|Year : 2015 | Volume
| Issue : 3 | Page : 402-406
A comparative study between the addition of MgSO 4 against dexamethasone to bupivacaine in the prolongation of ultrasound-guided interscalene nerve block for shoulder arthroscopy
Niven G Fahmy MD , Dalia M Ahmed, Ghada M Sameer
Department of Anaesthesiology, Faculty of Medicine, Ain Shams University, Cairo, Egypt
|Date of Submission||10-Dec-2014|
|Date of Acceptance||02-May-2015|
|Date of Web Publication||29-Jul-2015|
Niven G Fahmy
Department of Anaesthesiology, Faculty of Medicine, Ain Shams University, Cairo, 11672
Source of Support: None, Conflict of Interest: None
Local anesthetic adjuvants have been studied previously to prolong the duration of analgesia after peripheral nerve block and thus reduce postoperative adverse reactions associated with excessive systemic analgesic intake. The aim of this study was to compare the addition of MgSO 4 against dexamethasone to bupivacaine in the prolongation of ultrasound-guided interscalene brachial plexus block (ISPB) for shoulder arthroscopy.
Patients and methods
A total of 63 patients, ASA I and II grades, undergoing arthroscopic rotator cuff repair were enrolled in this study. The ISPB was performed with 0.5% bupivacaine 20 ml plus either 5 ml of 10% MgSO 4 (group M) or 5 ml of normal saline containing dexamethasone 8 mg (group D) or 5 ml of 0.9% NaCl (group C). The following data were collected: the onset of sensory block, the analgesic duration (time of the first call for analgesics), the occurrence of satisfactory motor block, the motor block duration, and postoperative analgesic consumption.
The magnesium sulfate group and the dexamethasone group patients showed significantly higher analgesic duration values and significantly lower total meperidine consumption values than control group patients.
The addition of either magnesium sulfate or dexamethasone to bupivacaine in ISPB prolongs the analgesic duration significantly and also decreases the postoperative analgesic consumption.
Keywords: bupivacaine, dexamethasone, interscalene brachial plexus block, magnesium sulfate, peripheral nerve stimulator, shoulder arthroscopy, ultrasound
|How to cite this article:|
Fahmy NG, Ahmed DM, Sameer GM. A comparative study between the addition of MgSO 4 against dexamethasone to bupivacaine in the prolongation of ultrasound-guided interscalene nerve block for shoulder arthroscopy. Ain-Shams J Anaesthesiol 2015;8:402-6
|How to cite this URL:|
Fahmy NG, Ahmed DM, Sameer GM. A comparative study between the addition of MgSO 4 against dexamethasone to bupivacaine in the prolongation of ultrasound-guided interscalene nerve block for shoulder arthroscopy. Ain-Shams J Anaesthesiol [serial online] 2015 [cited 2020 Apr 9];8:402-6. Available from: http://www.asja.eg.net/text.asp?2015/8/3/402/161719
| Introduction|| |
Shoulder arthroscopy has been performed not only as a diagnostic tool but also therapeutically, for example, for rotator cuff repair. The most suitable block for shoulder arthroscopy is the interscalene approach to the brachial plexus  .
The use of ultrasound in performing peripheral nerve block has gained wide recognition as it decreases the complications associated with blind techniques with better visualization of local anesthetic spread, therefore decreasing the amount of local anesthetic needed to provide surgical anesthesia. Patients develop severe pain on the first postoperative day after the effect of the local anesthetics has worn off; therefore, prolongation of the duration of local anesthetics is desirable , .
A number of local anesthetic adjuvants, such as ketamine  , clonidine  , dexmedetomidine  , and corticosteroids  have been evaluated for their ability to prolong the duration of local anesthetic block, and the results have been varied. Clonidine has been reported to prolong the duration of local anesthetic block, but with an increased risk of hypotension and sedation, which limit its use. Ketamine also has many adverse effects such as hallucinations, drowsiness, and unpleasant feelings  .
The addition of dexamethasone to bupivacaine has been shown to prolong the analgesic duration of brachial plexus blocks. This effect is due to its local action on nociceptive c-fiber mediated through glucocorticoid receptors and anti-inflammatory action  .
