|Year : 2015 | Volume
| Issue : 1 | Page : 129-133
Comparison between dexmedetomidine and magnesium sulfate as adjuvants for intravenous regional anesthesia
Mohamed El-Tahawy, Ahmad Ramzy Shaaban, Ayman Ahmad
Department of Anesthesia and Intensive Care, Faculty of Medicine, Ain Shams University, Cairo, Egypt
|Date of Submission||24-Aug-2014|
|Date of Acceptance||07-Nov-2014|
|Date of Web Publication||25-Mar-2015|
Ahmad Ramzy Shaaban
Department of Anesthesia and Intensive Care, Faculty of Medicine, Ain Shams University, Cairo
Source of Support: None, Conflict of Interest: None
Many adjuvants have been used to improve the quality of intravenous regional anesthesia (IVRA). The aim of this study was to compare the use of dexmedetomidine with that of magnesium sulfate as an adjuvant for IVRA as regards onset and duration of sensory and motor blocks, quality of anesthesia, intraoperative-postoperative hemodynamic variables, and intraoperative and postoperative pain.
Patients and Methods
This study was a prospective, randomized, double-blinded trial. Sixty patients scheduled for upper hand or forearm surgery were randomly divided into two groups, comprising 30 patients each. Group D received dexmedetomidine at 0.5 μg/kg diluted with saline to 20 ml in addition to 20 ml of 1% lidocaine to reach a total volume of 40 ml, whereas group M received 5 ml of 20% magnesium sulfate and 15 ml saline added to 20 ml of 1% lidocaine to reach a total volume of 40 ml.
Sensory and motor block onset, recovery times, anesthesia quality, and hemodynamic variables were recorded and compared between the two groups.
No statistically significant difference was observed between dexmedetomidine and magnesium sulfate as regards sensory block onset time and motor block onset time (P = 0.102 and 0.206, respectively) as well as intraoperative analgesic requirements (P = 0.76). However, dexmedetomidine showed more favorable hemodynamic variables and less tourniquet pain.
We concluded that dexmedetomidine seems to be superior to magnesium sulfate as an adjuvant to lidocaine in IVRA regarding tourniquet pain and intraoperative and postoperative hemodynamic stability.
Keywords: dexmedetomidine, intravenous regional anesthesia, magnesium sulfate
|How to cite this article:|
El-Tahawy M, Shaaban AR, Ahmad A. Comparison between dexmedetomidine and magnesium sulfate as adjuvants for intravenous regional anesthesia. Ain-Shams J Anaesthesiol 2015;8:129-33
|How to cite this URL:|
El-Tahawy M, Shaaban AR, Ahmad A. Comparison between dexmedetomidine and magnesium sulfate as adjuvants for intravenous regional anesthesia. Ain-Shams J Anaesthesiol [serial online] 2015 [cited 2021 Apr 21];8:129-33. Available from: http://www.asja.eg.net/text.asp?2015/8/1/129/153954
| Introduction|| |
Intravenous regional anesthesia (IVRA) is a commonly used anesthetic technique for surgical procedures on the upper extremities. It was first described by August Bier in 1902 and is technically simple and reliable, with success rates between 94 and 98%  .
Despite its simplicity and effectiveness, it has been limited in use because of tourniquet pain and lack of postoperative analgesia. The best IVRA solution should have the following characteristics: fast onset, low dose of local anesthetic, less tourniquet pain, and extended postdeflation analgesia  . At present, this can be reached only by adding adjuncts to local anesthetics. Thus, different agents have been used as additives to local anesthetics for IVRA, including phencyclidines, NSAIDs, opioids, and muscle relaxants, with an aim to improve its outcome ,, .
In a study by Turan et al.  adding magnesium to lidocaine in IVRA revealed diminished intraoperative fentanyl use and pain associated with the tourniquet. Turan and colleagues' study was the first one on this issue. However, the authors emphasized that more studies should be carried out to determine a relevant conclusion before its regular use.
