The Effect of Intravenously Administered Magnesium on Platelet Function in Patients After Cardiac Surgery

Serum magnesium level and hematoma expansion in patients with intracerebral hemorrhage

Spontaneous intracerebral hemorrhage (ICH) is a devastating subtype of stroke that results in significant rates of mortality and morbidities. The initial hematoma volume, hematoma expansion (HE), blood pressure (BP), and coagulopathy are considered strong predictors of clinical outcomes and mortality. Low serum magnesium (Mg⁺⁺) levels have been shown to be associated with larger initial hematoma and greater HE. Coagulopathy, platelet dysfunction, high BP, and increased inflammatory response might form the mechanistic link between low serum Mg⁺⁺ levels, larger hematoma size and greater HE. However, randomized clinical trials administering intravenous Mg⁺⁺ have shown no benefit over placebo in ICH patients. The confounding effect of hypocalcemia and a delay in Mg⁺⁺ trafficking across the blood-brain barrier might explain the futile results for intravenous Mg⁺⁺ therapy. In the current review, we will discuss the evidence regarding the possible role of low serum Mg⁺⁺ level on HE in acute ICH.

Estimation of Platelet Counts and Other Hematological Parameters in Pseudothrombocytopenia Using Alternative Anticoagulant: Magnesium Sulfate

The platelet count, mean platelet volume, and other hematological parameters were compared in blood samples anticoagulated with MgSO₄ and EDTA. A total of 15 samples were taken, and the platelet counts were observed to be significantly high in MgSO₄-anticoagulated blood samples ranging from 53 × 10³ to 499 × 10³/µL, whereas in EDTA-anticoagulated blood samples, the counts ranged from 10 × 10³ to 353 × 10³/µL. This increased platelet count was also statistically significant with the P value being .005. The morphology of red blood cells and white blood cells in Leishman-stained smears from MgSO₄-anticoagulated blood was below average. In conclusion, MgSO₄ can be used as an alternative anticoagulant only to estimate the platelet counts in EDTA-induced pseudothrombocytopenia.

The effect of magnesium sulfate on post off-pump coronary artery bypass grafting bleeding

BACKGROUND

Magnesium level alteration may cause coagulation abnormality resulting in bleeding complication after off-pump coronary artery bypass grafting. In this study, we investigated the effect of magnesium on the postoperative coagulation profile and bleeding in OPCAB patients.

METHODS

In a double blind clinical trial, six hundred patients were randomly allocated to two groups: group A (n=150) and group B (n=450). Group A received 50mg/kg of magnesium sulfate (MS) in 100ml 0.9% NaCl solution over 20min before the anesthesia induction. Group B or control group received only 100ml 0.9% NaCl solution at the same time points. OPCAB was performed with standard technique and device. Blood samples were collected 30min before and 6h after the surgery to analyze hemoglobin and blood coagulation tests. Postoperative exploration for bleeding, blood transfusion, and volume of transfusion was recorded. The two groups compared with t-test and χ(2) tests and p-valve <0.05 were considered as significant.

RESULTS

However, postoperative hemoglobin was statistically lower in group A compared with group B, but platelet, PT, and aPTT tests were not statistically different between two groups. The serum MS level, exploration for bleeding, volume of packed cell transfusion, and volume of postoperative bleeding were statistically different between group A vs group B.

CONCLUSION

Preoperative MS use may be associated with the postoperative platelet dysfunction and increased tendency to bleeding. This is an important risk factor for postoperative bleeding in the OPCAB in absence of CPB use.

The influence of drugs used in cardiac anaesthesia and critical care on multiple electrode aggregometry: an in-vitro volunteer study

BACKGROUND

Multiple electrode aggregometry (MEA) is a point-of-care test evaluating platelet function and the efficacy of platelet inhibitors. In MEA, electrical impedance of whole blood is measured after addition of a platelet activator. Reduced impedance implies platelet dysfunction or the presence of platelet inhibitors. MEA plays an increasingly important role in the management of perioperative platelet dysfunction. In vitro, midazolam, propofol, lidocaine and magnesium have known antiplatelet effects and these may interfere with MEA interpretation.

OBJECTIVE

To evaluate the extent to which MEA is modified in the presence of these drugs.

DESIGN

An in-vitro study using blood collected from healthy volunteers.

SETTING

Centre Hospitalier Universitaire Vaudois, Lausanne, Switzerland, 2010 to 2011.

