Obstetrics & Gynaecology
Severe Pre-eclampsia & Eclampsia: Antihypertensives, MgSO4 Regime & Toxicity
Contents
Severe pre-eclampsia and eclampsia in one place: drugs for severe hypertension, how to manage a fit, the magnesium sulphate (MgSO₄) regime, and how to monitor for toxicity. Based on the OLSS (Obstetric Life Saving Skills) lecture on hypertensive disorders in obstetrics at Hospital Sultan Haji Ahmad Shah (HOSHAS), Temerloh.
Pathophysiology
Pre-eclampsia is a disease of the placenta:
- Failure of the second wave of trophoblast invasion.
- Failure of the maternal spiral arteries to dilate.
- Uteroplacental insufficiency and placental bed ischaemia, which can cause IUGR (and fetal hypoxia or death).
- Release of placental factors into the maternal circulation.
- Maternal endothelial dysfunction, producing the maternal syndrome of pre-eclampsia.
Endothelial activation affects every system: cardiorespiratory (hypertension, pulmonary oedema, ARDS), CNS (eclampsia, stroke, PRES), renal (proteinuria, AKI), hepatic (dysfunction, haematoma, rupture) and haematological (haemolysis, thrombocytopenia, DIC).
Remark: IUGR = intrauterine growth restriction; ARDS = acute respiratory distress syndrome; PRES = posterior reversible encephalopathy syndrome; AKI = acute kidney injury; DIC = disseminated intravascular coagulation.
Complications
| Maternal | Fetal |
|---|---|
| Convulsions and coma (eclampsia) | IUGR |
| Cerebral haemorrhage | Intrauterine fetal death |
| Renal failure | Prematurity |
| Heart failure | |
| Liver failure | |
| DIC | |
| Abruptio placentae | |
| Residual chronic hypertension in about 1/3 | |
| Recurrent pre-eclampsia in later pregnancies |
Antihypertensives for severe hypertension
| Drug | Initial dose | Onset (min) | Peak (min) | Repeat dose | Comments |
|---|---|---|---|---|---|
| IV labetalol | 20 mg | 2-5 | 5-15 | 20, 40, 40 mg | Repeat every 10 minutes, up to a maximum of 300 mg. Avoid in bradycardia, heart block or severe asthma |
| Oral nifedipine | 10 mg | 20 | 30-120 | 10-20 mg | Maximum of 3 doses. She should not bite the capsule. Causes headache and tachycardia |
| IV hydralazine | 5-10 mg | 5-20 | 10-80 | 10 mg | Repeat every 20 minutes, up to a maximum of 30 mg. Avoid in mothers with headache and tachycardia |
Managing an eclamptic fit
Initiate resuscitation
- Call for help and trigger the emergency alert system; involve a senior multi-professional team.
- Do not leave the mother unattended.
- Oxygen at 15 L/min by face mask.
- There is no urgency to stop the first seizure: most seizures are self-limiting.
Prevent injury and aspiration
- Padded tongue blade; once the seizure stops, insert an oral airway until she regains consciousness.
- Turn her head to one side, put her in the left lateral or recovery position, and use oral suction to clear the airway.
- Raise the bed rails to prevent a fall.
Then
- Prevent recurrent seizures: give MgSO₄ as per protocol.
- Prevent intracranial haemorrhage: control severe hypertension.
- Manage complications: HELLP syndrome and acute pulmonary oedema are managed in a tertiary centre.
- Ensure fetal wellbeing, and plan delivery by the optimal mode and time.
Remark: HELLP = haemolysis, elevated liver enzymes, low platelets.
Magnesium sulphate regime
Start MgSO₄ and continue for 24 hours after delivery or after starting it, whichever is later. Once the decision for MgSO₄ is made, consider delivery.
| Regime | Route | Dose |
|---|---|---|
| Loading dose | IV | 4 g (8 mL) MgSO₄ with 12 mL normal saline over 15 minutes |
| IM | 10 g, given as 5 g (10 mL) MgSO₄ into each buttock (add 1 mL of 2% lignocaine) | |
| Maintenance dose | IV | 24.7 g (10 ampoules) MgSO₄ in 500 mL normal saline at 1 g/hour (21 mL/h) |
| IM | 5 g (10 mL) MgSO₄ deep IM into alternate buttocks every 4 hours | |
| Recurrent seizure | IV | 2 g (4 mL) + 8 mL normal saline over 15 minutes, then continue the maintenance dose at 1 g/hour |
Remark: IM = intramuscular. Doses and volumes as given in the lecture.
Magnesium toxicity
Monitor hourly
- ECG for a prolonged PR interval and wide QRS complex.
- Deep tendon reflexes must be present.
- Urine output >30 mL/h (0.5 mL/kg/h).
| Mg level (mmol/L) | Clinical features | Management |
|---|---|---|
| 2.0-4.0 | Therapeutic range | |
| 3.5-5.0 | ECG changes: prolonged PR interval, widened QRS complex | Stop the infusion |
| 5.5-6.5 | Loss of deep tendon reflexes | Initiate resuscitation and give calcium gluconate |
| >12.5 | Initiate resuscitation and give calcium gluconate |
Antidote: 1 g calcium gluconate (10 mL of 10% solution) by slow IV bolus over 3 minutes.
Monitoring the eclamptic mother
- Use the early obstetric warning score (EOWS): GCS, BP, pulse, respiratory rate, oxygen saturation and fetal heart rate.
- Watch for signs and symptoms of magnesium toxicity.
- Strict fluid balance and urine output:
- If there is oliguria (<0.5 mL/kg/h), stop the MgSO₄ infusion.
- Restrict fluids to reduce the risk of pulmonary oedema: total fluids 80 mL/h or 1 mL/kg/h.
- Oliguria is common in severe pre-eclampsia; diuretics are only for pulmonary oedema.
- If there is also maternal haemorrhage, fluid balance is harder and fluid restriction is inappropriate.
Differential diagnosis of a fit
Epilepsy, hysteria, encephalitis, meningitis, puerperal cerebral thrombosis, poisoning or drug overdose, cerebral malaria, intracranial tumour, intracranial haemorrhage and head trauma.
Postpartum care
- Avoid ergometrine in the third stage of labour.
- Most mothers should be nursed in HDU after delivery.
- Start thromboprophylaxis according to the VTE score.
- 42% of eclampsia occurs postpartum, so monitor closely for at least 5 days.
- Monitor bloods: renal profile, platelets, LFT and coagulation profile.
- Antihypertensives: reduce them as the BP settles; avoid continuing or starting methyldopa.
- Contraception and spacing of the next pregnancy.
- Plan the next pregnancy: early booking, low-dose aspirin, calcium and vitamin D.
Remark: HDU = high-dependency unit; VTE = venous thromboembolism; LFT = liver function test.
Take-home messages
- In collapse, the first priority is ABC, not drugs or fetal assessment.
- Maternal condition always takes priority over the fetal condition.
- Stay calm: never panic.
- Treat all hypertensive disorders in pregnancy with urgency.
- Hope for the best but prepare for the worst.
See also the pre-eclampsia diagnostic criteria.
Sources
- Obstetric Life Saving Skills (OLSS) lecture: Hypertensive Disorders in Obstetrics. Hospital Sultan Haji Ahmad Shah (HOSHAS), Temerloh, 2026.
- Magee LA, et al. Pregnancy Hypertension: An International Journal of Women's Cardiovascular Health. 2014;4:105-145 (pathophysiology figure, as reproduced in the lecture).