Cerebrospinal fluid levels of magnesium in patients with preeclampsia after treatment with intravenous magnesium sulfate: a preliminary report

Intravenous Magnesium Sulfate in Acute Stroke

Background and Purpose—

Acute stroke treatment is challenging, and stroke remains a major cause of death and disability. The purpose of this meta-analysis is to investigate the effects of postacute stroke intravenous administration of the neuroprotectant magnesium sulfate (MgSO 4 ) on global outcome, functional outcome, and mortality 90 days poststroke (ischemic and nonischemic).

Methods—

We searched in Pubmed, Science Direct, CENTRAL, and ClinicalTrials.gov, up to November 11, 2017, and we conducted a systematic review and meta-analysis of randomized controlled trials. We synthesized results by using random-effects model, weighted mean differences, standardized mean differences, and odds ratios.

Results—

Seven randomized controlled trials (4347 patients) met our criteria. Compared with placebo, treatment did not improve functional outcome defined as Barthel Index >60 (odds ratio =1.05; 95% CI, 0.92–1.19) and >95 (odds ratio =0.95; 95% CI, 0.76–1.20), 90 days poststroke. It also did not improve global outcome measured with modified Rankin Scale (standardized mean difference =−0.01; 95% CI, −0.12 to 0.10), 90 days poststroke. In an additional subgroup meta-analysis that exclusively included ischemic stroke patients, intravenous MgSO 4 resulted in lower modified Rankin Scale score (improved global outcome; weighted mean difference =−0.96; 95% CI, −1.34 to −0.58; I 2 =0%], 90 days poststroke. Finally, mortality stayed unaltered (odds ratio =1.10; 95% CI, 0.94–1.29).

Conclusions—

The findings of our meta-analysis showed that intravenous MgSO 4 generally did not improve global/functional outcomes and mortality at 90 days after stroke (combined ischemic stroke and nonischemic stroke). The finding of favorable neurological outcome, selectively in ischemic stroke patients, should be viewed with extreme caution given the limited number of patients included in this subgroup meta-analysis.

Effect of magnesium added to local anesthetics for caudal anesthesia on postoperative pain in pediatric surgical patients: A systematic review and meta-analysis with Trial Sequential Analysis

BACKGROUND

Magnesium has been investigated as an adjuvant for neuraxial anesthesia, but the effect of caudal magnesium on postoperative pain is inconsistent. The aim of this systematic review and meta-analysis was to evaluate the analgesic effect of caudal magnesium.

METHODS

We searched six databases, including trial registration sites. Randomized clinical trials reporting the effect of caudal magnesium on postoperative pain after general anesthesia were eligible. The risk ratio for use of rescue analgesics after surgery was combined using a random-effects model. We also assessed adverse events. The I2 statistic was used to assess heterogeneity. We assessed risk of bias with Cochrane domains. We controlled type I and II errors due to sparse data and repetitive testing with Trial Sequential Analysis. We assessed the quality of evidence with GRADE.

RESULTS

Four randomized controlled trials (247 patients) evaluated the need for rescue analgesics. In all four trials, 50 mg of magnesium was administered with caudal ropivacaine. The results suggested that the need for rescue analgesia was reduced significantly by caudal magnesium administration (risk ratio 0.45; 95% confidence interval 0.24-0.86). There was considerable heterogeneity as indicated by an I2 value of 62.5%. The Trial Sequential Analysis-adjusted confidence interval was 0.04-5.55, indicating that further trials are required. The quality of evidence was very low. The rate of adverse events was comparable between treatment groups.

CONCLUSION

Caudal magnesium may reduce the need for rescue analgesia after surgery, but further randomized clinical trials with a low risk of bias and a low risk of random errors are necessary to assess the effect of caudal magnesium on postoperative pain and adverse events.

TRIAL REGISTRATION

University Hospital Medical Information Network Clinical Trials Registry UMIN000025344.

Magnesium in obstetric anesthesia and intensive care

Magnesium, one of the essential elements in the human body, has numerous favorable effects that offer a variety of possibilities for its use in obstetric anesthesia and intensive care. Administered as a single intravenous bolus dose or a bolus followed by continuous infusion during surgery, magnesium attenuates stress response to endotracheal intubation, and reduces intraoperative anesthetic and postoperative analgesic requirements, while at the same time preserving favorable hemodynamics. Applied as part of an intrathecal or epidural anesthetic mixture, magnesium prolongs the duration of anesthesia and diminishes total postoperative analgesic consumption with no adverse maternal or neonatal effects. In obstetric intensive care, magnesium represents a first-choice medication in the treatment and prevention of eclamptic seizures. If used in recommended doses with close monitoring, magnesium is a safe and effective medication.

Comparison of the Effects of 3 Methods of Intrathecal Bupivacaine, Bupivacaine-Fentanyl, and Bupivacaine-Fentanyl-Magnesium Sulfate on Sensory Motor Blocks and Postoperative Pain in Patients Undergoing Lumbar Disk Herniation Surgery

BACKGROUND

The aim of this study was to investigate the effects of adding intrathecal (IT) fentanyl and magnesium sulfate (MgSO4) to bupivacaine on sensory motor blocks and postoperative pain in patients undergoing lumbar disk herniation surgery.

METHODS

In a double-blind randomized clinical trial, the patients undergoing lumbar disk herniation surgery were allocated to receive hyperbaric bupivacaine (A), or hyperbaric bupivacaine and fentanyl (B), hyperbaric bupivacaine, fentanyl and MgSO4 (C) IT. Data were collected regarding the onset of sensory block and time to regression to T10, time to complete motor block and full motor recovery, time to first analgesic requirement, postoperative pain score, and analgesic consumption and side effects. P<0.05 was considered to be statistically significant.

RESULTS

A total of 105 patients were randomized and assigned to 3 groups (n=35 in each groups). There were no significant differences between groups in regard to time to reach the T10 level of sensory block (P=0.82), time to regression to T10 (P=0.11), and the time to complete motor block (P=0.58). Meanwhile, the time to complete recovery of motor function was significantly longer in group C (116.4±18.4, 126.4±25.5, 130.2±15.7 min, respectively, P=0.016). Time to first analgesic requirement was also significantly longer in group C (3.26±1.12, 5.57±0.92, 6.91±1.27 h, respectively, P<0.001). Total morphine consumption was significantly less in group C (14.3±4.3, 8.3±3.5, 6±3.6 mg, respectively, P<0.001). The severity of pain was significantly less in C group (P<0.001).

CONCLUSION

In patients undergoing lumbar disk herniation surgery, IT MgSO4 in combination with bupivacaine-fentanyl can decrease severity of postoperative pain and analgesic consumption without additional side effect.

Clinical pharmacokinetic properties of magnesium sulphate in women with pre-eclampsia and eclampsia

BACKGROUND

The pharmacokinetic basis of magnesium sulphate (MgSO4 ) dosing regimens for eclampsia prophylaxis and treatment is not clearly established.

OBJECTIVES

To review available data on clinical pharmacokinetic properties of MgSO4 when used for women with pre-eclampsia and/or eclampsia.

SEARCH STRATEGY

MEDLINE, EMBASE, CINAHL, POPLINE, Global Health Library and reference lists of eligible studies.

SELECTION CRITERIA

All study types investigating pharmacokinetic properties of MgSO4 in women with pre-eclampsia and/or eclampsia.

DATA COLLECTION AND ANALYSIS

Two authors extracted data on basic pharmacokinetic parameters reflecting the different aspects of absorption, bioavailability, distribution and excretion of MgSO4 according to identified dosing regimens.