In contrast, α2-adrenergic receptor (adrenoceptor) agonists have been the focus of interest for their analgesic, sedative, and perioperative sympatholytic and cardiovascular stabilizing effects with reduced anesthetic requirements. Dexmedetomidine is a potent α2-adrenoceptor agonist that is approximately eight times more selective toward α2-adrenoceptors compared with clonidine , . Therefore, Kol et al.  were the first to study the addition of dexmedetomidine to lidocaine for IVRA and concluded that addition of 0.5 μg/kg dexmedetomidine to lidocaine for IVRA improves the quality of anesthesia and intraoperative and postoperative analgesia. Therefore, we designed our study to compare the efficacy, outcome, and possible side effects between dexmedetomidine and magnesium sulfate when added to lidocaine for IVRA.
| Patients and Methods|| |
This was a prospective, randomized, double-blinded study conducted in Dr Erfan Hospital (a tertiary care center in Jeddah, Saudi Arabia) from April 2013 to January 2014. Ethical approval for this study was provided by the institutional ethics committee of the hospital on 8th of January 2013. After obtaining written informed consent, 60 patients aged 20-60 years and with American Society of Anesthesiologists (ASA) Physical Status class I-II who were scheduled for hand or forearm surgery (i.e. carpal tunnel release and tendon release) were enrolled in our study. Exclusion criteria were history of allergy to any drug used in the study, sickle cell anemia, Raynaud's disease, and receipt of any analgesic drug in the previous 24 h.
The patients were randomly allocated to one of two groups, the dexmedetomidine (D) group or the magnesium sulfate (M) group, using a computer-generated sequence of random numbers and a sealed envelope technique. Study drugs were prepared by a pharmacist who did not participate in either the intraoperative management or the postoperative care. According to the randomization table, drugs were prepared in unlabeled 40 ml syringes. The unlabeled syringes were filled either with dexmedetomidine at 0.5 μg/kg diluted with saline to 20 ml added to 20 ml of 1% lidocaine to reach a total volume of 40 ml or with 5 ml of 20% magnesium sulfate and 15 ml saline added to 20 ml of 1% lidocaine to reach a total volume of 40 ml.
All patients received a standard anesthetic protocol, which included premedication with oral midazolam at 0.5 mg/kg given 30 min preoperatively. Once the patients had been taken to the operating room, the mean arterial blood pressure (MAP), peripheral oxygen saturation (SpO 2 ), and heart rate (HR) were monitored. Two cannulae were placed, one in a vein on the dorsum of the operative hand and the other in the contrary hand for intravenous fluid infusion and injection of drugs (sedatives or resuscitative) if needed. The operative arm was elevated for 3 min and then exsanguinated with an Esmarch bandage, and a double pneumatic tourniquet was placed around the upper arm, and the proximal cuff was inflated to 250 mmHg. Circulatory isolation of the arm was verified by inspection, absence of radial pulse, and loss of pulse oximetry tracing of the ipsilateral index finger.
The local anesthetic solution was injected slowly over 180 s. The sensory block was evaluated by pinprick test at 1-min intervals until 10 min after tourniquet inflation. The time of onset of sensory block was defined as the time between drug injection and the development of complete sensory block. Motor block was assessed by the inability to extend or flex wrist and fingers at 1-min intervals. Complete motor block was noted when no voluntary movement was possible. The time of onset of motor block was defined as the time between drug injection and the development of complete motor block. After establishment of complete sensory and motor block, the distal cuff was inflated to 250 mmHg before deflation of the proximal one. The surgeon then began the surgical procedure.
Hypotension (defined as 25% decrease in blood pressure from baseline value) was treated with incremental doses of intravenous ephedrine. Bradycardia (which was defined as 25% decrease in HR from the baseline value) was treated with 0.5 mg of intravenous atropine. SpO 2 less than 92% was treated by giving O 2 supplementation through a face mask.
Tourniquet pain was evaluated using a Pain Numerical Rating Score (NRS) (0 = no pain and 10 = worst pain). Recording of HR, MAP, and NRS was done at baseline and 10, 20, and 30 min after distal tourniquet inflation. If at any time NRS was more than 4, fentanyl at 1 μg/kg was administered intravenously and total fentanyl consumption was recorded. HR, MAP, and NRS were again recorded after the deflation and 30 min and 1, 6, 12, and 24 h later.
