|Year : 2016 | Volume
| Issue : 3 | Page : 409-415
The effect of adding magnesium to bupivacaine for popliteal nerve block on anesthesia and postoperative analgesia in achilles tendon repair patients: a randomized double-blinded study
Ayman A El Sayed MD
Department of Anesthesia, Faculty of Medicine, Ain Shams University, Abbassia, Cairo, Egypt
|Date of Submission||24-Aug-2015|
|Date of Acceptance||15-Apr-2016|
|Date of Web Publication||31-Aug-2016|
Ayman A El Sayed
Department of Anesthesia, Faculty of Medicine, Ain Shams University, Abbassia, Cairo 11381
Source of Support: None, Conflict of Interest: None
The aim of this prospective randomized double-blind study was to investigate the effect of adding magnesium to bupivacaine on the onset and duration of sensory and motor block, postoperative visual analog scale (VAS), and total opioid consumption in patients following Achilles tendon repair surgery with popliteal-sciatic nerve blockade.
Patients and methods
A total of 60 patients who underwent Achilles tendon repair surgery and were of American Society of Anesthesiologist I or II physical status with age between 18 and 50 years of age were included in the study. The patients were randomly assigned into two groups: group bupivacaine–magnesium (BM) (n=29) received 30 ml of 0.25% bupivacaine and 2 ml of 10% magnesium sulfate, and group bupivacaine (B) (n=28) received 30 ml of 0.25% bupivacaine and 2 ml of normal saline for popliteal-sciatic blockade using the nerve stimulator technique. We evaluated the patients as regards the onset and duration of sensory and motor block, postoperative VAS scores, and total opioid consumption.
The onset of motor block in group B was significantly longer in comparison with group BM (14.2±2 and 11.9±1.5 min, respectively). At the same time, the duration of sensory and motor block in group BM was significantly longer in comparison with group B (P<0.001). As regards total opioid consumption (tramadol) during the first 12 h postoperatively, it was significantly less in group BM in comparison with group B (190.67±21.8 and 237.86±25.8 mg, respectively). As regards VAS, it was significantly lower in group BM in comparison with group B at 4, 6, 8, 10, and 12 h postoperatively.
The addition of magnesium to bupivacaine prolonged the motor and sensory block duration without increasing side effects, and enhanced the quality of postoperative analgesia, which was manifested by lower VAS and less total opioid consumption. Moreover, the addition of magnesium speeds up the onset of motor block.
Keywords: bupivacaine;, magnesium, popliteal-sciatic block, achilles tendon
|How to cite this article:|
El Sayed AA. The effect of adding magnesium to bupivacaine for popliteal nerve block on anesthesia and postoperative analgesia in achilles tendon repair patients: a randomized double-blinded study. Ain-Shams J Anaesthesiol 2016;9:409-15
|How to cite this URL:|
El Sayed AA. The effect of adding magnesium to bupivacaine for popliteal nerve block on anesthesia and postoperative analgesia in achilles tendon repair patients: a randomized double-blinded study. Ain-Shams J Anaesthesiol [serial online] 2016 [cited 2021 Oct 17];9:409-15. Available from: http://www.asja.eg.net/text.asp?2016/9/3/409/189561
| Introduction|| |
The effectiveness of the anesthesia techniques has an important role in increasing the ambulatory orthopedic procedure . Regional anesthesia techniques are used frequently as an alternative to general anesthesia in these procedures . Foot and ankle surgery is accompanied by pain for the first 2 days following surgery . Traditional opioid-based postoperative pain management can lead to inadequate pain relief and is accompanied by side effects. Both popliteal-sciatic and femoral nerves provide innervation of the foot and ankle joint, including innervation of the ankle capsule and the talocalcaneonavicular joint .