MAIN RESULTS

Twenty-eight studies investigating pharmacokinetic properties of 17 MgSO4 regimens met our inclusion criteria. Most women (91.5%) in the studies had pre-eclampsia. Baseline serum magnesium concentrations were consistently <1 mmol/l across studies. Intravenous loading dose between 4 and 6 g was associated with a doubling of this baseline concentration half an hour after injection. Maintenance infusion of 1 g/hour consistently produced concentrations well below 2 mmol/l, whereas maintenance infusion at 2 g/hour and the Pritchard intramuscular regimen had higher but inconsistent probability of producing concentrations between 2 and 3 mmol/l. Volume of distribution of magnesium varied (13.65-49.00 l) but the plasma clearance was fairly similar (4.28-5.00 l/hour) across populations.

CONCLUSION

The profiles of Zuspan and Pritchard regimens indicate that the minimum effective serum magnesium concentration for eclampsia prophylaxis is lower than the generally accepted level. Exposure-response studies to identify effective alternative dosing regimens should target concentrations achievable by these standard regimens.

TWEETABLE ABSTRACT

Minimum effective serum magnesium concentration for eclampsia prophylaxis is lower than the generally accepted therapeutic level.

Neurochemical cascade of concussion

PRIMARY OBJECTIVE

The aim of this literature review was to systematically describe the sequential metabolic changes that occur following concussive injury, as well as identify and characterize the major concepts associated with the neurochemical cascade.

RESEARCH DESIGN

Narrative literature review.

CONCLUSIONS

Concussive injury initiates a complex cascade of pathophysiological changes that include hyper-acute ionic flux, indiscriminant excitatory neurotransmitter release, acute hyperglycolysis and sub-acute metabolic depression. Additionally, these metabolic changes can subsequently lead to impaired neurotransmission, alternate fuel usage and modifications in synaptic plasticity and protein expression. The combination of these metabolic alterations has been proposed to cause the transient and prolonged neurological deficits that typically characterize concussion. Consequently, understanding the implications of the neurochemical cascade may lead to treatment and return-to-play guidelines that can minimize the chronic effects of concussive injury.

Magnesium as an Effective Adjunct Therapy for Drug Resistant Seizures

Objective:

To explore the use of magnesium (Mg), an endogenous ion and enzymatic co-factor used in a variety of medical applications, for the treatment of epileptic seizures resistant to traditional medical therapy.

Background:

For almost a century, Mg has been used as prophylaxis and treatment of seizures associated with eclampsia. Mg is a CNS depressant, with numerous functions intracellularly and extracellularly. However, because of the availability of well studied anticonvulsant drugs, Mg has not been tested widely in the treatment of epileptic seizures.

Methods:

A retrospective chart review of 22 cases of drug resistant epilepsy, where a trial of empiric oral Mg supplementation (mainly in the form of Mg-oxide) was conducted.

Results:

Oral Mg supplementation was associated with a significant decrease in the number of seizure days per month, from 15.3 ± 13.2 (mean ± SD) to 10.2 ± 12.6 at first follow up (3-6 months, p=0.021), and to 7.8 ± 10.0 seizure days/month at second follow up (6-12 months, p=0.004). Thirty-six percent had a response rate of 75% or greater at second follow-up. Two patients reported seizure freedom. Most patients were well maintained on MgO 420mg twice a day, or in 2 cases, Mg Lactate, without significant adverse effects, the most frequent being diarrhea (4/22).

Discussion:

These results suggest that oral Mg supplementation may prove to be a worthwhile adjunctive medication in treating drug intractable epilepsy.

Conclusions:

A prospective, double-blinded, placebo controlled study is warranted to evaluate the potential of Mg for the treatment of drug-resistant seizures.

The Effect of Intravenous Magnesium Sulphate Treatment on the Spinal Anaesthesia Produced by Bupivacaine in Pre-eclamptic Patients

OBJECTIVE

In our study, the effect of intravenous magnesium sulphate in normal and pre-eclamptic patients on spinal anaesthesia produced by bupivacaine was investigated.

METHODS

Sixty-four pregnant (32 normal and 32 pre-eclamptic) were accepted in this study. Pregnants were divided into four groups as patients given intravenous magnesium sulphate and as control. Spinal anaesthesia was induced with 12.5 mg 0.5% hyperbaric bupivacaine. Intraoperative and postoperative haemodynamic variables, sensorial block periods, onset times of sensorial and motor block, maximum sensorial block levels, the time to reach maximum block level, Bromage scores, consumptions of intraoperative analgesic and ephedrine, the quality of anaesthesia, the duration of spinal anaesthesia and magnesium levels in blood and cerebrospinal fluid were measured and recorded.

RESULTS

The level of magnesium in blood and cerebrospinal fluid was significantly higher in the group given magnesium in pre-eclamptic patients (p<0.01). Onset of sensory block times were significantly longer in intravenous magnesium group than in groups 1, 2 and 3 (p<0.05). Onset of motor block times were significantly longer and the duration of anaesthesia was shorter in groups given magnesium (p<0.05). Although the quality of anaesthesia was similar, supplemental analgesic consumption was significantly higher in pre-eclamptic pregnants given magnesium sulphate than in pre-eclamptic pregnants who were not given magnesium sulphate (p<0.05).

CONCLUSION

Intravenous magnesium sulphate treatment during the spinal anaesthesia produced by bupivacaine extended the onset of sensory and motor block times, shortened the duration of spinal anaesthesia and therefore led to early analgesic requirement.

Magnesium Therapy in Pre-eclampsia Prolongs Analgesia Following Spinal Anaesthesia with Fentanyl and Bupivacaine: An Observational Study

BACKGROUND

Magnesium has anti-nociceptive effects and potentiates opioid analgesia following its systemic and neuraxial administration. However, there is no study evaluating the effects of intravenous (IV) magnesium sulphate (MgSO4) therapy on spinal anaesthesia characteristics in severely pre-eclamptic patients.

AIMS

The aim of this study was to compare spinal anaesthesia characteristics in severely pre-eclamptic parturients treated with MgSO4 and healthy preterm parturients undergoing caesarean section. Thus, our primary outcome was regarded as the time to first analgesic request following spinal anaesthesia.

STUDY DESIGN

Case-control Study.

METHODS

Following approval of Institutional Clinical Research Ethics Committee and informed consent of the patients, 44 parturients undergoing caesarean section with spinal anaesthesia were enrolled in the study in two groups: Healthy preterm parturients (Group C) and severely pre-eclamptic parturients with IV MgSO4 therapy (Group Mg). Following blood and cerebrospinal fluid (CSF) sampling, spinal anaesthesia was induced with 9 mg hyperbaric bupivacaine and 20 μg fentanyl. Serum and CSF magnesium levels, onset of sensory block at T4 level, highest sensory block level, motor block characteristics, time to first analgesic request, maternal haemodynamics as well as side effects were evaluated.

RESULTS

Blood and CSF magnesium levels were higher in Group Mg. Sensory block onset at T4 were 257.1±77.5 and 194.5±80.1 sec in Group C and Mg respectively (p=0.015). Time to first postoperative analgesic request was significantly prolonged in Group Mg than in Group C (246.1±52.8 and 137.4±30.5 min, respectively, p<0.001; with a mean difference of 108.6 min and 95% CI between 81.6 and 135.7). Side effects were similar in both groups. Group C required significantly more fluids.

CONCLUSION

Treatment with IV MgSO4 in severe pre-eclamptic parturients significantly prolonged the time to first analgesic request compared to healthy preterm parturients, which might be attributed to the opioid potentiation of magnesium.

Magnesium: potential roles in neurovascular disease

OBJECTIVE

Magnesium therapy has been studied extensively in pre-clinical and clinical trials in multiple organ systems. Cerebrovascular diseases may benefit from its neuroprotective properties. This review summarizes current studies of magnesium in a wide range of neurovascular diseases.

METHODS

We searched relevant terms in the National Library of Medicine PubMed database and selected research including basic science, translational reports, meta-analyses, and clinical studies.

