) in rodents and human volunteers. The study aimed to compare the effects of preoperative and postoperative flurbiprofen axetil (FA) on RIH after surgery.

MATERIALS AND METHODS

Ninety patients undergoing elective laparoscopic gynecologic surgery were randomly assigned to receive either intravenous placebo before anesthesia induction (Group C); or intravenous FA (1.0 mg/kg) before anesthesia induction (Group F1) or before skin closure (Group F2). Anesthesia consisted off sevoflurane and remifentanil (0.30 μg/kg/min). Postoperative pain was managed by sufentanil titration in the postanesthetic care unit, followed by sufentanil infusion via patient-controlled analgesia. Mechanical pain threshold (primary outcome), pain scores, sufentanil consumption, and side-effects were documented for 24 hours postoperatively.

RESULTS

Postoperative pain score in Group F1 was lower than Group C. Time of first postoperative sufentanil titration was prolonged in Group F1 than Group C (P=0.021). Cumulative sufentanil consumption in Group F1 was lower than Group C (P<0.001), with a mean difference of 8.75 (95% confidence interval, 5.21-12.29) μg. Mechanical pain threshold on the dominant inner forearm was more elevated in Group F1 than Group C (P=0.005), with a mean difference of 17.7 (95% confidence interval, 5.4-30.0) g. Normalized hyperalgesia area was decreased in Group F1 compared to Group C (P=0.007). No statistically significant difference was observed between Group F2 and Group C.

CONCLUSIONS

Preoperative FA reduces postoperative RIH in patients undergoing laparoscopic gynecologic surgery under sevoflurane-remifentanil anesthesia.

Equimolar mixture of nitroux oxyde and oxygen during post-operative physiotherapy in patients with cerebral palsy: A randomized, double-blind, placebo-controlled study

BACKGROUND

The administration of an equimolar mixture of nitrous oxide and oxygen (N2O) is recommended during painful procedures. However, the evaluation of its use during physiotherapy after surgery has not been reported, although pain may hamper physiotherapy efficiency. This study investigated whether the use of N2O improves the efficacy of post-operative physiotherapy after multilevel surgery in patients with cerebral palsy.

METHOD

It was a randomized 1:1, double-blind, placebo-controlled study. All patients had post-operative physiotherapy starting the day after surgery. Patients received either N2O or placebo gas during the rehabilitation sessions. All patients had post-operative pain management protocol, including pain medication as needed for acute pain. The primary objective was to reach angles of knee flexion of 110° combined with hip extension of 10°, with the patient lying prone, within six or less physiotherapy sessions. Secondary evaluation criteria were the number of sessions required to reach the targeted angles, the session-related pain intensity and the analgesics consumption for managing post-operative pain.

RESULTS

Sixty-four patients were enrolled. Targeted angles were achieved more often in the N2O group (23 of 32, 72%, vs. Placebo: 13/ of 32, 41%; p = 0.01).

CONCLUSION

The administration of N2O during post-operative physiotherapy can help to achieve more quickly an improved range of motion, and, although not significant in our study, to alleviate the need for pain medication. Further studies evaluating the administration of N2O in various settings are warranted.

SIGNIFICANCE

During this randomized placebo-controlled double-blind study, children receiving nitrous oxide and oxygen (N2O) achieved more often the targeted range of motion during physiotherapy sessions after multilevel surgery. Compared to placebo, nitrous oxide and oxygen (N2O) enabled a better management of acute pain related to physiotherapy procedures.

A comparison of intrathecal magnesium and ketamine in attenuating remifentanil-induced hyperalgesia in rats

Background

Activation of NMDA receptors play an important role in the development of remifentanil-induced hyperalgesia. We hypothesized that in addition to ketamine, intrathecal MgSO₄ could also relieve thermal and mechanical hyperalgesia in rats.

