|Year : 2018 | Volume
| Issue : 4 | Page : 343-348
Sensory and motor effects of dexmedetomidine as an adjuvant to bupivacaine for brachial plexus block
Assistance professor of Anesthesia, ICU, Department, Faculty of Medicine, Damietta
|Date of Submission||26-Apr-2018|
|Date of Acceptance||27-Jan-2019|
|Date of Web Publication||23-Apr-2019|
Faculty of Medicine, 34511, Damietta
Source of Support: None, Conflict of Interest: None
Background Dexmedetomidine is a highly selective (eight time more selective than clonidine), specific, and potent α2-adrenergic agonist having analgesic, sedative, antihypertensive, and anesthetic sparing effects when used in systemic routes.
Patients and methods Forty patients of both sexes, aged between 25 and 70 years; American Society of Anesthesiologists I–II, who were submitted to elective upper limb surgery by supraclavicular brachial plexus block were included in the present study. They were selected during the period from March 2016 to June 2017. The patients were divided randomly by sealed envelopes into two equal groups (n=20). Group I: 20 patients received 30 ml bupivacaine 0.25%. Group II: 20 patients received 30 ml bupivacaine 0.25% plus 100 μg dexmedetomidine.
Results The duration was reported in group II 13.13±1.10 and 16.50±1.63 min for the onset of sensory and motor blocks, respectively, and in group I 14.90±1.18 and 18.63±1.12 min for the onset of sensory and motor blocks, respectively. There was significant decrease of median pain score in group II when compared with group I at 4, 8, 12, 16, 20, and 24 h postoperatively.
Conclusion Dexmedetomidine had significantly better postoperative analgesic effects, longer duration of sensory and motor blockade, and earlier onset of action. However, it had unwanted side effects in the form of transient bradycardia and hypotension.
Keywords: brachial plexus block, bupivacaine, dexmedetomidine
|How to cite this article:|
Kandil Y. Sensory and motor effects of dexmedetomidine as an adjuvant to bupivacaine for brachial plexus block. Al-Azhar Assiut Med J 2018;16:343-8
|How to cite this URL:|
Kandil Y. Sensory and motor effects of dexmedetomidine as an adjuvant to bupivacaine for brachial plexus block. Al-Azhar Assiut Med J [serial online] 2018 [cited 2019 Oct 15];16:343-8. Available from: http://www.azmj.eg.net/text.asp?2018/16/4/343/256757
| Introduction|| |
Supraclavicular nerve block is a good alternative to general anesthesia for upper limb surgery. It is the most consistent and widely used method for anesthesia and perioperative pain management in surgery below the shoulder joint . This avoids the untoward effects of general anesthetic drugs and upper airway instrumentation. It achieves complete muscle relaxation, intraoperative hemodynamic stability, and postoperative analgesia .
Various local anesthetic agents are used in brachial plexus block (BPB) but the most commonly used drugs are bupivacaine and lidocaine. Bupivacaine is a widely used local anesthetic that is associated with a reduced requirement for repeat administration or top-up doses because of its prolonged action; at low concentrations, bupivacaine produces a greater degree of sensory than motor block (differential sensitivity), which is an advantage in labor and postoperative pain management, where motor paralysis is unwanted .
Dexmedetomidine is an α2-receptor agonist, and its selectivity is eight times more than clonidine. It has been reported to improve the quality of intrathecal and epidural anesthesia .
The interactions with central nervous system and spinal cord α2-adrenergic receptors mediate dexmedetomidine’s primary physiologic effects by the stimulation of parasympathetic outflow and inhibition of sympathetic outflow. The main site of inhibition of noradrenergic outflow is locus coeruleus .
Primary analgesic effects and potentiation of opioid-induced analgesia result from the activation of α2-adrenergic receptors in the dorsal horn of the spinal cord and the inhibition of substance P release . Dexmedetomidine acts through a G-coupled protein receptor that produces an inhibition of adenylyl cyclase and this results in decreased formation of cyclic AMP, which is an important regulator of many cellular functions acting in various intracellular subsystems like the control of phosphorylation state of regulatory proteins. Other effects of α2-adrenoreceptor agonists include activation of potassium ion channels causing an efflux of potassium and an inhibition of calcium entry into the calcium channels in the neuronal cell. These effects lead to a change in membrane ion conductance and produce α2-adrenoreceptor agonist hyperpolarization of the membrane which suppresses neuronal activity. The main effect is an inhibition of noradrenalin release causing a reduction of excitation, especially in locus coeruleus. The locus coeruleus is a small neuronal nucleus located bilaterally in the upper brainstem and is the major site of noradrenergic innervations in the brain. The locus coeruleus has also been implicated as the key modulator for a variety of important brain functions, including arousal, sleep, anxiety, and drug withdrawal associated with central nervous system depressant, like opioids .
| Patients and methods|| |
The study was carried out in Al-Azhar University Hospitals after approval of the Medical Ethics Committee; 40 patients of both sexes, aged between 25 and 70 years; American Society of Anesthesiologists I–II, who were submitted to elective upper limb surgeries by supraclavicular BPB were included in the present study. They were selected during the period from March 2016 to June 2017. The patients were divided randomly by sealed envelopes into two equal groups (n=20).