RESULTS

Studies examining magnesium administration in ischemic stroke have failed to show any benefit in clinical outcome. Data on magnesium for intracerebral hemorrhage (ICH) are limited. Preliminary investigations in subarachnoid hemorrhage (SAH) were promising, but definitive studies did not reveal differences in clinical outcome between magnesium and placebo-treated groups. Studies examining magnesium administration in global ischemia following cardiac arrest suggest a trend toward improved clinical outcome. The strongest evidence for clinically relevant neuroprotection following magnesium administration derives from studies of pre-term infants and patients undergoing cardiac bypass and carotid endarterectomy procedures. Magnesium was found to have an excellent safety profile across all investigations.

CONCLUSION

Magnesium is easy to administer and possesses a favorable safety profile. Its utility as a neuroprotectant in cardiac surgery, carotid endarterectomy, and pre-term infant hypoxia remain promising. Value as a therapeutic agent in ischemic stroke, ICH, and SAH is unclear and appears to be limited by late administration. Ongoing clinical trials assessing magnesium administration in the first hours following symptom onset may help clarify the role of magnesium therapy in these disease processes.

The role of magnesium in the management of cerebral vasospasm

Subarachnoid hemorrhage (SAH) is characterized by bleeding into the subarachnoid space, often caused by ruptured aneurysm. Aneurysmal rupture occurs in 700,000 individuals per year worldwide, with 40,000 cases taking place in the United States. Beyond the high mortality associated with SAH alone, morbidity and mortality are further increased with the occurrence of cerebral vasospasm, a pathologic constriction of blood vessels that can lead to delayed ischemic neurologic deficits (DIND). Treatment of cerebral vasospasm is a source of contention. One extensively studied therapy is Magnesium (Mg) as both a competitive antagonist of calcium at the N-methyl D-aspartate (NMDA) receptor, and a noncompetitive antagonist of both IP3 and voltage-gated calcium channels, leading to smooth muscle relaxation. In our literature review, several animal and human studies are summarized in addition to two Phase III trials assessing the use of intravenous Mg in the treatment of SAH (IMASH and MASH-2). Though many studies have shown promise for the use of Mg in SAH, there has been inconsistency in study design and outcomes. Furthermore, the results of the recently completed clinical trials have shown no significant benefit from using intravenous Mg as adjuvant therapy in the treatment of cerebral vasospasm.

Effect of intrathecal magnesium in the presence or absence of local anaesthetic with and without lipophilic opioids: a systematic review and meta-analysis

Spinal anaesthesia is the primary anaesthetic technique for many types of surgery. Adjuncts to the local anaesthetics (LA) used in spinal anaesthesia can exhibit undesirable side-effects, limiting their use, but magnesium may have advantages in this respect. We sought randomized control trials (RCTs) in patients undergoing all types of surgery and in women in labour to compare the effect of intrathecal magnesium sulphate ± LA ± lipophilic opioid (experimental group) with the use of either intrathecal lipophilic opioids ± LA or LA only (control group). The primary outcome was the duration of spinal anaesthesia. Secondary outcomes were: onset and time to maximal sensory blockade, onset of motor block, and duration of sensory and motor blockade. We found 15 RCTs comprising 980 patients. The duration of spinal anaesthesia was significantly increased in the experimental group [standardized mean difference (SMD) -1.05 (-1.70, -0.41) (P = 0.001)], compared with the control group. This increased duration of spinal anaesthesia was seen in non-obstetric studies, SMD -1.38 (-2.11, -0.66) (P = 0.0002), but not in obstetric studies, SMD -0.55 (-1.87, 0.77) (P = 0.41). There was no delay in the onset of sensory or motor blockade. The incidence of hypotension and pruritus was similar in both groups. Heterogeneity was high in all outcome measures. The duration of spinal anaesthesia may be increased by the addition of magnesium to lipophilic opioids ± LA.

Effect of modulating the allosteric sites of N-methyl-D-aspartate receptors in ischemia-reperfusion induced acute kidney injury

BACKGROUND

Acute kidney injury (AKI) is one of the major health problems in developed as well as developing countries. The literature regarding the role of N-methyl-D-aspartate receptors (NMDAR) and the impact of the modulation of its allosteric sites on renal function is inadequate. The present study investigated the effect of modulating allosteric sites of NMDAR in ischemia-reperfusion-induced AKI.

MATERIALS AND METHODS

We subjected rats to bilateral renal ischemia for 40 min followed by reperfusion for 24 h to induce AKI. We measured blood urea nitrogen, serum creatinine, uric acid, and lactate dehydrogenase to assess kidney injury. We assayed the thiobarbituric acid-reactive substances, reduced glutathione level, and myeloperoxidase and catalase activity to assess oxidative stress in renal tissue, and used hematoxylin-eosin staining to observe histopathologic changes.

RESULTS

Ischemia-reperfusion induced AKI, as demonstrated by an increase in serum parameters, oxidative stress and histopathologic changes in renal tissue. The NMDA agonist glutamic acid and polyamine binding site agonist spermidine significantly aggravated oxidative stress and ischemia-reperfusion-induced AKI. Various NMDA receptor antagonists, including glycine binding site inhibitor kynurenic acid, polyamine binding site inhibitor ketamine, and channel blocking agent magnesium sulfate, attenuated ischemia-reperfusion-induced AKI and significantly reduced oxidative stress, which suggests a role for NMDA receptors and the importance of regulating its allosteric sites in AKI.

CONCLUSIONS

Acute kidney injury is associated with the activation of NMDA receptors, as well as significant oxidative stress. The antagonism of various allosteric sites of NMDA receptors affords significant benefit against ischemia-reperfusion-induced AKI.

The analgesic efficacy and safety of neuraxial magnesium sulphate: a quantitative review

Eighteen published trials have examined the use of neuraxial magnesium as a peri-operative adjunctive analgesic since 2002, with encouraging results. However, concurrent animal studies have reported clinical and histological evidence of neurological complications with similar weight-adjusted doses. The objectives of this quantitative systematic review were to assess both the analgesic efficacy and the safety of neuraxial magnesium. Eighteen trials comparing magnesium with placebo were identified. The time to first analgesic request increased by 11.1% after intrathecal magnesium administration (mean difference: 39.6 min; 95% CI 16.3-63.0 min; p = 0.0009), and by 72.2% after epidural administration (mean difference: 109.5 min; 95% CI 19.6-199.3 min; p = 0.02) with doses of between 50 and 100 mg. Four trials monitored for neurological complications: of the 140 patients included, only a 4-day persistent headache was recorded. Despite promising peri-operative analgesic effect, the risk of neurological complications resulting from neuraxial magnesium has not yet been adequately defined.

Efficacy and Safety of an Intra-operative Intra-articular Magnesium/Ropivacaine Injection for Pain Control following Total Knee Arthroplasty

Eighty patients with osteoarthritis who underwent unilateral total knee arthroplasty were randomly assigned to two groups: the trial group received an intraoperative intra-articular injection of magnesium sulphate and ropivacaine, and the control group received an injection of normal saline. All patients received patient-controlled analgesia with morphine for 48 h post-operatively. It was found that an intra-articular injection of magnesium sulphate and ropivacaine significantly reduced morphine consumption during the 0 - 24 h post-operative period and total 48-h postoperative morphine consumption. Pain scores at rest and during motion in the trial group were significantly lower than in the controls during the first 24 h post-operatively. The time to be able to perform a straight leg raise and to reach a 90° knee flexion was significantly shorter in the trial group compared with the controls. This study demonstrated that an intra-operative intra-articular magnesium sulphate and ropivacaine injection reduced the use of post-operative morphine.

