Systemic daily morphine enhances the analgesic effect of intrathecal dexmedetomidine via up-regulation of alpha 2 adrenergic receptor subtypes A, B and C in dorsal root ganglion and dorsal horn

Comparison of the ED50 of intrathecal hyperbaric ropivacaine co-administered with or without intrathecal dexmedetomidine for cesarean section: A prospective, double-blinded, randomized dose-response trial using up-down sequential allocation method

STUDY OBJECTIVE

Studies have showed that intrathecal dexmedetomidine as supplements to local anesthetics can improve the quality of the spinal anesthesia and reduce the local anesthetic requirement of spinal anesthesia for cesarean section. However, the magnitude of this effect has not been fully quantified. Therefore, we conducted the present study to investigate the ED₅₀ of intrathecal hyperbaric ropivacaine with or without dexmedetomidine for cesarean section in healthy parturients. ED₅₀ values obtained were compared to estimate the effect of intrathecal dexmedetomidine versus placebo on ropivacaine requirement.

DESIGN

Single-blinded, prospective, randomized study.

SETTING

Department of Anesthesia, Women's Hospital, Zhejiang University School of Medicine.

PATIENTS

Sixty healthy parturients under elective cesarean section with combined spinal-epidural anesthesia were randomized into Group C (intrathecal ropivacaine alone) and Group D (intrathecal ropivacaine + 5 μg dexmedetomidine).

INTERVENTIONS

The dose of intrathecal ropivacaine for the first parturient in both groups was 11 mg. An increment or decrement of 0.5 mg intrathecal ropivacaine was made for the subsequent parturient based on the effective or ineffective response of the previous parturient. Effective dose was defined as a bilateral T6 or above sensory block level was achieved within 15 min after induce of spinal anesthesia and no additional epidural anesthetics was required during surgery. The Dixon and Massay sequential method and Probit regression were applied to calculate the ED₅₀ of intrathecal ropivacaine in both groups.

MEASUREMENTS

Characteristics of spinal anesthesia and side effects were recorded.

MAIN RESULTS

The ED₅₀ of hyperbaric ropivacaine calculated by Dixon and Massay formula was 11.4 mg (95% CI, 11.1-11.7 mg) in Group C, and 9.4 mg (95% CI, 9.0-9.7 mg) in Group D (P < 0.05). While using the Probit regression, the ED₅₀ of intrathecal hyperbaric ropivacaine was 11.1 mg (95% CI, 10.7-11.6 mg) in Group C, and 9.1 mg (95% CI, 8.6-9.5 mg) in Group D. Shivering was less observed in Group D than in Group C (P < 0.05). There was no significant difference in the onset time of sensory block or motor block, the incidence of hypotension, bradycardia, nausea and vomiting, sedation and pruritus between the two groups.

CONCLUSION

Under the conditions of the present study, intrathecal dexmedetomidine (5 μg) reduced the ED₅₀ of intrathecal hyperbaric ropivacaine by approximately 18% for cesarean section in healthy parturients under combined spinal-epidural anesthesia.

Fetal and Maternal Responses to Dexmedetomidine Intrathecal Application During Cesarean Section: A Meta-Analysis

Background

Intrathecal dexmedetomidine (DEX) can improve the blockade of spinal anesthesia, but there is no clear conclusion on whether it has an effect on the fetus during cesarean section. Our meta-analysis evaluated the safety and efficacy of intrathecal DEX in cesarean delivery.

Material/Methods

We searched Cochrane, Embase, PubMed, and CBM for eligible studies, and used the Revised Cochrane Risk of Bias Tool (RoB 2.0) to assess the risk of bias of each study. RevMan was used for statistical analyses. We have registered this meta-analysis on PROSPERO (CRD42019120995).