Group I: 20 patients received 30 ml bupivacaine 0.25%.
Group II: 20 patients received 30 ml bupivacaine 0.25% plus 100 μg dexmedetomidine.
Any significant coexisting diseases, including severe renal or hepatic disease, any contraindications to regional anesthesia, such as local infection or bleeding disorder or allergy to local anesthetic, patient refusal to give consent, and neuropathy.
After patient arrival to the theater, a 20 G intravenous line was inserted and fluid administration started at a rate of 10 ml/kg normal saline. Baseline hemodynamic parameters (mean arterial pressure, heart rate, respiratory rate, peripheral oxygen saturations), and ECG were monitored. The patient is placed in a supine position with the head rotated away from the site to be blocked and the shoulder pulled down. The supraclavicular block was done guided with ultrasound. Five minutes after the end of injections, the surgical area was started to be checked with the pin-prick test at 5 min intervals. Hemodynamic parameters (heart rate, mean arterial blood pressure, oxygen saturation, and respiratory rate) were recorded every 5 min for 30 min and every 10 min for 60 min and at 2 h, and then at a 4 h interval postoperatively up to 24 h. Sensory block was assessed by pin prick and touch, with a three-point scale (0=no sensory loss, 1=loss of sensation to pin prick, 2=loss of sensation to touch). Motor block was assessed by the modified Bromage scale (0=normal muscle function, 1=elbow flexion, 2=wrist flexion, 3=full motor block). Postoperative pain score was assessed postoperatively by the visual analog scale at 4 h intervals up to 24 h. The presence of any complications and their frequency were listed, such as Horner’s syndrome, recurrent laryngeal nerve palsy, pneumothorax, bradycardia, hypotension, and diaphragmatic paralysis and inadvertent intravenous or subarachnoid space injection and hematoma formation. Finally, time of first analgesic request and total dose of postoperative analgesia were documented.
Data were expressed as mean values±SD/SE, percentages (%), and numbers (n). The statistical analysis was performed by a statistician using Windostat, version 9.2. Two statistical tests were primarily used to analyze the data and a P value less than 0.05 was considered as statistically significant. (a) t tests were used to analyze differences between two groups. (b) Analysis of variance to analyze differences in parameters such heart rate, systolic blood pressure, diastolic blood pressure, and visual analog scale for pain over a period of time.
| Results|| |
In the present work, there was a statistically nonsignificant difference between the studied groups as regards demographic data ([Table 1]).
As regards oxygen saturation, there was no significant difference between the studied groups at any time ([Figure 1]).
|Figure 1 Oxygen saturation in the studied groups at different time intervals.|
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As regards respiratory rate, there was no significant difference between the studied groups at any time ([Table 2]).
|Table 2 Respiratory rate in studied groups at different time intervals in cycle/min|
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As regards the heart rate, there was a statistically significant decrease of heart rate in group II from 15 to 60 min intraoperatively. On the other hand, there was no significant difference between the studied groups as regards heart rate at preoperative values; and at 5, and 10 min intraoperatively and at 2, 6, 10, 14, 18, and 24 h postoperatively ([Table 3]).
As regards blood pressure, there was statistically significant decrease of blood pressure in group II from 20 to 60 min intraoperatively. On the other hand, there was no significant difference between the studied groups as regards blood pressure at preoperative values, and at 5, 10, and 15 min intraoperatively and at 2, 6, 10, 14, 18, and 24 h postoperatively ([Table 4]).
|Table 4 Mean arterial pressure in the studied groups at different time intervals (mmHg)|
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As regards onset of sensory and motor blocks was significantly different between group I and group II. The reported onset durations in group II are 13.13±1.10 and 16.50±1.63 min for sensory and motor blocks respectively, while in group I 14.90±1.18 and 18.63±1.12 min for onset of sensory and motor blocks, respectively. There was an increase in the duration of sensory and motor blocks in group II than in group I, but with no statistically significant differences ([Table 5]).
|Table 5 Onset and total duration of sensory and motor blocks in the studied groups (min)|
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As regards postoperative pain score, there was a significant decrease of pain score in group II when compared with group I at 4, 8, 12, 16, 20, and 24 h postoperatively ([Table 6]).
As regards the time of first analgesic request, there was a significant increase of this time in group II (16.16±2.55) when compared with group I (9.26±1.11) ([Table 7]).
As regards total dose of postoperative analgesia per patient in the studied cases, it ranged from 0.0 to 90 mg (ketorolac) with a mean of 40.0±22.03 mg and there was significant increase of total analgesia in group I (62.0±22.19) when compared with group II (26.0±10.37) ([Table 8]).
|Table 8 Total dose of analgesic (per patient) in the studied groups in mg|
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As regards complications in the studied groups, bradycardia in 15.6% of cases, hypotension in 8.9% of cases, and finally hematoma in 4.4% of cases; and there was significant increase of bradycardia and hypotension in group II when compared with group I. All complications were resolved with supportive care.
| Discussion|| |
The supraclavicular approach is the easiest and appropriate method for brachial plexus anesthesia and management of perioperative pain in surgery below the shoulder joint .