There are a lot of local anesthetics for peripheral nerve blockade, including levobupivacaine, bupivacaine, and ropivacaine. The analgesic duration after peripheral nerve blockade with bupivacaine is longer than  or the same as  the duration of analgesia provided by ropivacaine. Furthermore, bupivacaine is less expensive compared with levobupivacaine or ropivacaine.
Agents such as magnesium and clonidine are used as adjuvants to local anesthetics in peripheral nerve blockade . Magnesium has a role in various physiological processes that include vascular tone, transmembrane ion flux, control of calcium channel gating, neuronal activity, heart excitability, and neurotransmitter release . It is proved that the addition of magnesium sulfate to local anesthetics for neuraxial anesthesia improves the quality of analgesia and prolongs the duration of anesthesia . In-vitro and in-vivo studies have demonstrated that magnesium enhances the local anesthetics’ effect on peripheral nerves . Studies proved that it acts directly on peripheral nerves. The antinociceptive effect of magnesium is related to its calcium antagonist and N-methyl d-aspartate receptor blocking effect .
We conducted our study to investigate the effects of adding magnesium sulfate to bupivacaine for popliteal-sciatic block. We compared the onset and duration of sensory and motor block, postoperative visual analog scale (VAS) scores, and total opioid consumption in patients who underwent Achilles tendon repair with popliteal-sciatic nerve blockade.
| Patients and methods|| |
The study was a prospective, randomized, double-blinded, comparative clinical study. A total of 60 patients (30 patients in each group) who underwent Achilles tendon repair surgery at a tertiary hospital, Jeddah, Saudi Arabia, between January 2014 and January 2015 were selected for participation in this study. Approval was obtained from the local ethics committee and written informed consent from each patient was obtained. All patients were of American Society of Anesthesiologist I or II physical status and between 18 and 50 years of age. Exclusion criteria were as follows: a history of advanced renal, cardiac, or hepatic disease, known allergy to the study drugs (as shown on the topical use or when orally supplied), undergoing chronic treatment with calcium channel blockers, hypermagnesemia, central or peripheral neurological disease, pregnancy, drug or alcohol abuse, chronic pain, psychiatric diseases, localized infection at the site of the popliteal-sciatic block, and bleeding disorder.
The patients were randomly assigned using the closed envelope method into two groups: group bupivacaine–magnesium (BM) (n=29) received 30 ml of 0.25% bupivacaine (Hikma Pharmaceuticals, Amman, Jordan) and 2 ml of 10% magnesium sulfate (PSI, Jeddah, Saudi Arabia), and group bupivacaine (B) (n=28) received 30 ml of 0.25% bupivacaine and 2 ml normal saline for popliteal-sciatic blockade. All local anesthetic solutions were prepared immediately before administration by one of the authors not involved in either performing the blockade or collecting the data.
Upon arrival to the preoperative room, we applied the standard monitoring: noninvasive blood pressure, oxygen saturation (SpO2), and ECG. We inserted a 20 G intravenous cannula in the nondominant hand, and then we administered midazolam (Hikma Pharmaceuticals) 0.02 mg/kg intravenously before the procedure.
The sciatic nerve is considered a nerve bundle with two separate nerves: tibial and common peroneal. These two components eventually diverge 5–12 cm proximal to the crease of the popliteal fossa. We could block the sciatic nerve within the common epineural sheath and proximal to the terminal division through a posterior approach. The patient should be in the prone position with the foot protruding off the operating bed. This technique involved the detection of a point 1 cm lateral to the center of the popliteal fossa and 7–10 cm above the popliteal crease , as shown in [Figure 1].