PATIENTS

Twenty healthy volunteers.

INTERVENTION

Measurement of baseline MEA was using four activators: arachidonic acid, ADP, TRAP-6 and collagen. The study drugs were then added in three increasing, clinically relevant concentrations.

MAIN OUTCOME MEASURE

MEA was compared with baseline for each study drug.

RESULTS

Midazolam, propofol and lidocaine showed no effect on MEA at any concentration. Magnesium at 2.5 mmol l had a significant effect on the ADP and TRAP tests (31 ± 13 and 96 ± 39 AU, versus 73 ± 21 and 133 ± 28 AU at baseline, respectively), and a less pronounced effect at 1 mmol l on the ADP test (39 ± 0 AU).

CONCLUSION

Midazolam, propofol and lidocaine do not interfere with MEA measurement. In patients treated with high to normal doses of magnesium, MEA results for ADP and TRAP-tests should be interpreted with caution.

TRIAL REGISTRATION

Clinicaltrials.gov (no. NCT01454427).

Does magnesium-supplemented cardioplegia reduce cardiac injury? A meta-analysis of randomized controlled trials

BACKGROUND

Magnesium is often used to supplement cardioplegic solutions during cardiopulmonary bypass due to its cardioprotective effect during ischemia and reperfusion. The aim of this meta-analysis was to evaluate the effects of magnesium-supplemented cardioplegia versus an inactive (placebo) control cardioplegia on reducing cardiac injury after cardiac arrest surgery, as found by randomized, controlled trials.

METHODS

The Medline, Cochrane Library, and Chinese literature databases (CJFD, CBM, CSJD, Wanfang) were comprehensively searched for reports of randomized, controlled trials (RCTs) evaluating magnesium-supplemented cardioplegic solutions. The clinical parameters and outcomes of interest were the incidence of postoperative low cardiac output, auto-rebeating rate, ICU stay length, new onset postoperative atrial fibrillation, peak value of CK-MB (and/or cTnI), incidence of myocardial infarction, and in-hospital mortality.

RESULTS

Ten trials, with a total of 1214 patients, were included. The frequency of low cardiac output, inotropic utilization, and myocardial infarction, as well as auto-rebeating rate, length of ICU stay and in-hospital mortality, were similar between the two groups. There was a marginal reduction in the incidence of new-onset postoperative atrial fibrillation in the magnesium-supplemented cardioplegia group.

CONCLUSIONS

The advantage of magnesium-supplemented cardioplegia, compared with cardioplegia without magnesium, remains unconvincing based on the current evidence. The decision to add magnesium to the cardioplegic solution to a patient undergoing cardiac arrest surgery should be carefully considered.

Magnesium physiology and clinical therapy in veterinary critical care

OBJECTIVE

To review magnesium physiology including absorption, excretion, and function within the body, causes of magnesium abnormalities, and the current applications of magnesium monitoring and therapy in people and animals.

ETIOLOGY

Magnesium plays a pivotal role in energy production and specific functions in every cell in the body. Disorders of magnesium can be correlated with severity of disease, length of hospital stay, and recovery of the septic patient. Hypermagnesemia is seen infrequently in people and animals with significant consequences reported. Hypomagnesemia is more common in critically ill people and animals, and can be associated with platelet, immune system, neurological, and cardiovascular dysfunction as well as alterations in insulin responsiveness and electrolyte imbalance.

DIAGNOSIS

Measurement of serum ionized magnesium in critically or chronically ill veterinary patients is practical and provides information necessary for stabilization and treatment. Tissue magnesium concentrations may be assessed using nuclear magnetic resonance spectroscopy as well as through the application of fluorescent dye techniques.

THERAPY

Magnesium infusions may play a therapeutic role in reperfusion injury, myocardial ischemia, cerebral infarcts, systemic inflammatory response syndromes, tetanus, digitalis toxicity, bronchospasms, hypercoagulable states, and as an adjunct to specific anesthetic or analgesic protocols. Further veterinary studies are needed to establish the frequency and importance of magnesium disorders in animals and the potential benefit of magnesium infusions as a therapeutic adjunct to specific diseases.

PROGNOSIS

The prognosis for most patients with magnesium disorders is variable and largely dependent on the underlying cause of the disorder.