Methods

Initially, 24 Sprague–Dawley rats were divided into control group, remifentanil group, surgical incision group and remifentanil combined with surgical incision group to create an experimental model. Subsequently, 40 rats were divided into control group, model group, model group plus 100 μg MgSO₄, 300 μg MgSO₄ and 10 μg ketamine respectively. Paw withdrawal mechanical thresholds and paw withdrawal thermal latency tests were performed at −24 h, 2 h, 6 h, 24 h, 48 h, 72 h and 7 day after the surgical procedure. After behavior assessment on the 7th day, remifentanil was given again to ascertain whether or not NMDA antagonists could suppress the re-exposure of remifentanil-induced hyperalgesia.

Results

Remifentanil administration plus surgical incision induced significant postoperative hyperalgesia, as indicated by decreased paw withdrawal mechanical thresholds and paw withdrawal thermal latency to mechanical and thermal stimulation. In addition to ketamine, intrathecal MgSO₄ (100, 300 μg) dose-dependently reduced remifentanil-induced mechanical and thermal hyperalgesia. Ketamine had less mechanical hyperalgesia in 6 h (p = 0.018), 24 h (p = 0.014) and 48 h (p = 0.011) than 300 μg MgSO₄. There was no difference in inhibiting thermal hyperalgesia between the group ketamine and group MgSO₄ (300 μg). The rats were given remifentanil again 7 days later after the first exposure of remifentanil. The hyperalgesic effect induced by re-exposure of remifentanil was not reversed in any groups of MgSO₄ or ketamine.

Conclusions

In addition to ketamine, intrathecal administration of MgSO₄ dose-dependently reduced remifentanil-induced hyperalgesia in a surgical incision mode. Re-exposure to remifentanil 1 week later again produced hyperalgesia, and this was not altered by the prior intrathecal treatments in any 4 groups treated with MgSO₄ or ketamine.

Electronic supplementary material

The online version of this article (doi:10.1186/s12871-016-0235-9) contains supplementary material, which is available to authorized users.

Effects of propofol-based total intravenous anesthesia on recurrence and overall survival in patients after modified radical mastectomy: a retrospective study

Background

The optimal combination of anesthetic agent and technique may have an influence on long-term outcomes in cancer surgery. In vitro and in vivo studies suggest that propofol independently reduces migration of cancer cells and metastasis. Thus, the authors retrospectively examined the link between propofol-based total intravenous anesthesia (TIVA) and recurrence or overall survival in patients undergoing modified radical mastectomy (MRM).

Methods

A retrospective analysis of the electronic database of all patients undergoing MRM for breast cancer between January 2007 and December 2008 was undertaken. Patients received either propofol-based TIVA (propofol group) or sevoflurane-based anesthesia (sevoflurane group). We analyzed prognostic factors of breast cancer and perioperative factors and compared recurrence-free survival and overall survival between propofol and sevoflurane groups.

Results

A total of 363 MRMs were carried out during the period of the trial; 325 cases were suitable for analysis (173 cases of propofol group, and 152 cases of sevoflurane group). There were insignificant differences between the groups in age, weight, height, histopathologic results, surgical time, or postoperative treatment (chemotherapy, hormonal therapy, and radiotherapy). The use of opioids during the perioperative period was greater in propofol group than in sevoflurane group. Overall survival was no difference between the two groups. Propofol group showed a lower rate of cancer recurrence (P = 0.037), with an estimated hazard ratio of 0.550 (95% CI 0.311–0.973).

Conclusions

This retrospective study provides the possibility that propofol-based TIVA for breast cancer surgery can reduce the risk of recurrence during the initial 5 years after MRM.

