New therapeutic uses for an alpha2 adrenergic receptor agonist--dexmedetomidine in pain management

Prazosin as an Adjuvant to Increase Effectiveness of Duloxetine in a Rat Model of Oxaliplatin-Induced Peripheral Neuropathy

OBJECTIVES

Duloxetine, the only American Society of Clinical Oncology (ASCO) treatment recommended for chemotherapy-induced peripheral neuropathy (CIPN) in cancer survivors, is not effective for 40% of survivors. This study examined the ability of a duloxetine-prazosin combination to prevent the development of allodynia and hyperalgesia in a rat model of oxaliplatin-induced peripheral neuropathy (OPIN).

METHODS

Female (n = 24) and male (n = 41) rats were started on duloxetine (15 mg), prazosin (2 mg), or a duloxetine-prazosin combination one week prior to administration of the chemotherapy drug, oxaliplatin, and continued the duloxetine-prazosin combination for 32 days. Behavioral testing for mechanical allodynia and mechanical hyperalgesia was done with selected von Frey filaments over the course of the study.

RESULTS

Overall percent paw withdrawal for rats that received the duloxetine-prazosin combination was significantly lower in female (p < .001 for both conditions) and male (p = .029 for allodynia; p < .001 for hyperalgesia) than those that received water. No significant posttreatment differences were found for allodynia or hyperalgesia between rats treated with duloxetine and rats that received the duloxetine-prazosin combination in either sex.

CONCLUSIONS

These finding provide preliminary evidence that a duloxetine-prazosin combination can prevent the posttreatment development of allodynia and hyperalgesia in both male and female rats; however, the results suggest that the duloxetine-prazosin combination is no more efficacious than duloxetine alone in preventing chronic OIPN.

IMPLICATIONS FOR NURSING PRACTICE

The profession of nursing is built on clinical practice supported by scientific research. The current study addressed the clinical practice problem of prevention and management of painful OIPN, which is a priority area in oncology nursing.

Yangonin, one of the kavalactones isolated from Piper methysticum G. Forst, acts through cannabinoid 1 (CB1) receptors to induce an intrathecal anti-hyperalgesia

ETHNOPHARMACOLOGICAL RELEVANCE

Piper methysticum G. Forst (Piperaceae) is traditionally consumed in Polynesian culture. The roots are used to produce an entheogenic drink and traditional medicine with sedative and anxiolytic properties. There is also evidence that it functions as a pain reliever. Kavalactones, its main active ingredients, exhibit psychoactive effects on the central nervous system. However, the active ingredients and pharmacological mechanisms underlying the analgesic effect of kavalactones are unclear.

AIM OF THE STUDY

This study investigated the effects of kavain and yangonin on nociception, inflammatory hyperalgesia, and neuropathic mechanical allodynia at the spinal level.

MATERIALS AND METHODS

Male Sprague-Dawley rats were administered kavain and yangonin (27.14 and 19.36 nmol/rat) via intrathecal injection. Tail-flick tests were performed to evaluate the anti-nociceptive properties. The efficacy of kavain and yangonin on inflammatory hyperalgesia was examined using a plantar test in rats with carrageenan-induced paw inflammation. The von Frey test was used to assess mechanical allodynia induced by partial sciatic nerve ligation.

RESULTS

Intrathecal injection of yangonin demonstrated a relatively potent anti-nociceptive effect and attenuated carrageenan-induced hyperalgesia. These effects were completely reversed by the co-administration of PF 514273, a cannabinoid 1 (CB1) receptor antagonist. However, yangonin did not affect mechanical allodynia at the spinal level. Kavain, another abundant kavalactone, did not affect nociception, hyperalgesia, or mechanical allodynia at the spinal level.

CONCLUSIONS

Overall, our study demonstrated that yangonin exerts anti-nociception and anti-inflammatory hyperalgesia effects via CB1 receptors at the spinal level. We identified a single kavalactone, yangonin, extracted from kava as a promising treatment for pain.

Utility of dexmedetomidine on surgical site wound pain undergoing thoracoscopic surgery: A meta-analysis

