10.2 Hypertensive Disorders of Pregnancy: Pre-eclampsia & Eclampsia

Spectrum & Classification of Hypertensive Disorders in Pregnancy

Hypertensive disorders of pregnancy (HDP) complicate 5% to 10% of pregnancies worldwide and remain a leading cause of maternal and perinatal morbidity and mortality across the Caribbean. Pathophysiologically, pre-eclampsia stems from abnormal remodeling of maternal uterine spiral arteries: defective endovascular trophoblastic invasion prevents the conversion of narrow, high-resistance muscular spiral arteries into wide, low-resistance flaccid conduits. The resultant chronic placental ischemia stimulates the pathological release of anti-angiogenic factors into maternal circulation—predominantly soluble fms-like tyrosine kinase-1 (sFlt-1) and soluble endoglin (sEng)—which neutralize circulating vascular endothelial growth factor (VEGF) and placental growth factor (PlGF). The consequence is widespread maternal systemic endothelial cell dysfunction, microvascular vasospasm, and capillary hyperpermeability.

The International Society for the Study of Hypertension in Pregnancy (ISSHP) and ACOG classify hypertensive disorders into four distinct clinical categories:

• Chronic Hypertension: Blood pressure >= 140 mmHg systolic and/or >= 90 mmHg diastolic predating pregnancy, diagnosed before 20 weeks of gestation, or persisting beyond 12 weeks postpartum.
• Gestational Hypertension: New-onset hypertension (BP >= 140/90 mmHg on two readings at least 4 hours apart) developing at or after 20 weeks of gestation in the absence of proteinuria or systemic end-organ dysfunction. Blood pressure normalizes by 12 weeks postpartum.
• Pre-eclampsia: New-onset hypertension presenting at or after 20 weeks of gestation combined with either proteinuria or new-onset maternal systemic end-organ dysfunction:
  • Proteinuria: Urinary protein excretion >= 300 mg per 24-hour urine collection, spot urinary protein-to-creatinine ratio (PCR) >= 30 mg/mmol (>= 0.3 mg/mg), or >= 2+ on automated dipstick testing if quantitative methods are unavailable.
  • Absence of Proteinuria: In the absence of proteinuria, pre-eclampsia is definitively diagnosed if new-onset hypertension is accompanied by any of the following features of systemic end-organ compromise.
• Chronic Hypertension with Superimposed Pre-eclampsia: New proteinuria and/or maternal organ or uteroplacental dysfunction in a woman with chronic hypertension. A rise in previously controlled blood pressure warrants urgent assessment but does not establish superimposed pre-eclampsia by itself.

Pre-eclampsia with Severe Features

The presence of any of the following clinical or laboratory parameters categorizes the disease as pre-eclampsia with severe features, mandating immediate inpatient admission and aggressive medical stabilization:

1. Severe Hypertension: Systolic blood pressure >= 160 mmHg and/or diastolic blood pressure >= 110 mmHg on two occasions at least 15 minutes apart while the patient is at rest.
2. Thrombocytopenia: Platelet count < 100 x 10^9/L.
3. Impaired Renal Function: Serum creatinine concentration > 97 to 100 mcmol/L (1.1 mg/dL) or a doubling of serum creatinine in the absence of other renal disease.
4. Impaired Hepatic 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 unassociated with other diagnoses.
5. Pulmonary Edema: Acute dyspnea, orthopnea, crackles on auscultation, and arterial desaturation.
6. New-Onset Neurological Symptoms: Persistent, throbbing frontal headache unresponsive to simple analgesics, visual disturbances (scotomata, photopsia, cortical blindness), altered mental status, or brisk hyperreflexia with clonus (>= 3 beats).

Eclampsia & HELLP Syndrome

• Eclampsia: The occurrence of new-onset generalized tonic-clonic convulsions in a patient with pre-eclampsia that cannot be attributed to other neurological conditions (epilepsy, intracranial hemorrhage, encephalitis). Eclampsia may occur antepartum (38%), intrapartum (18%), or postpartum (44%, typically within the first 48 hours). It represents a cerebrovascular emergency caused by cerebral autoregulatory breakdown, microvascular endothelial leakage, and localized cerebral vasogenic edema (posterior reversible encephalopathy syndrome [PRES]).
• HELLP Syndrome: A severe, life-threatening variant of pre-eclampsia characterized by microangiopathic hemolytic anemia, hepatic necrosis, and profound consumption of platelets. Diagnostic criteria include:
  • Hemolysis (H): Microangiopathic blood smear demonstrating fragmented red blood cells (schistocytes, burr cells), elevated serum lactate dehydrogenase (LDH > 600 IU/L), elevated total bilirubin (>= 20.5 mcmol/L [1.2 mg/dL]), and low haptoglobin.
  • Elevated Liver Enzymes (EL): Serum AST or ALT >= 70 IU/L or twice the upper limit of normal.
  • Low Platelets (LP): Platelet count < 100 x 10^9/L. HELLP syndrome carries high risks of subcapsular hepatic hematoma formation and rupture (manifesting with sudden excruciating right upper quadrant pain radiating to the right shoulder, peritoneal irritation, and hypovolemic shock), acute kidney injury, and disseminated intravascular coagulation (DIC).

