Remifentanil Infusion Does Not Induce Opioid Tolerance After Cardiac Surgery

Effect of Remifentanil on Acute and Chronic Postsurgical Pain in Patients Undergoing Cardiac Surgery: A Systematic Review and Meta-analysis

OBJECTIVES

Our purpose was to explore the effect of remifentanil on acute and chronic postsurgical pain after cardiac surgery.

MATERIALS AND METHODS

Randomized controlled trials were retrieved from electronic databases, such as PubMed, Cochrane Library, China National Knowledge Internet databases, Scopus, and Web of Science. A systematic review, meta-analysis, and trial sequential analysis (TSA) were performed. Basic information and outcomes were extracted from the included studies. The primary outcome was chronic postsurgical pain. Secondary outcomes were scores of postsurgical pain and morphine consumption within 24 hours after cardiac surgery. Risk of bias (ROB) assessment was based on the Cochrane ROB tool version 2. The overall quality of the evidence was rated using the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) system.

RESULTS

Seven studies consisting of 658 patients were enrolled in the meta-analysis. A single study had a high ROB and 2 studies had a moderate ROB. The incidence of chronic postsurgical pain (4 studies [415 patients]; risk ratio: 1.02 [95% CI: 0.53 to 1.95]; P = 0.95; I2 = 59%; TSA-adjusted CI: 0.78 to 1.20) and the postsurgical pain score (2 studies [196 patients]; mean difference: 0.09 [95% CI: -0.36 to 0.55]; P = 0.69; I2 = 0%; TSA-adjusted CI: -0.36 to 0.55) were not statistically different between the 2 groups. However, morphine consumption (6 studies [569 patients]; mean difference: 6.94 [95% CI: 3.65 to 10.22]; P < 0.01; I2 = 0%; TSA-adjusted CI: 0.00 to 0.49) was higher in the remifentanil group than in the control group.

CONCLUSION

There was not enough evidence to prove that remifentanil can increase the incidence of chronic postsurgical pain after cardiac surgery, but interestingly, the results tended to support a trend toward increased complications in the intervention group. However, there was moderate certainty evidence that the use of remifentanil increases the consumption of morphine for analgesia, and more direct comparison trials are needed to inform clinical decision-making with greater confidence.

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).

Comparison of the effects of intraoperative remifentanil and sufentanil infusion on postoperative pain management in robotic gynecological surgery: a retrospective cohort study

BACKGROUND

Remifentanil and sufentanil are potent short-acting synthetic opioid analgesics. The administration of remifentanil has been associated with the incidence of opioid-induced hyperalgesia. Opioid-induced hyperalgesia may be alleviated when opioids, such as morphine, are switched to sufentanil. Therefore, this retrospective observational study aimed to compare the effects of remifentanil and sufentanil on postoperative pain in patients undergoing robotic gynecological surgery.

METHODS

We retrospectively analyzed the electronic medical records of patients who underwent elective robotic gynecological surgery between January 2016 and February 2021. The patients were classified into sufentanil (n = 159) or remifentanil (n = 359) groups according to the opioids administered continuously during anesthesia. The primary outcome assessed in this study was the postoperative pain score measured using the numeric rating scale (NRS). The secondary outcomes assessed included the recovery time (from discontinuation of opioid infusion to extubation) and frequency of rescue analgesic administration in the post-anesthesia care unit (PACU).

RESULTS

The recovery time did not differ significantly between the two groups. The NRS score for pain (median [1Q, 3Q]) in the PACU was significantly lower in the sufentanil group than in the remifentanil group (2 [2, 3] vs. 4 [3, 7], P < 0.001). The frequency of rescue analgesic administration in the PACU was 6.3% and 35.4% in the sufentanil and remifentanil groups, respectively (P < 0.001).

CONCLUSIONS

Sufentanil, as an adjunct to sevoflurane anesthesia is more advantageous than remifentanil in terms of postoperative pain control during robotic gynecological surgery.

Comparison of Intraoperative Infusion of Remifentanil Versus Fentanyl on Pain Management in Patients Undergoing Spine Surgery: A Double Blinded Randomized Clinical Trial

Background

Remifentanil is an ultra-short-acting opioid which facilitates hemodynamic management. However, there are concerns about postoperative Remifentanil hyperalgesia because of its potent fast onset and offset.

Objectives

The aim of this study was to determine visual analog scale (VAS), postoperative pain, and morphine used in two groups after spine surgery.