We conducted this study aimed to evaluate the analgesic effect of dexmedetomidine in thoracoscopic surgery on postoperative wound pain, and to provide a reference for clinical use of the drug. We searched PubMed, Embase, Cochrane Library, Web of Science, Wanfang, Chinese Biomedical Literature Database and China National Knowledge Infrastructure databases, and supplemented with manual searching. We searched from database inception to October 2023, to collect the randomised controlled trials (RCTs) on dexmedetomidine application in thoracoscopic surgery. Two researchers screened all the literature according to the inclusion and exclusion criteria and the literature included in the study was evaluated for quality, extracted information and required data. Stata 17.0 software was employed for data analysis and the outcomes were 2 6, 12, 24 and 48 h postoperative wound visual analog scores (VAS). Twenty-four RCTs totalling 2246 patients undergoing thoracoscopic surgery were finally included. The analysis revealed dexmedetomidine applied to thoracoscopic surgery significantly reduced the postoperative wound VAS scores at 2 h (SMD: -0.96, 95% CI: -1.57 to -0.36, p = 0.002), 6 h (SMD: -0.98, 95% CI: -1.27 to -0.69, p < 0.001), 12 h (SMD: -1.19, 95% CI: -1.44 to -0.94, p < 0.001), 24 h (SMD: -0.91, 95% CI: -1.16 to -0.66, p < 0.001) and 48 h (SMD: -0.75, 95% CI: -1.02 to -0.48, p < 0.001). Our results suggest dexmedetomidine applied to thoracoscopic surgery can significantly reduce postoperative wound pain, which is worthy of clinical application.

Enhancing fentanyl antinociception and preventing tolerance with α-2 adrenoceptor agonists in rats

Fentanyl (FEN) is a potent opioid analgesic used for pain management. Opioid analgesic tolerance poses a significant challenge to the clinical utility of opioid agonists. Preventing the development of tolerance to opioid analgesia is crucial for improving its efficacy and safety. The noradrenergic system is involved in pain regulation. This study examined the effects of α-2 adrenoceptor (AR) agonists, dexmedetomidine (DEX), and xylazine (XYL) on FEN tolerance and antinociception, and their impact on μ-opioid receptor (MOR) expression in the posterior horn of the spinal cord (SC). Male rats were divided into six groups and treated with different drug combinations for three consecutive days. Analgesia tests and motor performance assessments were conducted, followed by SC analysis using immunohistochemistry (IHC). Analgesia tests revealed the development of FEN tolerance on the second day, but the groups receiving combined drugs did not develop tolerance. Instead, FEN antinociception was enhanced, with a prolonged duration of its effects. None of the drugs caused sedation or motor impairment, and SC morphology appeared normal. MOR expression levels did not differ significantly between the groups based on IHC analysis. These findings suggest that changes in the secondary messenger system may play a role in the early development of FEN tolerance. Combining drugs can prevent tolerance, while enhancing FEN's antinociceptive effects. These results have promising implications for chronic pain management; however, further research is needed to explore the molecular effects of α-2 AR agonists on FEN tolerance. Overall, this study sheds light on the mechanism of FEN tolerance and identifies potential avenues for future research.

Perineural dexmedetomidine in femoral nerve blocks increases the duration of postoperative analgesia for anterolateral thigh flap donor sites in patients with oral cancer

Although the duration of analgesia provided by a single-shot nerve block is limited, perineural dexmedetomidine significantly enhances nerve blocks during extremity surgery. This study aimed to investigate the role of dexmedetomidine added to ropivacaine in femoral nerve blocks for postoperative analgesia of the anterolateral thigh (ALT) flap donor site in patients with oral cancer. Fifty-two participants scheduled for maxillofacial tumor resection and reconstruction using an anterolateral thigh flap were randomly allocated to either the Ropi group (femoral nerve block with ropivacaine) or the Ropi + Dex group (femoral nerve block with ropivacaine plus dexmedetomidine). The primary outcome was the duration of the sensory block, while the secondary outcomes were 24 h postoperative sufentanil use, number of patients using rescue analgesics, vital signs, postoperative pain score, incidence of agitation, and presence of adverse effects. Dexmedetomidine plus ropivacaine significantly prolonged the duration of sensory block compared with ropivacaine alone (10.4 ± 0.9 h vs 14.0 ± 1.3 h; P < 0.001). Age was positively correlated with increased duration of sensory block (r = 0.300; P = 0.033). Postoperative pain scores at the donor sites were lower in the Ropi + Dex group than in the Ropi group, at 12 h after surgery (P < 0.001). Although there were no statistically significant differences in the incidence of bradycardia between the two groups, four patients treated with dexmedetomidine experienced episodes of bradycardia. Perineural dexmedetomidine prolonged the duration of femoral nerve block and reduced postoperative pain scores at the ALT flap donor sites in patients with oral cancer.

Effect of Dexmedetomidine as an adjuvant in quadratus lumborum block in patient undergoing caesarean section - A randomised controlled study

STUDY OBJECTIVE

This study was conducted to evaluate the effect of Dexmedetomidine as an adjuvant in quadratus lumborum block (QLB) for postoperative pain relief at rest in patients undergoing caesarean section (CS). The primary objective was to compare the time to the first request of rescue analgesia. Secondary objectives were to compare the amount of rescue analgesia, patient satisfaction, Numeric rating scale (NRS), and Ramsay sedation score (RSS) during the first 24 h.

