Antinociception by epidural and systemic alpha(2)-adrenoceptor agonists and their binding affinity in rat spinal cord and brain

The optimal dose of dexmedetomidine as a 0.59% ropivacaine adjuvant for epidural anesthesia in great saphenous varicose vein surgery, based on hemodynamics and anesthesia efficacy: a randomized, controlled, double-blind clinical trial

Objective

This study aimed to explore the optimal dose of dexmedetomidine as a 0.59% ropivacaine adjuvant for epidural anesthesia on perioperative hemodynamics and anesthesia efficacy in patients undergoing great saphenous varicose vein surgery.

Methods

A total of 90 patients were randomly divided into three groups: 0.25 μg/kg dexmedetomidine combined with 0.59% ropivacaine epidural infusion group (ED1 group), 0.5 μg/kg dexmedetomidine combined with 0.59% ropivacaine epidural infusion group (ED2 group), and 0.75 μg/kg dexmedetomidine combined with 0.59% ropivacaine epidural infusion group (ED3 group). Hemodynamics, anesthesia efficiency, and adverse reactions were recorded.

Main results

Compared with the ED1 group, the ED2 group had lower systolic blood pressure at T1-3 (T1, 95%CIs, 6.52-21.93, p < 0.001; T2, 95%CIs, 2.88-18.21, p = 0.004; T3, 95%CIs, 0.49-18.17, p = 0.035), and the diastolic blood pressure at T1-2 was decreased (T1, 95%CIs, 4.55-14.36, p < 0.001; T2, 95%CIs, 0.37-12.17, p = 0.033). Compared with the ED2 group, the ED3 group had higher systolic blood pressure at T1-2 (T1, 95%CIs, 5.90-21.46, p < 0.001; T2, 95%CIs, 2.07-17.55, p = 0.008) and higher diastolic blood pressure at T1-3 (T1, 95%CIs, 2.91-12.81, p = 0.001; T2, 95%CIs, 1.32-13.23, p = 0.011; T3, 95%CIs, 0.14-11.52, p = 0.043). Compared with the ED2 group, the heart rate was significantly decreased at T1-4 in the ED3 group (T1, 95%CIs, 2.25-15.72, p = 0.005; T2, 95%CIs, 2.35-13.82, p = 0.003; T3, 95%CIs, 0.50-9.79, p = 0.025; T4, 95%CIs, 1.46-10.36, p = 0.005). The myocardial oxygen consumption in all three groups was significantly decreased at each time point compared to T0 (p < 0.05 or < 0.001), and no significant between-group differences were detected (P>0.05). Compared with the ED1 group, the anesthesia efficiency of ED2 and ED3 groups was markedly enhanced, but the risk of bradycardia in ED2 and ED3 groups was dramatically increased (6 of 28 [21.4%] vs. 14 of 30 [46.7%] and 14 of 27 [51.9%], p = 0.023), one patient in the ED3 group experienced difficulty urinating, and remaining adverse reactions were mild in all three groups.

Conclusion

A measure of 0.5 μg/kg dexmedetomidine is the optimal dose as a 0.59% ropivacaine adjuvant for epidural anesthesia in patients undergoing great saphenous varicose vein surgery.

Clinical trial registration

http://www.chictr.org.cn/, registration number: ChiCTR2200060619.

Whole-course application of dexmedetomidine as an adjuvant to spinal-epidural anesthesia for cesarean section: A randomized, controlled trial

Background

Dexmedetomidine is known to prolong the analgesic duration of spinal anesthesia, but it can be challenging to achieve further extension without opioids. Therefore, this study aimed to investigate a novel analgesic strategy using dexmedetomidine as an adjuvant to spinal-epidural anesthesia for elective cesarean surgery.

Methods

The study was a randomized, double-blind, controlled trial conducted at a single center. Sixty parturients who underwent elective cesarean were randomly assigned to either group C or group D. Group D received an intrathecal injection of 12.5 mg ropivacaine and 5 μg dexmedetomidine followed by continuous epidural patient-controlled analgesia (PCA) infusion with a total volume of 100 ml, containing 0.2 % ropivacaine and 0.5 μg/kg dexmedetomidine. Group C received an intrathecal injection of 12.5 mg ropivacaine with an equivalent saline placebo followed by a similar PCA infusion, containing 0.2 % ropivacaine and an equivalent saline placebo.

Results

The primary outcome was visual analog scale score on movement at 24 h after surgery. The results showed that the rest and motion pain scores in group D were significantly lower than those in group C at 6 h, 12 h, and 24 h after surgery (P < 0.05), with the differences at 24 h were 5.0 (5.0, 5.0)in group D versus 5.0 (5.0, 6.0) in group C (P = 0.04). Additionally, the time to the first PCA in group D was significantly longer than that in group C (P < 0.05), as well as the time of sensory and motor recovery.

Conclusions

Whole-course application of dexmedetomidine as an adjuvant to spinal-epidural anesthesia could effectively extend the analgesic duration of ropivacaine to 24 h following elective cesarean surgery.

Analgesic Efficacy of Adjuvant Medications in the Pediatric Caudal Block for Infraumbilical Surgery: A Network Meta-Analysis of Randomized Controlled Trials

Various adjuvants are added to local anesthetics in caudal block to improve analgesia. The comparative analgesic effectiveness and relative rankings of these adjuvants are unknown. This network meta-analysis (NMA) sought to evaluate the comparative analgesic efficacy and relative ranking of caudal adjuvants added to local anesthetics (versus local anesthetics alone) in pediatric infra-umbilical surgery. We searched the United States National Library of Medicine database (MEDLINE), PubMed, and Excerpta Medica database (Embase) for randomized controlled trials (RCTs) comparing caudal adjuvants (clonidine, dexmedetomidine, ketamine, magnesium, morphine, fentanyl, tramadol, dexamethasone, and neostigmine) among themselves, or to no adjuvant (control). We performed a frequentist NMA and employed Cochrane's 'Risk of Bias' tool to evaluate study quality. We chose the duration of analgesia (defined as 'the time from caudal injection to the time of rescue analgesia') as our primary outcome. We also assessed the number of analgesic dose administrations and total dose of acetaminophen within 24 h. The duration of analgesia [87 randomized control trials (RCTs), 5285 patients] was most prolonged by neostigmine [mean difference: 513 min, (95% confidence interval, CI: 402, 625)]. Dexmedetomidine reduced the frequency of analgesic dose administrations within 24 h [29 RCTs, 1765 patients; -1.2 dose (95% CI: -1.6, -0.9)] and the total dose of acetaminophen within 24 h [18 RCTs, 1156 patients; -350 mg (95% CI: -467, -232)] the most.  Among caudal adjuvants, neostigmine (moderate certainty), tramadol (low certainty), and dexmedetomidine (low certainty) prolonged the duration of analgesia the most. Dexmedetomidine also reduced the analgesic frequency and consumption more than other caudal adjuvants (moderate certainty).

Addition of Clonidine or Dexmedetomidine With Bupivacaine to Prolong Caudal Analgesia in Children Undergoing Infraumbilical Surgery

Introduction

Clonidine, a selective α2 adrenergic receptor agonist, combined with caudally administered bupivacaine, is frequently used in children to prolong the duration of postoperative analgesia following infraumbilical surgery. On the other hand, dexmedetomidine is highly selective and has a greater affinity toward α2 adrenergic receptors, especially toward its α2a subtype, accountable for more analgesic and hypnotic effects than clonidine.

Aims and objectives

We designed a prospective, double-blinded, randomized controlled trial to compare the analgesic efficacy and adverse effects of clonidine and dexmedetomidine when combined with bupivacaine for caudal analgesia in children undergoing infraumbilical surgeries.

Materials and methods

A total of 60 children aged one to eight years were randomly assigned into two different groups in a double-blinded manner. Following induction of general anesthesia, every patient received a single dose of caudal bupivacaine 0.25% (0.75 ml/kg) mixed with either clonidine (1 µ/kg) in normal saline or dexmedetomidine (1 µ/kg) in normal saline. We noted the hemodynamic variables and postoperative sedation scores. Duration and quality of postoperative analgesia and the number of rescue analgesic drug doses required were recorded during the first 24 hours postoperatively. We also observed the patients for any adverse effects to the study drugs.