Magnesium sulfate has been proved to have antinociceptive effects in animal and human models by blocking the N-methyl-D-aspartate receptor and associated calcium channels, thus preventing the central sensitization that is caused by peripheral nociceptive stimulation  .
The addition of magnesium sulfate to local anesthetics for neuroaxial anesthesia prolongs the duration of anesthesia and improves the quality of block , .
We conducted a clinical study to compare the effects of adding magnesium sulfate against adding dexamethasone to long-acting local anesthetics (bupivacaine) on the durations of sensory and motor blocks, and on the analgesic qualities of interscalene nerve block in patients undergoing arthroscopic rotator cuff repair.
| Patients and methods|| |
After obtaining approval from the hospital ethical committee and written informed consent from 63 patients, a sample of patients with ASA physical status I-II grades, of both sexes, age ranging between 30 and 50 years, and scheduled for shoulder arthroscopic rotator cuff repair under regional ultrasound nerve stimulation-guided interscalene brachial plexus block (ISPB), in the Ain Shams University Hospital during the period between March 2013 and December 2014, was enrolled prospectively in this prospective randomized double-blind study. Using a computer-generated randomization on the basis of patients' hospital number, they were allocated randomly to lie in three equal groups (21 each). Patients in group M received 20 ml bupivacaine 0.5% plus 5 ml of 10% MgSO 4 (the total volume injected in all patients was 25 ml), patients in group D received 20 ml bupivacaine 0.5% plus 8 mg dexamethasone plus 3 ml 0.9% NaCl, and lastly group C received 20 ml bupivacaine plus 5 ml 0.9% NaCl for ISPB. Injected solutions were prepared in a sterile manner before the technique and coded so that the investigator who performed the technique was blinded to the types of solutions injected. The sample size was calculated using the PASS 11 program: Dr. Jerry L. Hintze Kaysville, Utah 84037, USA.
Exclusion criteria included patients who refused regional anesthesia, those with a history of cardiac, hepatic, or renal disease, chronic treatment with calcium channel blockers or hypermagnesemia, those with coagulopathy, mental retardation, or neuropathy involving the brachial plexus, and patients with uncontrolled hypertension.
Preoperative investigations were performed (ECG, complete blood picture (CBC), the coagulation profile, and liver and kidney functions). Details of the anesthetic technique and study protocol were explained to the patients at the preoperative visit. All local anesthetic solutions were prepared and numerically coded immediately before administration by one of the authors not involved in either performing the interscalene nerve block or collecting data.
Patients were premedicated in the induction room with midazolam 0.02 mg/kg intravenously before the procedure. Upon arrival to the operating theatre, 500 ml lactated Ringer's solution was infused intravenously, and basic monitors were applied (ECG, pulse oximeter, noninvasive blood pressure). Patients were placed in the supine position with their heads rotated towards the nonoperative side. To identify the brachial plexus at the level of roots and trunks between the anterior and the middle scalene muscles, we used ultrasound (M-Turbo; Sonosite, Washington, DC, USA).
The operative side was cleaned using an antiseptic iodine solution and draped. Local infiltration of the skin at the point of needle insertion was carried out with 2 ml lidocaine 1%, and then a sterile 50-mm 22-G insulated needle (Stimuplex; B. Braun, Melsungen, Germany) was advanced using an in-plane technique. A multifrequency transducer (LOGIQe, 8L-RS 42 × 8 mm 4-12 MHz broad band; General Electric, Waukesha, Wisconsin, USA) was used in this study. It was held in the nondominant hand to locate the brachial plexus roots between the anterior and the middle scalene muscles at the level of the cervical vertebra number 6 deep to the sternocleidomastoid muscle. At the same time, a nerve stimulator was used for precise localization of the needle (Ezstim II ES 400 Dual-Purpose Peripheral Nerve Stimulator is Life-Tech International, Stafford, Texas, USA). When an output current of less than 0.5 mA elicited a slight distal motor response in muscles (deltoid, biceps, or triceps), the local anesthetic solution was administered after negative aspiration. Ultrasound guidance helps ensure proper deposition of the solution around nerve roots. After the completion of local anesthetic administration, the time was recorded as a baseline for the time interval. The anesthesiologist who performed the block and the researcher who recorded the data were blinded to the patient groups.
