Why is magnesium sulphate being given to the patient?

Why Magnesium Sulphate is Given to Patients

Magnesium sulphate is administered primarily for three critical indications: preventing and controlling eclamptic seizures in women with severe pre-eclampsia, providing fetal neuroprotection before anticipated preterm delivery, and treating acute hypomagnesemia. 1, 2

Primary Obstetric Indications

Seizure Prevention in Severe Pre-eclampsia

• Magnesium sulphate is the most effective anticonvulsant for preventing eclampsia in women with severe pre-eclampsia who have at least one clinical sign of seriousness (headache, visual disturbances, hyperreflexia, epigastric pain). 1, 3, 4
• It reduces the risk of eclampsia by approximately 50% compared to placebo and is superior to both phenytoin and diazepam for seizure prevention and control. 3, 5, 6
• The drug works by decreasing cerebral perfusion pressure, thereby preventing cerebral barotrauma that leads to seizures. 7

Eclampsia Treatment

• For active eclamptic seizures, magnesium sulphate is the first-line agent, given as a 4-6 gram IV loading dose over 10-15 minutes, followed by continuous infusion of 1-2 g/hour. 4, 6
• It is superior to benzodiazepines (which cause maternal and neonatal respiratory depression) and phenytoin for both stopping active seizures and preventing recurrence. 3, 4

Fetal Neuroprotection

• When preterm delivery is anticipated before 30-32 weeks gestation, magnesium sulphate provides significant neuroprotection to the fetus. 1, 5
• It reduces the incidence of cerebral palsy (relative risk 0.68) without increasing mortality when administered before early preterm birth. 1

Non-Obstetric Indications

Magnesium Deficiency

• Magnesium sulphate is indicated for replacement therapy in acute hypomagnesemia, especially when accompanied by tetany-like signs (serum magnesium <1.5 mEq/L). 2
• It may be added to total parenteral nutrition to correct or prevent hypomagnesemia during therapy. 1, 2

Critical Clinical Context

When to Initiate in Pre-eclampsia

• In high-income settings, use magnesium sulphate selectively for severe hypertension (≥160/110 mmHg) with significant proteinuria (≥3+), or moderate hypertension (≥150/100 mmHg) with ≥2+ proteinuria plus signs of imminent eclampsia. 5
• In low and middle-income countries, consider broader use due to favorable cost-benefit ratio and higher eclampsia rates. 5, 8
• Notably, 25% of eclamptic women are normotensive and 25% are asymptomatic before seizure, supporting a lower threshold for prophylaxis. 9

Duration of Treatment

• Continue magnesium sulphate for 24 hours postpartum in most cases, as pre-eclampsia may worsen or appear de novo between days 3-6 postpartum. 5, 4, 8
• Some evidence suggests that if ≥8 grams were given before delivery, continuing for 24 hours postpartum may not provide additional benefit. 5
• Never exceed 5-7 days of continuous administration, as this can cause fetal abnormalities; maximum dosage is 20 grams/48 hours in severe renal insufficiency. 5

Safety Monitoring and Contraindications

Essential Monitoring Parameters

• Monitor deep tendon reflexes (loss occurs at 3.5-5 mmol/L), respiratory rate (paralysis at 5-6.5 mmol/L), and urine output—serum levels are not routinely necessary. 6, 8
• Cardiac conduction alterations occur at >7.5 mmol/L, with cardiac arrest expected at >12.5 mmol/L. 6
• Therapeutic range for eclampsia prevention is 1.8-3.0 mmol/L. 6

Critical Drug Interactions

• Never combine magnesium sulphate with IV or sublingual nifedipine—this causes severe myocardial depression. 3, 4
• Oral long-acting nifedipine may be used cautiously for chronic blood pressure control, but avoid concurrent IV administration. 4
• Labetalol should not exceed 800 mg cumulative dose in 24 hours to prevent fetal bradycardia. 4

Special Populations

• Premature newborns exposed to maternal magnesium sulphate therapy may have elevated magnesium levels in the first days of life due to low glomerular filtration rates—limit magnesium intake and adapt to postnatal blood concentrations. 1
• In oliguria, iatrogenic magnesium toxicity risk increases significantly. 3

Common Pitfalls to Avoid

• Do not use magnesium sulphate as a tocolytic for preterm labor—it is ineffective for delaying birth and high cumulative doses may increase infant mortality. 10
• Do not withhold magnesium sulphate in mild pre-eclampsia if imminent signs are present (hyperreflexia, frontal headache, visual disturbances, epigastric tenderness), as 20% of eclamptic women had only mild-to-moderate hypertension before seizure. 8, 9
• Magnesium sulphate administration can be performed by trained midwives or nursing staff in resource-limited settings, but this does not replace the need for close maternal surveillance. 3, 8