Result

Adding dexmedetomidine to caudally administered bupivacaine significantly increased the duration of analgesia (15 ± 0.78 hours) and decreased the need for rescue drug doses than the addition of clonidine to bupivacaine (9.63 ± 1.95 hours) in children undergoing infraumbilical surgeries. Incidences of hemodynamic changes or other side effects were comparable between patients of two groups.

Conclusion

The addition of dexmedetomidine to caudally administered bupivacaine in children undergoing infraumbilical surgeries may provide a longer duration of analgesia than the addition of clonidine, with less requirement of rescue analgesic doses and without any significant differences in the hemodynamic parameters or other side effects.

Dexmedetomidine versus magnesium sulfate as an adjuvant to local anesthetics in spinal anesthesia: a meta-analysis of randomized controlled trials

Objective

To compare the efficacy of dexmedetomidine and magnesium sulfate as an adjuvant to local anesthetics in spinal anesthesia.

Methods

A search of PubMed, Medline, Embase, the Cochrane Library, and Google Scholar was performed. Randomized controlled trials comparing the efficacy of dexmedetomidine and magnesium sulfate as a local anesthetic adjuvant in spinal anesthesia were identified. The primary outcome was sensory block duration. The mean difference (MD) or odds ratio along with the 95% confidence interval (CI) was used to analyze the outcomes.

Results

Six studies involving 360 patients were included. Intrathecal dexmedetomidine was associated with a significantly longer sensory block duration (MD = −73.62; 95% CI = −101.09 to −46.15), faster onsets of sensory blockade and motor blockade, and a longer motor block duration than intrathecal magnesium sulfate. There was no significant difference between the regarding the rates of hypotension, bradycardia, shivering, and postoperative nausea and vomiting between the groups.

Conclusions

Dexmedetomidine is superior to magnesium sulfate as an adjuvant to local anesthetics in spinal anesthesia because of its more rapid onset and longer duration of spinal block without significant adverse effects.

The Effectiveness of Caudal Block with Low Doses of Dexmedetomidine and Pethidine in Transrectal Prostate Biopsy: Preliminary Results

PURPOSE

To evaluate the effectiveness of caudal block (CB) using dexmedetomidine and pethidine instead of local anesthesia (LA) for prostate needle biopsy and the effect of CB on urinary retention.

MATERIAL AND METHODS

A transrectal ultrasound-guided prostate needle biopsy (TRUS-Bx) was performed on 68 patients with a mean age of 65 ± 2.18 years. CB with a combination of dexmedetomidine and pethidine without LA was administered to the patients. The pain levels of the patients were determined using numeric rating scale (NRS) scores to evaluate the effectiveness of CB. Preoperative and postoperative postvoid residual urine volumes (PRUV) were also calculated.

RESULTS

The CB success rate was 93.15%. The NRS scores were 0.79 ± 0.19 and 0.89 ± 0.22 during probe entry and manipulation and biopsy, respectively, without any significant differences between them (p = 0.382). The mean PRUVs before and after biopsy did not differ significantly (41 ± 15.6 vs. 71.93 ± 22.3, p = 0.379). The degree of sedation, as assessed using the Ramsay scale, was 2 or 3 in all patients.

CONCLUSION

The combination of dexmedetomidine and pethidine for CB in TRUS-Bx provided quality analgesia for the patient and prevented the development of postoperative urinary retention.

Effect of Different Doses of Intrathecal Dexmedetomidine as an Adjuvant Combined With Hyperbaric Ropivacaine in Patients Undergoing Cesarean Section

Objective

In this study, we aim to investigate the effect of different doses of dexmedetomidine as an adjuvant to hyperbaric ropivacaine in spinal anesthesia for cesarean section.

Methods

Seventy-five parturients with American Society of Anesthesiologists (ASA) I or II were anesthetized with intrathecal ropivacaine (12.5 mg) alone (R group) or in combination with dexmedetomidine 3 μg (RD3 group) and 5 μg (RD5 group) to undergo a cesarean section. The anesthetic parameters, postoperative analgesia, stress responses and neonates outcomes were monitored.

Results

The onset time of sensory block to T10, T4, and peak level in the RD3 group and RD5 group were significantly shorter than those in the R group (p < 0.05). The time of the level of sensory block to descend two segments and to T10 in the RD3 group(57.28 ± 16.65 min, 3.87 ± 1.60 h) and RD5 group (71.92 ± 10.10 min, 3.99 ± 1.06 h) were longer than that in the R group (40.64 ± 12.06 min, 1.98 ± 1.01 h) (p < 0.05). The median time of motor blockade to both legs score 3 on the Bromage scale (B3B3) in the RD3 group and RD5 group was shorter than that in the R group (p < 0.001). The time of motor blockade recovery to both legs score 0 on the Bromage scale (B0B0) in the RD5 group (3.6 h) was longer than that in the R group (2 h) or RD3 group (2.2 h) (p < 0.001). Visceral traction response and abdominal muscle relaxation during the operation in the RD3 group and the RD5 group were better than that in the R group. The Visual Analogue Score (VAS) in the 12 h after the operation in the RD3 group (3.30 ± 1.17) and RD5 group (2.80 ± 0.87) was smaller than that in the R group (3.80 ± 1.47) (p < 0.05). The incidence of shivering in the RD3 group and RD5 group was significantly lower than that in the R group (p < 0.05). The postoperative concentrations of c-reactive protein (CRP), interleukin-6 (IL-6) and cortisol in the RD3 and RD5 groups were lower than that in the R group (p < 0.05).

Conclusion

3 µg intrathecal dexmedetomidine as an adjuvant to ropivacaine improved intraoperative somato-visceral sensory block characteristics and postoperative analgesia, alleviated shivering in parturients, and did not prolong the time of motor block or produce any side effects, which makes this dose appropriate for cesarean delivery.

Cinical Trial Registration

ChiCTR, identifier ChiCTR1800014454. Registered 15 January 2018, http://www.chictr.org.cn/edit.aspx?pid=24613&htm=4

Clinical effects of epidurally administered dexmedetomidine with or without lidocaine in sheep

BACKGROUND

The aims of this study were evaluate cardiopulmonary, sedative and antinociceptive effects of dexmedetomidine-lidocaine combination via lumbosacral epidural injection in sheep.

METHODS

Six Santa Inês breed sheep, 16±6 months old and weighing 42.2 ± 5.7 kg were used. Sheep were subjected to epidural anaesthesia with three treatments: L, lidocaine (1.2 mg/kg), D, dexmedetomidine (2.5 μg/kg) or DL, dexmedetomidine plus lidocaine (2.5 μg/kg + 1.2 mg/kg). Drugs were injected via pre-placed lumbosacral epidural catheters. Cardiopulmonary, arterial blood gases, electrolytes, degree of sedation and antinociceptive aspects were measured before drug administration (T0) and then at 15, 30, 60 and 120 min after drug injection (T15-T120) in all treatments and at T0 to T240 in DL.

RESULTS

There were significantly increases in PaCO₂ at times T60 and T120 in D, and at T30-T120 in DL, compared to baseline. The antinociceptive effects were observed up to 240 min in DL and 60 min in L, and were more intense in DL. Treatment D provided analgesia only in the perineal region, and only at T15.

CONCLUSION

The combination of DEX with lidocaine produced similar cardiopulmonary changes compared with either drug alone, but with greater and more prolonged antinociceptive effects.

Comparative study between intrathecal dexmedetomidine and intrathecal magnesium sulfate for the prevention of post-spinal anaesthesia shivering in uroscopic surgery; (RCT)

Background

Hypothermia and shivering are common complications after spinal anaesthesia, especially after uroscopic procedures in which large amounts of cold intraluminal irrigation fluids are used. Magnesium sulfate and dexmedetomidine are the most effective adjuvants with the least side effects. The aim of this study was to compare the effects of intrathecal dexmedetomidine versus intrathecal magnesium sulfate on the prevention of post-spinal anaesthesia shivering.