Results

The meta-analysis included 10 RCTs, but only 5 were prospectively registered. The results of preregistration studies, including the 1- or 5-min Apgar score (mean difference [MD], −0.03; 95% confidence intervals [CI], −0.16 to 0.10; P=0.64 or MD, 0.00; 95% CI, −0.09 to 0.09; P=1), the umbilical arterial oxygen or carbon dioxide partial pressure (MD, 0.90; 95% CI, −4.92 to 6.72; P=0.76 or MD, 1.20; 95% CI, −2.06 to 4.46; P=0.47), and the cord blood pH (MD, −0.01; 95% CI, −0.05 to 0.03; P=0.72), showed that intrathecal DEX had no significant difference in neonatal outcomes compared with placebo. In maternal outcomes, intrathecal DEX significantly prolonged postoperative pain-free period and reduced the incidence of postoperative shivering, which did not increase spinal anesthesia-associated adverse effects.

Conclusions

Intrathecal DEX is safe for the fetus during cesarean section and can improve the blockade effects of spinal anesthesia on puerperae.

Dexmedetomidine as a neuraxial adjuvant for prevention of perioperative shivering: Meta-analysis of randomized controlled trials

BACKGROUND

Dexmedetomidine, a highly selective α2-adrenoceptor agonist, has been investigated for anti-shivering effects in some trials. This current meta-analysis was conducted to evaluate the effectiveness of dexmedetomidine as a neuraxial adjuvant in preventing perioperative shivering.

METHODS

This systematic review and meta-analysis was registered in PROSPERO [www.crd.york.ac.uk/PROSPERO] with the unique identification number CRD42017055991. The electronic databases PubMed, Embase, Cochrane Central Register of Controlled Trials (CENTRAL) were searched to select high-quality randomized controlled trials (RCTs) that evaluated the anti-shivering efficacy for neuraxial application dexmedetomidine as local anesthetic adjuvant. Effects were summarized using pooled risk ratios (RRs), weighed mean differences (MDs), or standardized mean differences (SMDs) and corresponding 95% confidence intervals (Cls) with random effect model. Heterogeneity assessment, sensitivity analysis, and publication bias were performed. The primary outcome was perioperative shivering.

RESULTS

A total of 1760 patients from 24 studies were included in this meta-analysis. Compared with the placebo, dexmedetomidine reduced the incidence of perioperative shivering (RR: 0.34; 95% Cl: 0.21 to 0.55; P < 0.00001), with a maximum effective dose of 5μg via subarachnoid space injection (RR: 0.55; 95% CI: 0.32 to 0.92; P = 0.02), especially in cesarean section (RR: 0.20; 95% CI: 0.09 to 0.45; P = 0.0001). Dexmedetomidine also could improve the characteristics of the block, with an increase only in the incidence of bradycardia (RR: 2.11; 95% CI: 1.23 to 3.60; P = 0.006). No significant difference could be found compared dexmedetomidine with other adjuvants, except morphine.

CONCLUSIONS

This meta-analysis shows that dexmedetomidine as a neuraxial adjuvant had statistically significant efficacy on prevention of perioperative shivering. Moreover, dexmedetomidine could improve the characteristics of the block. However, the potential induction of bradycardia should be taken seriously.

Synergistic Interaction Between Dexmedetomidine and Ulinastatin Against Vincristine-Induced Neuropathic Pain in Rats

Antimicrotubulin chemotherapeutic agents such as vincristine (VCR), often induce peripheral neuropathic pain. It is usually permanent and seriously harmful to cancer patients' quality of life and can result in the hampering of clinical treatments. Currently, there is no definitive therapy, and many of the drugs approved for the treatment of other neuropathic pain have shown little or no analgesic effect. It is therefore vital to find new and novel therapeutic strategies for patients suffering from chemotherapeutic agent-induced neuropathic pain to improve patients' quality of life. This study shows that intrathecal injections of dexmedetomidine (DEX), or intraperitoneally administered ulinastatin (UTI) significantly reduces Sprague Dawley rats' mechanical allodynia induced by VCR via upregulation of interleukin-10 expression and activating the α2-adrenergic receptor in dorsal root ganglion (DRG). Moreover, when combined there is a synergistic interaction between DEX and UTI, which acts against VCR-induced neuropathic pain. This synergistic interaction between DEX and UTI may be partly attributed to a common analgesic pathway in which the upregulation of interleukin -10 plays an important role via activating α2-adrenergic receptor in rat dorsal root ganglion. The combined use of DEX and UTI does not affect the rat's blood pressure, heart rate, sedation, motor score, spatial learning, or memory function. All of these show that the combined use of DEX and UTI is an effective method in relieving VCR-induced neuropathic pain in rats.