Methods

In this randomized clinical trial study, 60 patients aged 18 - 60 years old, according to the American Society of Anesthesiology (ASA) I - II, who underwent spinal canal stenosis or scoliosis surgery, were divided into two groups. In the control group, patients received 0.07 - 0.1 µg/kg/h intraoperative Fentanyl infusion, and in the intervention group 0.1 - 0.2 µg/kg/min remifentanil was infused during the surgery. Both groups received 15 mg/kg intravenous Acetaminophen 20 minutes before the end of the surgery. Postoperative pain score and morphine consumption were measured 6, 12, 24, and 48 hours after discharge from the post-anesthesia care unit (PACU).

Results

During the first 12 hours, VAS and morphine consumption were significantly higher in remifentanil group (P < 0.001). However, no significant difference was found between the two groups in morphine consumption 12 - 48 hours after surgery.

Conclusions

These findings suggest that Remifentanil infusion during surgery may increase postoperative pain. Also, VAS and morphine consumption were higher during the first 12 hours.

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.

Intraoperative Remifentanil Infusion and Postoperative Pain Outcomes After Cardiac Surgery-Results from Secondary Analysis of a Randomized, Open-Label Clinical Trial

DESIGN

Report of secondary pain outcomes from a prospective, randomized, open-label clinical trial that compared remifentanil and fentanyl on perioperative hyperglycemic response in cardiac surgery.

SETTING

Single institution, tertiary university hospital.

PARTICIPANTS

The study comprised 116 adult elective cardiac surgical patients.

INTERVENTIONS

Participants were randomly assigned to receive either intermittent fentanyl boluses (F) or continuous remifentanil infusion (R) intraoperatively.

MEASUREMENTS AND MAIN RESULTS

Postoperative pain was evaluated with pain scores every 6 hours for 48 hours. Pain threshold to mechanical stimuli was measured around the sternotomy incision at 48 and 96 hours. The development of chronic pain was assessed using the numeric rating scale at 1, 3, 6, and 12 months after discharge. The final analysis included 106 patients. Pain scores and wound hyperalgesia were not significantly different postoperatively between the groups. The incidence of chronic pain at 3 months was comparable in both groups (61% in group F v 58% in group R; p = 0.79). Pain of more-than-mild degree was seen in 13 (32%) patients in group F and 8 (19%) in group R (p = 0.25) at 3 months. Median pain scores were not significantly different between the groups at 1, 3, 6, and 12 months after discharge from the hospital.

CONCLUSIONS

The present study's findings suggested that intraoperative remifentanil infusion does not significantly worsen pain outcomes in patients undergoing elective cardiac surgery.

Bioavailability of oxycodone by mouth in coronary artery bypass surgery patients - a randomized trial

Objective

Pain after coronary artery by-pass (CAB) surgery is severe. Analgesic administration by mouth is unreliable until after gastrointestinal function has recovered. We evaluated the bioavailability of oxycodone co-administered with naloxone by mouth in patients after CAB surgery using either a conventional extracorporeal circulation (CECC) or off-pump surgery (OPCAB).

Methods

Twenty-four patients, 50–73 years, 12 with CECC and 12 with OPCAB, were administered a 10/5 mg oxycodone-naloxone controlled-release tablet by mouth on the preoperative day and for the first seven postoperative days (PODs) thereafter. Blood samples were collected up to 24 h after the preoperative administration, and then randomly either on POD1 and POD3 or on POD2 and POD4. The oxycodone concentration in plasma was analyzed using liquid chromatography-mass spectrometry.

Results

On POD1 oxycodone absorption was markedly delayed in five of six patients after CECC and in all six patients after OPCAB surgery; median of t_max after CECC 630 [range 270–1420] minutes and after OPCAB 1020 [720–1410] minutes, compared to median of 120–315 min preoperatively and on POD2-POD4. The carry-over corrected AUC_0–24 values on the PODs did not differ from the preoperative values, but were higher on POD3 compared with POD1 in both CECC and OPCAB groups. The rate and extent of oxycodone absorption equaled preoperative values on POD2 and onwards in patients with CAB surgery.

Conclusions

Bioavailability of oxycodone by mouth was similar after CAB surgery via CECC or having OPCAB. Data indicate that POD2 is an appropriate time to start oxycodone administration by mouth after CAB surgery.

TRPV1 channel contributes to remifentanil-induced postoperative hyperalgesia via regulation of NMDA receptor trafficking in dorsal root ganglion

Background

Remifentanil is widely used in general anesthesia due to its reliability and rapid onset. However, remifentanil-induced postoperative hyperalgesia might be a challenge nowadays. Accumulating evidence suggests that the transient receptor potential vanilloid 1 (TRPV1) was involved in the development of neuropathic pain and hyperalgesia. However, the contribution of TRPV1 in modulating remifentanil-induced postoperative hyperalgesia is still unknown. The aim of this study is the contribution of TRPV1 to the surface expression of N-methyl-d-aspartate (NMDA) receptors in remifentanil-induced postoperative hyperalgesia.

