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Year : 2014  |  Volume : 7  |  Issue : 1  |  Page : 65-69

Intravenous regional anesthesia: effect of magnesium using two different routes of administration

1 Departments of Anesthesia and Intensive Care, Faculty of Medicine, Ain-ShamsUniversity, Cairo, Egypt
2 Departments of Anesthesia and Intensive Care, Faculty of Medicine, Suez Canal University, Ismaïlia, Egypt

Date of Web Publication31-May-2014

Correspondence Address:
Sherif S Wahba
MD, Departments of Anesthesia and Intensive Care, Faculty of Medicine, Ain-ShamsUniversity, Cairo
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/1687-7934.128419

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Magnesium has been reported as an adjuvant to local anesthetics to improve the quality of intravenous regional anesthesia (IVRA); however, different routes of administration have not been compared before. The aim of this study was to compare between the effect of intravenous infusion of magnesium and the effect when it is added to a local anesthetic on the quality of analgesia and opioid consumption during IVRA in patients undergoing hand surgery.
Patients and methods
Fifty-nine patients undergoing elective hand surgery were randomly allocated to one of three groups: the R group (n = 20 patients), which received IVRA using ropivacaine 0.2%; the RM group (n = 20 patients), which received IVRA using ropivacaine 0.2% and magnesium sulfate 10 mg/kg; and the RMV group (n = 19 patients), which received IVR using ropivacaine 0.2% and a systemic intravenous single dose of magnesium sulfate 30 mg/kg. The primary outcome measure included morphine consumption in the first 24 h andthe secondary outcome measure included onset of both sensory and motor blockade, tourniquet pain, intraoperative fentanyl consumption, and postoperative pain using the Verbal Rating Scale (VRS).
Onset times of sensory and motor blockades were shorter in the RM group (10.5 ± 4 and 14 ± 5 min) than in the R group (16.5 ± 6 and 21 ± 6 min) and RMV group (16 ± 5.5 and 20.5 ± 5.3 min). Time to first analgesic requirement was significantly longer in the RMV group (98 ± 12 min) than in the R group (70 ± 11 min) and RM group (75 ± 13 min), whereas the 24 h morphine consumption in the RMV group (14.5 ± 8.7 mg) was significantly lower than that in the RM group (25 ± 10 mg)and Rgroup (27 ± 15 mg). Tourniquet discomfort was significantly lower in the RM group [1 (0-2)] than in the R group [2 (1-4)] and RMV group [3 (1-4)]. Intraoperative fentanyl consumption was lower in the RM group (20.5 ± 9) than in the Rgroup (43.8 ± 9) and RMV group (38 ± 15),whereas VRS was significantly lower in the RM Vgroup at 1, 3, 6, and 12 h (P < 0.05) in comparison with the other groups.
The addition of magnesium to ropivacine in the IVRA improved the quality of block and reduced the tourniquet discomfort,and the systemic magnesium administration reduced the postoperative pain and morphine consumption.

Keywords: Intravenous regional anesthesia, local anesthetics, magnesium, postoperative pain

How to cite this article:
Wahba SS, Tammam TF. Intravenous regional anesthesia: effect of magnesium using two different routes of administration. Ain-Shams J Anaesthesiol 2014;7:65-9

How to cite this URL:
Wahba SS, Tammam TF. Intravenous regional anesthesia: effect of magnesium using two different routes of administration. Ain-Shams J Anaesthesiol [serial online] 2014 [cited 2022 Nov 27];7:65-9. Available from:

  Introduction Top

Intravenous regional anesthesia (IVRA) is one of the safest and easiest techniques of regional anesthesia for surgery of short procedures on the upper limbs [1]. However, tourniquet pain [2] and lack of postoperative analgesia are the main drawbacks of IVRA [3],[4]. Basically, obtaining a satisfactory degree of IVRA requires overcoming tourniquet pain, prolongation of postoperative analgesia, and obtaining fast onset with the least concentration of local anesthetic. Therefore, the addition of adjuncts has been shown to improve both tourniquet pain tolerance and postoperative analgesia [5].

