Severe Preeclampsia, HELLP Syndrome, and Eclampsia

Quick Answer

What is severe preeclampsia?

Severe preeclampsia is defined as preeclampsia with severe features that indicate end-organ dysfunction and increased risk of maternal and fetal complications. It affects 2-8% of pregnancies globally and remains a leading cause of maternal mortality worldwide. [1,2]

Key clinical features requiring intervention:

1. Severe hypertension - Systolic BP ≥160 mmHg or diastolic ≥110 mmHg on two occasions ≥4 hours apart while on bed rest
2. Thrombocytopenia - Platelets <100 × 10⁹/L (HELLP syndrome when combined with hemolysis and elevated liver enzymes)
3. Renal dysfunction - Serum creatinine >90 μmol/L or doubling from baseline
4. Hepatic dysfunction - Elevated transaminases (ALT/AST >2× ULN) or severe persistent RUQ/epigastric pain
5. Cerebral symptoms - Persistent severe headache, visual disturbances (scotomata, photopsia), altered consciousness
6. Pulmonary edema - New-onset respiratory symptoms with imaging evidence

HELLP syndrome (Hemolysis, Elevated Liver enzymes, Low Platelets) represents a severe variant affecting 0.5-0.9% of pregnancies and 10-20% of severe preeclampsia cases. It can occur antepartum (70%) or postpartum (30%), with peak presentation at 28-36 weeks gestation. [3,4]

Eclampsia is the occurrence of generalized tonic-clonic seizures in a woman with preeclampsia, affecting 0.3-0.5% of severe preeclampsia cases. It represents end-stage disease with maternal mortality 0.5-3% and perinatal mortality 10-20%. [5,6]

Definitive treatment is delivery of the placenta. However, immediate management priorities:

1. Blood pressure control - Labetalol IV (preferred first-line), hydralazine, or nifedipine. Target: 140-150/90-100 mmHg (avoid hypotension that compromises placental perfusion)
2. Magnesium sulfate prophylaxis/treatment - 4 g IV loading over 15-20 min, then 1 g/hr infusion. Reduces seizure risk by 50% and maternal mortality by 40% in severe preeclampsia
3. Fluid management - Restricted regimen (80-100 mL/hr or 1 mL/kg/hr) due to capillary leak and risk of pulmonary edema
4. Multidisciplinary care - Obstetrics, anaesthesia, neonatology, hematology, intensive care
5. Timing of delivery - Immediate if severe features present ≥34 weeks; individualized <34 weeks based on maternal/fetal status

Clinical Pearl: In severe preeclampsia, the decision to deliver should never be delayed for "optimization." While BP control and magnesium loading should occur, delivery is the only cure. A common exam trap is spending too long on "stabilization" - remember that ongoing endothelial damage continues until the placenta is delivered.

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Clinical Overview

Definition and Classification

Preeclampsia is defined as new-onset hypertension (BP ≥140/90 mmHg on two occasions ≥4 hours apart) after 20 weeks gestation in a previously normotensive woman, accompanied by EITHER:

• Proteinuria (≥300 mg/24h or protein/creatinine ratio ≥30 mg/mmol)
• OR evidence of maternal organ dysfunction (thrombocytopenia, renal insufficiency, hepatic dysfunction, cerebral symptoms, pulmonary edema)

Severe Features (ACOG 2019; ISSHP 2018):

HELLP Syndrome Criteria (Tennessee Classification):

Partial HELLP (presence of 1-2 criteria) carries similar maternal risk to complete HELLP and requires equivalent management. [7,8]

Epidemiology

Risk factors for progression to severe disease:

• Early-onset preeclampsia (<34 weeks)
• Multiple gestation
• Pre-existing hypertension or renal disease
• Previous severe preeclampsia/HELLP
• Molar pregnancy
• Fetal growth restriction
• Thrombophilia
• Obesity (BMI >35)
• Advanced maternal age (>40 years) [9,10]

Pathophysiology

The Two-Stage Model:

Stage 1: Abnormal Placentation (1st trimester)

• Incomplete trophoblastic invasion of spiral arteries
• Spiral arteries remain narrow, muscular, high-resistance vessels
• Reduced placental perfusion → placental ischemia
• Release of anti-angiogenic factors (sFlt-1, soluble endoglin)
• Decreased pro-angiogenic factors (PlGF - placental growth factor)

Stage 2: Maternal Systemic Response (2nd-3rd trimester)

Endothelial dysfunction is the central mechanism:

HELLP-Specific Pathophysiology:

1. Hemolysis - Microangiopathic process from endothelial damage causing mechanical destruction of RBCs passing through abnormal microcirculation
2. Liver injury - Fibrin deposition in hepatic sinusoids causes periportal necrosis and intrahepatic hemorrhage
3. Thrombocytopenia - Consumption from platelet activation at sites of endothelial injury

Eclampsia Pathophysiology:

Seizures result from:

• Loss of cerebral autoregulation (normally maintains constant CBF between MAP 60-160 mmHg)
• Cerebral hyperperfusion and vasogenic edema
• Posterior reversible encephalopathy syndrome (PRES) - preferential involvement of posterior circulation due to poorer sympathetic innervation
• Possible excitotoxicity from glutamate and other neurotransmitters