Pharmacotherapy for Acute Severe Hypertension

Severe acute hypertension in pregnancy (systolic BP >= 160 mmHg or diastolic BP >= 110 mmHg) constitutes an obstetric emergency requiring prompt pharmacological intervention within 30 to 60 minutes. The overriding clinical objective is to lower blood pressure into a safe therapeutic window—target systolic 135 to 145 mmHg and diastolic 85 to 95 mmHg—to protect the maternal cerebral circulation from hemorrhagic stroke while preserving adequate uteroplacental perfusion. Overly aggressive, precipitous reduction of blood pressure is avoided because it compromises placental blood flow and precipitates acute fetal distress.

First-Line Emergency Antihypertensive Agents

1. Intravenous Labetalol: Combined competitive alpha-1 and non-selective beta-adrenergic blocker that decreases systemic vascular resistance without producing reflex tachycardia.
   • Dosing Protocol: Initial bolus of 20 mg IV over 2 minutes. If severe hypertension persists after 10 to 20 minutes, administer 40 mg IV, then 80 mg every 10 to 20 minutes to a maximum cumulative dose of 220 to 300 mg; alternatively, maintain via continuous infusion (1 to 2 mg/min).
   • Contraindications: Moderate-to-severe bronchial asthma, severe sinus bradycardia (heart rate < 60 bpm), second- or third-degree heart block, or overt decompensated heart failure.
2. Oral Immediate-Release Nifedipine: Dihydropyridine calcium channel blocker promoting peripheral arteriolar smooth muscle relaxation.
   • Dosing Protocol: 10 to 20 mg orally swallowed whole with water (never bitten or administered sublingually, as sublingual absorption produces uncontrolled, precipitous maternal hypotension and secondary fetal distress). Repeat 10 to 20 mg in 20 to 30 minutes if BP remains above threshold, followed by 10 to 20 mg every 4 to 6 hours as needed (maximum cumulative daily dose 180 mg).
   • Side Effects: Maternal reflex tachycardia, peripheral flushing, headache.
3. Intravenous Hydralazine: Direct arteriolar vasodilator.
   • Dosing Protocol: 5 to 10 mg IV slowly over 2 minutes. If blood pressure remains severe after 20 to 30 minutes, administer a second dose of 5 to 10 mg (maximum cumulative dose 20 to 30 mg).
   • Side Effects: Maternal hypotension, profound reflex tachycardia, nausea, headache, and fetal decelerations.

Maintenance Antihypertensives & Absolute Contraindications

For non-emergent maintenance control of chronic or gestational hypertension, first-line oral agents include oral Labetalol (100 to 400 mg two to three times daily), extended-release Nifedipine (30 to 90 mg once daily), and Methyldopa (centrally acting alpha-2 adrenergic agonist, 250 to 500 mg two to three times daily).

Absolute Pharmacological Contraindications: Angiotensin-Converting Enzyme (ACE) inhibitors (e.g., enalapril, lisinopril) and Angiotensin Receptor Blockers (ARBs, e.g., losartan) are strictly contraindicated throughout pregnancy. Exposure in the second and third trimesters produces severe fetopathy: impaired fetal renal perfusion, renal tubular dysgenesis, anuria, profound oligohydramnios, secondary fetal pulmonary hypoplasia, intrauterine growth restriction, calvarial hypoplasia, and neonatal renal failure (Potter sequence).

Magnesium Sulfate Protocols & Toxicity Monitoring

Magnesium sulfate (MgSO4) is the undisputed international drug of choice for the prevention and treatment of eclamptic seizures, demonstrated to be vastly superior to diazepam and phenytoin in both the landmark Collaborative Eclampsia Trial and the Magpie Trial. Magnesium acts as a central N-methyl-D-aspartate (NMDA) receptor antagonist, blocks calcium channels, stabilizes excitable neuronal membranes, induces cerebral vasodilation, and decreases acetylcholine release at the motor endplate.