Methods

This prospective randomized, double-blinded controlled study included 105 patients who were scheduled for uroscopic surgery at the Kasr El-Aini Hospital. The patients were randomly allocated into three groups. Group C (n = 35) received 2.5 ml of hyperbaric bupivacaine 0.5% (12.5 mg) + 0.5 ml of normal saline, Group M (n = 35) received 2.5 ml of hyperbaric bupivacaine 0.5% (12.5 mg) + 25 mg of magnesium sulfate in 0.5 ml saline, and Group D (n = 35) received 2.5 ml of hyperbaric bupivacaine 0.5% (12.5 mg) + 5 μg of dexmedetomidine in 0.5 ml saline. The primary outcomes were the incidence and intensity of shivering. The secondary outcomes were the incidence of hypothermia, sedation, the use of meperidine to control shivering and complications.

Results

Group C had significantly higher proportions of patients who developed shivering (21), developed grade IV shivering (20) and required meperidine (21) to treat shivering than group M (8,5,5) and group D (5,3,6), which were comparable to each other.

The time between block administration and meperidine administration was similar among the three groups. Hypothermia did not occur in any of the patients.

The three groups were comparable regarding the occurrence of nausea, vomiting, bradycardia and hypotension. All the patients in group C, 32 patients in group M and 33 patients in group D had a sedation score of 2. Three patients in group M and 2 patients in group D had a sedation score of 3.

Conclusions

Intrathecal injections of both dexmedetomidine and magnesium sulfate were effective in reducing the incidence of post-spinal anaesthesia shivering. Therefore, we encourage the use of magnesium sulfate, as it is more physiologically available, more readily available in most operating theatres and much less expensive than dexmedetomidine.

Trial registration

Clinical trial registration ID: Pan African Clinical Trial Registry (PACTR) Trial Number PACTR201801003001727; January 2018, “retrospectively registered”.

Monoamines as Drug Targets in Chronic Pain: Focusing on Neuropathic Pain

Monoamines are involved in regulating the endogenous pain system and indeed, peripheral and central monoaminergic dysfunction has been demonstrated in certain types of pain, particularly in neuropathic pain. Accordingly, drugs that modulate the monaminergic system and that were originally designed to treat depression are now considered to be first line treatments for certain types of neuropathic pain (e.g., serotonin and noradrenaline (and also dopamine) reuptake inhibitors). The analgesia induced by these drugs seems to be mediated by inhibiting the reuptake of these monoamines, thereby reinforcing the descending inhibitory pain pathways. Hence, it is of particular interest to study the monoaminergic mechanisms involved in the development and maintenance of chronic pain. Other analgesic drugs may also be used in combination with monoamines to facilitate descending pain inhibition (e.g., gabapentinoids and opioids) and such combinations are often also used to alleviate certain types of chronic pain. By contrast, while NSAIDs are thought to influence the monoaminergic system, they just produce consistent analgesia in inflammatory pain. Thus, in this review we will provide preclinical and clinical evidence of the role of monoamines in the modulation of chronic pain, reviewing how this system is implicated in the analgesic mechanism of action of antidepressants, gabapentinoids, atypical opioids, NSAIDs and histaminergic drugs.

Epidural dexmedetomidine infusion for perioperative analgesia in patients undergoing abdominal cancer surgery: randomized trial

Objective

To assess the postoperative analgesic efficacy of epidural dexmedetomidine added to bupivacaine infusion for patients undergoing major abdominal cancer surgery.

Methods

Patients scheduled for major upper abdominal cancer surgery were allocated to group bupivacaine (n =32), in which patients received epidural bupivacaine infusion (6 mL/h bupivacaine 0.1%) for 48 hours postoperatively, or group bupivacaine + dexmedetomidine (n=32), in which patients received epidural dexmedetomidine added to bupivacaine infusion (6 mL/h of bupivacaine 0.1% + dexmedetomidine, 0.5 µg/mL) for 48 hours postoperatively. The cumulative morphine consumption, the time to first analgesic request, and the VAS pain score were evaluated.

Results

The cumulative morphine consumption was significantly reduced in group bupivacaine + dexmedetomidine compared with group bupivacaine: mean ± SD of 10.40±5.16 mg vs 23.23±8.37 mg with an estimated difference (95% CI) of −12.83 (−16.43, −9.24), (P<0.001). The time to the first analgesic demand was significantly delayed in group bupivacaine + dexmedetomidine compared with group bupivacaine: median (IQR) of 6 (1.75, 8.25) h vs 1 (0, 4)h, (P<0.001). The mean collapsed over time of overall VAS pain scores at rest and movement was significantly reduced in group bupivacaine + dexmedetomidine compared with group bupivacaine : mean ± SE of 1.6±0.08 vs 2.38±0.08 with an estimated difference (95% CI) of −0.8 (−1, −0.86), (P<0.001), and mean ± SE of 2.17±0.07 vs 3.25±0.07 with an estimated difference (95% CI) of −1.1 (−1.27, – 0.89), (P<0.001), respectively.

Conclusion

Epidural infusion of dexmedetomidine added to bupivacaine for patients undergoing major abdominal cancer surgery significantly reduced morphine consumption, delayed time to first analgesic supplementation, and decreased pain intensity during the first 48 hours postoperatively without harmful derangement on hemodynamics.

A Comparative Study of Dexmedetomidine and Clonidine as an Adjuvant to Intrathecal Bupivacaine in Lower Abdominal Surgeries

CONTEXT

Spinal block is the first choice for lower abdominal surgeries. Bupivacaine is the most common local anesthetic used but has a shorter duration of action. Many adjuvants have been used to improve the quality of analgesia till postoperative period. In this study, we used α2-agonists.

AIMS

The aim of this study is to compare the effects of intrathecal dexmedetomidine and clonidine as adjuvants to hyperbaric bupivacaine with respect to onset and duration of sensory and motor blockade duration of analgesia and incidence of side effects.

SETTINGS AND DESIGN

This was a prospective randomized double-blind study.

SUBJECTS AND METHODS

One hundred and fifty patients of physical status American Society of Anesthesiologists Classes I and II were randomly divided into Groups B, C, and D each administered with bupivacaine with normal saline, clonidine, and dexmedetomidine, respectively.

STATISTICAL ANALYSIS USED

Data were entered into Microsoft excel data sheet. Analysis software used in this study was SPSS 22 version IBM. Categorical data were represented in the form of frequencies and proportions. Chi-square test was the test of significance. Continuous data were represented as mean and standard deviation. Independent t-test was used for mean difference between two groups. P < 0.05 was statistically significant.

RESULTS

Mean sensory onset in Group B was 2.8 ± 0.7 min, in Group C was 1.4 ± 0.5 min, and in Group D was 1.2 ± 0.4 min. Mean sensory regression by two segments in Group B was 78.5 ± 9.9 min, in Group C was 136.7 ± 10.7 min, and in Group D was 136.4 ± 11.7 min.

CONCLUSIONS

α2-agonists with hyperbaric bupivacaine intrathecally have a faster onset of both motor and sensory block. It also prolongs the duration of analgesia.

Stimulation of alpha2-adrenergic receptors impairs influenza virus infection

Influenza A viruses cause seasonal epidemics and occasional pandemics. The emergence of viruses resistant to neuraminidase (NA) inhibitors and M2 ion channel inhibitors underlines the need for alternate anti-influenza drugs with novel mechanisms of action. Here, we report the discovery of a host factor as a potential target of anti-influenza drugs. By using cell-based virus replication screening of a chemical library and several additional assays, we identified clonidine as a new anti-influenza agent in vitro. We found that clonidine, which is an agonist of the alpha2-adrenergic receptor (α2-AR), has an inhibitory effect on the replication of various influenza virus strains. α2-AR is a Gi-type G protein-coupled receptor that reduces intracellular cyclic AMP (cAMP) levels. In-depth analysis showed that stimulation of α2-ARs leads to impairment of influenza virus replication and that α2-AR agonists inhibit the virus assembly step, likely via a cAMP-mediated pathway. Although clonidine administration did not reduce lung virus titers or prevent body weight loss, it did suppress lung edema and improve survival in a murine lethal infection model. Clonidine may thus protect against lung damage caused by influenza virus infection. Our results identify α2-AR-mediated signaling as a key pathway to exploit in the development of anti-influenza agents.