Opioid-induced redistribution of 6TM and 7TM μ opioid receptors: A hypothesized mechanistic facilitator model of opioid-induced hyperalgesia

Opioids are still the most popular form of pain treatment, but many unavoidable side effects make opioids a big challenge in effective pain management. Opioid-induced hyperalgesia (OIH), a paradoxical phenomenon, portrays an increased sensitivity to harmful stimuli caused by opioid exposure. Changes in the neural modulation are considered a major contributor to the development of OIH. Activation of opioid receptors (ORs) and corresponding downstream molecules are the vital composition of functional performance of opioids. Increasing interests were proposed of the interaction between ORs and other neural transmitter systems such as glutamatergic, GABAergic and adrenergic ones to the genesis of OIH. G protein coupled μ-opioid receptor (MOR) was studied comprehensively on its role in the development of OIH. In addition to the relationship between MOR and other neurotransmitter receptors, a new intracellular MOR that has six transmembrane (6TM) domains was identified, and found to perform a pro-nociceptive task in contrast to the counterpart 7TM isoform. A mechanistic model of OIH in which both 6TM and 7TM MORs undergoing membrane redistribution upon opioid exposure is proposed which eventually facilitates the neurons more sensitive to nociceptive stimulation than that of the preceding opioid exposure.

Gradual withdrawal of remifentanil infusion may prevent opioid-induced hyperalgesia

BACKGROUND

The aim of this study was to examine if gradual withdrawal of remifentanil infusion prevented opioid-induced hyperalgesia (OIH) as opposed to abrupt withdrawal. OIH duration was also evaluated.

METHODS

Nineteen volunteers were enrolled in this randomized, double-blinded, placebo-controlled, crossover study. All went through three sessions: abrupt or gradual withdrawal of remifentanil infusion and placebo. Remifentanil was administered at 2.5 ng ml(-1) for 30 min before abrupt withdrawal or gradual withdrawal by 0.6 ng ml(-1) every five min. Pain was assessed at baseline, during infusion, 45-50 min and 105-110 min after end of infusions using the heat pain test (HPT) and the cold pressor test (CPT).

RESULTS

The HPT 45 min after infusion indicated OIH development in the abrupt withdrawal session with higher pain scores compared with the gradual withdrawal and placebo sessions (both P<0.01. Marginal mean scores: placebo 2.90; abrupt 3.39; gradual 2.88), but no OIH after gradual withdrawal compared with placebo (P=0.93). In the CPT 50 min after end of infusion there was OIH in both remifentanil sessions compared with placebo (gradual P=0.01, abrupt P<0.01. Marginal mean scores: placebo 4.56; abrupt 5.25; gradual 5.04). There were no differences between the three sessions 105-110 min after infusion.

CONCLUSIONS

We found no development of OIH after gradual withdrawal of remifentanil infusion in the HPT. After abrupt withdrawal OIH was present in the HPT. In the CPT there was OIH after both gradual and abrupt withdrawal of infusion. The duration of OIH was less than 105 min for both pain modalities.

CLINICAL TRIAL REGISTRATION

NCT 01702389. EudraCT number 2011-002734-39.

Remifentanil-acute opioid tolerance and opioid-induced hyperalgesia: a systematic review

The use of opioids may seem to be a double-edged sword; they provide straight analgesic and antihyperalgesic effects initially, but subsequently are associated with the expression of acute opioid tolerance (AOT) and opioid-induced hyperalgesia (OIH) that have been reported in experimental studies and clinical observations. It has been suggested that opioids can induce an acute tolerance and hyperalgesia in dose- and/or time-dependent manners even when used within the clinically accepted doses. Recently, remifentanil has been used for pain management in clinical anesthesia and in the intensive care units because of its rapid onset and offset. We reviewed articles analyzing AOT and/or OIH by remifentanil and focused on the following issues: (1) evidence of remifentanil inducing AOT and/or OIH and (2) importance of AOT and/or OIH in considering the reduction of remifentanil dosage or adopting preventive modulations. Twenty-four experimental and clinical studies were identified using electronic searches of MEDLINE (PubMed, Ovid, Springer, and Elsevier). However, the development of AOT and OIH by remifentanil administration remains controversial. There is no sufficient evidence to support or refute the existence of OIH in humans.

Differential Opioid Tolerance and Opioid-induced Hyperalgesia

Differential opioid tolerance (different degrees and speed of tolerance to various opioid side effects) and opioid-induced hyperalgesia (increased pain with escalating doses of opioids) potentially complicate the postoperative management.