To evaluate the efficacy of intrathecal magnesium sulphate for hysterectomy under subarachnoid block with bupivacaine and fentanyl: A prospective randomized double blind clinical trial

BACKGROUND

Intrathecal magnesium has been found to prolong the duration of analgesia in various surgical procedures like lower limb surgeries and as adjuncts to general anesthesia for pain management. The present study was designed to examine whether addition of intrathecal magnesium sulfate would enhance the analgesic efficacy of intrathecal bupivacaine and fentanyl in patients undergoing total abdominal hysterectomy.

METHODS

After taking informed consent, 60 patients were randomised into two groups with 30 patients. Group "S" received 2.5 mL (12.5 mg) of hyperbaric bupivacaine + 0.5 mL (25 mcg) of fentanyl + 0.5 mL of normal saline and Group "M" received 2.5 mL (12.5 mg) of hyperbaric bupivacaine + 0.5 mL (25 mcg) of fentanyl + 0.5 mL (100 mg) of magnesium sulfate. Onset of sensory, motor block and duration of analgesia was noted.

RESULTS

Demographic profile and duration of surgery were comparable (P>0.5). Time of onset of sensory and motor blockade was delayed in Group M compared with Group S, and this was statistically significant. A statistically significant longer duration of analgesia was observed in Group M compared with the control Group S. However, the recovery of motor blockade was found to be statistically insignificant in both the groups. The hemodynamic parameters were comparable in the perioperative period (P>0.05). The incidence of side-effects in both the groups were also comparable (P>0.05).

CONCLUSION

The addition of 100 mg intrathecal magnesium led to prolonged duration of analgesia significantly without increasing the incidence of side-effects. Also, there was a significant delay in the onset of both sensory and motor blockade.

Changes in cerebrospinal fluid magnesium levels in patients undergoing spinal anaesthesia for hip arthroplasty: does intravenous infusion of magnesium sulphate make any difference? A prospective, randomized, controlled study

BACKGROUND

Most investigators have attributed the reduced postoperative pain or anaesthetic drug requirements in patients receiving i.v. magnesium sulphate (MgSO(4)) infusion during spinal or general anaesthesia to central N-methyl-d-aspartate (NMDA) receptor magnesium (Mg) activity. In this study, we investigated how cerebrospinal fluid (CSF) Mg concentrations change after spinal anaesthesia, and whether peripherally infusing MgSO(4) influences central Mg levels.

METHODS

Forty-five patients undergoing continuous spinal anaesthesia for hip arthroplasty were randomly assigned to receive either i.v. MgSO(4) at a dose of 50 mg kg(-1) diluted in 100 ml 0.9% saline solution followed by 15 mg kg(-1) h(-1) for 6 h or saline at the same volume [mean (sd) 64 (10) ml]. The changes in CSF and serum total and ionized Mg concentrations were assessed at six time points before and after spinal anaesthesia. Secondary outcome variables included serum and CSF electrolytes and proteins.

RESULTS

Thirty-five patients completed the study. We found that spinal anaesthesia reduced total and ionized Mg concentrations in CSF by about 10%. Increasing serum Mg concentration over 80% of the baseline value left CSF Mg levels unchanged.

CONCLUSIONS

Spinal anaesthesia unexpectedly reduced CSF total and ionized Mg concentrations in patients undergoing hip arthroplasty, although the mechanism is unclear. The dose used for peripheral MgSO(4) infusion in this study had no influence on central Mg concentrations in neurologically healthy patients undergoing spinal anaesthesia. If CSF Mg concentration is a reliable marker of Mg brain bioavailability, peripherally infused MgSO(4) during spinal anaesthesia is unlikely to influence central NMDA receptor activity.

Magnesium sulfate and nimesulide have synergistic effects on rescuing brain damage after transient focal ischemia

Magnesium sulfate and nimesulide are commonly used drugs with reported neuroprotective effects. Their combination as stroke treatment has the potential benefits of decreasing individual drug dosage and fewer adverse effects. This study evaluated their synergistic effects and compared a low-dose combination with individual drug alone and placebo. Sprague-Dawley rats underwent 90 min of focal ischemia with intraluminal suture occlusion of the middle cerebral artery followed by reperfusion. The rats were randomly assigned to receive one of the following treatments: placebo, magnesium sulfate (MgSO₄; 45 mg/kg) intravenously immediately after the induction of middle cerebral artery occlusion, nimesulide (6 mg/kg) intraperitoneally before reperfusion, and combined therapy. Three days after the ischemia-reperfusion insult, therapeutic outcome was assessed by 2,3,5-triphenyltetrazolium chloride staining and a 28-point neurological severity scoring system. Cyclooxygenase-2, prostaglandin E₂, myeloperoxidase, and caspase-3 expression after treatment were evaluated using Western blot analyses and immunohistochemical staining, followed by immunoreactive cell analysis using tissue cytometry. Only the combination treatment group showed a significant decrease in infarction volume (10.93±6.54% versus 26.43±7.08%, p<0.01), and neurological severity score (p<0.05). Low-dose MgSO₄ or nimesulide showed no significant neuroprotection. There was also significant suppression of cyclooxygenase-2, prostaglandin E₂, myeloperoxidase, and caspase-3 expression in the combination treatment group, suggesting that the combination of the two drugs improved the neuroprotective effects of each individual drug. MgSO₄ and nimesulide have synergistic effects on ischemia-reperfusion insults. Their combination helps decrease drug dosage and adverse effects. Combined treatment strategies may help to combat stroke-induced brain damage in the future.

Lumbosacral epidural magnesium prolongs ketamine analgesia in conscious sheep

PURPOSE: To determine the analgesic, motor, sedation and systemic effects of lumbosacral epidural magnesium sulphate added to ketamine in the sheep. METHODS: Six healthy adult male mixed-breed sheep; weighing 43 ± 5 kg and aged 20-36 months. Each sheep underwent three treatments, at least 2 weeks apart, via epidural injection: (1) ketamine (KE; 2.5 mg/kg), (2) magnesium sulphate (MG; 100 mg), and (3) KE + MG (KEMG; 2.5 mg/kg + 100 mg, respectively). Epidural injections were administered through the lumbosacral space. Analgesia, motor block, sedation, cardiovascular effects, respiratory rate, skin temperature, and rectal temperature were evaluated before (baseline) and after drug administration as needed. RESULTS: The duration of analgesia with the lumbosacral epidural KEMG combination was 115 ± 17 min (mean ± SD), that is, more than twice that obtained with KE (41 ± 7 min) or MG (29 ± 5 min) alone. KE and KEMG used in this experiment induced severe ataxia. The heart rate and arterial blood pressures changes were no statistical difference in these clinically health sheep. CONCLUSION: The dose of magnesium sulphate to lumbosacral epidural ketamine in sheep is feasible, and can be used in procedures analgesics in sheep.

Is magnesium sulfate by the intrathecal route efficient and safe?

The polypharmacological approach to the treatment of postoperative pain has become routine in an attempt to minimize the adverse side effects of opioids. Magnesium sulphate is a noncompetitive antagonist of the N-methyl-d-aspartate (NMDA) receptor and thus can modify nociceptive modulation. Intravenous administration of magnesium sulphate can improve postoperative analgesia and decrease the requirement for postoperative opiates, but the effects are inconsistent and have not been reliably accompanied by a reduction in the incidence of morphine-related adverse events. Several studies have shown that the administration of magnesium by the intrathecal route is safe and, in combination with opiates, extends the effect of spinal anaesthesia in both animal and human studies. The analysis of these studies justifies further investigation of the use of magnesium sulphate by the intrathecal route.

Intracellular free magnesium of brain and cerebral phosphorus-containing metabolites after subarachnoid hemorrhage and hypermagnesemic treatment: a 31P–magnetic resonance spectroscopy study

Object

Disturbance of cerebral phosphorus-containing metabolites occurs in many disease entities and has not been widely studied in patients with subarachnoid hemorrhage (SAH). Pilot studies have indicated that hypermagnesemic treatment may improve outcome in patients with aneurysmal SAH, but the precise mechanism is not known. The authors hypothesized that, by raising intracellular brain free magnesium in aneurysmal SAH, hypermagnesemic treatment would alter the cerebral energy status.