Effects of intrathecal dexmedetomidine as an additive to low-dose bupivacaine in patients undergoing transurethral resection of prostate

Background and Aims:

In patients undergoing transurethral resection of prostate (TURP), it is vital to restrict the level of block to T₁₀dermatome during spinal anaesthesia. Low-dose bupivacaine causes minimum haemodynamic alterations, but may provide insufficient surgical anaesthesia. Dexmedetomidine, a selective α₂-adrenoreceptor agonist, is a potent anti-nociceptive agent when given intrathecally. The aim of this study was to compare the adjuvant effects of intrathecal dexmedetomidine with low-dose bupivacaine spinal anaesthesia versus a higher dose of bupivacaine in patients undergoing TURP.

Methods:

The study was designed as a prospective, double-blind, randomised trial that included sixty patients of American Society of Anesthesiologists Grade I–III scheduled for TURP. They were allocated into two groups: Group I receiving only hyperbaric bupivacaine intrathecally and Group II receiving dexmedetomidine with low dose bupivacaine. The time to regression of two dermatomes from the peak sensory block level was the primary outcome of the study.

Results:

With comparable baseline and demographic attributes, both groups had similar peak sensory block levels (T₉). Patients in Group II had quicker onset with the time to reach T₁₀being faster (10.72 ± 3.50 vs. 12.72 ± 3.90 min, P = 0.041), longer duration of motor block (200 ± 18.23 vs. 190 ± 10.15 min, P = 0.011) and increased time to first analgesic requirement (300 ± 25.30 vs. 220 ± 15.12 min, P = 0.0001).

Conclusion:

Intrathecal dexmedetomidine with low-dose bupivacaine provides faster onset, prolonged sensory and motor block and reduced rescue analgesic requirement in patients undergoing TURP.

Comparison of dexmedetomidine and fentanyl as local anesthetic adjuvants in spinal anesthesia: a systematic review and meta-analysis of randomized controlled trials

Purpose

To compare the effects of dexmedetomidine (Dex) and fentanyl as adjuvants to local anesthetics in spinal anesthesia.

Methods

Two researchers independently searched the PUBMED, EMBASE, Cochrane library, and CBM for randomized controlled trials comparing the effects of Dex and fentanyl as adjuvants to local anesthetics for intrathecal injection.

Results

A total of 639 patients from nine studies were included in this meta-analysis. The results showed that Dex resulted in statistically significant longer duration of stable sensory block (mean difference [MD] =27.12; 95% confidence interval [CI] [9.89, 44.34], P<0.01, I²=97%), sensory block (standardized mean difference [SMD] =3.81; 95% CI [2.35, 5.27], P<0.01, I²=97%), motor block (SMD =3.64; 95% CI [2.19, 5.08], P<0.01, I²=97%), and pain free period (SMD =2.98; 95% CI [1.69, 4.27], P<0.01, I²=96%); reducing the incidence of pruritus (relative risk [RR] =0.15; 95% CI [0.06, 0.39], P<0.01, I²=0%) compared with fentanyl. However, the onset of sensory and motor block, the time to peak sensory level, and the incidence of hypotension and bradycardia, and the side effects (nausea, vomiting, shivering and respiratory depression) were not significantly different between Dex and fentanyl.

Conclusion

Compared to fentanyl, Dex as local anesthetics adjuvant in spinal anesthesia prolonged the duration of spinal anesthesia, improved postoperative analgesia, reduced the incidence of pruritus, and did not increase the incidence of hypotension and bradycardia.

The activation of α2-adrenergic receptor in the spinal cord lowers sepsis-induced mortality

The effect of clonidine administered intrathecally (i.t.) on the mortality and the blood glucose level induced by sepsis was examined in mice. To produce sepsis, the mixture of D-galactosamine (GaLN; 0.6 g/10 ml)/lipopolysaccharide (LPS; 27 µg/27 µl) was treated intraperitoneally (i.p.). The i.t. pretreatment with clonidine (5 µg/5 µl) increased the blood glucose level and attenuated mortality induced by sepsis in a dose-dependent manner. The i.t. post-treatment with clonidine up to 3 h caused an elevation of the blood glucose level and protected sepsis-induced mortality, whereas clonidine post-treated at 6, 9, or 12 h did not affect. The pre-treatment with oral D-glucose for 30 min prior to i.t. post-treatment (6 h) with clonidine did not rescue sepsis-induced mortality. In addition, i.t. pretreatment with pertussis toxin (PTX) reduced clonidine-induced protection against mortality and clonidine-induced hyperglycemia, suggesting that protective effect against sepsis-induced mortality seems to be mediated via activating PTX-sensitive G-proteins in the spinal cord. Moreover, pretreatment with clonidine attenuated the plasma tumor necrosis factor α (TNF-α) induced by sepsis. Clonidine administered i.t. or i.p. increased p-AMPKα1 and p-AMPKα2, but decreased p-Tyk2 and p-mTOR levels in both control and sepsis groups, suggesting that the up-regulations of p-AMPKα1 and p-AMPKα2, or down-regulations of p-mTOR and p-Tyk2 may play critical roles for the protective effect of clonidine against sepsis-induced mortality.

Epidural Dexmedetomidine Reduces the Requirement of Propofol during Total Intravenous Anaesthesia and Improves Analgesia after Surgery in Patients undergoing Open Thoracic Surgery

The aim of this study was to assess the systemic and analgesic effects of epidural dexmedetomidine in thoracic epidural anaesthesia (TEA) combined with total intravenous anaesthesia during thoracic surgery. Seventy-one patients undergoing open thoracotomy were included in this study and randomly divided into three groups: Control group (Group C): patients received TEA with levobupivacaine alone and were intravenously infused with saline; Epidural group (Group E): patients received TEA with levobupivacaine and dexmedetomidine, and were intravenously infused with saline; Intravenous group (group V): patients received TEA with levobupivacaine alone and were intravenously infused with dexmedetomidine. The doses of propofol used in the induction and maintenance of general anaesthesia, cardiovascular response, dose and first time of postoperative analgesia and verbal rating scale were recorded. The induction and maintenance were significantly lower in the Groups E and V. Verbal rating scale and postoperative analgesic requirements were significantly lower in Group E than in Groups C and V. Patients in Group C had more severe cardiovascular responses, as compared with Groups E and V. Epidural administration of dexmedetomidine reduced the induction and maintenance of propofol, and inhibited the cardiovascular response after intubation and extubation. Moreover, epidural dexmedetomidine provided better analgesia after open thoracotomy.

Comparison of Dexmedetomidine and Fentanyl as an Adjuvant to Ropivacaine for Postoperative Epidural Analgesia in Pediatric Orthopedic Surgery

PURPOSE

Opioids are commonly used as an epidural adjuvant to local anesthetics, but are associated with potentially serious side effects, such as respiratory depression. The aim of this study was to compare the efficacy and safety of dexmedetomidine with that of fentanyl as an adjuvant to epidural ropivacaine in pediatric orthopedic surgery.

MATERIALS AND METHODS

This study enrolled 60 children (3-12 years old) scheduled for orthopedic surgery of the lower extremities and lumbar epidural patient-controlled analgesia (PCA). Children received either dexmedetomidine (1 μg/kg) or fentanyl (1 μg/kg) along with 0.2% ropivacaine (0.2 mL/kg) via an epidural catheter at 30 minutes before the end of surgery. Postoperatively, the children were observed for ropivacaine consumption via epidural PCA, postoperative pain intensity, need for rescue analgesics, emergence agitation, and other adverse effects.