For many years, magnesium has been successfully used in the treatment of eclampsiaand some forms of cardiac arrhythmias and inthe management of introperative and postoperative analgesia [6],[7]. Also, magnesium has been shown to reduce pain associated with propofol [8] and rocuronium [9] injection. Several studies have evaluated the role of magnesium during IVRA. The role of magnesium sulfate to overcome the drawbacks of IVRA using different routes of administration has not been evaluated before. Therefore, this study was designed to compare the effects of two different routes of administration of magnesium on postoperative pain and tourniquet pain during IVRA.

  Patients and methods Top

After obtaining approval of the hospital's Research Ethics Committee and written informed consent from each patient, 59 patients between the ages of 18 and 60 years with ASA physical status I-II scheduled for elective hand surgery under IVRA were enrolled in a prospective comparative randomized clinical study. The study was conducted from November 2011 to October 2012 in Al Jahra Hospital, Kuwait Ministry of Health. Exclusion criteria were hepatic, renal, cardiac dysfunction, heart block, pregnancy, treatment with calcium channel blockers, and known allergy to study drugs. The patients were randomly assigned on a one-to-one ratio into three groups. Randomization was performed by means of a computer-generated random-numbers table. Before placement of the block, intravenous access and standard monitoring of electrocardiography, pulse oximetry, and noninvasive blood pressure were established. All patients were premedicated with oral diazepam (7.5 mg) 30 min before the block procedure. In group R (n = 20), IVRA was performed using 30 ml of ropivacaine 0.2%. Patients in group RM (n = 20) received IVRA using 30 ml of ropivacaine 0.2% and magnesium sulfate 10mg/kg. In group RMV (n = 19), the IVRA was performed using 30 ml of ropivacaine 0.2%, whereas systemic magnesium sulfate (30 mg/kg) was also administered by intravenous infusion over 30 min before the start of the procedure.

Each of the medications was mixed with 0.9% saline in a syringe to a total volume of 40 ml by a nurse, and then the injection was administered by a blinded anesthetist to the medication and to the group assignment. Before injection of study drugs, a 20-Gintravenous cannula was placed in the dorsum of the hand. After exsanguination with an Esmarch bandage, circulation to the arm was occluded by the proximal cuff of a double-cuff pneumatic tourniquet placed at the upper arm and inflated to a pressure of at least 100 mmHg above baseline systolic blood pressure or a minimum of 250 mmHg. In the opposite arm, an isotonic saline infusion was started at a rate of 10 ml/kg/h throughout the surgery.

Patient demographics, type and duration of surgery, tourniquet time, and patient's ASA physical status were recorded. For the primary outcome, the analgesic efficacy of the IVRA was assessed by measuring the total amount of intravenousmorphine consumed over the first 24 h postoperatively. Postoperative analgesia was maintained using intravenous patient-controlled analgesia of1mg morphine bolus on demand with a 10-min lock-out interval for a period of 24 h postoperatively (after training of the patient on its use). Secondary outcomes included onset times of sensory and motor block, intraoperative fentanyl requirements, postoperative pain scores, and time to first request of analgesia.

Sensory and motor testings were performed just before injection of medications and then at 2 min intervals until establishment of the block by an investigator blinded to the treatment group. Sensory function was tested in the distribution of median, ulnar, radial, and musculocutaneous nerves by a pinprick test performed with a 22-Gneedle. Motor function was assessed by asking the individualto flex and extend the wrist and finger, and complete motor block was noted when no voluntary movement was recorded.

The onset time of sensory blockade was defined as the time interval from drug injection until complete loss of sensation to pinprick in the distribution of all dermatomes. The motor block onset time was defined as the time interval from drug injection until complete motor blockade. After anesthesia was achieved, the distal tourniquet was inflated and the proximal tourniquet was deflated. The tourniquet was not deflated before 30 min and was not inflated for more than 90 min.