The sensory block was assessed by a pin-prick test using a three-point scale [0 = normal sensation; 1 = loss of sensation of pin prick (analgesia); and 2 = loss of sensation to touch (anesthesia)]. Also, motor block was assessed according to shoulder movement using a three-point scale: 0 = normal movement; 1 = diminished but not totally absent motor strength (paresis); and 2 = unable to elevate the arm (lack of movement). The onset of sensory block was defined as the period between the completion of local anesthetic administration and the loss of sensation of pin prick performed every minute (sensory score = 1), whereas the onset of motor block was defined as the period between the completion of local anesthetic administration and absent movement (motor score = 2). The duration of motor block was defined as the period between the onset of motor block till complete recovery of motor function (motor score = 0).
Postoperative pain was measured using a numeric rating scale (NRS, from 0 = no pain to 100 = worst pain ever experienced) at 4, 8, 12, and 24 h after the end of surgery. Hemodynamic parameters, mean arterial blood pressure, heart rate, and SpO 2 were recorded throughout the whole procedure and at 4, 8, 12, and 24 h postoperatively.
The duration of analgesia was defined as the time interval between the onset of sensory block till the first call for analgesia. Postoperative analgesia was standardized. Meperidine 0.5 mg/kg was administered intravenously when patients complained of considerable pain (NRS ≥ 40). If the NRS exceeded 40 at any time after 30 min of meperidine administration, , an additional dose of 0.25 mg/kg meperidine was given with a maximum of 1 mg/kg in 2 h duration. The cumulative meperidine consumption was recorded during the first postoperative 24 h.
Data were analyzed using SPSS 18.0 for Windows (SPSS Inc., Chicago, Illinois, USA). Analysis of variance was used to compare the three groups for quantitative data, and if there was a significant difference among the groups, a post-hoc Tukey's test was performed. The χ2 -test was used for the comparison of qualitative data. Continuous numerical data were presented as mean and SD, and categorical data were presented as the number of patients. P-values of 0.05 were considered significant.
| Results|| |
Sixty-three patients undergoing shoulder arthroscopic rotator cuff repair were enrolled successfully in this study: 21 in each group. The variables in the demographic data did not show a statistically significant difference between the three groups with respect to the age, the sex, the weight, the height, the ASA physical status, and the duration of surgery [Table 1].
There were no significant differences in the onset of sensory block and also the time for occurrence of satisfactory motor block between the three groups. The onset of the block was 13.5 ± 0.92 min in group C, 14.3 ± 1.4 min in group M, and 13.5 ± 1.1 min in group D (P > 0.05). The time for the occurrence of satisfactory motor block was 15.7 ± 0.85 min in group C, 15.9 ± 0.88 min in group M, and 16 ± 0.74 min in group D (P > 0.05) [Table 2].
Regarding the motor block duration also, there were no significant differences between the three groups. It was 240.6 ± 18.8 min in group C, 244.1 ± 38.4 min in group M, and 247 ± 19.8 min in group D (P > 0.05) [Table 2].
The analgesic duration was 254 ± 15.2 min in group C, 721.85 ± 98.6 min in group M, and 744.8 ± 20.8 min in group D, with a P-value of less than 0.05, thus implying that the analgesic duration was significantly longer in the magnesium and dexamethasone group than in the control group [Figure 1] and [Table 2].
|Figure 1: The analgesic duration (time of the first call for analgesics) in the three groups. Columns are mean and error bars are SD.|
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Postoperative cumulative meperidine consumption was 38.4 ± 6.7 mg in M group and 42.6 ± 6.4 mg in D group, which means that it was significantly less than that in C group (88 ± 5.4 mg) (P < 0.05) [Table 2] and [Figure 2].
|Figure 2: Meperidine consumption in the three groups. Columns are mean and error bars are SD.|
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| Discussion|| |
This study showed that the addition of either 500 mg magnesium sulfate or 8 mg dexamethasone to a long-acting anesthetic (bupivacaine) prolonged the duration of analgesia and reduced the postoperative pain after ultrasound-guided interscalene nerve block in patients undergoing rotator cuff repair. The sensory onset and the motor block duration were similar in all groups, showing that the addition of either magnesium sulfate or dexamethasone to bupivacaine enhanced neither the sensory onset nor the motor block duration.
