Effects of sevoflurane on carrageenan- and fentanyl-induced pain hypersensitivity in Sprague-Dawley rats

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).

American Society of Regional Anesthesia and Pain Medicine 2021 John J. Bonica Award Lecture

I am as deeply inspired and humbled to receive this prestigious award, as I am profoundly indebted to the Bonica Award selection committee and the American Society of Regional Anesthesia and Pain Medicine Board of Directors for recognizing my contributions to the development, teaching, and practice of pain medicine in the tradition of Dr John J Bonica. I would also like to recognize my parents, Aura and Tito for providing me with the support and the environment to fulfill my professional goals. Moreover, the support that I have gotten from my team at the hospital, and the Chair of my Department, Dr Mark Lema needs to be underscored.

Pharmacological Interventions for Opioid-Induced Hyperalgesia: A Scoping Review of Preclinical Trials

BACKGROUND

Opioid analgesics are the most effective pharmacological agents for moderate and severe pain. However, opioid use has several limitations such as opioid-induced hyperalgesia (OIH), which refers to the increased pain sensitivity that occurs once analgesia wears off after opioid administration. Several pharmacological interventions have been suggested for OIH, but the current literature does not provide guidelines on which interventions are the most effective and whether they differ depending on the opioid that induces hyperalgesia. This scoping review aimed to identify and describe all the preclinical trials investigating pharmacological interventions for OIH caused by remifentanil, fentanyl, or morphine as the first step towards evaluating whether the most effective OIH interventions are different for different opioids.

METHODS

Electronic database searches were carried out in Embase, PubMed, and Web of Science. Detailed data extraction was conducted on the eligible trials.

RESULTS

72 trials were eligible for the review. Of these, 27 trials investigated remifentanil, 14 trials investigated fentanyl, and 31 trials investigated morphine. A total of 82 interventions were identified. The most studied interventions were ketamine (eight trials) and gabapentin (four trials). The majority of the interventions were studied in only one trial. The most common mechanism suggested for the interventions was inhibition of N-methyl-D-aspartate (NMDA) receptors.

CONCLUSION

This scoping review identified plenty of preclinical trials investigating pharmacological interventions for OIH. Using the current literature, it is not possible to directly compare the effectiveness of the interventions. Hence, to identify the most effective interventions for each opioid, the interventions must be indirectly compared in a meta-analysis.

Involvement of Nrf-2/HO-1 pathway in sevoflurane-induced cognitive improvement in rats with traumatic brain injury

Traumatic brain injury (TBI) is an increasingly common emergency disease that usually leads to prolonged physical and cognitive impairments. In this study, we investigated if sevoflurane could induce cognitive improvement in TBI rats. Rats were subjected to head trauma induced by a fluid percussion device. A two-hour exposure to 3% sevoflurane was performed in a chamber immediately after TBI. Sevoflurane inhalation reduced the neurological and cognitive deficits induced by TBI with ameliorated synaptic injuries in the hippocampus. Moreover, after sevoflurane treatment, the expression of nuclear factor erythroid-2-related factor-2 (Nrf-2) and hemeoxygenase-1 (HO-1) in the hippocampus was enhanced 1 d after TBI and maintained at high levels 14 days later, and oxidative stress induced by TBI was inhibited. However, the HO-1 inhibitor, Zinc protoporphyrin (ZnPP), used to demonstrate the involvement of HO-1, suppressed the protective effect of sevoflurane. These results indicate that sevoflurane administered immediately after TBI may protect against TBI-induced synaptic and cognitive impairments by promoting the antioxidant Nrf-2/HO-1 pathway. Sevoflurane may be a promising anesthetic for patients with TBI.

Regulatory Effects of Propofol on High-Dose Remifentanil-Induced Hyperalgesia

We aimed to evaluate the regulatory effects of propofol on high-dose remifentanil-induced hyperalgesia. A total of 180 patients receiving laparoscopic cholecystectomy were randomly divided into sevoflurane + high-dose remifentanil (SH) group, sevoflurane + low-dose remifentanil (SL) group and propofol + high-dose remifentanil group (PH) group (n=60). After intravenous administration of midazolam, SH and SL groups were induced with sevoflurane and remifentanil, and PH group was induced with propofol and remifentanil. During anesthesia maintenance, SH and SL groups were given 0.3 μg/kg/min and 0.1 μg/kg/min sevoflurane and remifentanil respectively, and PH group was given 0.3 μg/kg/min propofol and remifentanil. The three groups had significantly different awakening time, extubation time and total dose of remifentanil (P<0.001). Compared with SL group, periumbilical mechanical pain thresholds 6 h and 24 h after surgery significantly decreased in SH group (P<0.05), and the visual analog scale (VAS) scores significantly increased 30 min, 2 h and 6 h after surgery (P<0.05). Compared with SH group, periumbilical mechanical thresholds 6 h and 24 h after surgery were significantly higher in PH group (P<0.05), and VAS scores 30 min, 2 h and 6 h after surgery were significantly lower (P<0.05). PH group first used patient-controlled intravenous analgesia pump significantly later than SL group did (P<0.05). The total consumptions of sufentanil in PH and SL groups were significantly lower than that of SH group (P<0.05). The incidence rates of bradycardia and postoperative chill in PH and SH groups were significantly higher than those of SL group (P<0.05). Anesthesia by infusion of high-dose remifentanil plus sevoflurane caused postoperative hyperalgesia which was relieved through intravenous anesthesia with propofol.