Methods

The hot plate test and the Von Frey test were performed to evaluate thermal and mechanical hyperalgesia. Capsazepine (CPZ) was administrated intrathecally to confirm our results. TRPV1, NMDA receptors, CaMKII (calcium/calmodulin-dependent kinase II), and protein kinase C (PKC) in the dorsal root ganglion (DRG) were detected by Western blotting. Immunofluorescence assay was applied to analyze the distribution of TRPV1 and the relationship between TRPV1 and NMDA receptor subunit 1 (NR1).

Results

Remifentanil-induced both thermal and mechanical postoperative hyperalgesia. Here, we found the membrane trafficking of NR1, possibly due to the activation of TRPV1 in DRG neurons after remifentanil infusion. Furthermore, intrathecal injection of CPZ was able to relieve remifentanil-induced postoperative hyperalgesia according to a behavioral test and CPZ confirmed that TRPV1 is involved in NR1 trafficking. In addition, CaMKII/PKC but not protein kinase A (PKA) contributed to remifentanil-induced postoperative hyperalgesia.

Conclusion

Our study demonstrates that TRPV1 receptors are involved in remifentanil-induced postoperative hyperalgesia. TRPV1 contributes to the persistence of remifentanil-induced postoperative hyperalgesia through the trafficking of NMDA receptors via the activation of CaMKII-PKC signaling pathways in DRG neurons.

Enhancement of spinal dorsal horn neuron NMDA receptor phosphorylation as the mechanism of remifentanil induced hyperalgesia: Roles of PKC and CaMKII

Background

Modulation of N-methyl-D-aspartate receptor subunits NR1 and NR2 through phosphorylation mediates opioid-induced hyperalgesia, and activations of protein kinase C and extracellular signal-regulated kinase 1/2 potentiate while activation of calcium/calmodulin-dependent protein kinase II inhibits opioid-induced hyperalgesia. However, the mechanism of opioid-induced hyperalgesia development and in particular the potential interplay between N-methyl-D-aspartate receptors and protein kinase C or calcium/calmodulin-dependent protein kinase II or extracellular signal-regulated kinase 1/2 in the development of remifentanil-induced hyperalgesia is unclear.

Methods

Remifentanil (1 µg ċ kg−1 ċ min−1) was given intravenously over 60 min in rats, followed by the infusion of either vehicle solution or the respective inhibitors of protein kinase C (chelerythrine), extracellular signal-regulated kinase II (KN93), or extracellular signal-regulated kinase 1/2 (PD98059). Thereafter, the pain behaviors were evaluated by the paw withdrawal mechanical threshold and paw withdrawal thermal latency. In in vitro studies, fetal spinal cord dorsal horn neurons were primary cultured in the presence of 4 nM remifentanil for 60 min, and then the remifentanil was washed out and replaced immediately by culturing in the absence or presence of chelerythrine, KN93 or PD98059, respectively for up to 8 h. The expressions of N-methyl-D-aspartate receptors subunits and their phosphorylation (NR1, NR2B, p-NR1, p-NR2B) were analyzed by Western blotting after the completion of treatments. Functional changes of N-methyl-D-aspartate receptors were evaluated by electrophysiologic recordings of N-methyl-D-aspartate currents.

Results

Remifentanil induced significant thermal and mechanical hyperalgesia, which were significantly attenuated by Chelerythrine or KN93 but not PD98059. The expressions of NR1, NR2B, p-NR1, and p-NR2B were increased significantly and progressively over time after remifentanil administration, and these increases were all significantly attenuated by either chelerythrine or KN93 but not PD98059. Intriguingly, N-methyl-D-aspartate receptor functional enhancement induced by remifentanil was attenuated by Chelerythrine, KN93, and PD98059.

Conclusions

It is concluded that the enhancements in function and quantity of N-methyl-D-aspartate receptor via phosphorylation of its subunits through protein kinase C and calcium/calmodulin-dependent protein kinase II activation may represent the major mechanism whereby remifentanil induced hyperalgesia.