Acute Effect of Intravenous Administration of Magnesium Sulfate on Serum Levels of Interleukin-6 and Tumor Necrosis Factor-α in Patients Undergoing Elective Coronary Bypass Graft With Cardiopulmonary Bypass

Background:

Cardiovascular problems are among the most common health issues. A considerable number of cardiac patients undergo cardiac surgery, and coronary artery disease patients constitute about two-thirds of all these surgeries. The application of cardiopulmonary bypass (CBP) usually results in some untoward effects.

Objectives:

Studies have suggested magnesium sulfate (MgSO4) as an anti-inflammatory agent in a coronary artery bypass graft (CABG). This study aimed to assess the effect of an IV MgSO₄ infusion during elective CABG (with CBP) on the blood levels of interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF-α).

Materials and Methods:

During a 12 month period, after review board approval and based on inclusion and exclusion criteria, 90 patients were selected and entered randomly into one of the two study groups (MgSO4 or placebo). Anesthesia, surgery and CBP were performed in exactly the same way, except for the use of MgSO4 or a placebo. Both preoperative and postoperative plasma levels of IL-6 and TNF-α were checked and compared between the two groups using an ELISA.

Results:

There was no difference found between the two groups with regard to; gender, basic variables, Ejection Fraction (EF), CBP time and aortic cross-clamp time. The preoperative levels of IL-6 and TNF-α were not different; however, their postoperative levels were significantly higher in the placebo group (P value = 0.01 for IL-6 and 0.005 for TNF-α).

Conclusions:

This study showed that MgSO4 infusion could suppress part of the inflammatory response after CABG with CBP. This was demonstrated by decreased levels of interleukin-6 and TNF-α in postoperative serum levels in elective CABG with CBP.

Effects of antenatal magnesium sulfate treatment on cerebral blood flow velocities in preterm neonates

OBJECTIVE

The objective of this study is to investigate the effects of antenatal magnesium sulfate (MgSO4) on cerebral blood flow (CBF) velocities in preterm neonates.

STUDY DESIGN

In this prospective case-control study, we included 53 neonates born between 26 and 34 weeks of gestation. Twenty neonates were exposed to MgSO4 antenatally and 33 were not. Serial daily Doppler flow measurements of middle cerebral artery (MCA) were performed.

RESULT

Significantly increased MCA mean velocities were found in the MgSO4 group. A progressive increase in serial Doppler measurements of MCA mean velocity from day 1 to day 5 of life was detected in both groups.

CONCLUSION

There is significant increase in MCA mean velocities in preterm neonates receiving antenatal MgSO4. This increment in CBF velocities might explain the protective role of MgSO4 in ischemic events and hypoxic brain damage.

The effects of magnesium on the course of atrial fibrillation and coagulation in patients with atrial fibrillation undergoing mitral valve annuloplasty

Background

Atrial fibrillation (AF) is the most common cardiac arrhythmia. Magnesium has been reported to be effective in reducing the incidence or prophylaxis of AF. Magnesium is also an essential constituent of many enzyme systems and plays a physiological role in coagulation regulation. The aim of the present study was to examine the effects of magnesium, whether magnesium infusion might decrease the incidence of AF and induce hypocoagulable state in patients with AF, who were undergoing mitral valve annuloplasty.

Methods

This prospective laboratory study was performed using blood from patients with AF undergoing mitral valve annuloplasty. The radial artery was punctured with a 20 gauge catheter and used for monitoring continuous arterial pressure and blood sampling. After anesthesia induction, 4 g of magnesium was mixed with 100 ml normal saline and infused for 5 minutes. Magnesium, calcium, activated clotting time (ACT) and thromboelastographic parameters were checked before and 60 minutes after the magnesium infusion. The electrocardiography changes after magnesium infusion were also checked before commencing cardiopulmonary bypass.

Results

After magnesium infusion, the serum level of magnesium increased significantly but serum calcium did not change significantly. ACT did not change significantly before or after magnesium infusion. The thromboelastographic parameters showed no significant changes before or after magnesium infusion. None of the patients converted to sinus rhythm from AF after the magnesium infusion.

Conclusions

A magnesium infusion did not influence the course of AF and coagulation in patients during prebypass period with AF undergoing mitral valve annuloplasty.