DESIGN

A randomised, double-blinded study.

SETTING

The study was conducted at AIIMS Bhubaneswar from December 2019 to February 2021in the Operating Theatre complex (for the immediate postoperative follow-up) and in the Obstetric Ward (for follow-up at the later time points).

PATIENTS

A total of 70 patients were enrolled with singleton term pregnancies scheduled for CS under spinal anaesthesia after written informed consent.

INTERVENTION

Bilateral QLB was given in the recovery area. Group A received 30 ml of 0.25% Bupivacaine and group B received 30 ml 0.25% bupivacaine with Dexmedetomidine 1 μg/kg. They received inj. Paracetamol 15 mg/kg intravenously TDS and Inj. Tramadol 1 mg/kg as rescue analgesia (if Numeric rating scale (NRS) Score ≥ 4). We also compared the rescue analgesia in the first 24 h, patient satisfaction scores, Ramsay sedation score (RSS), and NRS scores at 2, 4, 6, 8, 12, 18, and 24 h.

MAIN RESULTS

The time to request the first rescue analgesia was significantly prolonged in group B [Mean ± SD (95% CI)] 880 ± 351 (720-1040) min. vs group A 439 ± 208 (368-510) min., p < 0.001). There was a significant decrease in the amount of rescue analgesia [(Inj. Tramadol (1 mg/ kg)] used in the group with dexmedetomidine [group B Mean ± SD (95% CI) (57 ± 18 (49-65) mg. vs group A - 81 ± 25 (73-90)] mg., p < 0.001]. A significant difference was seen in patient satisfaction scores and pain scores between the groups up to 18 h. (p < 0.05) but not in RSS.

CONCLUSION

Dexmedetomidine can be considered an effective adjuvant for QLB in CS in the absence of intrathecal morphine.

Effects of ultrasound-guided erector spinae plane block with dexmedetomidine combined with ropivacaine of the same dose and different concentrations on analgesic effect and rehabilitation quality of patients undergoing thoracoscopic wedge resection of the lung: a prospective, randomized, controlled trial

Objective

To investigate the analgesic effect and rehabilitation quality of patients undergoing thoracoscopic wedge resection of the lung under erector spinae plane (ESP) block with dexmedetomidine combined with the same dose and different concentrations of ropivacaine.

Methods

Seventy patients undergoing thoracoscopic wedge resection were randomly divided into groups A (n = 35) and B (n = 35). To perform ESP block, the groups were administered dexmedetomidine (0.5 μg/kg) combined with 30 mL of 0.33% ropivacaine or 20 mL of 0.5% ropivacaine, respectively, half an hour before general anesthesia induction. We compared the onset time of anesthesia, the block level, and the duration of the block between the two groups. The number of compressions of the analgesic pump within 24 h and 48 h postoperatively and the time of the first compression were noted. The visual analog scale (VAS) scores of static and cough at 0.5 h, 6 h, 12 h, 24 h, and 48 h postoperatively were noted. Furthermore, the 40-item quality of recovery questionnaire (QoR-40) score was recorded at 24 h postoperatively. In addition, we noted the time taken to get out of the bed for the first time, the length of hospital stay, analgesia satisfaction, and the occurrence of related adverse reactions and complications within 48 h postoperatively.

Results

The range of ESP block was wider in Group A than in Group B (P < 0.05). Group B had a significantly shorter onset time (P < 0.05) and lower static and cough VAS scores at 6 h and 12 h postoperatively (P < 0.05); this was associated with significantly fewer compressions of the analgesic pump within 24 h and 48 h postoperatively and significantly more time until the first compression of the analgesic pump was required (P < 0.05). Group B was associated with significantly superior QoR-40 scores 24 h postoperatively and significantly shorter time to get out of the bed for the first time than Group A (P < 0.05).

Conclusion

Dexmedetomidine combined with 0.5% ropivacaine for ESP block is better than 0.33% ropivacaine for overall analgesia and postoperative rehabilitation of patients undergoing thoracoscopic wedge resection.

Trial registration

ChiCTR2200058114, Date of registration: 30/03/2022.

Dexmedetomidine combined with ropivacaine for erector spinae plane block after posterior lumbar spine surgery: a randomized controlled trial

Purpose

Due to lumbar spinal surgery is frequently accompanied with moderate-to-severe postoperative pain, it is necessary to find an effective postoperative analgesia for patients with this surgery. This study aimed to observe the analgesic effect of dexmedetomidine combined with ropivacaine erector spinae plane block (ESPB) used in posterior lumbar spine surgery.