RESULTS

The mean dose of bolus epidural ropivacaine was significantly lower within the first 6 h after surgery in the dexmedetomidine group, compared with the fentanyl group (0.029±0.030 mg/kg/h vs. 0.053±0.039 mg/kg/h, p=0.012). The median pain score at postoperative 6 h was also lower in the dexmedetomidine group, compared to the fentanyl group [0 (0-1.0) vs. 1.0 (0-3.0), p=0.039]. However, there was no difference in the need for rescue analgesia throughout the study period between groups.

CONCLUSION

The use of dexmedetomidine as an epidural adjuvant had a significantly greater analgesic and local anesthetic-sparing effect, compared to fentanyl, in the early postoperative period in children undergoing major orthopedic lower extremity surgery.

Noradrenergic inhibition of spinal hyperexcitation elicited by cutaneous cold stimuli in rats with oxaliplatin-induced allodynia: electrophysiological and behavioral assessments

We investigated the spinal action of noradrenaline on cold-elicited hyperexcitation detected in dorsal horn neurons of rats with allodynia induced by an oxaliplatin (6 mg/kg, i.p.) injection. In vivo extracellular recordings from the spinal dorsal horn showed that wide dynamic range neurons responded to cutaneous acetone (10 μl) stimulation in normal rats, and cold-elicited firings in oxaliplatin-administered rats were increased with a longer duration, correlated with behavioral responses. These responses were significantly attenuated by spinal administration (50 μM) of noradrenaline or its agonists, clonidine (α2), phenylephrine (α1) and isoprenaline (β), in descending order of efficacy. Thus, the inhibitory effect of noradrenaline on spinal oxaliplatin-induced cold hyperexcitation is mediated mainly by activation of α2- and/or α1-adrenoceptors.

Optimal Dose of Intrathecal Dexmedetomidine in Lower Abdominal Surgeries in Average Indian Adult

BACKGROUND

Dexmedetomidine, a selective alpha2 adrenoceptor agonist, has been used as adjuvant to spinal anaesthesia.

AIM

To find out the optimum dose of dexmedetomidine to be used in lower abdomen surgery intrathecally.

MATERIALS AND METHODS

This was a randomized, controlled, double blinded study which included adult ASA I and II patients. They were allocated into five groups (n=20). Patients allergic to drugs to be used in the study and those with co-existing neurological disorders, coagulopathies, cardiac diseases, obesity and hypertension were excluded. Groups were designed as 2.5ml hyperbaric bupivacaine with 0.5ml saline (Control) or 0.5ml dexmedetomidine: 5mcg (D1), 10mcg (D2), 15 mcg (D3) and 20mcg (D4). Data were collected for 10 point VRS for pain, Bromage motor block, Ramsay sedation score, haemodynamics, time of first rescue analgesia (TRA) and any adverse effects and groups were analysed using one way analysis of variance (ANOVA) by SPSS16.0 (p-value <0.05 significant).

RESULTS

The mean duration of analgesia and need of first rescue analgesics are 201.5±29.1 mins in control group but in D1 group 259.1±15.2 mins, D2 310.7±48.1mins, D3 540.3±51.6 mins and D4 702.4±52 mins. p=0.003. The mean highest VRS score along with analgesic requirements were significantly reduced in dexemeditomidine groups, but D3 and D4 had hypotension which needed correction.

CONCLUSION

Weighing the prolongation of anesthesia and analgesia and side effects we conclude that 10 mcg of dexmedetomidine is optimum intrathecal dose.

Epidural Co-Administration of Dexmedetomidine and Levobupivacaine Improves the Gastrointestinal Motility Function after Colonic Resection in Comparison to Co-Administration of Morphine and Levobupivacaine

Gastrointestinal motility may be impaired after intestinal surgery. Epidural morphine is effective in controlling postoperative pain, but can further reduce gastrointestinal motility. Here, we aimed to investigate the effects of epidural dexmedetomidine on gastrointestinal motility in patients undergoing colonic resection. Seventy-four patients undergoing colonic resection were enrolled in this clinical trial and allocated randomly to treatment with dexmedetomidine (D group) or morphine (M group). The D group received a loading dose epidural administration of 3 ml dexmedetomidine (0.5 μg kg(-1)) and then a continuous epidural administration of 80 μg dexmedetomidine in 150 ml levobupivacaine (0.125%) at 3 ml h(-1) for two days. The M group received a loading dose epidural administration of 3 ml morphine (0.03 mg kg(-1)) and then a continuous epidural administration of 4.5 mg morphine in 150 ml levobupivacaine at 3 ml h(-1) for two days. Verbal rating score (VRS), postoperative analgesic requirements, side effects related to analgesia, the time to postoperative first flatus (FFL) and first feces (FFE) were recorded. VRS and postoperative analgesic requirements were not significantly different between treatment groups. In contrast, the time to FFL and time to FFE were significant longer in M group in comparison to D group (P < 0.05). Moreover, patients in M group had a significantly higher incidence of nausea, vomiting, and pruritus (P < 0.05). No patients showed neurologic deficits in either group. In comparison to morphine, epidural dexmedetomidine is safe and beneficial for the recovery of gastrointestinal motility after colonic resection when used as an adjunct with levobupivacaine for postoperative pain control.

TRIAL REGISTRATION

Chinese Clinical Trial Registry ChiCTR-TRC-14004644.

Comparison of two different doses of intrathecal dexmedetomidine as adjuvant with isobaric ropivacaine in lower abdominal surgery

Background:

To augment the subarachnoid block utility, the efficacy of newer molecules as an adjuvant is investigated constantly. Considering the favorable profile of dexmedetomidine, it could have a potential role as an adjuvant to ropivacaine.

Aim:

We evaluated the efficacy of two different doses of dexmedetomidine as an adjuvant to isobaric ropivacaine, intrathecally.

Methods:

Ninety patients scheduled for lower abdominal surgery under spinal anesthesia were randomized into three groups to receive 2.5 ml of isobaric ropivacaine (0.75%, 7.5 mg/ml) added to 5 µg (10 µg/ml) or 10 µg (20 µg/ml) of dexmedetomidine or 0.5 ml of normal saline in group A, B or C, respectively. Block characteristics were compared as a primary outcome.

Statistical Analysis:

One-way analysis of variance test, Fisher's exact test/Chi-square test, whichever appropriate. A P < 0.05 was considered significant.

Results:

Time to achieve desired block was least in group B and maximum in group C. The sensory-motor blockade remained significantly prolonged in group B compared to other groups. Hemodynamic parameters remained stable in all three groups.

Conclusion:

Among the investigated doses, dexmedetomidine augments the efficacy of intrathecal ropivacaine in a dose-dependent manner, without any untoward side effects.

A comparative study of intrathecal clonidine and dexmedetomidine on characteristics of bupivacaine spinal block for lower limb surgeries

Introduction:

Intrathecal clonidine or dexmedetomidine has improved the quality of spinal anesthesia, this clinical study was undertaken to assess the behavior of intrathecal clonidine as an adjuvant to bupivacaine in augmenting sensory block in patients undergoing lower limb surgeries.

Materials and Methods:

We studied 150 patients, between 18 and 60 years of age, patients were randomly divided into three groups of 50 each Group B: 0.5% bupivacaine 15 mg + 0.5 ml normal saline Group C: 0.5% bupivacaine 15 mg + 50 μg clonidine Group D: 0.5% bupivacaine 15 mg + 5 μg dexmedetomidine. Onset and duration of sensory block and motor block, the highest level of sensory blockade, duration of analgesia, and side-effects were assessed.