Microcirculatory changes during open label magnesium sulphate infusion in patients with severe sepsis and septic shock

Background

Microcirculatory alterations play a pivotal role in sepsis and persist despite correction of systemic hemodynamic parameters. Therefore it seems tempting to test specific pro-microcirculatory strategies, including vasodilators, to attenuate impaired organ perfusion. As opposed to nitric oxide donors, magnesium has both endothelium-dependent and non-endothelium-dependent vasodilatory pathways.

Methods

In a single-center open label study we evaluated the effects of magnesium sulphate (MgS) infusion on the sublingual microcirculation perfusion in fluid resuscitated patients with severe sepsis and septic shock within the first 48 hours after ICU admission. Directly prior to and after 1 hour of magnesium sulphate (MgS) infusion (2 gram) systemic hemodynamic variables, sublingual SDF images and standard laboratory tests, were obtained.

Results

Fourteen patients (12 septic shock, 2 severe sepsis) with a median APACHE II score of 20 were enrolled. No significant difference of the systemic hemodynamic variables was found between baseline and after MgS infusion. We did not observe any significant difference pre and post MgS infusion in the primary endpoint microvascular flow index (MFI) of small vessels: 2.25(1.98-2.69) vs. 2.33(1.96-2.62), p = 0.65. Other variables of microcirculatory perfusion were also unaltered. In the overall unchanged microvascular perfusion there was a non-significant trend to an inverse linear relationship between the changes of MFI and its baseline value (y = -0.7260 × + 1.629, r² = 0.270, p = 0.057). The correlation between baseline Mg concentrations and the change in MFI pre- and post MgS infusion was non-significant (r_s = -0.165, p = 0.67).

Conclusions

In the setting of severe sepsis and septic shock sublingual microcirculatory alterations were observed despite fulfillment of sepsis resuscitation guidelines. After infusion of a limited and fixed dose of MgS, microcirculatory perfusion did not improve over time.

Trial registration

ClinicalTrials.gov NTC01332734.

Platelet dysfunction during cardiopulmonary bypass assessed by a novel whole-blood aggregometer

OBJECTIVE

The purpose of this study was to assess perioperative platelet function with 2 types of monitors (a whole-blood aggregometer [WBA analyzer; Mebanix, Tokyo, Japan]) and the Sonoclot monitor [Sienco, Wheat Ridge, CO]) in patients undergoing hypothermic cardiopulmonary bypass (CPB).

DESIGN

Prospective, observational study.

SETTING

Single-center study at a university hospital.

PARTICIPANTS

Twenty-six patients who underwent coronary artery bypass grafting or valve replacement under hypothermic CPB without platelet transfusion or fresh frozen plasma administration.

INTERVENTIONS

Blood sampling was performed at the following time periods: after anesthetic induction, after CPB, and on the first postoperative day. These samples were assessed with the WBA analyzer and the Sonoclot.

MEASUREMENTS AND MAIN RESULTS

Significant attenuation of adenosine diphosphate-induced platelet aggregation was detected shortly after CPB by 2 WBA analyzer-derived parameters: a decrease in the filtration pressure rate and an increase in the platelet aggregatory threshold index. Platelet aggregation returned to the preoperative level on the next day. There was no correlation between the amount of postoperative mediastinal drainage and defects in platelet aggregation. On the other hand, time to peak obtained by the Sonoclot did not show any significant changes.

CONCLUSIONS

Whole-blood aggregation measured with the WBA analyzer detected transient platelet dysfunction shortly after CPB, whereas the Sonoclot was less sensitive to this change.

A survey of peri-operative use of magnesium sulphate in adult cardiac surgery in the UK

We conducted a postal survey of cardiac anaesthetists in the UK, to determine the extent of magnesium sulphate (MgSO4) use and the main indications for its administration. Questionnaires were sent to anaesthetists at 35 UK hospitals undertaking adult cardiac surgery. Responses were received from 24 hospitals (69%) totalling 124 individual responses. Twenty-five (20%) of the anaesthetists responding to the questionnaire routinely gave magnesium other than in cardioplegia. The most common indications for administration were arrhythmia prophylaxis and treatment, myocardial protection, and the treatment of hypomagnesaemia.

Magnesium as part of balanced general anaesthesia with propofol, remifentanil and mivacurium: a double-blind, randomized prospective study in 50 patients

BACKGROUND AND OBJECTIVE

To test the hypothesis that magnesium sulphate reduces the amount of remifentanil needed for general anaesthesia in combination with propofol and mivacurium, we studied 50 patients undergoing elective pars plana vitrectomy in a double-blind, randomized prospective fashion.