Methods

In this clinical trial, patients undergoing posterior lumbar spine surgery were recruited and randomly divided into two groups: intervention and control. The intervention group (Group E) received 0.375% ropivacaine with 1 µg/kg dexmedetomidine in a total of 20 ml for ESPB; the control group (Group C) received 20 ml ropivacaine 0.375% for ESPB. US-guided ESPB was performed preoperatively in all patients. Demographics, anesthesia time, surgery time, and ASA grade from the participants were recorded at baseline. The primary clinical outcome measures were 2-, 4-, 8-, 12-, 24-and 48-h visual analog scale (VAS) pain scores after surgery at rest and movement state. Other end points included opioid consumption, number of PCIA presses, flurbiprofen-axetil consumption, quality of recovery and pain management after surgery.

Results

One hundred twenty patients were enrolled in the study (mean [SD] ages: Group E, 54.77 [8.61] years old; Group C,56.40 [7.87] years old; P = 0.280). The mean anesthesia time was 152.55 (15.37) min in Group E and 152.60 (16.47) min in Group C (P = 0.986). Additionally, the surgery time was 141.70 (15.71) min in Group E compared to 141.48 (17.13) min in Group C (P = 0.943). In addition, we found that the VAS pain scores in the resting state during the postoperative period at 8–48 h were lower in Group E than in Group C. However, the VAS pain scores in the active state were lower in Group E at 12–48 h (P < 0.05). More importantly, the consumption of opioids and flurbiprofen-axetil after surgery was also lower in Group E (P < 0.05). Subsequently, we administered questionnaires on the quality of recovery and pain management after surgery that were positively correlated with the postoperative analgesic effect. It was worth affirming that the QoR-15 scores and APS-POQ-R questionnaire results were different between the two groups, further confirming that the combination of drugs not only could obtain an ideal analgesic effect but also had no obvious adverse reactions (P < 0.05).

Conclusions

All the findings suggested that dexmedetomidine could significantly relieve postoperative pain and reduce the consumption of opioids in patients undergoing posterior lumbar spine surgery without obvious adverse reactions as a local anesthetic adjuvant. Further studies with larger sample sizes and different drug dosages may be useful in understanding the potential clinical benefits of dexmedetomidine.

Suppression of P2X3 receptor-mediated currents by the activation of α2A -adrenergic receptors in rat dorsal root ganglion neurons

Aims

The α₂‐adrenergic receptor (α₂‐AR) agonists have been shown to be effective in the treatment of various pain. For example, dexmedetomidine (DEX), a selective α_2A‐AR agonist, can be used for peripheral analgesia. However, it is not yet fully elucidated for the precise molecular mechanisms. P2X3 receptor is a major receptor processing nociceptive information in primary sensory neurons. Herein, we show that a functional interaction of α_2A‐ARs and P2X3 receptors in dorsal root ganglia (DRG) neurons could contribute to peripheral analgesia of DEX.

Methods

Electrophysiological recordings were carried out on rat DRG neurons, and nociceptive behavior was quantified in rats.

Results

The activation of α_2A‐ARs by DEX suppressed P2X3 receptor‐mediated and α,β‐methylene‐ATP (α,β‐meATP)‐evoked inward currents in a concentration‐dependent and voltage‐independent manner. Pre‐application of DEX shifted the α,β‐meATP concentration‐response curve downwards, with a decrease of 50.43 ± 4.75% in the maximal current response of P2X3 receptors to α,β‐meATP in the presence of DEX. Suppression of α,β‐meATP‐evoked currents by DEX was blocked by the α_2A‐AR antagonist BRL44408 and prevented by intracellular application of the G_i/o protein inhibitor pertussis toxin, the adenylate cyclase activator forskolin, and the cAMP analog 8‐Br‐cAMP. DEX also suppressed α,β‐meATP‐evoked action potentials through α_2A‐ARs in rat DRG neurons. Finally, the activation of peripheral α_2A‐ARs by DEX had an analgesic effect on the α,β‐meATP‐induced nociception.

Conclusions

These results suggested that activation of α_2A‐ARs by DEX suppressed P2X3 receptor‐mediated electrophysiological and behavioral activity via a G_i/o proteins and cAMP signaling pathway, which was a novel potential mechanism underlying analgesia of peripheral α_2A‐AR agonists.

Effect of different administration and dosage of dexmedetomidine in the reduction of emergence agitation in children: a meta-analysis of randomized controlled trials with sequential trial analysis

BACKGROUND

Beneficial effects of dexmedetomidine (DEX) against emergence agitation (EA) in children remain controversial. We performed a more comprehensive meta-analysis to evaluate the protective effect of different administration routes, timing, patterns, and doses of DEX on EA in children.