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.

Does Fentanyl Lead to Opioid-induced Hyperalgesia in Healthy Volunteers?

Background

Although opioids in general and remifentanil in particular have been shown to induce hyperalgesia, data regarding fentanyl are scarce. Thus, the authors investigated the effect of fentanyl dosing on pain perception and central sensitization in healthy volunteers using established pain models.

Methods

Twenty-one healthy, male volunteers were included in this randomized, double-blind, crossover study and received either intravenous low-dose (1 μg/kg) or high-dose (10 μg/kg) fentanyl. Pain intensities and hyperalgesia were assessed by intracutaneous electrical stimulation, and cold pressor pain was used as an additional measure of acute pain. The primary outcome was hyperalgesia from 4.5 to 6.5 h after fentanyl administration.

Results

A higher dose of fentanyl led to significantly decreased pain scores as measured by the numeric rating scale (0.83 units lower [95% CI, 0.63 to 1.02]; P &lt; 0.001) but increased areas of hyperalgesia (+30.5% [95% CI, 16.6 to 44.4%]; P &lt; 0.001) from 4.5 to 6.5 h after fentanyl administration. Allodynia did not differ between groups (+4.0% [95% CI, −15.4 to 23.5%]; P = 0.682).The high dose also led to both increased cold pressor pain threshold (+43.0% [95% CI, 29.7 to 56.3%]; P &lt; 0.001) and tolerance (+32.5% [95% CI, 21.7 to 43.4%]; P &lt; 0.001) at 4.5 to 6.5h. In the high-dose group, 19 volunteers (90%) required reminders to breathe, 8 (38%) required supplemental oxygen, and 12 (57%) experienced nausea.

Conclusions

A higher dose of fentanyl increased hyperalgesia from 4.5 to 6.5 h in healthy volunteers while simultaneously decreasing pain scores.

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.

Effects of intraoperative low dose ketamine on remifentanil-induced hyperalgesia in gynecologic surgery with sevoflurane anesthesia

Background

Remifentanil is useful during general anesthesia because of its rapid onset and short acting time. However, some studies report that due to opioid-induced hyperalgesia (OIH) and tolerance, remifentanil also increases early postoperative pain. The occurrence of OIH and opioid-induced tolerance is mainly thought to be due to central sensitization by the activation of NMDA receptors. Therefore, we investigated the effects of continuous infusion of ketamine, an NMDA receptor antagonist, on postoperative pain and the quantity of opioids used.

Methods

40 patients scheduled to undergo laparoscopic gynecologic surgery were randomly allocated into two groups. Anesthesia was equally maintained with sevoflurane and 4 ng/ml of remifentanil in all patients. Ketamine (0.3 mg/kg) was injected and followed with a continuous dosage of 3 µl/kg/min in the ketamine group (n = 20) while the control group was injected and infused with an equal amount of normal saline. We compared postoperative VAS up to 7 hours and morphine demand through PCA.

Results

Postoperative VAS and morphine demand was significantly lower in the ketamine group 2 and 3 hours after surgery, respectively.

Conclusions

When general anesthesia is maintained with sevoflurane and remifentanil in patients undergoing laparoscopic gynecologic surgery, continuous infusion of low dose ketamine decreased early postoperative pain and the quantity of opioids used.

Long-term sedation in intensive care unit: a randomized comparison between inhaled sevoflurane and intravenous propofol or midazolam

PURPOSE

To evaluate efficacy and adverse events related to inhaled sevoflurane for long-term sedation compared with standard intravenous (i.v.) sedation with propofol or midazolam.

METHODS

Randomized controlled trial. Sixty intensive care unit (ICU) patients expected to require more than 24 h sedation were randomly assigned to one of three groups: group S, inhaled sevoflurane; group P, i.v. propofol; group M, i.v. midazolam. All patients also received i.v. remifentanil for goal-directed sedation (Ramsay scale and pain score) until extubation or for a maximum of 96 h. Primary end points were wake-up times and extubation delay from termination of sedative administration. Proportion of time within Ramsay score 3-4, i.v. morphine consumption at 24 h post extubation, hallucination episodes after end of sedation, adverse events, inorganic fluoride plasma levels, and ambient sevoflurane concentrations were recorded.

RESULTS

Forty-seven patients were analyzed. Wake-up time and extubation delay were significantly (P<0.01) shorter in group S (18.6 ± 11.8 and 33.6 ± 13.1 min) than in group P (91.3 ± 35.2 and 326.11 ± 360.2 min) or M (260.2 ± 150.2 and 599.6 ± 586.6 min). Proportion of time within desired interval of sedation score was comparable between groups. Morphine consumption during the 24 h following extubation was lower in group S than in groups P and M. Four hallucination episodes were reported in group P, five in group M, and none in group S (P=0.04). No hepatic or renal adverse events were reported. Mean plasma fluoride value was 82 μmol l(-1) (range 12-220 μmol l(-1)), and mean ambient sevoflurane concentration was 0.3 ± 0.1 ppm.

CONCLUSIONS

Long-term inhaled sevoflurane sedation seems to be a safe and effective alternative to i.v. propofol or midazolam. It decreases wake-up and extubation times, and post extubation morphine consumption, and increases awakening quality.

Endogenous opiates and behavior: 2009

This paper is the 32nd consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2009 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 and thermoregulation (Section 16); and immunological responses (Section 17).