Methods

The authors designed the current study to use 31P-MR spectroscopy (MRS) to investigate intracellular brain free magnesium and cerebral phosphorus-containing metabolites in patients with good-grade aneurysmal SAH, both those receiving and not receiving hypermagnesemic therapy. A total of 37 eligible patients and 23 healthy volunteers were recruited. A total of 81 MRS studies were performed.

Results

Hypermagnesemic treatment after aneurysmal SAH produced a small (mean difference 0.018 ± 0.007 mM [+ 13.0%]) but significant elevation of intracellular free magnesium during the 1st week. Aneurysmal SAH produced a depressed membrane metabolism with lower phosphodiester/total phosphate.

Conclusions

The MRS finding of elevated brain free intracellular magnesium after intravenous magnesium sulfate infusion is novel, and the changes in membrane metabolism provide insight into the metabolic effects of aneurysmal SAH and future pathophysiological studies.

Zuspan's scheme versus an alternative magnesium sulfate scheme: Randomized clinical trial of magnesium serum concentrations

OBJECTIVE

The purpose of this study was to determine whether magnesium serum concentrations in patients with severe preeclampsia or eclampsia treated with two different magnesium sulfate schemes were different.

METHODS

Fourteen patients were randomly assigned in the alternative scheme group and 15 in the Zuspan's group. The difference between the groups was that the intravenously administered maintenance dose was done with 1 g/h by continuous intravenous infusion in the Zuspan's group and 2g in bolus every two hours in the alternative scheme. Blood samples were collected previously to treatment and every 15 minutes during four hours after the beginning of treatment. The primary outcome measure was area under the curve and the t-test was used for statistical analysis with level of statistical significance of 5%. The evaluation of the punctual means at all moments in the alternative group was done with the repeated measures analysis of variance.

RESULTS

There was no significant difference in the baseline characteristics between groups. In both schemes, magnesium serum concentration reaches a peak within 15 minutes and a new peak was observed after maintenance dose in the alternative scheme. The area under the curve was significantly lower in the alternative scheme than in the Zuspan's scheme (702.1 +/- 73.5 mg/dL vs 796.1 +/- 94.6 mg/dL).

CONCLUSION

The serum magnesium concentration of this randomized clinical trial doesn't support the use of the alternative scheme of magnesium sulfate to prevent or treat eclampsia.

Use of magnesium in traumatic brain injury

Depletion of magnesium is observed in animal brain and in human blood after brain injury. Treatment with magnesium attenuates the pathological and behavioral changes in rats with brain injury; however, the therapeutic effect of magnesium has not been consistently observed in humans with traumatic brain injury (TBI). Secondary brain insults are observed in patients with brain injury, which adversely affect clinical outcome. Systemic administration studies in rats have shown that magnesium enters the brain; however, inducing hypermagnesemia in humans did not concomitantly increase magnesium levels in the CSF. We hypothesize that the neuroprotective effects of magnesium in TBI patients could be observed by increasing its brain bioavailability with mannitol. Here, we review the role of magnesium in brain injury, preclinical studies in brain injury, clinical safety and efficacy studies in TBI patients, brain bioavailability studies in rat, and pharmacokinetic studies in humans with brain injury. Neurodegeneration after brain injury involves multiple biochemical pathways. Treatment with a single agent has often resulted in poor efficacy at a safe dose or toxicity at a therapeutic dose. A successful neuroprotective therapy needs to be aimed at homeostatic control of these pathways with multiple agents. Other pharmacological agents, such as dexanabinol and progesterone, and physiological interventions, with hypothermia and hyperoxia, have been studied for the treatment of brain injury. Treatment with magnesium and hypothermia has shown favorable outcome in rats with cerebral ischemia. We conclude that coadministration of magnesium and mannitol with pharmacological and physiological agents could be an effective neuroprotective regimen for the treatment of TBI.

Efficacy and Safety of an Intra-Operative Intra-Articular Magnesium/Ropivacaine Injection for Pain Control following Total Knee Arthroplasty

Eighty patients with osteoarthritis who underwent unilateral total knee arthroplasty were randomly assigned to two groups: the trial group received an intra-operative intra-articular injection of magnesium sulphate and ropivacaine, and the control group received an injection of normal saline. All patients received patient-controlled analgesia with morphine for 48 h post-operatively. It was found that an intra-articular injection of magnesium sulphate and ropivacaine significantly reduced morphine consumption during the 0-24 h post-operative period and total 48-h postoperative morphine consumption. Pain scores at rest and during motion in the trial group were significantly lower than in the controls during the first 24 h post-operatively. The time to be able to perform a straight leg raise and to reach a 90° knee flexion was significantly shorter in the trial group compared with the controls. This study demonstrated that an intraoperative intra-articular magnesium sulphate and ropivacaine injection reduced the use of post-operative morphine.

Development of morphine induced tolerance and withdrawal symptoms is attenuated by lamotrigine and magnesium sulfate in mice

The goal of this study was to evaluate the effects of lamotrigine and magnesium sulfate on morphine induced tolerance and withdrawal symptoms in mice. Different groups of mice were received morphine (30 mg kg(-1), s.c.) or morphine (30 mg kg(-1), s.c.)+lamotrigine (10, 20, 30 or 40 mg kg(-1), i.p.) or morphine (30 mg kg(-1), s.c.) + magnesium sulfate (20, 40 or 60 mg kg(-1), i.p.) or morphine (30 mg kg(-1), s.c.) + [lamotrigine (10 mg kg(-1), i.p.) + magnesium sulfate (20mg kg(-1), i.p.)] daily for 4 days. Tolerance was assessed using hot plate after administration of a test dose of morphine (9 mg kg(-1), i.p.) on fifth day. Withdrawal zsymptoms (Jumping and Rearing) were assessed by administration of naloxone (5 mg kg(-1), i.p.) 2 h after the last dose of morphine in fourth day. It was found that administration of lamotrigine or magnesium sulfate or their combination decreased the morphine induced tolerance and withdrawal symptoms. From these results it is concluded that lamotrigine and magnesium sulfate alone or in combination could prevent the development of morphine tolerance and withdrawal symptoms. Glutamate release inhibitory effect of lamotrigine and its possible mechanism and property of magnesium, blocking the N-Methyl-D-Aspartate (NMDA) receptor calcium channel, is probably its mechanism on preventing morphine induced tolerance and dependence.

Magnesium sulfate for the treatment of eclampsia: a brief review

BACKGROUND AND PURPOSE

Magnesium sulfate is used extensively for prevention of eclamptic seizures. Empirical and clinical evidence supports the effectiveness of magnesium sulfate; however, questions remain as to its safety and mechanism. This review summarizes current evidence supporting the possible mechanisms of action and several controversies for magnesium sulfate treatment.

SUMMARY OF REVIEW

Several mechanisms are presented, including the effects of magnesium sulfate on peripheral and cerebral vasodilation, blood-brain barrier protection, and as an anticonvulsant.

CONCLUSIONS

Though the specific mechanisms of action remain unclear, the effect of magnesium sulfate in the prevention of eclampsia is likely multi-factorial. Magnesium sulfate may act as a vasodilator, with actions in the peripheral vasculature or the cerebrovasculature, to decrease peripheral vascular resistance or relieve vasoconstriction. Additionally, magnesium sulfate may also protect the blood-brain barrier and limit cerebral edema formation, or it may act through a central anticonvulsant action.

Cerebral spinal fluid and serum ionized magnesium and calcium levels in preeclamptic women during administration of magnesium sulfate

OBJECTIVE

To study the distribution of ionized and total magnesium (Mg) in serum and cerebral spinal fluid (CSF) in preeclamptic women receiving MgSO(4) and how this treatment affects the ionized calcium (Ca(2+)) and ionized Ca:Mg ratios compared with healthy nonpregnant women and pregnant control women (HP).