METHODS

The randomized controlled trials about DEX preventing EA in children were searched in PubMed, Cochrane Library, Embase, and Web of Sciences up to October 7, 2020. The traditional meta-analysis and subgroup analysis were performed to study the influence of DEX on EA in children. The sequential trial analysis (TSA) further analyzed the pooled results to evaluate meta-analyses' robustness. Grading of recommendation, assessment, development, and evaluation (GRADE) was used to assess evidence quality.

RESULTS

Sixty-seven studies with 5,688 pediatric patients were included. DEX significantly decreased EA in children compared to placebo [RR 0.29, 95% confidence intervals (CI): 0.25-0.34] and midazolam (RR 0.34, 95% CI: 0.25-0.45), with firm evidence from TSA. Notably, using DEX significantly reduced severe EA incidence (RR 0.23, 95% CI: 0.16-0.32), with firm evidence by TSA and high quality of GRADE. Pre-specified subgroup analyses revealed firm and high-quality evidence for a reduction of EA, only if the perineural route administers DEX (RR 0.24, 95% CI: 0.14-0.41), as premedication (RR 0.27, 95% CI: 0.20-0.36), as continuous dosage (RR 0.25, 95% CI: 0.18-0.33), at high dose (RR 0.24, 95% CI: 0.18-0.31). The pooled results also showed that DEX reduced the incidence of PONV compared to placebo (RR 0.43, 95% CI: 0.33-0.55). Evidence for DEX's influence on other secondary outcomes (emergence time, time in PACU, rescue analgesia, hypotension, and bradycardia) is insufficient to draw any conclusion.

CONCLUSIONS

Our findings confirm the beneficial effects of DEX on EA, severe EA, and PONV in children. There was firm and high-quality evidence for the efficacy of DEX in preventing EA in children when perineural routes administered DEX, as premedication, as continuous dosage, and at a high dose. The best dose, route, patterns, and timing of DEX and influence on other outcomes call for further studies.

Mechanisms, diagnosis, prevention and management of perioperative opioid-induced hyperalgesia

Opioid-induced hyperalgesia (OIH) occurs when opioids paradoxically enhance the pain they are prescribed to ameliorate. To address a lack of perioperative awareness, we present an educational review of clinically relevant aspects of the disorder. Although the mechanisms of OIH are thought to primarily involve medullary descending pathways, it is likely multifactorial with several relevant therapeutic targets. We provide a suggested clinical definition and directions for clinical differentiation of OIH from other diagnoses, as this may be confusing but is germane to appropriate management. Finally, we discuss prevention including patient education and analgesic management choices. As prevention may serve as the best treatment, patient risk factors, opioid mitigation, and both pharmacologic and non-pharmacologic strategies are discussed.

Adjuvants in pain medicine. Selection of the drug depending on the desired effect – so which drug to choose?

To date, much research has focused on finding the ideal adjuvant for local anesthetics. Each of them can have different effects. In anesthesiology and pain medicine, depending on the purpose, one or another effect may be desirable. For example, in some situations it is desirable to accelerate the onset of action or prolong the duration of the block, in others the desired effect may be a “response to intravascular administration”, it should also be borne in mind that not all adjuvants are allowed for intrathecal administration.

Mechanisms of Dexmedetomidine in Neuropathic Pain

Dexmedetomidin is a new-generation, highly selective α2 adrenergic receptor agonist with a large number of advantages, including its sedative and analgesic properties, its ability to inhibit sympathetic nerves, its reduced anesthetic dosage, its hemodynamic stability, its mild respiratory depression abilities, and its ability to improve postoperative recognition. Its safety and effectiveness, as well as its ability to provide a certain degree of comfort to patients, make it a useful anesthetic adjuvant for a wide range of clinical applications. For example, dexmedetomidine is commonly used in patients undergoing general anesthesia, and it also exerts sedative effects during tracheal intubation or mechanical ventilation in intensive care unit patients. In recent years, with the deepening of clinical research on dexmedetomidine, the drug is still applied in the treatment of spastic pain, myofascial pain, neuropathic pain, complex pain syndrome, and chronic headache, as well as for multimodal analgesia. However, we must note that the appropriateness of patient and dose selection should be given attention when using this drug; furthermore, patients should be observed for adverse reactions such as hypotension and bradycardia. Therefore, the safety and effectiveness of this drug for long-term use remain to be studied. In addition, basic experimental studies have also found that dexmedetomidine can protect important organs, such as the brain, heart, kidney, liver, and lung, through various mechanisms, such as antisympathetic effects, the inhibition of apoptosis and oxidative stress, and a reduction in the inflammatory response. Moreover, the neuroprotective properties of dexmedetomidine have received the most attention from scholars. Hence, in this review, we mainly focus on the characteristics and clinical applications of dexmedetomidine, especially the role of dexmedetomidine in the nervous system and the use of dexmedetomidine in the relief of neuropathic pain.