The tourniquet was not deflated earlier than 30 min and was not inflated for more than 1.5 h. At the end of surgery, the tourniquet deflation was carried out by cyclic deflation, but not earlier than 30 min from local anesthetic injection.
Postoperative pain was assessed by NRS after tourniquet release and 30 min and 1, 6, 12, and 24 h later. The first analgesic requirement time was also noted (the time elapsed from tourniquet release until the first patient demand for analgesic drug). Patients received intravenous morphine at 0.05 mg/kg when NRS more than 4. The total amount of morphine administered to each group was recorded.
After the operation, the quality of the block was assessed by asking the surgeon to rate it on a numeric scale from 1 to 4 (1 = unsuccessful block with use of general anaesthesia; 2 = poor block with frequent complaint from the patient; 3 = good block with minimal complaint from the patient; and 4 = excellent block with no complaint from the patient).
Sensory block recovery time (time from tourniquet deflation to return of pain assessed by pinprick test) and motor block recovery time (time from tourniquet deflation to restoration of finger movement) were recorded.
Hypotension (defined as 25% decrease in blood pressure from baseline value) was treated with intravenous ephedrine at incremental doses. Bradycardia (defined as 25% decrease in HR from the baseline value) was treated with intravenous atropine at 0.5 mg. SpO 2 less than 92% was treated by giving O 2 supplementation through a face mask.
During the study period, any local or systemic complications including nausea, vomiting, skin rash, tachycardia, bradycardia, hypotension, hypertension, headache, dizziness, tinnitus, hypoxemia, sedation, respiratory depression, bradypnea, tachypnea, and other side effects were noted. These measurements were recorded by an anesthesiologist who was blinded to the medication administered. All measurements were taken by the same person.
We accepted a type I error of 0.05 and a type II error of 0.80 for detecting a true difference. A difference of 0.5 or greater in independent variables was considered clinically significant. An estimate of SD in independent variables was 1. As a result, we calculated that a minimum number of 27 patients was needed in each group to obtain 5% type 1 error and an 80% power of detecting a difference of 0.5 or more. For each group, 30 patients were included to compensate for possible dropouts. The power calculation was performed with nQuery Advisorw (version 7.0; Statistical Solutions, Saugus, Massachusetts, USA).
Data were analyzed using SPSS (version 16.0; SPSS Inc., Chicago, Illinois, USA). Numerical variables were presented as mean and SD or as median (first to third quartiles) as appropriate, whereas categorical variables were presented as frequency (%). The unpaired Student t-test or the Mann-Whitney test was used for between-group comparisons of numerical variables as appropriate. Within-group comparisons for such variables were made using repeated-measures ANOVA or the Kruskal-Wallis test. Fisher's exact test was used for comparisons of categorical variables. A P-value less than 0.05 was considered statistically significant.
| Results|| |
Sixty-eight patients scheduled for elective hand or forearm surgery expected to last for more than 30 min participated in this study. Six patients were excluded on the basis of the exclusion criteria.
Two patients, one from each group, were excluded after enrollment because of study protocol violations. Of the remaining 60 patients, 30 were randomly assigned to the dexmedetomidine group (group D) or to the magnesium sulfate group (group M).
The two groups were not statistically different with respect to ASA status and demographic data ([Table 1]). There were no statistically significant differences between the two groups in terms of tourniquet time, duration of surgery, sensory block onset time, and motor block onset time, whereas the sensory and motor block recovery time was more prolonged in group D compared with group M, although not statistically significant (P = 0.102 and 0.206) ([Table 2]).
|Table 2 Clinical data tourniquet time, duration of surgery, onset and recovery times of sensory and motor blocks, and intraoperative fentanyl requirement in the two groups (mean and SD)|
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The number of patients who needed additional fentanyl administration intraoperatively was comparable in both groups (P = 0.761). More patients complained of tourniquet pain in the M group compared with the D group, but this was not statistically significant (P = 0.234).