|Figure 1 Posterior approach to Popliteal nerve block (posterior approach). Reprinted from: Wildsmith JAW, Armitage EN. Principles and Practice of Regional Anaesthesia, 2nd Edn. Edinburgh: Churchill-Livingston, 1993, with permission from Elsevier.|
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We sterilized the block site using betadine and alcohol. A 100 mm 22 G sterile insulated needle (Echoplex; Vygon, Paris, France) was connected to a nerve stimulator (Plexygon; Vygon Italia, Padua, Italy) that delivers a pulsed electrical current at several milliamperes (mA). Palpable or visible twitches of the foot or toes at 0.2–0.5 mA current were our target. Either dorsiflexion and eversion or plantar flexion and inversion were accepted responses. If the evoked response persisted at 0.2 mA, the needle was slightly withdrawn until the response was maintained between 0.2 and 0.5 mA. The tested solution was injected slowly with a negative aspiration test for blood and meticulously slow injection (e.g. ≤20 ml/min) . A volume of 20 ml of xylocaine 0.5% was administered using a 25 G spinal needle around the mid-thigh by means of multiple injections to guard against tourniquet pain. Tourniquet pressure was adjusted at 300 mmHg. All blocks were performed by the same experienced anesthesiologist, who was blinded to the solution used for the blockade.
After block achievement, common peroneal and tibial nerve distributions were tested by a blinded researcher for sensory and motor loss every 3 min until complete sensory and motor effects were achieved. Any cases without complete sensory loss in the distributions of the nerves within half an hour after the end of the injection were considered failure of the block.
The motor block was evaluated using a modified Bromage scale .
- 2, full strength of motor activity (no change).
- 1, decreased strength of motor activity.
- 0, no motor activity.
Similarly, the sensory block was tested with ice as follows:
- 2, no change of sensation.
- 1, decreased sensation.
- 0, no sensation.
After surgery, a nurse anesthetist who was blinded to the allocation of patients assessed the patients every 15 min until complete restoration of sensory and motor functions.
The sensory block duration was defined as the time period between the end of administration of local anesthetic and return of normal sensation (i.e. sensory score 0, compared with the contralateral lower limb as a reference). The motor block duration was defined as the time period between the end of administration of local anesthetic and the complete recovery of motor function (i.e. motor score 0).
Mean blood pressure and heart rate (HR) during surgery were recorded before the block, 30 min after the end of injection of local anesthetic, at the end of the surgery, and 2 h postoperatively. When the mean blood pressure decreased by 20% of the baseline, ephedrine 5 mg intravenously was given. Bradycardia was defined as a HR less than 50 beats/min and was treated with atropine 0.5 mg intravenously. Postoperative pain was measured using a VAS (from 0=no pain to 100=the worst pain that have been experienced) at 2, 4, 6, 8, 10, and 12 h postoperatively .
Patient-controlled analgesia pump (SIMS Graseby Limited, Watford, UK) was started for postoperative analgesia using tramadol (tramadol HCl 100 mg, 2 ml; German pharmaceutical company Grünenthal GmbH, West Germany) (3 mg/ml tramadol in 50 ml of 0.9% normal saline, 10 mg/h infusion, 15 mg bolus with a 15-min lock-out time and no 4 h limit).
Adverse events such as nausea, vomiting, bradycardia, hypotension, and pruritus were recorded at 4, 8, and 12 h after surgery.
The primary outcome was the duration of sensory block, which was recorded every 15 min. The secondary outcomes included onset of sensory and motor block, duration of motor block, total opioid consumption, and postoperative VAS.
Sample size calculation was carried out using PASS 11 software program (NCSS LLC, Kaysville, USA). The power analysis was performed on the basis of the duration of sensory block as the primary outcome. Group sample sizes of 25 patients per group would achieve an 80% power to detect a difference of 60 min in the duration of sensory block, with estimated means of 5 and 6 h, estimated group SDs of 40 and 50, and a significance level (α) of 0.05 using a two-sided two-sample t-test.