Dexmedetomidine improves neurodevelopment and cognitive impairment in infants with congenital heart disease

Aim: Explore if dexmedetomidine (DEX) improves neurodevelopment and cognitive impairment in infants with congenital heart disease. Materials & methods: We retrospectively analyzed 256 pediatric patients aged less than 2 years with heart disease undergoing thoracic surgery. The intelligence quotient and neurodevelopment were tested. Mortality, incidence of postoperation adverse events, duration of mechanical ventilation, and length of stay were recorded and compared. Results: Compared with those not administered DEX, intelligence quotient scores and neurodevelopment evaluation scores increased in patients receiving perioperative DEX. There were no significant differences in mortality, duration of mechanical ventilation or length of stay. Conclusion: The administration of DEX might improve neural development and reduce the adverse effects of general anesthesia in infants with congenital heart disease undergoing surgery and extracorporeal circulation.

Pain Management for Orthopedic Injuries

Pain management in acute orthopedic injury needs to be tailored to the presentation and patient. Subjective and objective assessment, in conjunction with pathophysiology, should be used to provide symptom control. Ideally, treatment should be administered in an escalating fashion, attempting to manage pain with the lowest dose of the safest medication available. There are also adjunctive therapies, including those that are nonpharmacologic, that can provide additional relief.

Comparison of dexmedetomidine and dexamethasone as adjuvant for ropivacaine in ultrasound-guided erector spinae plane block for video-assisted thoracoscopic lobectomy surgery: a randomized, double-blind, placebo-controlled trial

Background

Adding an adjuvant, such as dexmedetomidine or dexamethasone, to a nerve block improves its quality and reduces perioperative opioid consumption. We aimed to compare the effect of dexmedetomidine and dexamethasone as an adjuvant for the erector spinae plane block (ESPB) to control postoperative pain after video-assisted thoracoscopic lobectomy surgery (VATLS).

Methods

Ninety patients, aged 20-65 years who were scheduled to undergo VATLS were enrolled in this trial. The visual analogue scale (VAS) score changes at various time points [waking up in post-anesthesia care unit (PACU) and 2, 4, 6, 8, 12, 24, 48, 72 h after surgery], duration of sensory block, first request to use the patient controlled analgesia (PCA) device, total PCA use, postoperative nausea and vomiting (PONV), rate of rescue analgesia use, and post-surgical hospital stay were recorded.

Results

VAS score was lower in the ropivacaine with dexmedetomidine (RM) group at wake up and at postoperative 2, 4, 12, and 24 h. The median duration of sensory blockade was significantly longer in the RM group (P=0.001). First request to use the PCA machine in the RM group was prolonged significantly compared with that in the ropivacaine alone (R) group and ropivacaine with dexamethasone (RS) group (P<0.001). Total PCA use, post-surgical hospital stay, and rate of rescue analgesia use in The RM group were reduced significantly compared with those in the R and RS groups.

Conclusions

Using dexmedetomidine (1 µg/kg), instead of dexamethasone (10 mg), as an adjuvant of ESPB with ropivacaine, prolonged sensory block duration, provided effective acute pain control, and required lesser rescue analgesia and shorter hospital stays.

An Experimental Study on Spinal Cord µ-Opioid and α2-Adrenergic Receptors mRNA Expression Following Stress-Induced Hyperalgesia in Male Rats

Background:

Intense stress can change pain perception and induce hyperalgesia; a phenomenon called stress-induced hyperalgesia (SIH). However, the neurobiological mechanism of this effect remains unclear. The present study aimed to investigate the effect of the spinal cord µ-opioid receptors (MOR) and α2-adrenergic receptors (α2-AR) on pain sensation in rats with SIH.

Methods:

Eighteen Sprague-Dawley male rats, weighing 200-250 g, were randomly divided into two groups (n=9 per group), namely the control and stress group. The stress group was evoked by random 1-hour daily foot-shock stress (0.8 mA for 10 seconds, 1 minute apart) for 3 weeks using a communication box. The tail-flick and formalin tests were performed in both groups on day 22. The real-time RT-PCR technique was used to observe MOR and α2-AR mRNA levels at the L4-L5 lumbar spinal cord. Statistical analysis was performed using the GraphPad Prism 5 software (San Diego, CA, USA). Student’s t test was applied for comparisons between the groups. P<0.05 was considered statistically significant.

Results:

There was a significant (P=0.0014) decrease in tail-flick latency in the stress group compared to the control group. Nociceptive behavioral responses to formalin-induced pain in the stress group were significantly increased in the acute (P=0.007) and chronic (P=0.001) phases of the formalin test compared to the control group. A significant reduction was also observed in MOR mRNA level of the stress group compared to the control group (P=0.003). There was no significant difference in α2-AR mRNA level between the stress and control group.