Patients in the D group showed significantly lower HRs at 10, 20, and 30 min after tourniquet inflation as compared with the M group (P < 0.05; [Table 3]). These patients in the D group also showed significantly lower HRs postoperatively, which extended up to 120 min after tourniquet release (P < 0.05; [Table 3]).
As regards MAP, there were statistically significant differences between the two groups. The patients in D group showed lower MAP values at 20 and 30 min after tourniquet inflation as compared with the M group. This effect was obvious 20 min after inflation of tourniquet and extended up to 120 min after tourniquet release (P < 0.05; [Table 4]). Postoperative morphine consumption (mean ± SD) was less at 6, 12, and 24 h in group D compared with group M, but it was not statistically significant (P = 0.211).
None of the patients had significant intraoperative bleeding, nausea, or vomiting. Hypotension occurred in one patient in the D group, who was treated with intravenous ephedrine at 5 mg, intravenous, in increments, with a total dose of 15 mg ([Table 5]).
| Discussion|| |
IVRA is a simple, effective, and widely used method for producing analgesia of an extremity by intravenous injection of a local anesthetic  . Different anesthetic agents and adjuvants have been used for reducing tourniquet pain, for shortening the onset time of sensory and motor block, for improving the quality of anesthesia, and for prolonging postoperative analgesia  .
In our study, we compared the efficacy of two established adjuvants to lidocaine in IVRA, dexmedetomidine and magnesium sulfate.
Dexmedetomidine has evolved as panacea for various applications and procedures with multiple promising delivery routes. The peripheral analgesic effects of dexmedetomidine that potentiate local anesthetics are mediated by α2-adrenergic receptor agonists. It causes hyperpolarization of noradrenergic neurons, which suppresses neuronal firing in the locus ceruleus along with inhibition of norepinephrine release. These actions lead to modulation of nociceptive neurotransmission causing analgesia ,, .
Magnesium sulfate was also demonstrated as a good adjuvant for IVRA. This could be attributed to the antagonistic properties of magnesium on the NMDA receptor and its inhibitory properties for calcium channels. NMDA receptor antagonists can inhibit the induction of central sensitization owing to peripheral nociceptive stimulation and can eliminate hypersensitivity. Calcium channel blockers have revealed antinociceptive effects in animals  .
Kol et al.  in a prospective, randomized, double-blinded study of 75 patients scheduled for hand or forearm surgery found that addition of dexmedetomidine (0.5 μg/kg) to prilocaine improved the quality of anesthesia, decreased tourniquet pain, and decreased analgesic requirements as determined by hemodynamic variables and pain scores. Tramer and Glynn  used magnesium for the treatment of chronic limb pain in IVRA and showed that the addition of magnesium to lidocaine increases the quality of the block and decreases overall failure rate.
In our study we found no significant difference between the two groups as regards sensory onset time, motor onset time, quality of anesthesia, and postoperative analgesia, but there was a nonsignificant difference with regard to tourniquet pain, which was reduced by the dexmedetomidine-containing lidocaine solution in our study.
Tourniquet pain is a common problem complicating the use of a pneumatic tourniquet during surgical procedures involving the upper or lower limb. The mechanism of tourniquet pain remains unclear despite the role of A fibers and unmyelinated C fibers  . Clonidine has also been reported to depress nerve action potentials, especially in C fibers, by a mechanism independent of the stimulation of α2-adrenergic receptors  . This mechanism accounts for strengthening of the local anesthetic block achieved by perineural administration of the drug and could be implicated in the effect seen in our study. Furthermore, the D group also showed significantly lower fluctuation in HR and MAP, which can be attributed to hemodynamic responses related to tourniquet use. These findings also correlate with the study by Memis et al.  , who compared the use of lidocaine alone and mixture of lidocaine and dexmedetomidine for IVRA.
| Conclusion|| |
In our study, dexmedetomidine seems to be superior to magnesium sulfate as an adjuvant to lidocaine in IVRA with respect to tourniquet pain and hemodynamic stability both intraoperatively and postoperatively.
| Acknowledgements|| |
Conflicts of interest
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[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]