Chronic pain relief after the exposure of nitrous oxide during dental treatment: longitudinal retrospective study

The objective was to investigate the effect of nitrous/oxygen in chronic pain. Seventy-seven chronic pain patients referred to dental treatment with conscious sedation with nitrous oxide/oxygen had their records included in this research. Data were collected regarding the location and intensity of pain by the visual analogue scale before and after the treatment. Statistical analysis was performed comparing pre- and post-treatment findings. It was observed a remarkable decrease in the prevalence of pain in this sample (only 18 patients still had chronic pain, p < 0.001) and in its intensity (p < 0.001). Patients that needed fewer sessions received higher proportions of nitrous oxide/oxygen. Nitrous oxide may be a tool to be used in the treatment of chronic pain, and future prospective studies are necessary to understand the underlying mechanisms and the effect of nitrous oxide/oxygen in patients according to the pain diagnosis and other characteristics.

Opioid induced hyperalgesia in anesthetic settings

Pain is difficult to investigate and difficult to treat, in part, because of problems in quantification and assessment. The use of opioids, combined with classic anesthetics to maintain hemodynamic stability by controlling responses to intraoperative painful events has gained significant popularity in the anesthetic field. However, several side effects profiles concerning perioperative use of opioid have been published. Over the past two decades, many concerns have arisen with respect to opioid-induced hyperalgesia (OIH), which is the paradoxical effect wherein opioid usage may decrease pain thresholds and increase atypical pain unrelated to the original, preexisting pain. This brief review focuses on the evidence, mechanisms, and modulatory and pharmacologic management of OIH in order to elaborate on the clinical implication of OIH.

The effect of nitrous oxide anesthesia on early postoperative opioid consumption and pain

BACKGROUND AND OBJECTIVES

Many patients experience moderate to severe postoperative pain. Nitrous oxide (N₂O) exerts analgesia by inhibition of N-methyl-D-aspartate receptors. Ketamine, another N-methyl-D-aspartate receptor antagonist, reduces postoperative opioid consumption and pain. A similar effect of N₂O is plausible, yet understudied. The goal of this study was to determine the effects of N₂O anesthesia on early postsurgical opioid consumption and pain.

METHODS

This was a retrospective, secondary analysis of the Vitamins In Nitrous Oxide trial, where 500 patients undergoing general anesthesia for noncardiac surgery received 60% N₂O and 125 received no N₂O (otherwise, inclusion/exclusion criteria were identical). Exclusion criteria for this study were regional anesthesia, not extubated after surgery, transfer to intensive care unit, no available postanesthesia care unit record, postsurgical sedation, or treated with naloxone. Primary outcomes were cumulative opioid consumption measured in morphine equivalents and pain scores during the immediate recovery phase.

RESULTS

Four hundred forty-two patients met inclusion criteria. No difference in intraoperative and postoperative opioid consumption was observed between patients who received N₂O (n = 353) and patients who did not (n = 89). The median [interquartile range] postoperative morphine equivalent dose was 6.7 mg [1.7-14.1 mg] for patients who received N₂O and 6.7 mg [2.1-15.4 mg] for patients who did not (P = 0.73). The maximum pain score was 6 [4-8] for patients who received N₂O versus 6 [3-8] for patients who received N₂O-free anesthesia (P = 0.52). The prevalence of moderate to severe pain was 69% for patients who received N₂O and 68% for patients who did not (P = 0.90).

CONCLUSIONS

Nitrous oxide anesthesia was not associated with decreased opioid administration, pain, or incidence of moderate to severe pain in the early postoperative phase.