Results:

The onset of motor block was faster in Group C and Group D as compared to Group B, The time to reach Bromage scale 3 was fastest in Group C followed by Group D P < 0.001. The duration of sensory, motor blockade and duration of analgesia was longer in Groups C and D as compared to Group B, longest in Group D followed by C and B. The time to regression time to S1 dermatome was. It was longest in Group D followed by Group C and then Group B. Intergroup comparison B to C, B to D and C to D was significant. Duration of analgesia was significantly prolonged in Group C and Group D (P < 0.001) with a mean duration of 309.6 ± 50.99 min in Group C and 336.8 ± 55.38 min in Group D as compared to 204.8 ± 16.81 min in Group B. Intergroup comparison B to C, B to D and Group C to D was significant. Duration was longest in Group D followed by Group C and then Group B.

Conclusion:

Supplementation of bupivacaine spinal block with a low dose of intrathecal dexmedetomidine (5 μg) or clonidine (50 μg) produces a significantly shorter onset of motor and sensory block and a significantly longer sensory and motor block than bupivacaine alone.

A comparative study between intrathecal dexmedetomidine and fentanyl as adjuvant to intrathecal bupivacaine in lower abdominal surgeries: A randomized trial

Context:

Spinal anesthesia is preferred choice of anesthesia in lower abdominal surgeries since long time. However problem with this is limited duration of action, so for long duration surgeries alternative are required. Dexmedetomidine is a highly selective alpha-2-adrenergic agonist has property to potentiate the action of local anesthetic used in spinal anesthesia. Fentanyl is an opioid and it has also the same property.

Aims:

To compare the efficacy, analgesic effects, and side-effects of dexmedetomidine and fentanyl as adjuvant to bupivacaine for lower abdominal surgery.

Settings and Design:

The type of this study was double-blind randomized trial.

Subjects and Methods:

A total of 80 patients were randomly allocated in two Group D and Group F. Group D were injected injection bupivacaine 0.5% heavy × 3.0 ml + 0.5 ml of preservative free normal saline containing 5 μg dexmedetomidine. Group F were received injection bupivacaine 0.5% heavy × 3.0 ml + 0.5 ml fentanyl equivalent to 25 μg.

Statistical Analysis Used:

The statistical analysis was performed using SPSS (Statistical Package for Social Sciences) version 15.0 statistical analysis software.

Results:

The results show that highest sensitivity level of T6 and T8 was achieved by higher proportion of subjects from Group D when compared to Group F and sensitivity level T7 was achieved by higher proportion of subjects of Group F when compared to Group D. Duration of analgesic properties was significantly higher in Group D when compared to Group F.

Conclusion:

The findings in the present study suggested that intrathecal adjuvant use of dexmedetomidine as compared to fentanyl provides a longer sensory and motor blockade and also prolongs the postoperative analgesic effect.

Evaluation of Efficacy of Epidural Clonidine with 0.5% Bupivacaine for Postoperative Analgesia for Orthopaedic Lower Limb Surgeries

OBJECTIVE

The objective of this study is to evaluate the efficacy of epidural clonidine in intra and postoperative analgesia, the level of sedation caused by clonidine and monitor its side effects.

MATERIALS AND METHODS

Forty patients of ASA1 & ASA2 scheduled for lower limb orthopaediac surgeries were chosen for the study. Study group received 50μg of clonidine diluted to 1ml along with first dose of epidural injection and Control group received 1ml of normal saline along with first dose of epidural. Intra and postoperative vitals, verbal pain rating scale (VRS), sedation score and number of rescue anlgesics required postoperatively were noted. Patients received rescue analgesic when VRS was 1.

RESULTS

Addition of clonidine to bupivacaine definitely improves the quality of analgesia by reducing the overall pain score, prolonging the duration of the time of first rescue analgesia and causing reduction of total analgesic consumption in the postoperative period without any hemodynamic instability. Sedation may be beneficial during the intraoperative period.

CONCLUSION

Epidural clonidine produces long lasting, good quality analgesia with good level of sedation and with minimal side effects.

Topical clonidine for neuropathic pain

BACKGROUND

Clonidine is a presynaptic alpha-2-adrenergic receptor agonist used for many years to treat hypertension and other conditions, including chronic pain. Adverse events associated with systemic use of the drug have limited its application. Topical use of drugs is currently gaining interest, as it may limit adverse events without loss of analgesic efficacy. Topical clonidine (TC) formulations have been investigated recently in clinical trials.

OBJECTIVES

The objectives of this review were to assess the analgesic efficacy of TC for chronic neuropathic pain in adults and to assess the frequency of adverse events associated with clinical use of TC for chronic neuropathic pain.

SEARCH METHODS

We searched the Cochrane Register of Studies (CRS) Online (Cochrane Central Register of Controlled Trials (CENTRAL)), MEDLINE and EMBASE databases, reference lists of retrieved papers and trial registries, and we contacted experts in the field. We performed the most recent search on 17 September 2014.

SELECTION CRITERIA

We included randomised, double-blind studies of at least two weeks' duration comparing TC versus placebo or other active treatment in patients with chronic neuropathic pain.

DATA COLLECTION AND ANALYSIS

Two review authors extracted data from the studies and assessed bias. We planned three tiers of evidence analysis. The first tier was designed to analyse data meeting current best standards, by which studies reported the outcome of at least 50% pain intensity reduction over baseline (or its equivalent) without use of the last observation carried forward or other imputation method for dropouts, reported an intention-to-treat (ITT) analysis, lasted eight weeks or longer, had a parallel-group design and included at least 200 participants (preferably at least 400) in the comparison. The second tier was designed to use data from at least 200 participants but in cases in which one of the above conditions was not met. The third tier of evidence was assumed in other situations.

MAIN RESULTS

We included two studies in the review, with a total of 344 participants. Studies lasted 8 weeks and 12 weeks and compared TC versus placebo. 0.1%. TC was applied in gel form to the painful area two to three times daily.Studies included in this review were subject to potential bias and were classified as of moderate or low quality. One drug manufacturer supported both studies.We found no top-tier evidence for TC in neuropathic pain. Second-tier evidence indicated slight improvement after the drug was used in study participants with painful diabetic neuropathy (PDN). A greater number of participants in the TC group had at least 30% reduction in pain compared with placebo (risk ratio (RR) 1.35, 95% confidence interval (CI) 1.03 to 1.77; number needed to treat for an additional beneficial outcome (NNTB) 8.33, 95% CI 4.3 to 50). Third-tier evidence indicated that TC was no better than placebo for achieving at least 50% reduction in pain intensity and on the Patient Global Impression of Change Scale. The two included studies could be subject to significant bias. We found no studies that reported other neuropathic pain conditions.The rate of adverse events did not differ between groups, with the exception of a higher incidence of mild skin reactions in the placebo group, which should have no clinical significance.

AUTHORS' CONCLUSIONS

Limited evidence from a small number of studies of moderate to low quality suggests that TC may provide some benefit in peripheral diabetic neuropathy. The drug may be useful in situations for which no better treatment options are available because of lack of efficacy, contraindications or adverse events. Additional trials are needed to assess TC in other neuropathic pain conditions and to determine how patients who have a chance to respond to the drug should be selected for treatment.

Addition of epidural Clonidine enhances postoperative analgesia: A double-blind study in total knee- replacement surgeries

Background:

This study was undertaken to evaluate the analgesic effect of the combination of epidural Clonidine with Bupivacaine versus epidural Bupivacaine alone in patients undergone knee replacement surgery.

Materials and Methods:

A randomized double-blind design was used, and 60 adult patients (40-60 years) of ASA grade I and II scheduled for post-operative pain relief in total knee replacement surgeries by epidural Clonidine were studied. Patients received either an epidural Clonidine (1μg/kg) with Bupivacaine (1.5mg/kg) group CL (n=30) or Bupivacaine alone group CT (n=30) for Knee replacement surgeries. The pain score, blood pressure, heart rate, respiratory rate were measured at fixed times during the first 24 h after operation. Onset and duration of sensory and motor blockade, duration of analgesia, and analgesic requirement were compared.