DESIGN

Controlled clinical study.

SETTING

An academic medical center.

PATIENT(S)

African-American women older than 20 and less than 35 years. The pregnant preeclamptic study and pregnant control groups each consisted of 16 women; the nonpregnant group consisted of 10 subjects.

INTERVENTION(S)

The preeclamptic women received a 6-g bolus of MgSO(4) IV started at least 4.5 hours before delivery during 15-20 minutes, then 2 g/h baseline.

MAIN OUTCOME MEASURE(S)

The CSF and serum levels of Ca(2+) and Mg(2+) and total Mg were measured in all three groups of women. The Ca(2+):Mg(2+) ratios were determined. Physiologic monitoring was done and recorded every 4 hours where appropriate. Bloods were drawn every 6 hours for complete blood count, metabolic panel, lactate dehydrogenase, uric acid, and electrolytes. Serum pH, total Mg, Apgar scores, and general health of the infants born to preeclamptic mothers given MgSO(4) were followed.

RESULT(S)

The HP showed a reduction in mean serum ionized and total Mg, increase in ionized Ca, and a large increase in Ca(2+):Mg(2+) ratios compared with healthy nonpregnant women. Although the CSF ionized and total Mg and Ca(2+):Mg(2+) ratios were not altered with MgSO(4) treatment in the preeclamptic women receiving MgSO(4), the mean serum Mg values increased 3-fold. All infants were full-term, regardless of MgSO(4) treatment, and normal with respect to birth weight, Apgar scores, blood pH, total Mg, and neurologic scores.

CONCLUSION(S)

The data indicate that there is a direct relationship between the serum and CSF Ca(2+):Mg(2+) ratios in HP and this ratio may be crucial in preventing vascular and neurologic complications in preeclampsia-eclampsia.

Pre-incisional epidural magnesium provides pre-emptive and preventive analgesia in patients undergoing abdominal hysterectomy

BACKGROUND

This prospective, randomized, double-blind study was designed to evaluate the preemptive and preventive analgesic efficacy of adding magnesium to a multimodal regimen of patient-controlled epidural analgesia (PCEA) in patients undergoing abdominal hysterectomy.

METHODS

Ninety patients were randomly assigned to one of the three groups. Pre-magnesium patients received bolus of magnesium 50 mg epidurally before induction of anaesthesia followed by infusion of 10 mg h(-1) until end of surgery. Post-magnesium patients received epidural saline during the same time periods plus bolus epidural magnesium 50 mg at the end of surgery. Patients in the control group received epidural saline during all three periods. Patients in the magnesium groups received PCEA with fentanyl 1 microg ml(-1), bupivacaine 0.08%, and magnesium 1 mg ml(-1) after operation. Patients in the control group received PCEA with fentanyl 1 microg ml(-1) and bupivacaine 0.08%. Data were recorded for three postoperative days.

RESULTS

There were significantly lower pain scores on rest or movement in the pre-magnesium group compared with the post-magnesium and control groups (P<0.05). The daily analgesic consumption in the pre-magnesium group was significantly less than the other two groups (P<0.05) and the dose consumed in the post-magnesium group was significantly smaller than the control group (P<0.05). The groups were similar with respect to haemodynamic and respiratory variables, sedation, pruritus, nausea, and vomiting.

CONCLUSIONS

Continuous epidural magnesium started before anaesthesia provided preemptive, preventive analgesia, and an analgesic-sparing effect that improved postoperative analgesia without increasing the incidence of side-effects.

Effects of magnesium sulphate on intraoperative anaesthetic requirements and postoperative analgesia in gynaecology patients receiving total intravenous anaesthesia

BACKGROUND

This randomized, double-blind, prospective study was undertaken to evaluate the effects of magnesium sulphate on anaesthetic requirements and postoperative analgesia in patients undergoing total i.v. anaesthesia (TIVA).

METHODS

Fifty patients who underwent gynaecological surgery were randomly divided into two groups. Before induction of anaesthesia, the magnesium group (Group M) received magnesium sulphate 50 mg kg(-1) i.v. as a bolus and then 15 mg kg(-1) h(-1) i.v. by continuous infusion. The control group (Group S) received the same amount of isotonic saline. TIVA (propofol+remifentanil) was administered under bispectral index monitoring during anaesthesia induction and maintenance. Rocuronium was administered before orotracheal intubation and during surgery when the train-of-four count was 2 or more. After operation, patient-controlled analgesia with a solution of ketorolac and morphine was used and the consumption of this solution was recorded. Pain scores at rest and upon movement were evaluated 30 min, 4, 24, and 48 h after surgery.

RESULTS

Patients in Group M required less rocuronium than those in Group S [mean (SD) 0.44 (0.09) vs 0.35 (0.07) microg kg(-1) min(-1), P<0.05]. The total amounts of propofol and remifentanil administered were similar in the two groups. Postoperative pain scores, cumulative analgesic consumption, and shivering incidents were significantly lower in Group M (P<0.05). Mean arterial pressure just after intubation and during the immediate postoperative period was also significantly lower in Group M (P<0.05).

CONCLUSIONS

I.v. magnesium sulphate during TIVA reduced rocuronium requirement and improved the quality of postoperative analgesia.

Magnesium sulphate reduces cell volume in physiological conditions but not in the cytotoxic oedema during global brain ischemia

PRIMARY OBJECTIVE

To establish the effect of MgSO4 on brain cellular volume during physiological and global ischemia using impedanciometric method.

RESEARCH DESIGN

Impedanciometric measure in the brain before and during global brain ischemia, with or without intravenous infusion of MgSO4.

METHODS AND PROCEDURES

Male Sprague-Dawley rats were anaesthetized (thiobarbital, 60 mg kg-1 i.p.). Ringer solution (n=9) or MgSO4 (n=8; 1 mmol Kg-1) where i.v. isovolumetrically administered. Sub-cortical impedance was recorded before and after the infusion of ringer or MgSO4 and during global cerebral ischemia induced by a cardiopulmonary arrest.

MAIN OUTCOMES AND RESULTS

In non-ischemic conditions, MgSO4 infusion induced higher voltage values than those of ringer infusion (Wilcoxon, Z=2.49; p=0.01). During global cerebral ischemia, the MgSO4 infused animals showed a fast drop of voltages (82%) in the first 5 minutes, 4-fold the values of ringer infused animals (p<0.0001). In the following 15 minutes no differences were found between ringer and MgSO4 infused animals.

CONCLUSIONS

The results suggest that MgSO4 significantly reduced brain cell volume in physiological conditions but not in global brain ischemia.

Useful adjuvants for postoperative pain management

Adjuvants are compounds which by themselves have undesirable side-effects or low potency but in combination with opioids allow a reduction of narcotic dosing for postoperative pain control. Adjuvants are needed for postoperative pain management due to side-effects of opioid analgesics, which hinder recovery, especially in the increasingly utilized ambulatory surgical procedures. NMDA antagonists have psychomimetic side-effects at high doses, but at moderate doses do not cause stereotypic behavior but allow reduction in opioid dose to obtain better pain control. Alpha-2 adrenergic agonists cause sedation, hypotension and bradycardia at moderate doses, but at low doses can be opioid sparing especially in spinal administration. Gabapentin-like compounds have low potency against acute pain, but in combination with opioids allow a reduction in opioid dose with improved analgesia. Corticosteroids may have only a limited role as adjuvants while acetylcholine esterase inhibitors may have too many side-effects. Newer adjuvants will be needed to reduce opioid dose and concomitant side-effects, even more as same day surgeries become more routine.

