The anticonvulsant of choice for pre-eclampsia prophylaxis and treatment according to Magpie Trial3
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Indications for use
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Magnesium sulphate is used in pregnancy for:
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- the prophylaxis of pre-eclampsia seizures and
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- treatment of eclamptic convulsion
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Presentation
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50mL vials = 493 mg/mL (49.3%) (Treat as ~ 50% solution)
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- (493 mg/mL = 2 mmol/mL of Mg2++ and 2mmol/ML SO4= )
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Route of administration
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IV Infusion: Via a 50ml syringe pump through a peripheral intravenous line. IV line should not be used to inject other drugs.
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- 50 mL of 50% MgSO(4) solution (undiluted from the vial) drawn up for infusion.
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Note: MgSO(4) infusions should only be administered in Birth Suites, Theatre or High Dependency Unit.
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Dose
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Prophylaxis of pre-eclampsia seizure
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Loading Dose: 4 gram (ie 8mL) bolus is given over 15 minutes (at a rate of 32ml/hr) continue
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Maintenance: at 1 gram/hr (ie 2mL/hr) until at least 24 hours post delivery.
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Treatment of Eclamptic Convulsions
| The priorities are to terminate the seizure and prevent maternal and fetal hypoxia.
| Loading Dose: 4 gram (ie 8mL) bolus is given over 5 to 10 minutes at a rate of 48 mL/hr to 96 mL/hr) then continue maintenance (see below)
| The rapid infusion of magnesium in this setting requires ECG monitoring and the presence of an anaesthetist.
| Maintenance: at 1 gram/hr (ie 2 mL/hr) until at least 24 hours post delivery
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Experience from the Collaborative Eclampsia trial indicates that magnesium sulphate (administered according to the above regimen) can be used safely without the need to monitor serum levels.
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Magnesium is excreted by the kidneys and regular monitoring of serum levels should be considered in women with oliguria (urine output <100mL over 4 hours) or urea >10mmol/L.
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Measure of magnesium levels may facilitate management where there are signs of toxicity or in the prescence of renal impairment.
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Magnesium level monitoring
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There is no indication to measure magnesium levels routinely except in the presence of oliguria or renal impairment.
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| | | | | | | ECG changes (P-Q interval prolongation, widen QRS complex)
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| | Reduction in deep tendon reflexes
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| | Loss of deep tendon reflexes
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| | Sinoatrial and atrioventricular blockade. Respiratory paralysis and CNS depression
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Side effects
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Rapid administration can lead to hypotension secondary to reductions in systemic vascular resistance (so fluid loading is usually required in Pre-Eclampsia), facial flushing, flushing at the site of injection, nasal stuffiness and chest pain.Clinical effects are related directly to plasma levels (see monitoring above).
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The following side effects may occur, but are very rare
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- Tissue necrosis at the injection site
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Contraindications and Precautions
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Patients with heart block or myocardial damage
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Caution in patients with impaired renal function or electrolyte imbalance (magnesium levels should be monitored closely).
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Monitoring
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During administration of the loading dose;
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- Observe for the development of side effects
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- Check patellar reflexes after completion of the loading dose
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During maintenance infusion;
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- 1 hourly Blood Pressure, Pulse, Respiratory Rate
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- 1 hourly patellar reflexes
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- Continuous CTG monitoring of the viable fetus
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Have resuscitation and ventilatory support available during and after dose administration. Calcium Gluconate is the available antidote.
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Record Patellar reflexes as;
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Request magnesium level and review management if:
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- Respiratory rate < 16 breaths / minute. (CARE: Lower rate may be appropriate if on opiates)
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- Urine output < 100 mLs in 4 hours
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- Loss of patellar reflexes
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Antidote for Magnesium toxicity
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Calcium Gluconate (10 mL of 10% solution over 10 minutes) by slow intravenous injection
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Ceasing a Magnesium infusion
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- Magnesium to continue for 24 hours post delivery (continue hourly clinical observation for 4 hours following the discontinuation of magnesium infusion). Cease according to Doctor's orders.
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- Clinical signs of magnesium toxicity must be reviewed by Obstetricians
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 | - Urine output <100 mL in 4 hours (dose reduction if no clinical signs of toxicity)
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- Respiratory arrest CALL ADULT CODE BLUE
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- Cardiac arrest CALL ADULT CODE BLUE
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References
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Link to Magpie Trial
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Royal Women's Hospital Clinical Practice Guidelines (CPGs) are intended to provide guidance to health care professionals, based on a thorough evaluation of research evidence, on the practical assessment and management of specific clinical issues or situations. The guidelines allow some flexibility on the part of the health care professional based on the needs of the specific patient for whom they are caring.
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