The times for tourniquet and drug administration were recorded. All the patients were asked to rate their tourniquet discomfort (pain related tourniquet) andpostoperative surgical pain using the Verbal Rating Scale (VRS: 0 = no pain, 10 = the worstpain) at regular predefined time intervals (1, 3, 6, 12, and 24 h) after surgery.

The incidence of intraoperative and postoperative adverse events and complications was noted. Patients were evaluated for any signs of cardiac arrhythmias or CNS side effects such as dizziness, tinnitus, or metallic taste intraoperatively and after tourniquet deflation. Sideeffects such as nausea, vomiting, itching, or pruritis were also recorded.

Statistical analysis

A sample size of 17 patients per group would allow us to detect a difference of at least 0.15 mg/kg in morphine consumption over the first 24 postoperative hours. We assumed a SD of 0.15 and α = 0.05 and β = 0.2. The sample size was increased to 20 patients in each group considering the patients who might be excluded.

Data were analyzed using an IBM computer with SPSS, version 12 (SPSS Inc., Chicago, Illinois, USA). The data were presented as mean ± SD for normally distributed continuous variables and as median (interquartile range) for not normally distributed continuous quantitative or ordinal variables. The one-way analysis of variance test for independent means, Pearson's χ2 -test, and the Kruskal-Wallis test where appropriate were used to identify differences between the groups.

  Results Top

There were no significant differences between the groups with respect to patient characteristics, duration of surgery, and tourniquet time (P > 0.05; [Table 1]). There were significant differences in the onset times of sensory block among the groups (P < 0.001). The onset time of the sensory block was significantly faster in the RM group (10.5 ± 4 min) in comparison with the R and RMV groups (16.5 ± 6 and 16 ± 5.5 min, respectively, P < 0.01), as shown in [Table 2]. Also, there were significant differences in the onset times of motor block (P < 0.01) among the groups. The motor blockade developed significantly faster in the RM group (14 ± 5 min) in comparison with the R and RMV groups (21 ± 6 and 20.5 ± 5.3 min, respectively), as shown in [Table 2]. The tourniquet discomfort was significantly lower in the RM group 1 (0-2) in comparison with the R group 2 (1-4) and RMV group 3 (1-4) (P < 0.05); intraoperative fentanyl consumption was also lower for the RM group compared with the R group and RMV group (20.5 ± 9, 43.8 ± 9, and 38 ± 15 μg, respectively) (P < 0.01), as shown in [Table 2]. There were significant differences in the time to first request for analgesiaamong the groups (P < 0.05). Patients in the RMV group had significantly the longest time to the first request for analgesia (98 ± 12 min) in comparison with the R and RM groups (70 ± 11 and 75 ± 13 min, respectively). The RMV group had significantly lower (14.5 ± 8.7 mg) postoperative morphine consumption over the first 24 h in comparison with the R and RM groups (27 ± 15 and 25 ± 10 mg, respectively) [Table 2]. The postoperative pain score of the RMV group was significantly lower in comparison with the R and RM groupsat 1, 3, 6, and 12 postoperative hours, as shown in [Table 3](P < 0.05). However, there was no significant difference in the pain score between the groups at the 24 th postoperative hour [Table 3]. There were no statistically insignificant differences between the groups regarding the incidence of adverse effects of local anesthetic and narcotics. There was no major complication recorded in the three groups. One patient had dizziness and vomiting in the R and RMV groups during the tourniquet deflation, which resolved without intervention. Also, one patient developed vomiting during the first 24 postoperative hours in the R and RM groups.
Table 1: Patient demographics and clinical characteristics

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Table 2: The block outcomesin the three groups

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Table 3: Post operative pain scores among the groups

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  Discussion Top

In the current study, adding magnesium to ropivacine for IVRA enhanced the speed of both sensory and motor blockade onset time, and decreased the tourniquet pain and the intraoperative fentanyl consumption. In contrast, the systemic intravenous magnesium reduced the postoperative pain scores in the first 12 h and reduced the postoperative morphine consumption in the first 24 h. To our knowledge, this is the first study investigating different routes of magnesium administration during IVRA.

