Magnesium therapy: regimens and monitoring
Magnesium sulfate (Magnesii sulfas) is the baseline drug for the prevention and cessation of seizures. Treatment of severe forms is initiated immediately at the site of the initial examination and continued in the ICU setting.
Administration regimen:
- Loading dose: 4–6 g IV over 15–20 minutes (in eclampsia — over 5–10 minutes).
- Maintenance infusion: 1–2 g/h via syringe pump (up to 3 g/h in eclampsia).
- Additional dose: 2 g over 3–5 minutes if no effect is observed.
The infusion rate is reduced to 0.15 g/h if diuresis falls below 100 mL over 4 hours. In case of loss of tendon reflexes or respiratory depression, administration is stopped immediately and the antidote — calcium gluconate — is administered.
Antihypertensive therapy
Drugs are prescribed if systolic BP exceeds baseline by 30 mm Hg and diastolic BP by 15 mm Hg. Monotherapy is used for moderate preeclampsia, while a combination of 2–3 drugs is used for severe preeclampsia.
Main drugs:
- Methyldopa (first line) — up to 3 g/day.
- Nifedipine (second line) — up to 80 mg/day. Also used for rapid BP reduction (20–40 mg/day).
- β-blockers — metoprolol (up to 200 mg), propranolol (up to 320 mg), bisoprolol (up to 20 mg).
Verapamil, amlodipine, or clonidine may be used as reserve drugs. All prescriptions must be strictly weighed against their effect on the fetus.
Infusion therapy and microcirculation
The main principle of infusion is fluid restriction to prevent pulmonary edema. The infusion rate is 40–80 mL/h under strict diuresis monitoring. The drugs of choice are balanced crystalloids.
Infusion loading (1–1.5 L) is justified only in regional anesthesia, hemoconcentration (hematocrit $\ge$ 40), or oliguria against the background of reduced circulating blood volume. Colloids (albumin) are used for bleeding and shock, and fresh frozen plasma for hypocoagulability.
To normalize microcirculation, the following are used:
- Low-molecular-weight heparins (LMWH): for hypercoagulability and hemostatic defects. Contraindicated at high BP levels.
- Antiplatelet agents: for impaired hemodynamics in the mother-placenta-fetus system.
Management of eclamptic seizures
A seizure lasts 1–3 minutes. Care is provided in two stages: first, breathing is restored and seizures are stopped, then organ functions are stabilized and delivery is performed.
Algorithm of actions during a seizure:
- Injury and aspiration prevention: place the patient on her left side (roll under the right buttock), apply pressure to the cricoid cartilage.
- Oxygenation: insert an airway, clear the oral cavity. In case of respiratory failure after the seizure, ventilate with 100% $O_2$ via face mask.
- Seizure cessation: baseline therapy with magnesium sulfate. If seizures persist, an additional 2 g of magnesium or 20 mg of diazepam IV is administered.
- Refractory seizures: general anesthetics (sodium thiopental 100–300 mg), muscle relaxants, and mechanical ventilation are indicated.
Delivery tactics
In severe preeclampsia, tactics depend on the response to therapy. If treatment is effective, expectant management is chosen with daily condition assessment.
Emergency delivery is indicated for:
- Inefficacy of ongoing therapy.
- Acute fetal hypoxia.
- Grade III fetal growth restriction (FGR) with oligohydramnios.
- Premature rupture of membranes or onset of labor.
At 30–32 weeks, pregnancy prolongation for 48 hours is possible for fetal RDS prevention with glucocorticoids. This is permissible only in the absence of life-threatening conditions (cerebral hemorrhage, DIC syndrome, placental abruption).
Briefly: answers to topical questions
What clinical symptoms indicate magnesium sulfate overdose (magnesium intoxication)?
Direct clinical symptoms of magnesium sulfate overdose are loss of tendon reflexes and respiratory depression. When diuresis drops below 100 mL over 4 hours, the infusion is reduced to 0.15 g/h. In severe cases, respiratory arrest and cardiac arrest develop.
What are the absolute contraindications to prolonging pregnancy in severe preeclampsia at 30–32 weeks?
Absolute contraindications to prolonging pregnancy at 30–32 weeks are life-threatening conditions. These include:
- Cerebral hemorrhage — a life-threatening central nervous system complication.
- DIC syndrome — a severe hemostatic disorder.
- Premature placental abruption — an acute obstetric pathology.
- Severe preeclampsia and eclampsia — critical forms of gestosis.
Specifically, which drugs and in what doses are used for fetal RDS prevention in threatened preterm labor?
To prevent fetal respiratory distress syndrome, glucocorticoids are administered intramuscularly in a total dose of 24 mg. The following drug regimens are used:
- Betamethasone — 12 mg twice 24 hours apart.
- Dexamethasone — 6 mg 4 times 12 hours apart.
What are the contraindications to prescribing low-molecular-weight heparins (LMWH) in preeclampsia?
A contraindication to prescribing low-molecular-weight heparins (LMWH) in preeclampsia is high blood pressure. Indications for LMWH are congenital hemostatic defects, confirmed chronometric or structural hypercoagulability, and a burdened obstetric history including preeclampsia, miscarriages, and antenatal fetal death in the past.
To monitor the safety of magnesium administration, remember the "RRDU" rule: Respiratory rate (>16/min), Diuresis (>30 mL/h), Saturation (95–100%), and Knee reflexes (must be preserved).
Class and exam questions
When is it necessary to transfer the patient to mechanical ventilation?
Indications for mechanical ventilation include respiratory failure, coma after an eclamptic seizure, cerebral hemorrhage, aspiration, pulmonary edema, and the development of multiple organ dysfunction syndrome.
How long should magnesium sulfate administration be continued postpartum?
Magnesium therapy is not interrupted during labor and must be continued for at least 24–48 hours after delivery or the last eclamptic seizure.
In which cases are a combination of anticoagulants and antiplatelet agents prescribed?
Combined use is indicated for early-onset disease (before 32–34 weeks) proceeding with the simultaneous development of placental insufficiency and fetal growth restriction.
What else to study on this topic
- Criteria for switching from expectant management to emergency delivery
- Features of infusion therapy: choice between crystalloids, albumin, and FFP
- Indications for transferring the patient to mechanical ventilation
- Specifics of using anticoagulants and antiplatelet agents in placental insufficiency
- Organization of hemodynamic and hemostatic monitoring in the ICU
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