Bupivacaine was used frequently for supraclavicular nerve block as it has a long duration of action from 3 to 6 h. Adding various drugs to local anesthetics for BPB may prove the blockade as a quick onset and prolong duration .
Efforts have been made to enhance the outcomes of the block by adding various adjuncts to the anesthetic agent. Drugs such as opioids , naloxone , clonidine , midazolam , epinephrine , and dexamethasone  have been used along with local anesthetics for this purpose with varying degrees of success.
Dexmedetomidine is a selective α2-adrenergic receptor agonist, with a dose-dependent α2 selectivity that is ∼7- to 8-fold greater than that of clonidine, specific and potent α2-adrenergic agonist having analgesic, sedative, antihypertensive, and anesthetic sparing effects when used in systemic route .
Adding dexmedetomidine to local anesthetics during peripheral nerve block  and regional anesthesia  procedures may also prove efficacious for the surgical patients.
In the present study, the onset of sensory and motor blockade was quick in group II when compared with group I (P<0.05); these results are in agreement with Jung et al.  in his study on dexmedetomidine added to levobupivacaine in axillary BPB, who observed that sensory and motor block onset time were significantly shorter in group LD (levobupivacaine+dexmedetomidine) than in group L (levobupivacaine), and the difference was statistically significant (P<0.05) .
The duration of sensory and motor blockade was prolonged in group II (bupivacaine+dexmedetomidine) group when compared with group I (bupivacaine) (P<0.05). Ammar and Mahmoud  and Jung et al.  also found in their studies that administering perineural dexmedetomidine as part of a BPB resulted in a prolongation of motor block duration. The mechanism by which α2-adrenergic receptor agonists produce analgesia and sedation is not fully understood but is likely to be multifactorial. Peripherally, α2-agonists produce analgesia by reducing the release of norepinephrine and causing α2-receptor independent inhibitory effects on nerve fiber action potentials.
In the present work, there was a significant decrease of median pain score in group II when compared with groups I at 4, 8, 12, 16, 20, and 24 h postoperatively. In addition, there was significant increase of time for first analgesic request in group II (16.16±2.55) when compared with group I (9.26±1.11). In addition, there was a significant increase of time for the first analgesic request in group II when compared with group I.
These results are in agreement with Ammar and Mahmoud  who designed a study to test the efficacy of adding 0.75 μg/kg of dexmedetomidine to 30 ml of 0.33% bupivacaine during ultrasound-guided infraclavicular BPB in 60 adult patients. They noted a statistically significant lower pain scores, prolonged analgesia (403 vs. 233 min), and lower morphine rescue requirements lasting up to 48 h (4.9 vs. 13.6 mg) in the study group as compared with the control group. In addition, Obayah et al.  found an increase in the time to first analgesic request (22 vs. 14.2 h) following greater palatine nerve blocks with bupivacaine and dexmedetomidine (1 μg/kg) as compared with bupivacaine alone in children posted for cleft palate repair. The pain scores in the study group were also significantly lower in the first 24 h.
Furthermore, in a recent meta-analysis, Abdallah and Brull  investigated the use of dexmedetomidine as an adjuvant for central and peripheral nerve blocks. Accordingly, perineural use of dexmedetomidine for BPB prolonged the mean duration of sensory block by 284 min (95% confidence interval, 1566; P=0.05), but this difference was not statistically significant. The duration of motor block and time to the first analgesic request were also prolonged. Dexmedetomidine produced reversible bradycardia in 7% of patients, but did not cause significant hypotension. No patients experienced respiratory depression. The authors concluded that dexmedetomidine has potential as an local anesthetic (LA) adjuvant; its efficacy appeared to be comparable to that of buprenorphine and dexamethasone and exceeded that of clonidine, magnesium, and midazolam. Unlike clonidine, dexmedetomidine appeared to prolong the duration of the block with both intermediate as well as long acting LAs .
In a recent review, Biyani et al.  reported that the literature shows that the addition of single doses of adjuvants, in doses equivalent to or less than those systemically administered can speed up the onset, prolong sensorimotor anesthesia as well as analgesia in patients receiving peripheral nerve blocks. The advantages of some adjuvants like clonidine have been demonstrated in a meta-analysis. Advantages of others like ketamine and magnesium sulfate are more apparent when low-dose intravenous infusions are combined with blocks. Furthermore, some drugs such as midazolam, ketamine, and dexmedetomidine are being used ‘off-label’ or in the absence of enough clinical trials to support their use when used as adjuvants with local anesthetics. Are we justified in using these adjuvants? Obviously we need more randomized controlled trials and meta-analyses before this can be irrefutably decided. The debate continues.
| Conclusion|| |
On the basis of the results of the present study, it had been concluded that dexmedetomidine had a significantly better postoperative analgesic effects, longer duration of sensory and motor blockade, and earlier onset of action. However, it had unwanted side effects in the form of transient bradycardia and hypotension.
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Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7], [Table 8]