Protective effect of prior administration of magnesium on delayed hyperalgesia induced by fentanyl in rats

PURPOSE

Magnesium exerts a physiological block of the ion channel on the N-methyl-D-aspartate receptor, and may therefore prevent the induction of central sensitization. The purpose of this study was to assess whether systemic magnesium can prevent long-lasting hyperalgesia induced by sc fentanyl administration in uninjured rats.

METHODS

Long-lasting hyperalgesia was induced in male Sprague Dawley rats with sc fentanyl (four injections, 60 microg x kg(-1) per injection at 15-min intervals). Magnesium sulphate (100 mg x kg(-1)) was injected ip 30 min prior to the first sc fentanyl injection. Sensitivity to nociceptive stimuli (paw-pressure test) was assessed for several days after injections.

RESULTS

Subcutaneous fentanyl led to delayed hyperalgesia associated with a decrease in the nociceptive threshold lasting two days (35% decrease for the maximum effect). Intraperitoneal magnesium sulphate partially but significantly (P < 0.05) prevented the delayed decrease in the nociceptive threshold following sc administration of fentanyl.

CONCLUSIONS

This study shows that magnesium may prevent the delayed and prolonged hyperalgesia following fentanyl administration in rats.

Magnesium as a neuroprotectant in cardiac surgery: A randomized clinical trial

OBJECTIVE

We sought to evaluate magnesium as a neuroprotectant in patients undergoing cardiac surgery with cardiopulmonary bypass.

METHODS

From February 2002 to September 2003, 350 patients undergoing elective coronary artery bypass grafting, valve surgery, or both were enrolled in a randomized, blinded, placebo-controlled trial to receive either magnesium sulfate to increase plasma levels 1(1/2) to 2 times normal during cardiopulmonary bypass (n = 174) or no intervention (n = 176). Neurologic function, neuropsychologic function, and depression were assessed preoperatively, at 24 and 96 hours after extubation (neurologic) and at 3 months (neuropsychologic, depression). Neurologic scores were analyzed using ordinal longitudinal methods, and neuropsychologic and depression inventory data were summarized by principal component analysis, followed by linear regression analysis using component scores as response variables.

RESULTS

Seven (2%) patients had a postoperative stroke, 2 (1%) in the magnesium and 5 (3%) in the placebo group (P = .4). Neurologic score was worse postoperatively in both groups (P < .0001); however, magnesium group patients performed better than placebo group patients (P = .0001), who had prolonged declines in short-term memory and reemergence of primitive reflexes. Three-month neuropsychologic performance and depression inventory score were generally better than preoperatively, with few differences between groups (P > .6); however, older age (P = .0006), previous stroke (P = .003), and lower education level (P = .0007) were associated with worse performance.

CONCLUSIONS

Magnesium administration is safe and improves short-term postoperative neurologic function after cardiac surgery, particularly in preserving short-term memory and cortical control over brainstem functions. However, by 3 months, other factors and not administration of magnesium influence neuropsychologic and depression inventory performance.

Magnesium moderately decreases remifentanil dosage required for pain management after cardiac surgery †

BACKGROUND

Magnesium is a calcium and an NMDA-receptor antagonist and can modify important mechanisms of nociception. We evaluated the co-analgesic effect of magnesium in the postoperative setting after on-pump cardiac surgery.

METHODS

Forty patients randomly received either magnesium gluconate as an i.v. bolus of 0.21 mmol kg(-1) (86.5 mg kg(-1)) followed by a continuous infusion of 0.03 mmol(-1) kg(-1) h(-1) (13.8 mg kg(-1) h(-1)) or placebo for 12 h after tracheal extubation. After surgery, remifentanil was decreased to 0.05 microg kg(-1) min(-1) and titrated according to a pain intensity score (PIS, range 1-6) in the intubated, awake patient and a VAS scale (range 1-100) after extubation. If PIS was > or =3 or VAS > or =30, the infusion was increased by 0.01 microg kg(-1) min(-1); if ventilatory frequency was < or =10 min(-1) it was decreased by the same magnitude.

RESULTS

Magnesium lowered the cumulative remifentanil requirement after surgery (P<0.05). PIS > or =3 was more frequent in the placebo group (P<0.05). Despite increased remifentanil demand, VAS scores were also higher in the placebo group at 8 (2 vs 8) and 9 h after extubation (2 vs 7) (P<0.05). Dose reductions attributable to a ventilatory frequency < or =10 min(-1) occurred more often in the magnesium group (17 vs 6; P<0.05). However, time to tracheal extubation was not prolonged.

CONCLUSIONS

Magnesium gluconate moderately reduced the remifentanil consumption without serious side-effects. The opioid-sparing effect of magnesium may be greater at higher pain intensities and with increased dosages.

Intravenous regional anesthesia using lidocaine and magnesium

We conducted this study to evaluate the effects of magnesium, when added to lidocaine for IV regional anesthesia (IVRA), on tourniquet pain. Thirty patients undergoing elective hand surgery during IVRA were randomly assigned to two groups. IVRA was achieved with 10 mL of saline plus 3 mg/kg lidocaine 0.5% diluted with saline to a total of 40 mL in group C or with 10 mL of 15% magnesium sulfate (12.4 mmol) plus 3 mg/kg lidocaine 0.5% diluted with saline to a total of 40 mL in group M. Injection pain, sensory and motor block onset and recovery time, tourniquet pain, and anesthesia quality were noted. Patients were instructed to receive 75 mg of IM diclofenac when the visual analog scale (VAS) score was >4, and analgesic requirements were recorded. Sensory and motor block onset times were shorter and recovery times were prolonged in group M (P < 0.05). VAS scores of tourniquet pain were lower in group M at 15, 20, 30, 40, and 50 min (P < 0.001). Anesthesia quality, as determined by the anesthesiologist and surgeon, was better in group M (P < 0.05). Time to the first postoperative analgesic request in group C was 95 +/- 29 min and in group M was 155 +/- 38 min (P < 0.05). Postoperative VAS scores were higher for the first postoperative 6 h in group C (P < 0.05). Diclofenac consumption was significantly less in group M (50 +/- 35 mg) when compared with group C (130 + 55 mg) (P < 0.05). We conclude that magnesium as an adjunct to lidocaine improves the quality of anesthesia and analgesia in IVRA.

Analysis of the brain bioavailability of peripherally administered magnesium sulfate: A study in humans with acute brain injury undergoing prolonged induced hypermagnesemia*

OBJECTIVE

Based on preclinical investigations, magnesium sulfate (MgSO4) has gained interest as a neuroprotective agent. However, the ability of peripherally administered MgSO4 to penetrate the blood-brain barrier is limited in normal brain. The current study measured the passage of intravenously administered Mg into cerebrospinal fluid in patients with brain injury requiring ventricular drainage.

DESIGN

A prospective evaluation of the cerebrospinal fluid total and ionized magnesium concentration, [Mg], during sustained hypermagnesemia was performed.

SETTING

Neurosciences intensive care unit at a major teaching institution.

PATIENTS

Thirty patients with acute brain injury secondary to subarachnoid hemorrhage, traumatic brain injury, primary intracerebral hemorrhage, subdural hematoma, brain tumor, central nervous system infection, or ischemic stroke were studied.

INTERVENTIONS

Patients underwent 24 hrs of induced hypermagnesemia during which total and ionized cerebrospinal fluid [Mg] was measured. Serum [Mg] was adjusted to 2.1-2.5 mmol/L. Cerebrospinal fluid [Mg] was measured at baseline, at 12 and 24 hrs after onset of infusion, and at 12 hrs following infusion termination.

MEASUREMENTS AND MAIN RESULTS

At baseline, total (1.25 +/- 0.14 mmol/L) and ionized (0.80 +/- 0.10 mmol/L) cerebrospinal fluid [Mg] was greater than serum total (0.92 +/- 0.18 mmol/L) and ionized (0.63 +/- 0.07 mmol/L) [Mg] (p < .05). Total (1.43 +/- 0.13 mmol/L) and ionized (0.89 +/- 0.12 mmol/L) cerebrospinal fluid [Mg] was maximally increased by 15% and 11% relative to baseline, respectively, during induced hypermagnesemia (p < .05).