Magnesium has been shown to possess analgesic properties through suppression of neuropathic pain [10] and reduction of morphine tolerance [11]. However, the mechanism of analgesic effect is not fully clarified yet. Until now, most studies havefollowed two main mechanisms of action. The first is the interference with calcium influx into the cell [12], which could mediate analgesic action by increasing the nociceptive threshold of opioid receptors and preventing the release of neurotransmitters and other mediators involved in nociception. The second is the antagonism of postsynaptic N-methyl-d-aspartate (NMDA) calcium channel [13] located in the central nervous system (CNS). Moreover, magnesium deficiency causes hyperalgesia during painful or stressful medical conditions [14], which could be controlled by an NMDA antagonist [15].

Several studies have investigated the role of magnesium during IVRA [16],[17].

Tramer et al. [18] reported that perioperative administration of magnesium as an adjuvant had analgesic properties. Thereafter, several studies have reported conflicting outcomes for the perioperative analgesic benefit of magnesium [19-21]. Moreover, two systemic review articles concluded that perioperative magnesium infusion did not provide analgesic action [22],[23].

However, a recently published review article [24] concluded that perioperative intravenous administration of magnesium reduced morphine consumption by 24.4% and numeric pain score at rest and on movement in the first 24 postoperative hours. Discrepancy between different results could be explained by differences in time and dose of magnesium administration as well as in techniques of introperative and postoperative analgesia.

Consistent with the results of Turan et al. [16], the present study showed that the values of postoperative VRS score were lower in the second group in comparison with the control group. However, postoperative morphine consumption and VRS scores of the third group were significantly lower than those of the other two groups. This finding could be attributed to the central antagonism of intravenous infused magnesium on NMDA receptors in the CNS and on preemptive analgesia.

However, Albrecht et al. [25] postulated that the conflicting results regarding the efficiency of intravenous magnesium [17],[18],[19] would be explained on the basis of limited passage of magnesium molecules through the blood-brain barrier, which was reported even in the presence of systemic hypermagnesimia [26],[27],[28]; consequently, intrathecal route of administration was suggested. Buranendran et al. [29] reported that intrathecal magnesium increases the duration of analgesia. Another study reported that epidural magnesium reduced postoperative opioid consumption by 25% [30].

In contrast, lower VRS scores of tourniquet pain were recorded in the RM group in comparison with the RMV and R groups. Moreover, intraoperative fentanyl consumption was significantly lower in the RM group compared with the RMV and R groups. This is most likely attributed to the local effect of magnesium on vascular endothelium to release nitric oxide in response to pneumatic tourniquet-induced ischemia [31],[32]. In fact, reports from pain studies indicate that other mechanisms of action exist. For instance, in a randomized double-blind cross-over study, adding magnesium to lidocaine during Bier's block had been shown to improve and prolong relief from pain [33]. A possible explanation for the difference in analgesic efficacy of magnesium between the two routes of administration could be due to the limited passage of magnesium molecule when given locally; thereby, its molecular mechanism of site of action could be different from that when given systemically.

In the present study magnesium shortened the onset time for motor blockade in the RM group, which might be attributed to the inhibitory effect of magnesium on acetyl choline release from motor nerve endings.

There are two limitations in this study. First, we did not measure magnesium level in the plasma; however, it was reported that intracellular and extracellular magnesium concentration would not reflect its body tissue level [34]. Second, it may be argued that the study design did not provide another dose or continuous infusion of magnesium during or after surgery, which should be explored, but we believe that the study regimen was enough to provide adequate postoperative analgesia.

  Conclusion Top

Addition of magnesium to ropivacaine in IVRA decreased the severity of tourniquet pain and intraoperative fentanyl consumption and fastened the onset of sensory and motor blockade. However, the systemic intravenous magnesium reduced the postoperative morphine consumption and improved the postoperative analgesia. Further studies are needed to evaluate which route of administration would be more effective because of the limited number of patients in the present study.

  Funding Top

Study equipment support was provided by our institutional resources.

Conflicts of interest

None declared.

  References Top

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  [Table 1], [Table 2], [Table 3]

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