The statistical analysis was performed using a standard SPSS software package, version 17 (SPSS Inc., Chicago, Illinois, USA). Student’s t-test was used to analyze normally distributed data and were expressed as mean±SD. Categorical variables were analyzed using the χ2-test and were expressed as numbers (%). Non-normally distributed data were compared using the Mann–Whitney test and were expressed as median (interquartile range). A P value less than 0.05 was considered statistically significant.
| Results|| |
A total of 60 patients were enrolled in the study. The following patients were excluded: two patients in the group B because of failed block, and one patient in group BM because of a failure of communication. There were no statistically significant differences between the two groups as regards the patients’ demographic data, duration of surgery [Table 1] or the HR and mean arterial pressure [Table 2]. Moreover, there was no significant difference between the two groups as regards the incidence of side effects. In group BM, two patients complained of nausea and one patient vomited, whereas in group B one patient complained of nausea and one patient vomited. Only one patient in group BM developed bradycardia and atropine 0.5 mg intravenously was given. No patients in either groups developed hypotension or pruritis.
The characteristics of block are shown in [Table 3]. As regards the onset of motor block, there was a significant delay in group B in comparison with group BM (14.2±2 and 11.9±1.5 min, respectively).
|Table 3 Onset and duration of sensory and motor block and total opioid consumption|
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At the same time, the duration of motor block was significantly longer in group BM in comparison with group B (340±19 and 285±17 min, respectively). However, there was no significant difference in the onset of sensory block between the two groups. Finally, as regards the duration of sensory block, it was significantly longer in group BM in comparison with group B (423.3±15.3 and 350.36±18.1 min, respectively).
As regards total opioid consumption (tramadol) during the first 12 h postoperatively, it was significantly less in group BM in comparison with group B (190.67±21.8 and 237.86±25.8 mg, respectively).
As regards the VAS, it was significantly lower in group BM in comparison with group B at 4, 6, 8, 10, and 12 h postoperatively [Figure 2].
|Figure 2 Visual analog scale (VAS). Lines represent median data and error bars are IQR, *mean significant (P value <0.05).|
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No significant differences were shown between the two groups as regards the adverse events.
| Discussion|| |
The most important findings of the present study were that the addition of magnesium to bupivacaine for popliteal-sciatic block prolonged the duration of motor and sensory block, decreased the onset time of motor block, improved postoperative analgesia quality, and decreased the total opioid consumption postoperatively.
Popliteal fossa nerve blocks have well-documented efficacy and safety when performed for ankle and foot surgery . The popliteal-sciatic nerve block procedure was described in 1923, but it has a lot of limitations such as dysesthesia and problems with the effectiveness of the block on sciatic nerves or its branches . However, with improvements in nerve stimulators and insulator needles, popliteal-sciatic nerve block procedure has been succeeded as regional anesthesia for surgeries or postsurgical pain control because of its reliability, value with high success, and short-time procedure . Borgeat et al.  reported that plantar flexion and inversion increase the success rate to be not less than 97%.
Bupivacaine (0.5%) has been used frequently for lower limb anesthesia with peripheral nerve blockade , whereas some researchers used bupivacaine 0.25%, which was considered an appropriate alternative for 0.5% bupivacaine with adequate surgical anesthesia .
Although there is no exact mechanism of analgesia due to magnesium administration, many authors have proved that magnesium is accompanied by a reduced analgesic requirement . Most of these studies have investigated the administration of magnesium sulfate either neuraxial , or systemic , whereas there are some studies on the using of magnesium for peripheral nerve block ,,.
Our choice of the dose of magnesium sulfate (10%, 2 ml, i.e. 200 mg of magnesium sulfate) was based on other studies conducted by Lee and colleagues and Ekmekci and colleagues, which used 200 and 150 mg magnesium sulfate, respectively .
In accordance with our study, there are multiple studies that investigated the role of magnesium in increasing the duration of sensory and motor block or decreasing analgesic requirements when given systemically, neuroaxially, or for peripheral nerve blockade.
On the basis of a study by Ekmekci et al. , in which a total of 107 patients underwent elective anterior crucial ligament reconstruction, 1 ml of 15% magnesium sulfate was added to 19 ml of 0.25% levobupivacaine for femoral nerve block. It was observed that magnesium decreased rescue analgesic requirements and block onset time and increased the motor and sensory block duration without any additional side effects.