Conclusion:

The results indicate that chronic stress can affect nociception and lead to hyperalgesia. The data suggest that decreased expression of spinal cord MOR causes hyperalgesia.

Adjuvants in clinical regional anesthesia practice: A comprehensive review

Adjuvants are medications that work synergistically with local anesthetics to help enhance the duration and quality of analgesia in regional techniques. Regional anesthesia has become more prevalent as evidence continues to show efficacy, enhancement of patient care, increased patient satisfaction, and improved patient safety. Practitioners in the perioperative setting need to not only be familiar with regional techniques but also the medications used for them. Some examples of adjuvant medications for regional techniques include dexamethasone, alpha 2 agonists such as clonidine and dexmedetomidine, midazolam, buprenorphine, NMDA antagonists, including ketamine and magnesium, neostigmine, sodium bicarbonate, epinephrine, and non-steroidal anti-inflammatory drugs. The aim of the present investigation, therefore, is to provide a comprehensive review of the most commonly used non-opioid adjuvants in clinical practice today. Regional adjuvants can improve patient safety, increase patient satisfaction, and enhance clinical efficacy. Future studies and best practice techniques can facilitate standardization of regional anesthesia adjuvant dosing when providing nerve blocks in clinical practice.

Intraoperative and postoperative infusion of dexmedetomidine combined with intravenous butorphanol patient-controlled analgesia following total hysterectomy under laparoscopy

The present prospective, randomized, double-blinded, controlled study aimed to investigate the efficacy and safety of dexmedetomidine (DEX) combined with butorphanol for patient-controlled intravenous analgesia (PCIA) following total laparoscopic hysterectomy. A total of 88 patients undergoing total laparoscopic hysterectomy and receiving postoperative PCIA were divided into two groups following surgery. Patients received DEX 0.5 µg/kg intravenously in the DEX group or 0.9% normal saline in the control (CON) group following anesthesia induction. Postoperatively, the PCIA (10 mg butorphanol with 300 µg dexmedetomidine in the DEX group or without DEX in the CON group) was delivered as a 0.5 ml bolus (lockout interval of 15 min) with a continuous background infusion of 2 ml/h. Cardiovascular and respiratory variables, cumulative butorphanol consumption, pain scores, level of sedation, concerning adverse events and the degree of patient satisfaction were recorded for 24 h post-surgery. A total of 81 patients completed the study. Blood pressure and heart rate exhibited no significant difference between the two groups during surgery and for 24 h post-surgery. Compared with the CON group, patients in the DEX group required ~19% less butorphanol (P<0.05). During the first 24 h post-surgery, patients from the DEX group had a significantly lower visual analogue scale score at rest and movement states compared with the CON group (P<0.05). There was no significant difference in sedation score between the groups. The satisfaction scores were significantly higher in the DEX group compared with those in the CON group (P<0.05). Compared with the CON group, the DEX group exhibited a lower rate of postoperative nausea and vomiting (P<0.05). There was no occurrence of serious adverse events, including respiratory depression, hypotension, bradycardia and somnolence. In conclusion, following total laparoscopic hysterectomy, the loading dose of DEX (0.5 µg/kg) followed by a continuous infusion as an adjunct to butorphanol PCIA resulted in effective analgesia, significant butorphanol sparing and less butorphanol-induced nausea and vomiting without excessive sedation or adverse effects. The trial registration number was ChiCTR1800015675 at the Chinese Clinical Trial Registry (chictr.org.cn) and the date of registration was 4th April 2018.

The influence of dexmedetomidine on remifentanil-induced hyperalgesia and the sex differences

In the clinical settings, patients often develop opioid-induced hyperalgesia (OIH) after utilization of high dose intra-operative remifentanil. Systemic α2 agonists, including dexmedetomidine, are believed to reduce pain and opioid requirements after surgery, thus decreasing the incidence of hyperalgesia. The present study aimed to investigate the effect of dexmedetomidine on remifentanil-induced hyperalgesia and explored the sex differences. A total of 48 patients (24 male, 24 female) with an American Society of Anesthesiologists physical status of I-II that were undergoing thyroidectomy were randomly assigned to one of the following six groups: Male controlled group (MC) and female controlled group (FC) (group MC, n=8 and group FC, n=8), which received a preoperative placebo of 0.2 µg.kg^-1 normal saline and intraoperative remifentanil 0.2 µg.kg^-1.min^-1; male and female group with low-dose dexmedetomidine (group MD1, n=8 and group FD1, n=8), which received preoperative dexmedetomidine 0.2 µg.kg^-1 and intraoperative remifentanil 0.2 µg.kg^-1.min^-1; and male and female groups with high-dose dexmedetomidine (group MD2, n=8 and group FD2, n=8), which received dexmedetomidine 0.6 µg.kg^-1 and intraoperative remifentanil 0.2 µg.kg^-1.min^-1. Result indicated that the visual analog scale (VAS) scores and morphine dosing frequency were significantly higher in MC and FC groups compared with the other same sex groups. Furthermore, the mechanical hyperalgesia threshold and patients' analgesia satisfaction score after surgery were significantly lower in MC and FC groups. Notably, the frequency of post-operative chills, nausea and vomiting were significantly lower in groups MD1, MD2, FD1 and FD2. The present findings indicated that low- and high-dose dexmedetomidine injection significantly decreased the patient's risk of enhanced pain intensity and increased postoperative morphine dosing caused by remifentanil-induced hyperalgesia. These findings suggest that the influence of dexmedetomidine displayed minimal significant differences between sex. Trial registration no., IRB2018-YX-001 (Name of registry: Institutional Medical Ethics Committee of Tianjin Medical University General Hospital; date of registration: February 1, 2016).