Withdrawal from spinal application of remifentanil induces long-term potentiation of c-fiber-evoked field potentials by activation of Src family kinases in spinal microglia

It is well known that remifentanil, a widely used intravenous anesthesia drug, can paradoxically induce hyperalgesia. The underlying mechanisms are still not clear despite the wide investigations. The present study demonstrated that withdrawal from spinal application of remifentanil could dose-dependently induce long term potentiation (LTP) of C-fiber evoked field potentials. Remifentanil withdrawal could activate Src family kinases (SFKs) in microglia, and upregulate the expression of tumor necrosis factor alpha (TNFα) in spinal dorsal horn. Furthermore, pretreatment with either microglia inhibitor Minocycline, SFKs inhibitor PP2 or TNF αneutralization antibody could block remifentanil withdrawal induced spinal LTP, whereas supplement of recombinant rat TNFα to the spinal cord could reverse the inhibitory effect of Minocycline or PP2 on remifentanil withdrawal induced LTP. Our results suggested that TNFαrelease following SFKs activation in microglia is involved in the induction of LTP induced by remifentanil withdrawal.

Sufentanil sublingual formulation for the treatment of acute, moderate to severe postoperative pain in adult patients

INTRODUCTION

Sufentanil is a highly selective µ-opioid agonist commonly used by intravenous and intrathecal routes for acute pain. Sublingual sufentanil formulation for patient controlled analgesia (PCA) uses an innovative administration device that suspends a 15 µg nanotablet with a fixed lockout interval. The system is a non-invasive, less burdensome method of opioid delivery compared to intravenous and intrathecal routes. Sublingual nanotablet PCA transmucosal bioavailability is 59% and the meaningful analgesic onset time is 60 minutes. Areas covered: This paper focuses on the effectiveness, safety and feasibility of sufentanil PCA sublingual formulation for the management of postoperative pain. The paper is based on PubMed searches and the European Medicine Agency assessment report. Expert commentary: Under-treatment of acute pain is a substantial clinical problem. The initial experiences with the sublingual delivery system are encouraging. Sufentanil sublingual nanotablets intended for PCA device use are approved in Europe, and approval is pending in the United States.

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.

The effect of two different doses of remifentanil on postoperative pain and opioid consumption after cardiac surgery--a randomized controlled trial

BACKGROUND

Remifentanil, an ultra-short-acting opioid, provides intensive analgesia without prolonged respiratory depression and is widely used in cardiac surgery. Diminished dosing may also offer stable hemodynamics, even during sternotomy and sternal retraction. However, increased postoperative pain and induced opioid tolerance after remifentanil dosing during abdominal surgery was reported. We tested whether remifentanil 0.3 μg/kg/min infusion increased postoperative opioid consumption and pain compared to 0.1 μg/kg/min dosing.

METHODS

Ninety coronary artery bypass grafting or heart valve surgery patients were randomized to remifentanil 0.1 μg/kg/min or 0.3 μg/kg/min infusions during surgery. All patients received oxycodone bolus 0.15 μg/kg postoperatively, and patient-controlled analgesia (PCA) with oxycodone thereafter. Postoperative pain was estimated thrice daily by visual analogue scale, and 48-h opioid consumption was recorded from the PCA-device.

RESULTS

Total remifentanil dosing was 64 μg/kg in the higher and 22 μg/kg in the lower dosing group during the 3-h cardiac operations. Mean postoperative opioid consumption was 107 (SD 36) mg in the lower and 104 (SD 33) mg in the higher dose remifentanil groups. Postoperative pain did not differ between groups, at rest or during deep breathing, at any time (P = 0.110 and 0.941, respectively).

CONCLUSIONS

Remifentanil 0.3 μg/kg/min infusion did not increase postoperative pain or opioid consumption after cardiac surgery compared to the 0.1 μg/kg/min infusion. Remifentanil infusion 0.1-0.3 μg/kg/min during cardiac surgery was safe, with no exaggerated postoperative pain or opioid consumption.

Remifentanil added to sufentanil-sevoflurane anesthesia suppresses hemodynamic and metabolic stress responses to intense surgical stimuli more effectively than high-dose sufentanil-sevoflurane alone

BACKGROUND

Even extremely high-doses of the potent opioid, sufentanil, cannot reliably suppress stress responses to intense surgical stimuli such as sternotomy. The chemically related opioid remifentanil with its different pharmacokinetics and binding affinities for delta- and kappa-opioid receptors might be more effective in attenuating these responses.

METHODS

ASA I-III patients scheduled for a surgical procedure with sternotomy under balanced anesthesia (sevoflurane and sufentanil 3 μg.kg(-1) bolus, 0.017 μg.kg(-1).min(-1) infusion) were randomized into two groups. Patients in the study group were supplemented with remifentanil (2 μg.kg(-1) bolus, 2-7 μg.kg(-1).min(-1) infusion) starting ten minutes before sternotomy. Heart rate, arterial blood pressures, cardiac index, ejection fraction, systemic vascular resistance index (SVRI), total body oxygen uptake (VO2) and electric dermal response were measured and compared between the groups.

