13.3 Obstetric & Gynecologic Emergencies: Preeclampsia, Eclampsia & PPH

13.3 Obstetric & Gynecologic Emergencies: Preeclampsia, Eclampsia & PPH

Preeclampsia with Severe Features & Eclampsia: Pathophysiology & Diagnosis

Preeclampsia is a multisystem gestational disorder characterized by abnormal placental cytotrophoblast invasion, spiral artery remodeling failure, and placental hypoperfusion. This triggers widespread maternal vascular endothelial dysfunction, diffuse microvascular vasospasm, and end-organ ischemia.

Diagnostic Criteria for Severe Features

Preeclampsia is conventionally defined as new-onset hypertension (systolic BP ≥140 mmHg or diastolic BP ≥90 mmHg on two occasions at least 4 hours apart) occurring after 20 weeks of gestation in a previously normotensive patient, accompanied by proteinuria (≥300 mg per 24-hour urine collection or urine protein-to-creatinine ratio ≥0.3 mg/mg). However, in the absence of proteinuria, the presence of new-onset hypertension with any of the following severe features establishes the diagnosis of Preeclampsia with Severe Features:

1. Severe Hypertension: Systolic BP ≥160 mmHg or diastolic BP ≥110 mmHg on two occasions at least 15 minutes apart while resting.
2. Thrombocytopenia: Platelet count <100,000 cells/mcL.
3. Impaired Liver Function: Serum transaminases (AST or ALT) elevated to greater than twice the upper limit of normal, or severe persistent right upper quadrant or epigastric pain unresponsive to analgesics and not explained by alternative diagnoses.
4. Renal Insufficiency: Serum creatinine >1.1 mg/dL, or a doubling of baseline serum creatinine in the absence of preexisting renal disease.
5. Pulmonary Edema.
6. New-Onset Persistent Cerebral or Visual Disturbances: Severe throbbing headache unresponsive to medication, scotoma, photopsia, cortical blindness, or altered mental status.

Eclampsia

Eclampsia is defined as the occurrence of new-onset generalized tonic-clonic seizures in a woman with preeclampsia that cannot be attributed to other neurological causes (e.g., intracranial hemorrhage, epilepsy, arteriovenous malformation). While most cases occur intrapartum or within 48 hours postpartum, late postpartum eclampsia can develop up to 4 to 6 weeks after delivery.

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Magnesium Sulfate for Neuroprotection & Seizure Management

Magnesium sulfate (MgSO₄) is the undisputed first-line agent for both the prevention and treatment of eclamptic seizures (proven superior to phenytoin, diazepam, and nimodipine in the landmark Collaborative Eclampsia Trial and Magpie Trial). Importantly, magnesium sulfate is not an antihypertensive agent; its therapeutic role is strictly central neuroprotection and anticonvulsant activity.

Mechanism of Action

• NMDA Receptor Blockade: Blocks central N-methyl-D-aspartate (NMDA) receptor channels in a voltage-dependent manner, suppressing neuronal excitability and raising seizure threshold.
• Cerebral Vasodilation: Promotes smooth muscle relaxation and selective cerebral arteriolar vasodilation, reversing cerebral vasospasm and reducing blood-brain barrier permeability and cerebral edema.
• Neuromuscular Junction Inhibition: Decreases presynaptic acetylcholine release at the motor endplate and depresses post-junctional membrane sensitivity.

Standard Dosing Protocol

• Loading Dose: 4 to 6 g IV diluted in 100 mL of 0.9% normal saline or D5W, infused intravenously over 15 to 20 minutes.
• Maintenance Infusion: 1 to 2 g/hour IV continuous infusion.
• Duration: Continued throughout labor and delivery and for at least 24 hours postpartum (or 24 hours after the last recorded seizure).
• Recurrent Seizures: If seizures recur during maintenance infusion, administer an additional 2 g IV bolus over 3 to 5 minutes.

Therapeutic Monitoring & Toxicity Spectrum

Magnesium is eliminated exclusively by renal glomerular filtration. In patients with renal insufficiency (serum creatinine >1.1 mg/dL or oliguria <30 mL/hour), magnesium accumulates rapidly, requiring maintenance infusion rate reduction to 1 g/h or frequent serum concentration monitoring.

Emergency Toxicity Reversal

If clinical signs of magnesium toxicity appear (loss of patellar reflexes or respiratory rate <12 breaths/min):

1. Immediately discontinue the magnesium sulfate infusion.
2. Administer 10% Calcium Gluconate 1 g (10 mL) IV over 3 to 5 minutes (or Calcium Chloride 1 g IV via central access). Calcium directly antagonizes magnesium at the motor endplate and cardiac sarcolemma.
3. Provide immediate respiratory support (supplemental oxygen, bag-valve-mask ventilation, or endotracheal intubation if respiratory arrest occurs).

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Acute Severe Hypertension Management in Pregnancy

Severe acute maternal hypertension (systolic BP ≥160 mmHg or diastolic BP ≥110 mmHg) represents an immediate hypertensive emergency requiring pharmacologic reduction within 30 to 60 minutes. The clinical objective is to lower blood pressure into a safe range (systolic BP 140-150 mmHg and diastolic BP 90-100 mmHg) to prevent maternal hemorrhagic stroke, encephalopathy, and placental abruption, while avoiding precipitous drops that compromise uteroplacental perfusion.