CONCLUSIONS

Hypermagnesemia produced only marginal increases in total and ionized cerebrospinal fluid [Mg]. Regulation of cerebrospinal fluid [Mg] is largely maintained following acute brain injury and limits the brain bioavailability of MgSO4.

Magnesium and bupivacaine-induced convulsions in awake pregnant rats

BACKGROUND

Magnesium sulfate (MgSO(4)) is widely used for the treatment and prevention of convulsions associated with preeclampsia. The aim of this study was to determine whether it alters the dose of bupivacaine required to produce convulsions in awake pregnant rats.

METHOD

Twelve pregnant rats were pretreated with an intravenous infusion of either MgSO(4) or saline. Following 2 h of the pretreatment, bupivacaine was concomitantly infused in all animals until the onset of convulsions. Mean arterial pressure (MAP) and heart rate (HR) were monitored throughout. Serial arterial samples were obtained during the infusion. At the onset of convulsions, fetuses were delivered and maternal and fetal blood, as well as various tissue samples, were obtained. All samples were assayed for bupivacaine and magnesium concentrations.

RESULTS

Maternal MAP and HR decreased significantly shortly after the initiation of MgSO(4), while saline did not affect these measurements. Baseline concentrations of magnesium in plasma were similar in both MgSO(4) and saline groups; magnesium increased significantly during the infusion of MgSO(4). The dose (mean+/-SD) of bupivacaine required to produce convulsions in the animals receiving MgSO(4) was significantly larger (10.2+/-1.9 mg/kg) than that in the saline group (5.9+/-1.0 mg/kg) (P<0.05). As a consequence, bupivacaine concentrations in the brain and liver at the onset of convulsions were greater in animals receiving MgSO(4) (16.0+/-8.4 and 18.2+/-4.3 microg/g wet weight, respectively) than in those given saline (12.1+/-2.2 and 9.9+/-2.0 microg/g wet weight, respectively). Fetal bupivacaine concentrations at the onset of convulsions in the MgSO(4) group were also higher than those in saline group. However, the rate of placental transfer of this drug was similar between MgSO(4) and saline animals.

CONCLUSION

This study demonstrates that the clinically used concentration of magnesium sulfate increased the threshold of bupivacaine-induced convulsions in awake rats.

Intrathecal magnesium prolongs fentanyl analgesia: a prospective, randomized, controlled trial

Magnesium is a noncompetitive, N-methyl-D-aspartate receptor antagonist that does not effectively cross the blood-brain barrier when given IV. Intrathecal magnesium potentiates opioid antinociception in rats, and the safety of intrathecal magnesium has been demonstrated in animals. This is the first prospective human study evaluating whether intrathecal magnesium could prolong spinal opioid analgesia. Fifty-two patients requesting analgesia for labor were randomized to receive either intrathecal fentanyl 25 micro g plus saline or fentanyl 25 micro g plus magnesium sulfate 50 mg as part of a combined spinal-epidural technique. The duration of analgesia of the intrathecal drug combination was defined by the time of patient request for additional analgesia. There was significant prolongation in the median duration of analgesia (75 min) in the magnesium plus fentanyl group compared with the fentanyl alone group (60 min). There was no associated increase in adverse events in the group that received intrathecal magnesium. Larger doses of intrathecal magnesium were not studied in this group of patients because of the limitations on cephalad spread when hyperbaric solutions are injected in the sitting position. Our data indicate that intrathecal magnesium prolongs spinal opioid analgesia in humans and suggest that the availability of an intrathecal N-methyl-D-aspartate antagonist could be of clinical importance for pain management.

IMPLICATIONS

Magnesium occurs naturally in the spinal cord and blocks the NMDA glutamate channel. In animal studies, intrathecal magnesium sulfate improves spinal morphine analgesia. For patients receiving spinal analgesia for labor, the addition of magnesium sulfate to the opioid fentanyl prolonged analgesia with no increase of side effects.

Intrathecal magnesium prolongs fentanyl analgesia: a prospective, randomized, controlled trial

Magnesium is a noncompetitive, N-methyl-D-aspartate receptor antagonist that does not effectively cross the blood-brain barrier when given IV. Intrathecal magnesium potentiates opioid antinociception in rats, and the safety of intrathecal magnesium has been demonstrated in animals. This is the first prospective human study evaluating whether intrathecal magnesium could prolong spinal opioid analgesia. Fifty-two patients requesting analgesia for labor were randomized to receive either intrathecal fentanyl 25 micro g plus saline or fentanyl 25 micro g plus magnesium sulfate 50 mg as part of a combined spinal-epidural technique. The duration of analgesia of the intrathecal drug combination was defined by the time of patient request for additional analgesia. There was significant prolongation in the median duration of analgesia (75 min) in the magnesium plus fentanyl group compared with the fentanyl alone group (60 min). There was no associated increase in adverse events in the group that received intrathecal magnesium. Larger doses of intrathecal magnesium were not studied in this group of patients because of the limitations on cephalad spread when hyperbaric solutions are injected in the sitting position. Our data indicate that intrathecal magnesium prolongs spinal opioid analgesia in humans and suggest that the availability of an intrathecal N-methyl-D-aspartate antagonist could be of clinical importance for pain management.

IMPLICATIONS

Magnesium occurs naturally in the spinal cord and blocks the NMDA glutamate channel. In animal studies, intrathecal magnesium sulfate improves spinal morphine analgesia. For patients receiving spinal analgesia for labor, the addition of magnesium sulfate to the opioid fentanyl prolonged analgesia with no increase of side effects.

Magnesium for neuroprotection in ischaemic stroke: rationale for use and evidence of effectiveness

Magnesium exhibits a range of neuronal and vascular actions that may ameliorate ischaemic CNS insults, including stroke. Significant neuroprotection with magnesium has been observed in different models of focal cerebral ischaemia in many laboratories, with infarct volume reductions between 25 and 61%. Maximal neuroprotection is evident at readily attainable serum concentrations, and neuroprotection is still seen when administration is delayed up to 6 hours after onset of ischaemia. Clinical use of magnesium in pre-eclampsia and acute myocardial infarction confirms its safety and tolerability. Five small trials in acute stroke have reported reduced odds of death or dependence with administration of magnesium, but confidence intervals are wide, and definitive data from ongoing large trials are awaited.

Intravenous magnesium sulfate does not increase ventricular CSF ionized magnesium concentration of patients with intracranial hypertension

Magnesium sulfate has attracted interest as a potential neuroprotectant but passage of magnesium ion into the central nervous system has not been well documented. For this study, we quantified plasma and cerebrospinal fluid (CSF) ionized magnesium concentration after systemic magnesium sulfate infusion in patients with intracranial hypertension. Patients ( N = 9) received an intravenous infusion of 5 g/20 mmol magnesium sulfate (125 mL of a 4% wt/vol solution) over 30 minutes. Before and after dosing, CSF (from an indwelling ventricular catheter) and blood samples were collected at hourly intervals. Ionized magnesium concentration in all samples was determined using an electrolyte analyzer. Baseline plasma and CSF ionized magnesium concentrations were 0.58 +/- 0.05 and 0.82 +/- 0.06 mmol/L, respectively. Intravenous magnesium sulfate infusion significantly increased plasma ionized magnesium concentration (peak, 0.89 +/- 0.11 mmol/L), but CSF magnesium levels did not change during the 4-hour study. Systemic administration of magnesium sulfate failed to increase CSF ionized magnesium concentration in patients with intracranial hypertension despite increasing plasma magnesium levels by >50%.