Results:

The onset of sensory anesthesia was faster (493.8±31.66 in sec.) and the duration was significantly longer in Clonidine group (334.2 min). Requirement of supplementary analgesia (Inj. diclofenac) was markedly decreased in Clonidine group as evident from the findings that in control group 18 patients required 3 supplemental analgesic doses in first 24 hours as compared to only 3 patients in Clonidine group. Epidural Clonidine produced a significant decrease (P less than 0.05) in heart rate and blood pressure, whereas the respiratory rate was not affected. We also observed for side effects in both the groups. Incidence of significant hypotension was higher, 8 patients (26%) in Clonidine group compared to 2 patient (6%) in control group. Incidence of dryness of mouth was higher, 12 patients (48%) in Clonidine group compared to 5 (18%) in control group.

Conclusion:

The addition of Clonidine to Bupivacaine epiduraly prolongs motor and sensory block and analgesia, without an increased incidence of side effects.

A comparative study of the effect of caudal dexmedetomidine versus morphine added to bupivacaine in pediatric infra-umbilical surgery

BACKGROUND

One of the most commonly used regional anesthetic techniques in pediatric surgeries is the caudal epidural block. Its main disadvantage remains the short duration of action. Hence, different additives have been used. Dexmedetomidine is a potent as well as highly selective α2 adrenergic receptor agonist. The aim of this randomized, double-blinded, study was to compare the duration of postoperative analgesia of caudal dexmedetomidine versus morphine in combination with bupivacaine in pediatric patients undergoing lower abdominal or perineal surgery.

PATIENTS AND METHODS

A total of 50 pediatric patients 1-5 years old The American Society of Anesthesiologists status I, II scheduled for lower abdominal and perineal surgeries were included in the study. The patients were enrolled into 2 equal groups: Group A patients (n = 25) received dexmedetomidine with bupivacaine while Group B patients (n = 25) received morphine with bupivacaine. Patients were placed in a supine position then inhalational general anesthesia was induced, and laryngeal mask airway (LMA) was placed. Patients were then given caudal epidural analgesia. By the end of surgery reversal of muscle relaxation was done and the LMA was removed. Post-operatively, the sedation as well as pain score were observed and recorded.

RESULTS

The current study showed that minor complications were recorded in the post-anesthesia care unit; in addition, significantly longer periods of analgesia and sedation were detected in Group A. However, no significant differences in demographic data, as well as in the duration of surgery, and the time of emergence from anesthesia and patient condition during recovery were detected.

CONCLUSION

The present study suggested that use of dexmedetomidine, during single dose injection, as an additive to the local anesthetic bupivacaine in caudal epidural analgesia prolongs the duration of post-operative analgesia following lower abdominal as well as perineal surgery compared with caudal morphine with no side-effects on the vital signs. Postoperative side effects were seen with caudal morphine injection rather than with dexmedetomidine.

Action of dexmedetomidine on the substantia gelatinosa neurons of the rat spinal cord

Dexmedetomidine is a highly specific, potent and selective alpha(2)-adrenoceptor agonist. Although intrathecal and epidural administration of dexmedetomidine has been found to produce analgesia, whether this analgesia results from an effect on spinal cord substantia gelatinosa (SG) neurons remains unclear. Here, we investigated the effects of dexmedetomidine on postsynaptic transmission in SG neurons of rat spinal cord slices using the whole-cell patch-clamp technique. In 92% of the SG neurons examined (n = 84), bath-applied dexmedetomidine induced outward currents at -70 mV in a concentration-dependent manner, with the value of effective concentration producing a half-maximal response (0.62 microM). The outward currents induced by dexmedetomidine were suppressed by the alpha(2)-adrenoceptor antagonist yohimbine, but not by prazosin, an alpha(1)-, alpha(2B)- and alpha(2C)-adrenoceptor antagonist. Moreover, the dexmedetomidine-induced currents were partially suppressed by the alpha(2C)-adrenoceptor antagonist JP-1302, while simultaneous application of JP-1302 and the alpha(2A)-adrenoceptor antagonist BRL44408 abolished the current completely. The action of dexmedetomidine was mimicked by the alpha(2A)-adrenoceptor agonist oxymetazoline. Plots of the current-voltage relationship revealed a reversal potential at around -86 mV. Dexmedetomidine-induced currents were blocked by the addition of GDP-beta-S [guanosine-5'-O-(2-thiodiphosphate)] or Cs+ to the pipette solution. These findings suggest that dexmedetomidine hyperpolarizes the membrane potentials of SG neurons by G-protein-mediated activation of K+ channels through alpha(2A)- and alpha(2C)-adrenoceptors. This action of dexmedetomidine might contribute, at least in part, to its antinociceptive action in the spinal cord.

Thermal antinociception after dexmedetomidine administration in cats: a dose-finding study

The optimum dose of dexmedetomidine for antinociception to a thermal stimulus was determined in a crossover study of 12 cats. In five treatment groups (n = 10 per group), dexmedetomidine was administered intramuscularly (i.m.) at 2, 5, 10, 20 and 40 microg/kg; positive and negative controls were administered buprenorphine (20 microg/kg, i.m.) and 0.9% saline (0.006 mL/kg, i.m.) respectively. Baseline thermal thresholds and visual analogue scale (VAS) sedation scores were obtained prior to drug treatment and then at regular intervals until 24 h after administration. The summary measures of overall mean thresholds and overall mean VAS scores were investigated using a univariate general linear model for multiple factors with post hoc Tukey's tests (P < 0.05). Only dexmedetomidine at 40 microg/kg displayed an analgesic effect (less than that of buprenorphine). The VAS for sedation did not significantly affect the thresholds obtained and treatment was the only significant factor to influence VAS. Dexmedetomidine resulted in higher VAS for sedation than saline and buprenorphine. Dexmedetomidine at 40 microg/kg significantly increased nociceptive thresholds compared with saline control, but less than buprenorphine. Dexmedetomidine produced dose-dependent sedation, but only the highest dose produced analgesia, suggesting that induction of analgesia requires the highest dose (or an additional analgesic) in the clinical setting.

Sex-specific modulation of spinal nociception by alpha2-adrenoceptors: differential regulation by estrogen and testosterone

Sex-related differences in antinociception produced by the activation of alpha(2)-adrenoceptors (alpha(2)-ARs) have been reported, however, the precise role of gonadal steroids is still unknown. Hence, we hypothesized that estrogen and testosterone modulate antinociceptive effects of clonidine (an alpha(2)-AR agonist) on N-methyl-D-aspartate- (NMDA) and heat-induced spinal nociception. We also investigated whether estrogen or testosterone alters the expression of alpha(2A)-adrenoceptors in the spinal cord. Sprague-Dawley (SD) rats were implanted with PE10 cannulae in the intrathecal space of the lumbosacral spinal cord and divided into male, proestrous and diestrous female, ovariectomized (OVX), estradiol-treated OVX (OVX+E), castrated male (GDX), testosterone (GDX+T) and estradiol-treated castrated male (GDX+E) groups. Clonidine dose-dependently inhibited NMDA-induced scratching behavior in the male and OVX groups but to a significantly lesser extent in the OVX+E group. It also increased the tail withdrawal latency in the male, OVX, diestrous and GDX+T groups but not in the OVX+E, proestrous, GDX and GDX+E groups. Levels of alpha(2A)-AR mRNA were significantly higher in the OVX, estradiol-treated OVX, GDX and GDX+E animals. In contrast, alpha(2A)-AR protein levels were higher in estradiol-treated OVX, GDX, GDX+T and GDX+E animals as compared with the male. Indeed, no correlations were observed between changes in the mRNA or protein levels of alpha(2A)-AR and behavioral observations. These results support our hypothesis that sex-related differences in alpha(2)-AR-mediated modulation of spinal nociception are gonadal hormone-dependent: estrogen attenuates antinociceptive effects in females whereas testosterone is required for the expression of antinociception in males. In addition, results also revealed that the mechanism of action of gonadal hormones may not involve a global alternation in expression of alpha(2A)-AR in the spinal cord. Estrogen-induced attenuation of alpha(2)-AR-mediated inhibition of nociception could contribute to the higher prevalence of pain syndromes in women.