First-Line Antihypertensive Agents

                 ACUTE SEVERE HYPERTENSION IN PREGNANCY (BP ≥160/110)
  ┌─────────────────────────────────────────────────────────────────────────────┐
  │ Initial Choice: IV Labetalol, IV Hydralazine, or Oral Nifedipine IR         │
  └──────────────────────────────────────┬──────────────────────────────────────┘
                                         │
         ┌───────────────────────────────┼───────────────────────────────┐
         ▼                               ▼                               ▼
  ┌───────────────────────┐       ┌───────────────────────┐       ┌───────────────────────┐
  │   IV LABETALOL        │       │   IV HYDRALAZINE      │       │  ORAL NIFEDIPINE IR   │
  │ • 20 mg IV over 2 min │       │ • 5-10 mg IV over 2m  │       │ • 10-20 mg PO capsule │
  │ • Wait 10-20 min      │       │ • Wait 20 min         │       │ • Wait 20-30 min      │
  │ • If BP high: 40 mg IV│       │ • If BP high: 10 mg IV│       │ • If BP high: 20 mg PO│
  │ • Then: 80 mg IV q10m │       │ • Max: 20-30 mg total │       │ • Max: 50 mg initial  │
  │ • Max: 220-300 mg     │       │ • Caution: tachycardia│       │ • Do NOT bite / chew  │
  │ • Avoid in asthma/CHF │       │   and delayed drop    │       │   or give sublingually│
  └───────────────────────┘       └───────────────────────┘       └───────────────────────┘

• Intravenous Labetalol:
  • Mechanism: Combined non-selective beta-blocker and selective alpha-1 blocker (alpha-to-beta blockade about 1:7 when given IV). Lowers systemic vascular resistance without reducing cardiac output or uteroplacental blood flow.
  • Dosing: Initial 20 mg IV bolus over 2 minutes. If BP remains ≥160/110 mmHg after 10 to 20 minutes, administer 40 mg IV, then 80 mg IV every 10 minutes to a maximum cumulative dose of 220 to 300 mg.
  • Contraindications: Active asthma, severe sinus bradycardia, second- or third-degree heart block, or uncompensated heart failure.
• Intravenous Hydralazine:
  • Mechanism: Direct arteriolar vasodilator.
  • Dosing: Initial 5 to 10 mg IV over 2 minutes. If BP remains elevated after 20 minutes, administer 10 mg IV. Maximum cumulative dose is 20 to 30 mg.
  • Clinical Considerations: Slower onset (10-20 minutes) and longer half-life; risk of reflex tachycardia, maternal hypotension, and fetal heart rate decelerations.
• Oral Immediate-Release Nifedipine:
  • Mechanism: Dihydropyridine calcium channel blocker.
  • Dosing: 10 to 20 mg PO (swallowed whole with water). Repeat with 20 mg PO in 20 to 30 minutes if needed (maximum initial dose 50 mg).
  • Critical Warning: Capsules must never be bitten, chewed, or administered sublingually; rapid sublingual absorption can cause catastrophic precipitous hypotension and fetal distress.

Strictly Contraindicated Antihypertensives

• ACE Inhibitors (e.g., Lisinopril, Enalaprilat) and Angiotensin Receptor Blockers (ARBs, e.g., Losartan): Carries an FDA black box warning for fetopathy. Second- and third-trimester exposure causes severe oligohydramnios, fetal renal dysgenesis, anuria, pulmonary hypoplasia, neonatal renal failure, skull hypoplasia, and fetal demise.
• Sodium Nitroprusside: Carries high risk of maternal and fetal cyanide toxicity and profound rebound intracranial pressure elevation; restricted strictly to refractory intensive care unit emergencies for ultra-short-term bridge therapy (<4 hours).

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Postpartum Hemorrhage (PPH): Stepwise Uterotonic Cascade & TXA

Postpartum hemorrhage (PPH) is defined as a cumulative blood loss ≥1,000 mL or blood loss accompanied by signs or symptoms of hypovolemia (tachycardia, hypotension, tachypnea, oliguria) within 24 hours of delivery. Uterine atony (failure of myometrial contraction after placental detachment) accounts for 70% to 80% of PPH cases.

Stepwise Uterotonic Pharmacotherapy

When uterine atony is identified, fundal massage must be paired immediately with a sequential pharmacologic protocol. Clinicians must select second-line uterotonics based strictly on patient-specific contraindications:

Tranexamic Acid in PPH: The WOMAN Trial

The landmark WOMAN trial (World Maternal Antifibrinolytic trial; 20,060 women with postpartum hemorrhage) established the role of TXA in obstetric resuscitation:

• Dose & Timing: Administer 1 g IV infused over 10 minutes within 3 hours of delivery.
• Repeat Dose: A second 1 g IV dose is administered if bleeding continues after 30 minutes, or if bleeding restarts within 24 hours of the first dose.
• Clinical Benefit: TXA significantly reduced maternal mortality due to bleeding (RR 0.81, 95% CI 0.65-1.00; p=0.045) when administered early, with greatest efficacy seen when given within 1 hour of birth, without any increase in maternal venous thromboembolism, pulmonary embolism, or ischemic stroke.