METHODS

Magnesium sulphate (50 mg kg(-1) body weight) or placebo (equal volume of NaCl) was given slowly intravenously after induction of anaesthesia with propofol 1-2 mg kg(-1). Anaesthesia was maintained with propofol (using electroencephalographic control), mivacurium (according to train-of-four monitoring of neuromuscular blockade) and remifentanil (according to heart rate and arterial pressure).

RESULTS

We observed a significant reduction in remifentanil consumption from 0.14 to 0.09 microg kg(-1) min(-1) (P < 0.01). Mivacurium consumption was also markedly reduced from 0.01 to 0.008 mg kg(-1) min(-1) (P < 0.01), whereas propofol consumption remained unchanged. There was a trend towards lower postoperative pain scores, less pain medication requirements in 24 h after surgery and less postoperative nausea and vomiting in the magnesium group but not statistically significant. No side-effects were observed.

CONCLUSION

We can recommend the use of magnesium sulphate as a safe and cost-effective supplement to a general anaesthetic regimen with propofol, remifentanil and mivacurium, although we cannot clearly distinguish between a mechanism as a (co)analgesic agent at the NMDA-receptor site or its properties as a sympatholytic. The effect of a single bolus dose of 50 mg kg(-1) on induction lasts for about 2 h. For longer cases, either a continuous infusion or repeated bolus doses might be necessary.

Hypomagnesemic disorders

Adequate magnesium stores are vitally important for life. Critically ill patients will almost always have diminished levels of circulating magnesium, and this predisposes them to a variety of adverse effects, some life threatening. The causes of hypomagnesemia are many and varied, but in the critically ill, losses from the kidneys, often secondary to medications and from the gastrointestinal (GI) tract, predominate. The measurement of magnesium is not straightforward, although many clinicians are now switching to the use of ionized magnesium from ion selective electrodes. The use of supplemental magnesium in acute flares of asthma has some support in medical literature, especially for those patients with severe disease who fail traditional therapy. Magnesium holds the preeminent position in the treatment of pre-eclampsia and eclampsia in the minds of most obstetricians, who have decades of experience showing it to be both effective and safe. Magnesium is clearly useful for certain types of ventricular tachycardia, and probably assists in the treatment of several types of supraventricular tachycardia. Its role in acute myocardial ischemia is less certain, although there is no benefit once reperfusion therapy has already been carried out. Finally, the role of magnesium in the treatment of acute cerebral insults is an exciting area of active investigation with initial studies suggesting much promise.

Acute effects of nicotine infusion on platelets in nicotine users with normal and impaired renal function

The role of platelets in cardiovascular disease associated with smoking is becoming more established, but the effects of nicotine on platelets are unclear. Nicotine therapy is used for smoking cessation in both health and disease. Consequently, the effects of nicotine on platelets are of particular significance in disorders such as renal disease, which is associated with defective platelet function, increased cardiovascular morbidity, and altered nicotine metabolism. Thus, the aim of the present study was to investigate the acute effects of nicotine infusion (NI) on platelets in seven healthy subjects (HS) and seven patients with renal failure (RF). All subjects were nicotine users and had refrained from using nicotine for 36 h before NI. Blood was collected before, immediately after, and 2 h after NI. The plasma concentrations of nicotine and its main metabolite cotinine were determined by gas chromatography. Platelet responsiveness was assessed by aggregometry and flow cytometry in whole blood (P-selectin surface expression, fibrinogen- and von Willebrand factor-binding), P-selectin expression in isolated platelets, and immunoassays of platelet release (beta-thromboglobulin, platelet factor 4, and soluble P-selectin) and nitric oxide (NO) products. The plasma levels of cotinine, but not nicotine, were significantly higher in RF compared to HS at all time points. In both groups, collagen-induced platelet aggregation was restrained immediately after NI, when the plasma concentration of nicotine was maximal, and was restored after 2 h. Two hours after NI, activation-dependent P-selectin surface expression in isolated platelets increased in both groups. This increased platelet responsiveness occurred simultaneously with a significant increase of plasma cotinine and a decrease of NO products. Thus, the present study suggests that nicotine, directly or through some secondary mechanism or metabolite, only slightly potentiates some of the platelet responses. Renal failure appears not to influence the effects of nicotine on platelets.