Characterization of spinal alpha-adrenergic modulation of nociceptive transmission and hyperalgesia throughout postnatal development in rats

BACKGROUND AND PURPOSE

The selective alpha(2)-adrenergic agonist dexmedetomidine is used clinically for analgesia and sedation, but effects in early life are not well characterized. Investigation of age-related effects of dexmedetomidine is important for evaluating responses to exogenously administered analgesics and provides insight into postnatal function of noradrenergic pathways.

EXPERIMENTAL APPROACH

We examined effects of epidural dexmedetomidine in anaesthetized rat pups (3, 10 and 21 postnatal days) using a quantitative model of nociception and C-fibre induced hyperalgesia. Electromyographic recordings of withdrawal responses to hindpaw mechanical stimuli measured effects of dexmedetomidine upon the baseline reflex and the response to mustard oil application on the hindpaw (primary hyperalgesia) or hindlimb (secondary hyperalgesia). In addition, we compared epidural with systemic administration, examined effects of spinal transection and evaluated heart rate changes following dexmedetomidine.

KEY RESULTS

Epidural dexmedetomidine dose-dependently prevented mustard oil-induced hyperalgesia at all ages but dose requirements were lower in the youngest pups. Higher doses also suppressed the baseline nociceptive reflex when given epidurally, but had no effect when given systemically. Analgesic efficacy was the same for primary and secondary hyperalgesia, and was not diminished by spinal cord transection.

CONCLUSIONS AND IMPLICATIONS

Our laboratory studies predict that spinally mediated alpha(2)-agonist analgesia would be effective throughout postnatal development, dose requirements would be lower in early life and selective anti-hyperalgesic effects could be achieved with epidural administration at doses lower than associated with antinociceptive or cardiovascular effects. Clinical trials of alpha(2) agonists in neonates and infants should consider developmentally regulated changes.

Effect of low-dose dexmedetomidine or clonidine on the characteristics of bupivacaine spinal block

BACKGROUND

The purpose of this study was to compare the onset and duration of sensory and motor block, as well as the hemodynamic changes and level of sedation, following intrathecal bupivacaine supplemented with either dexmedetomidine or clonidine.

METHODS

In a prospective, double-blind study, 60 patients undergoing transurethral resection of prostate or bladder tumor under spinal anesthesia were randomly allocated to one of three groups. Group B received 12 mg of hyperbaric bupivacaine, group D received 12 mg of bupivacaine supplemented with 3 microg of dexmedetomidine and group C received 12 mg of bupivacaine supplemented with 30 microg of clonidine. The onset times to reach peak sensory and motor levels, and the sensory and motor regression times, were recorded. Hemodynamic changes and the level of sedation were also recorded.

RESULTS

Patients in groups D and C had a significantly shorter onset time of motor block and significantly longer sensory and motor regression times than patients in group B. The mean time of sensory regression to the S1 segment was 303 +/- 75 min in group D, 272 +/- 38 min in group C and 190 +/- 48 min in group B (B vs. D and B vs. C, P < 0.001). The regression of motor block to Bromage 0 was 250 +/- 76 min in group D, 216 +/- 35 min in group C and 163 +/- 47 min in group B (B vs. D and B vs. C, P < 0.001). The onset and regression times were not significantly different between groups D and C. The mean arterial pressure, heart rate and level of sedation were similar in the three groups intra-operatively and post-operatively.

CONCLUSIONS

Dexmedetomidine (3 microg) or clonidine (30 microg), when added to intrathecal bupivacaine, produces a similar prolongation in the duration of the motor and sensory block with preserved hemodynamic stability and lack of sedation.

Mechanisms for the Anti-nociceptive Actions of the Descending Noradrenergic and Serotonergic Systems in the Spinal Cord

The sensation of pain plays a critical role as an alert and as a protection system against tissue damage from mechanical, chemical, and thermal stimuli. Despite the protective role of pain, the severity of pain sensation is markedly attenuated by the endogenous pain inhibitory systems that predominantly originate at the brain stem. Both behavioral and in vivo extracellular recording studies have sought the loci producing analgesia and clarification of the anti-nociceptive actions. Among those loci, the main descending systems to the spinal dorsal horn are noradrenergic and serotonergic. Although, in vivo studies have provided basic knowledge of these systems, the precise synaptic mechanisms underlying the analgesic actions have not yet been elucidated until recently. The newly developed in vitro slice and in vivo patch-clamp recordings have disclosed the synaptic mechanisms of the noradrenergic and serotonergic effects at the level of spinal dorsal horn. This paper reviews the anti-nociceptive action of these systems, while particularly focusing on the electrophysiological aspects of the systems at the single neuron level in the spinal dorsal horn as well as their origins and responsible receptor subtypes.

Isoflurane sparing action of epidurally administered xylazine hydrochloride in anesthetized dogs

OBJECTIVE

To evaluate the influence of epidural administration of xylazine hydrochloride on the minimum alveolar concentration of isoflurane (MAC(ISAO)) and cardiopulmonary system in anesthetized dogs.

ANIMALS

6 clinically normal dogs.

PROCEDURE

Dogs were anesthetized with isoflurane in oxygen after randomly being assigned to receive 1 of the following 4 treatments: epidural administration of saline (0.9% NaCl) solution or xylazine at a dose of 0.1, 0.2, or 0.4 mg x kg(-1). Experiments were performed on 5 occasions with at least a 1-week interval between experiments; each dog received all 4 treatments. Following instrumentation, the concentration of isoflurane was maintained constant for 15 minutes at the MAC(ISO) that had been determined for each dog, and data on heart rate, arterial blood pressure, respiratory rate, tidal volume, minute volume, arterial partial pressure of oxygen, arterial partial pressure of carbon dioxide, and arterial pH were collected. The epidural treatment was administered, and 30 minutes later, data were again collected. From this point on, determination of the MAC(ISO) following epidural treatment (ie, MAC(ISO+EPI)) was initiated. Cardiopulmonary data were collected before each electrical supramaximal stimulus during MAC(ISO+EPI) determinations.

RESULTS

The mean (+/-SD) MAC(ISO) was 1.29 +/- 0.04%. The epidural administration of xylazine at doses of 0.1, 0.2, and 0.4 mg x kg(-1) decreased the MAC(ISO), respectively, by 8.4 +/- 2.4%, 21.7 +/- 4.9%, and 33.4 +/- 2.64%. Cardiopulmonary effects were limited.

CONCLUSIONS AND CLINICAL RELEVANCE

Epidural administration of xylazine decreases the MAC(ISO) in a dose-dependent manner and is associated with few cardiopulmonary effects in anesthetized dogs.

Descending control of pain

Upon receipt in the dorsal horn (DH) of the spinal cord, nociceptive (pain-signalling) information from the viscera, skin and other organs is subject to extensive processing by a diversity of mechanisms, certain of which enhance, and certain of which inhibit, its transfer to higher centres. In this regard, a network of descending pathways projecting from cerebral structures to the DH plays a complex and crucial role. Specific centrifugal pathways either suppress (descending inhibition) or potentiate (descending facilitation) passage of nociceptive messages to the brain. Engagement of descending inhibition by the opioid analgesic, morphine, fulfils an important role in its pain-relieving properties, while induction of analgesia by the adrenergic agonist, clonidine, reflects actions at alpha(2)-adrenoceptors (alpha(2)-ARs) in the DH normally recruited by descending pathways. However, opioids and adrenergic agents exploit but a tiny fraction of the vast panoply of mechanisms now known to be involved in the induction and/or expression of descending controls. For example, no drug interfering with descending facilitation is currently available for clinical use. The present review focuses on: (1) the organisation of descending pathways and their pathophysiological significance; (2) the role of individual transmitters and specific receptor types in the modulation and expression of mechanisms of descending inhibition and facilitation and (3) the advantages and limitations of established and innovative analgesic strategies which act by manipulation of descending controls. Knowledge of descending pathways has increased exponentially in recent years, so this is an opportune moment to survey their operation and therapeutic relevance to the improved management of pain.