PERSPECTIVE

This article documents the synergistic interaction between 2 widely used drugs, DEX and UTI, against VCR-induced neuropathic pain. The results provide a potential target and novel drug administrated method for the clinical treatment of chemotherapy-induced peripheral neuropathic pain.

Foetal responses to dexmedetomidine in parturients undergoing caesarean section: a systematic review and meta-analysis

Objective This current meta-analysis was conducted to evaluate effects of dexmedetomidine on neonatal maternal factors. Methods The electronic databases of PubMed, Embase, and Cochrane Central Register of Controlled Trials were searched. The primary outcomes were neonatal parameters, including umbilical blood gases and Apgar scores. The secondary outcomes were maternal parameters. Results We identified six randomized controlled trials (RCTs). No differences in neonatal umbilical blood gases, and Apgar scores at 1 min (WMD: -0.09; 95% CI: -0.21 to 0.04; I²= 0%) and 5 min (weighted mean difference (WMD): 0.03; 95% CI: -0.05 to 0.11; I²= 37%) were observed with dexmedetomidine. For maternal parameters, characteristics of motor and sensory block and postoperative analgesia (standard mean difference (SMD): 3.99; 95% CI: 2.85 to 5.12; I²= 78%) were significantly improved after dexmedetomidine treatment. Adverse events, including nausea/vomiting and shivering (risk ratio (RR): 0.26; 95% CI: 0.11 to 0.60; I²= 0%), were lower after dexmedetomidine treatment. Conclusion This meta-analysis shows that dexmedetomidine is safe for neonates who are delivered by caesarean section. Moreover, dexmedetomidine used in neuraxial anaesthesia can improve the characteristics of motor and sensory block and prolong the maternal pain-free period. Dexmedetomidine can also reduce the maternal incidence of postoperative adverse effects.

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.

Neurotoxicity of intrathecal injections of dexmedetomidine into the rat spinal dorsal horn

To investigate the neurotoxicity of intrathecal injections of dexmedetomidine, Sprague-Dawley rats were intrathecally injected with dexmedetomidine at doses of 0.75, 1.50 and 3.00 μg/kg into the spinal dorsal horn. We found that c-Fos expression in the rat spinal dorsal horn peaked at 7 hours following the 3.00 μg/kg dexmedetomidine injection, while the levels of c-Fos expression following 0.75 and 1.50 μg/kg dexmedetomidine were similar to those in the spinal dorsal horn of normal rats. At 48 hours following administration, the level of c-Fos expression was similar to normal levels. In addition, the intrathecal injections of dexmedetomidine increased paw withdrawal mechanical thresholds and prolonged thermal tail flick latencies. These results indicate that dexmedetomidine has pronounced antinociceptive effects. However, dexmedetomidine appears to have neurotoxic effects in the spinal cord because it increased c-Fos expression in the spinal dorsal horn within 7 hours following administration.

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.

Epigenetic modification of DRG neuronal gene expression subsequent to nerve injury: etiological contribution to complex regional pain syndromes (Part I)

DRG is of importance in relaying painful stimulation to the higher pain centers and therefore could be a crucial target for early intervention aimed at suppressing primary afferent stimulation. Complex regional pain syndrome (CRPS) is a common pain condition with an unknown etiology. Recently added new information enriches our understanding of CRPS pathophysiology. Researches on genetics, biogenic amines, neurotransmitters, and mechanisms of pain modulation, central sensitization, and autonomic functions in CRPS revealed various abnormalities indicating that multiple factors and mechanisms are involved in the pathogenesis of CRPS. Epigenetics refers to mitotically and meiotically heritable changes in gene expression that do not affect the DNA sequence. As epigenetic modifications potentially play an important role in inflammatory cytokine metabolism, neurotransmitter responsiveness, and analgesic sensitivity, they are likely key factors in the development of chronic pain. In this dyad review series, we systematically examine the nerve injury-related changes in the neurological system and their contribution to CRPS. In this part, we first reviewed and summarized the role of neural sensitization in DRG neurons in performing function in the context of pain processing. Particular emphasis is placed on the cellular and molecular changes after nerve injury as well as different models of inflammatory and neuropathic pain. These were considered as the potential molecular bases that underlie nerve injury-associated pathogenesis of CRPS.