RESULTS

62 patients were studied (study group 32, control group 30). Systolic and mean arterial blood pressures, SVRI, VO2 and skin conductance increased during sternotomy and sternal spread in the control group but not in the study group. Systolic blood pressure increase: 7.5 ± 19 mmHg vs. -3.4 ± 8.9 (p = 0.005); VO2 increase: 31 ± 46% vs. -0.4 ± 32%; incidence of systolic blood pressure increase greater than 15 percent: 20% vs. 3% (p = 0.035) (control vs. study group).

CONCLUSION

High-dose remifentanil added to sevoflurane-sufentanil anesthesia suppresses the sympathoadrenergic response to sternotomy and sternal spread better than high-dose sufentanil alone.

TRIAL REGISTRATION

CLINICAL TRIAL NUMBER

DRKS00004327, August 31, 2012.

Risk factors and early pharmacological interventions to prevent chronic postsurgical pain following cardiac surgery

Chronic postsurgical pain (CPSP) after cardiac surgery represents a significant clinical problem. The prevalence of CPSP varies widely between studies, but severe CPSP is present in less than 10% of the patients. Important differential diagnoses for CPSP after cardiac surgery are myocardial ischemia, sternal instability and mediastinitis. CPSP after cardiac surgery may be thoracic pain present at the site of the sternotomy or leg pain due to vein-graft harvesting. The CPSP can be neuropathic pain, visceral pain, somatic pain or mixed pain. Potential risk factors for CPSP are young age, female gender, overweight, psychological factors, preoperative pain, surgery-related factors and severe postoperative pain. In addition to standard postoperative analgesics, the use of N-methyl-D-aspartate (NMDA) antagonists, alpha-2 agonists, local anesthetics, gabapentinoids, and corticosteroids are all proposed to reduce the risk for CPSP after cardiac surgery. Still, no specific pharmacological therapy, cognitive therapy or physical therapy is established to protect against CPSP. The only convincing prevention of CSPS is adequate treatment of acute postoperative pain irrespective of method. Hence, interventions against acute pain, preferably in a step-wise approach titrating the interventions for each patient's individual needs, are essential concerning prevention of CPSP after cardiac surgery. It is also important that surgeons consider the risk for CPSP as a part of the basis for decision-making around performing a surgical procedure and that patients are informed of this risk.

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.

No evidence for the development of acute analgesic tolerance during and hyperalgesia after prolonged remifentanil administration in mice

Background

Acute opioid tolerance (AOT) and opioid-induced hyperalgesia (OIH) are undesirable effects of opioids that have been reported in both animals and humans. However, the development of AOT and OIH in cases of potent, short-acting μ-opioid receptor agonist remifentanil administration remains controversial. It has been suggested that the emergence of AOT and OIH by remifentanil could be dose and infusion duration dependent, i.e., low dose and short infusions may lead to negative results. In this study, we determined whether AOT and OIH could be elicited by prolonged, continuous administration of remifentanil at maximally tolerable doses in C57BL/6 mice.

Results

The analgesic effects of continuously administered remifentanil [by short (1 h) and prolonged (4 h) intraperitoneal infusions] were studied. These experiments involved repeated measurements of thermal thresholds during remifentanil administration. Therefore, particular attention was paid to prevent cumulative tissue injury, which could mimic pronociceptive effects of remifentanil. To exclude the possibility of pseudoAOT during infusion, we used brief cooling of all ipsilateral hindpaws that exhibited analgesic response. Thermal thresholds remained steadily elevated over a 1-h period during continuous administration at infusion rates of 120, 180, and 240 mg/kg/h, which indicated no AOT development. To exclude the possibility of pseudoOIH after infusion, intact contralateral hindpaws were used for all postinfusion threshold measurements. Thermal thresholds at each infusion rate returned to the baseline values within 15 min after the termination of the administration. They did not decrease below the baseline values during 1 h following infusion, which indicated no OIH development. Similar threshold dynamics were also observed for thermal and mechanical testing modalities in animals infused at 120 mg/kg/h for 4 h as well as in animals with rapidly attained and maintained maximum analgesia for 3 h.

Conclusions

These results suggest that neither intra-infusion AOT nor postinfusion OIH develops in mice receiving continuous remifentanil when the possibility of cumulative tissue injury mimicking AOT or OIH is carefully avoided.