Clinical Regimens

• Pritchard Regimen (Intravenous + Intramuscular Combination): Extensively utilized in regional Caribbean hospitals and district facilities where automated infusion pumps are limited:
  • Loading Dose: 4 g IV as a 20% solution administered slowly over 5 to 15 minutes, accompanied immediately by 10 g IM (5 g deep IM into each upper outer quadrant of the buttock as a 50% solution, mixed with 1 mL of 1% lidocaine to minimize local pain).
  • Maintenance Dose: 5 g IM (50% solution) every 4 hours into alternating buttocks for 24 hours postpartum or 24 hours following the last seizure.
• Zuspan Regimen (Intravenous Infusion):
  • Loading Dose: 4 g IV in 100 mL 0.9% normal saline over 15 to 20 minutes.
  • Maintenance Dose: Continuous intravenous infusion of 1 to 2 g/hour via a dedicated infusion pump for 24 hours postpartum or 24 hours after the last convulsion.
• Recurrent Seizure Management: If an eclamptic convulsion recurs while the patient is receiving maintenance magnesium sulfate, an additional intravenous bolus of 2 g MgSO4 is administered over 5 minutes.

Toxicity Monitoring & Antidote Administration

Because magnesium is eliminated almost exclusively by maternal renal excretion, impaired renal function rapidly produces life-threatening hypermagnesemia. Prior to administering each intramuscular dose or every hour during continuous intravenous infusion, the following three clinical parameters must be strictly confirmed:

1. Deep Tendon (Patellar) Reflexes: Must be present. Loss of the patellar reflex is the earliest and most sensitive clinical sign of magnesium toxicity, manifesting at serum levels of 4.0 to 5.0 mmol/L (8 to 10 mEq/L; therapeutic level is 2.0 to 3.5 mmol/L [4 to 7 mEq/L]).
2. Respiratory Rate: Must be >= 12 breaths per minute. Respiratory depression and central apnea occur at serum concentrations exceeding 5.0 to 6.0 mmol/L (10 to 12 mEq/L).
3. Hourly Urinary Output: Must exceed 30 mL/hour (or >= 100 mL over 4 hours). If urine output falls below 30 mL/h, magnesium administration must be withheld or the infusion rate halved, with urgent serum magnesium testing.

If patellar reflexes are lost, respiratory depression occurs, or cardiac conduction abnormalities emerge:

• Step 1: Discontinue magnesium sulfate immediately.
• Step 2: Administer 10 mL of 10% Calcium Gluconate (1 g) intravenously slowly over 3 to 5 minutes. Calcium competitively antagonizes magnesium at the neuromuscular junction.
• Step 3: Support maternal ventilation with 100% supplemental oxygen via bag-valve-mask or endotracheal intubation if respiratory arrest supervenes.

Delivery Timing & Obstetric Stabilization

Delivery of the fetus and placenta is the sole definitive cure for pre-eclampsia. Timing of delivery balances maternal safety against neonatal risks of iatrogenic prematurity:

• Pre-eclampsia Without Severe Features: Deliver at 37+0 weeks of gestation (or upon reaching 37 weeks).
• Pre-eclampsia With Severe Features >= 34+0 Weeks: Deliver promptly once maternal hemodynamics are stabilized with antihypertensives and magnesium sulfate.
• Pre-eclampsia With Severe Features at 24+0 to 33+6 Weeks: In a specialized tertiary center with neonatal intensive care capabilities, expectant management can be considered for 24 to 48 hours to complete a course of antenatal corticosteroids (Betamethasone 12 mg IM two doses 24 hours apart, or Dexamethasone 6 mg IM four doses 12 hours apart) for fetal lung maturity and magnesium sulfate for fetal neuroprotection (< 32 weeks), provided maternal and fetal status remain stable.
• Mandatory Immediate Delivery (Regardless of Gestational Age): Eclampsia, pulmonary edema, disseminated intravascular coagulation, refractory severe hypertension despite multi-agent pharmacotherapy, progressive renal failure, suspected placental abruption, or non-reassuring fetal status.

Emergency Management of Eclamptic Seizures

When an eclamptic convulsion occurs, the clinical priority is maternal resuscitation:

1. Call for Help: Activate the multidisciplinary emergency obstetric response team.
2. Airway & Breathing: Place the patient in the left lateral tilt position to prevent aspiration and alleviate aortocaval compression. Clear the oropharynx, maintain an open airway, and administer 100% high-flow oxygen via a non-rebreather mask.
3. Control Seizures: Administer magnesium sulfate 4 g IV loading dose over 5 to 15 minutes.
4. Control Severe Blood Pressure: Administer IV labetalol or oral nifedipine once the convulsion ceases to bring blood pressure into the safe range.
5. Fetal Assessment: Transient fetal heart rate deceleration and loss of variability typically occur during and immediately following an eclamptic seizure. This represents maternal hypoxia and uterine vasoconstriction rather than irreversible fetal compromise. The clinician must avoid rushing into an emergency cesarean section during the active convulsion; resuscitation of the mother almost invariably results in fetal heart rate recovery within 5 to 10 minutes.
6. Plan Delivery: Once the mother is stable and alert, proceed with delivery. Choose induction or cesarean according to gestational age, cervical findings, urgency and maternal/fetal condition; eclampsia alone does not mandate cesarean delivery.

Diagnostic Criteria & Clinical Management of Hypertensive Disorders in Pregnancy