Differential expression of alpha-adrenoceptor subtypes in rat dorsal root ganglion after chronic constriction injury

mRNAs of alpha-adrenoceptor (α-AR) subtypes are found in neurons in dorsal root ganglion (DRG) and change after peripheral nerve injury. In this study, the distribution of α-AR subtype proteins was studied in L5 DRG of normal rats and rats with chronic constriction injury of sciatic nerve (CCI). Using immunofluorescence technique, it was found that α1A-, α1B-, and α2A-AR proteins were expressed in large, medium, and small size neurons in normal DRG, and significantly increased in all size neurons 14 days after CCI. α1D- and α2C-AR was also expressed in all size neurons in normal DRG. However, α1D-AR was significantly increased and α2C-AR was decreased in small size neurons 14 days post CCI. α2B-AR neurons were not detectable in normal and CCI DRG. Co-expression of α1A- and α2A-AR in the same neuron was observed in normal DRG and increased post CCI. Collectively, these results indicated that there is distinct distribution of α-AR subtypes in DRG neurons, and the distribution and levels of expression of α-AR subtypes change differently after CCI. The up-regulation of α-AR subtypes in DRG neurons may play an important role in the process of generating and transmitting neuropathic pain.

The effects of 2 µg and 4 µg doses of dexmedetomidine in combination with intrathecal hyperbaric bupivacaine on spinal anesthesia and its postoperative analgesic characteristics

OBJECTIVE

To compare the postoperative analgesic characteristics and side effects of two different doses of intrathecal dexmedetomidine in combination with hyperbaric bupivacaine, and to evaluate the effects of these combinations on spinal anesthesia.

METHODS

After obtaining approval from the local ethics committee, 60 male patients who were undergoing inguinal surgery and were classified as American Society of Anesthesiologists physical status class I were included in the study. The present study was conducted in 2003 in a military hospital with a capacity of 100 beds. The patients were randomly assigned to three groups of 20 patients: group 1, 0.5 mL saline added to 3 mL (15 mg) hyperbaric bupivacaine; and groups 2 and 3, 2 µg dexmedetomidine and 4 µg dexmedetomidine added to 3 mL (15 mg) hyperbaric bupivacaine, respectively. Medications were administered by intrathecal injection in a total volume of 3.5 mL. The postoperative analgesic characteristics, effects on spinal anesthesia and side effects were recorded.

RESULTS

Demographic characteristics were similar among the groups. The mean (±SD) time to onset of pain was 220.75±112.7 min in group 1, 371.5±223.5 min in group 2 and 1042.50±366.78 min in group 3. Time to first pain sensation in group 3 was significantly longer than that in groups 1 and 2 (P<0.001).

CONCLUSION

Two different doses of dexmedetomidine, an α2-adrenoceptor agonist with analgesic effects, resulted in an increased duration of analgesia and efficacy, decreased postoperative analgesic use and was associated with no notable adverse effects.

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

Dexmedetomidine was initially approved for clinical use as a sedative. Its development in pain management has been limited. Dexmedetomidine has analgesic effects and analgesic-sparing properties, especially for patients with obstructed airways. Mixing dexmedetomidine with local anesthetics is a promising new avenue to enhance local anesthetics' effectiveness. Peripheral, spinal and supraspinal α(2A)-ARs are responsible for the analgesic function of dexmedetomidine. Animal studies have shown that antinociceptive synergism results from co-application of dexmedetomidine and opioids or local anesthetics. Dexmedetomidine has potential adverse effects such as hypotension and bradycardia. Therefore, dexmedetomidine is contraindicated for patients suffering from bradycardia or using β-adrenergic antagonists. Clinical trials of dexmedetomidine in chronic pain or hyperalgesia are lack.

Endogenous opiates and behavior: 2010

This paper is the thirty-third consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2010 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration (Section 16); and immunological responses (Section 17).