To the best of our knowledge, this is the first study that evaluated the effect of addition of magnesium to bupivacaine for popliteal-sciatic blockade.
Magnesium is a good adjuvant that has been proven to decrease analgesic and anesthetic requirements in various applications (intravenous, peripheral nerve blockade, intrathecal, and epidural) .
As regards the systemic infusion of magnesium sulfate, there was a study by Koinig et al. , which involved 46 patients who underwent arthroscopic knee surgery under general anesthesia. They proved that the administration of preoperative (50 mg/kg) and postoperative (8 mg/kg/h) magnesium infusion decreases both postoperative and intraoperative analgesic requirements. This study indicates that, when magnesium sulfate was given systemically or for peripheral nerve block, it has the same effect as regards the decreased analgesic requirements.
In a clinical study of epidural anesthesia , when 50 mg of magnesium sulfate was used epidurally with bupivacaine for patients undergoing lower limb surgeries, the onset of epidural anesthesia was accelerated without significant complications. However, when 50 mg of magnesium sulfate was added to 0.25% ropivacaine for caudal analgesia in children, there was a reduction in the anesthetic requirements . These two studies were similar to our study as regards the onset of anesthesia and the total anesthetic requirements, respectively.
In accordance with our study, Anbarci et al.  have demonstrated that, during brachial plexus block using 40 ml of 1.25% lidocaine, a 5 mg/kg bolus and a 500 mg/h magnesium infusion decreased total opioid consumption and increased sensory block duration in a study involving 70 patients who were scheduled for upper limb surgery.
Moreover, Gunduz et al.  proved that adding 150 mg magnesium to 5 mg/kg of 2% prilocaine for axillary brachial plexus block developed pronounced prolongation of motor and sensory block.
Ozalevli and colleagues compared bupivacaine, fentanyl, and magnesium combination intrathecally injected in patients with lower extremity surgeries. They concluded that magnesium delayed the motor and sensory block onset. Moreover, the duration of spinal anesthesia was prolonged . This study was different from our study as regards the onset of motor and sensory block. This difference may be attributed to the route of injection (intrathecal vs. peripheral nerve blockade in our study).
In contrast to our results, a study by Birbicer et al.  found no difference in analgesia when 50 mg of magnesium was added to 0.25% ropivacaine for caudal anesthesia in pediatric patients. There is no exact mechanism for this contradictory finding. However, it does not seem to be dependent on the ropivacaine action and magnesium sulfate on the receptors within the Na channel and may be due to a relatively inadequate dose of magnesium sulfate used in that study.
However, in the study by Hung et al. , the results were different from our study. Unexpectedly, the addition of magnesium sulfate significantly decreased the duration of blockade by bupivacaine and lidocaine of sciatic nerve block in rats. Thus, it does not seem to be an important adjuvant for peripheral nerve blockade.
The mechanism by which magnesium sulfate decreases the duration of the block is unclear. The explanation of this unexpected response (shortening sciatic block duration in vivo) may be due to local vasodilatation in the perineural injection compartment. As magnesium sulfate mostly causes vasodilatation of the tissues around the site of injection, it will accelerate the uptake of local anesthetics, and then shorten the duration of the block .
Our study had some limitations. First, magnesium was not examined as a sole analgesic agent. Second, we did not include a group that received systemic magnesium. Third, we investigated only an exact dose and concentration of magnesium sulfate. Further studies on the effects of different doses and methods of administration of magnesium are necessary.
| Conclusion|| |
The addition of magnesium to bupivacaine prolonged the motor and sensory block duration without increasing side effects, and enhanced the quality of postoperative analgesia, which was manifested by lower VAS values and less total opioid consumption. Moreover, the addition of magnesium speeds up the onset of motor block.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3]