Intraoperative use of remifentanil and opioid induced hyperalgesia/acute opioid tolerance: systematic review

INTRODUCTION

The use of opioids has been increasing in operating room and intensive care unit to provide perioperative analgesia as well as stable hemodynamics. However, many authors have suggested that the use of opioids is associated with the expression of acute opioid tolerance (AOT) and opioid-induced hyperalgesia (OIH) in experimental studies and clinical observations in dose and/or time dependent exposure even when used within the clinically accepted doses. Recently, remifentanil has been used for pain management during anesthesia as well as in the intensive care units because of its rapid onset and offset.

OBJECTIVES

Search of the available literature to assess remifentanil AOT and OIH based on available published data.

METHODS

We reviewed articles analyzing remifentanil AOT and OIH, and focused our literature search on evidence based information. Experimental and clinical studies were identified using electronic searches of Medline (PubMed, Ovid, Springer, and Elsevier, ClinicalKey).

RESULTS

Our results showed that the development of remifentanil AOT and OIH is a clinically significant phenomenon requiring further research.

DISCUSSIONS AND CONCLUSIONS

AOT - defined as an increase in the required opioid dose to maintain adequate analgesia, and OIH - defined as decreased pain threshold after chronic opioid treatment, should be suspected with any unexplained pain report unassociated with the disease progression. The clinical significance of these findings was evaluated taking into account multiple methodological issues including the dose and duration of opioids administration, the different infusion mode, the co-administrated anesthetic drug's effect, method assessing pain sensitivity, and the repetitive and potentially tissue damaging nature of the stimuli used to determine the threshold during opioid infusion. Future studies need to investigate the contribution of remifentanil induced hyperalgesia to chronic pain and the role of pharmacological modulation to reverse this process.

Effect of intraoperative high-dose remifentanil on postoperative pain: a prospective, double blind, randomized clinical trial

BACKGROUND

Remifentanil, an ultra-short-acting opioid, is widely used for pain control during surgery. However, regular dose (RD) remifentanil exacerbates postoperative pain in a dose-dependent manner. Recent studies suggest that high-dose (HD) remifentanil offers sustained analgesia in experimental studies. We thus hypothesized that intraoperative administration of high-dose remifentanil may attenuate postoperative pain.

METHODS

In this prospective, randomized, double blind, controlled clinical study, sixty patients undergoing thyroidectomy (18-60 years-of-age) received an intraoperative infusion of 0.2 (RD group) or 1.2 μg kg(-1) min(-1) (HD group) remifentanil during thyroidectomy. A visual analogue scale (VAS) was used to measure pain intensity. Mechanical pain threshold on the forearm was assessed using von Frey filaments before surgery (baseline), 2 h postoperatively and 18-24 h postoperatively. The primary outcome was to compare the difference of VAS score at different time points after operation and morphine consumption 24 h postoperatively between RD and HD groups. The second outcome was to compare the difference of mechanical pain thresholds in the forearm postoperatively between RD and the HD groups.

RESULTS

VAS scores were lower 30 min postoperatively in the HD group (1.29 ± 1.67, 95% CI 0.64-1.94) compared with the RD group (2.21 ± 1.67, 95% CI 1.57-2.84) (t = 3.427, p = 0.0043, RD group vs. HD group). Postoperative morphine consumption was much lower in the HD group compared with the RD group (1.27 ± 1.88 mg vs. 0.35 ± 1.25 mg, p = 0.033). In both groups, mechanical pain threshold was decreased 18-24 h postoperatively (2.93 ± 0.209 Ln(g) vs. 3.454 ± 2.072 Ln(g), p = 0.032 in RD group; 2.910 ± 0.196 Ln(g) vs. 3.621 ± 0.198 Ln(g), p = 0.006 in HD group, 18-24 h postoperatively vs baseline).

CONCLUSIONS

Intraoperative administration of high-dose remifentanil decreased VAS scores and morphine consumption postoperatively. Thus, modulation of intraoperative opiates may be a simple and effective method of postoperative pain management.

TRIAL REGISTRATION

This trial is registered in ClinicalTrials.gov, with the Name: Effect of Higher Doses of Remifentanil on Postoperative Pain in Patients Undergoing Thyroidectomy, and ID number: NCT01761149.