Antinociceptive effects of dexmedetomidine via spinal substance P and CGRP

The aim of this study was to examine the role played by substance P and calcitonin gene-related peptide (CGRP) within the dorsal horn of the spinal cord in engagement of antinociception evoked by dexmedetomidine (DEX). Paw withdrawal threshold (PWT) to mechanical stimulation was determined after chronic intrathecal infusion of DEX and enzyme-linked immunosorbent assay (ELISA) was employed to examine the levels of spinal substance P and CGRP. Our results show that PWT was significantly increased by intrathecal administration of DEX in rats (P < 0.05 vs. vehicle control, n = 20 in each group). Also, intrathecal infusion of DEX significantly decreased the concentrations of substance P and CGRP as compared with vehicle control (P < 0.05 DEX vs. vehicle control, n = 20 in each group). Blocking α₂-adrenoreceptors (α₂-AR) blunted the decreases of substance P and CGRP levels and the enhancement of PWT evoked by DEX. Additionally, a linear relationship was observed between PWT and the levels of spinal substance P (r = 0.87; P < 0.005) and CGRP (r = 0.85; P < 0.005). Moreover, blocking individual substance P and CGRP receptors amplified PWT without altering substance P and CGRP levels. Thus, DEX plays a role in stimulating α₂-AR receptors, which thereby decreases substance P and CGRP levels within the dorsal horn. This contributes to DEX-evoked antinociception.

Plasticity of α2-adrenergic spinal antinociception following nerve injury: selective, bidirectional interaction with the delta opioid receptor

Interactions of opioid receptors with other receptor families can be made use of to improve analgesia and reduce adverse effects of opioid analgesics. We investigated interactions of the α2-adrenergic receptor (α2AR) with opioid receptors of the mu (MOR) and delta (DOR) types in the spinal dorsal horn in an animal model of neuropathic pain induced by spinal nerve ligation. Nine days after nerve injury, immunoreactivity for the α2AR subtype A (α2AAR) was increased both in tissue homogenates and at pre- and post-synaptic sites in transverse sections. The efficacy of spinally administered α2AAR agonist guanfacine at reducing C-fiber-evoked field potentials was increased in nerve-ligated rats. This reducing effect was impaired by simultaneous administration of DOR antagonist naltrindole, but not MOR antagonist CTOP, suggesting that concurrent DOR activation was required for α2AAR-mediated inhibition. While DOR agonist deltorphin II and MOR agonist DAMGO both effectively depressed C-fiber-evoked spinal field potentials, DOR- but not MOR-mediated depression was enhanced by subclinical guanfacine. In conscious, nerve-ligated rats, chronically administered deltorphin II produced stable thermal and mechanical antinociception over the 9 following days after nerve injury without apparent signs of habituation. Such an effect was dramatically enhanced by co-administration of a low dose of guanfacine, which reversed thermal and mechanical thresholds to levels near those prior to injury. The results suggest that spinal, α2AAR-mediated antinociception is increased after nerve injury and based on DOR co-activation. We demonstrate in vivo that α2AAR/DOR interaction can be exploited to provide effective behavioral antinociception during neuropathic pain.

From FUS to Pandora syndrome

New concepts:

Ideas about the causes of lower urinary tract signs (LUTS) in cats have changed significantly in the past 40 years. Recent research is challenging the conventional view that the bladder is always the perpetrator of LUTS, and suggests that the bladder can also be one victim of a systemic process associated with a sensitized central stress response system.

Aim:

In this article the authors provide their perspective on the implications of these findings for the diagnosis and treatment of cats with LUTS, provide some historical context, and suggest ways that the veterinary profession might work together to better understand the disorders underlying these signs, and possibly reduce their prevalence.