ISPB is preferable to general anesthesia for shoulder surgery because it results in lesser nonsurgical intraoperative time, a shorter stay in the postanesthesia care unit, and lesser postoperative nausea and vomiting  . Also, the use of ultrasound together with peripheral nerve stimulation enhanced the accuracy of the block because it ensures proper deposition of the local anesthetic solution around the plexus roots.
The mechanism of analgesia produced by magnesium is not fully understood; most of the studies investigated systemic  or neuroaxial roots  , whereas studies on the administration of magnesium for peripheral nerve block are minimal  . The surface charge theory is the primary hypothesis for the analgesic properties of magnesium on peripheral nerves. Many authors supported this theory as Akutagawa et al.  showed that the modulation of the external magnesium concentration that bathe a nerve bundle resulted in the enhancement of the conduction block due to local anesthetics.
Also, Mert et al.  reported that a high concentration of Mg 2+ and Ca 2+ ions attracted by the negative charges of the outer membrane surface affected Na + channel gating, which could cause hyperpolarization. When the nerve fiber is hyperpolarized, it is more difficult to reach the threshold level, and this causes conduction block of this nerve.
The voltage-dependent antagonism of NMDA receptors is another possible mechanism for the analgesic action of magnesium; this leads to the prevention of central sensitization from peripheral nociceptive stimulation and decreases acute pain after injury.
Several investigations , have proved that effective analgesia was achieved by magnesium sulfate; magnesium was administered through the intravenous or the neuroaxial routes, and so NMDA receptors can be reached; however, it is less certain whether NMDA receptors are involved in the peripheral blocks. Lee et al.  documented that no enhancement of the duration of the interscalene nerve block occurred when the NMDA antagonist (ketamine) was added to ropivacaine.
In agreement with our results, Gunduz et al.  investigated the effect of perineural magnesium on the duration of axillary plexus block, and proved that the addition of magnesium to the intermediate-acting local anesthetic (prilocaine) prolonged the duration of the sensory block significantly; however, they did not evaluate the effect of magnesium on the consumption of postoperative analgesics.
Also, Weissberg et al.  found an inverse relationship between the serum magnesium level and the severity of pain. However, it was not confirmed whether the antinociceptive effect was due to the local action of magnesium on the brachial plexus fibers or was related to the systemic absorption of magnesium.
Turan et al.  proved that the addition of magnesium to lidocaine enhanced the quality of anesthesia and analgesia in intravenous regional block.
In contrast, unexpectedly, Hung et al.  found that three different concentrations of magnesium had shortened the block duration by lidocaine, bupivacaine, and ropivacaine when injected around the sciatic nerve. They concluded that magnesium, when added to an amide local anesthetic, in peripheral nerve block is not useful. This antagonism was unclear and appeared to be independent of the local anesthetic and magnesium sulfate action at the local anesthetic receptor within a Na + channel.
Meanwhile, dexamethasone has been found to prolong the duration of lidocaine when used in axillary blocks  and intravenous regional anesthesia, which resulted in significantly lower mean postoperative analgesic requirements  .
The mechanism of corticosteroid-produced analgesia is not fully understood. It is suspected to be mediated by the inhibition of synthesis and the release of various inflammatory mediators; this effect has been suggested to last up to 48 h ,, .
Peter et al.  investigated whether the duration of analgesia could be extended by adding dexamethasone to bupivacaine 5 mg/ml (with epinephrine 1 : 200 000) with 75 μg clonidine; they found that the dexamethasone group had an ~12-h longer sensory duration and less postoperative opioid requirement.
None of the previous studies can rule out a systemic effect for the improved analgesia found from peripherally administered steroids.
| Conclusion|| |
The addition of either 500 mg magnesium sulfate or 8 mg dexamethasone to 20 ml bupivacaine 0.5% in ultrasound nerve stimulation-guided ISPB for shoulder arthroscopic surgery prolonged the duration of analgesia significantly and decreased the postoperative analgesic requirement. Hence, this study suggests that either magnesium or dexamethasone may be a useful alternative as an adjuvant to long-acting local anesthetics for interscalene nerve block.
| Acknowledgements|| |
Conflicts of interest
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[Figure 1], [Figure 2]
[Table 1], [Table 2]