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Clinical Presentation

Severe Preeclampsia Presentation

Symptoms:

Signs:

HELLP Syndrome Presentation

Classic triad may be incomplete:

Complications of HELLP:

Eclampsia Presentation

Seizure characteristics:

Status eclampticus:

• Repeated seizures without full recovery of consciousness between
• Medical emergency with high mortality
• Requires airway protection, magnesium optimization, possible thiopental/propofol

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Investigations and Monitoring

Laboratory Investigations

Essential Tests:

sFlt-1/PlGF Ratio (Angiogenic Markers):

• Elevated sFlt-1 (soluble fms-like tyrosine kinase-1) and decreased PlGF (placental growth factor)
• Ratio >38 predicts severe preeclampsia within 4 weeks with 90% sensitivity
• Useful for risk stratification and timing delivery decisions [11,12]

Monitoring Requirements

Hemodynamic Monitoring:

Fetal Monitoring:

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Management

Immediate Stabilization (First Hour)

Airway, Breathing, Circulation:

1. Left lateral tilt (if >20 weeks) or wedge to prevent aortocaval compression
2. High-flow oxygen via facemask (10-15 L/min)
3. Two large-bore IV cannulae (14-16G)
4. Arterial line if hemodynamically unstable or frequent BP monitoring needed
5. Urinary catheter for hourly urine output monitoring

Blood Pressure Management

Target: 140-150/90-100 mmHg (avoid "normalizing" BP which reduces placental perfusion)

First-line agents:

Contraindicated agents:

• ACE inhibitors/ARBs - Fetal renal dysfunction, oligohydramnios, teratogenic
• Nitroprusside - Cyanide toxicity risk with prolonged use
• Nitroglycerin - Tolerance, limited efficacy

Refractory hypertension:

• Magnesium sulfate (see below)
• Consider esmolol (ultra-short acting β-blocker)
• General anesthesia for delivery if uncontrolled

Magnesium Sulfate

Indications:

• Severe preeclampsia (seizure prophylaxis)
• Eclampsia (seizure treatment and prevention of recurrence)
• HELLP syndrome (neuroprotection, though evidence less robust)

Regimen:

Alternative IM regimen (if IV not available):

• Loading: 4 g IV + 10 g IM (5 g in each buttock with 1 mL 2% lignocaine to reduce pain)
• Maintenance: 5 g IM q4h alternating buttocks

Monitoring:

Toxicity levels and management:

Calcium gluconate (antidote): 1 g (10 mL of 10% solution) IV over 10 minutes. Reverses magnesium-induced cardiac and neuromuscular effects. [13,14,15]

Fluid Management

Restrictive approach:

Pulmonary artery catheter rarely indicated; use if:

• Severe oliguria despite fluid challenge
• Refractory pulmonary edema
• Unclear hemodynamic status

Timing and Mode of Delivery

General principle: Delivery is the definitive treatment.

Corticosteroids for fetal lung maturation:

• Betamethasone 11.4 mg IM × 2 doses, 24 hours apart
• Dexamethasone 6 mg IM × 4 doses, 12 hours apart
• Maximum benefit 48 hours after first dose

Mode of delivery:

• Vaginal preferred if fetal condition allows and cervix favorable
• Cesarean section for:
  • Fetal compromise
  • Maternal instability
  • Unfavorable cervix with urgent delivery needed
  • Placental abruption

Anesthetic Management

Preoperative Assessment:

Regional Anesthesia:

Epidural preferred (if platelets adequate):

• Platelet threshold controversial: generally >80 × 10⁹/L acceptable; >50 × 10⁹/L with normal coagulation and stable platelet trend may be acceptable at experienced centers
• Benefits: Controlled BP, avoids airway manipulation, excellent postoperative analgesia
• Caution: Hypotension may reduce placental perfusion; treat aggressively with phenylephrine/ephedrine

Spinal anesthesia:

• Generally safe if platelets >80 × 10⁹/L
• Rapid onset may limit ability to control BP response
• Avoid in hemodynamically unstable patients

General Anesthesia (indications):

• Thrombocytopenia/coagulopathy contraindicating neuraxial
• Fetal compromise requiring rapid delivery
• Patient refusal of regional
• Failed regional

GA technique:

• RSI with cricoid pressure (full stomach, delayed gastric emptying)
• Pre-oxygenation 3-5 minutes
• Induction: Thiopental 3-5 mg/kg or propofol 2-3 mg/kg + suxamethonium 1-1.5 mg/kg
• Blunt hypertensive response: Fentanyl 2-4 mcg/kg, labetalol 10-20 mg, or lignocaine 1.5 mg/kg before laryngoscopy
• Maintenance: Low-dose volatile (avoid excessive MAC which reduces uterine tone and causes fetal depression)
• Muscle relaxation: Rocuronium (avoid if MgSO4 toxicity; potentiation)
• Reversal: Sugammadex preferred over neostigmine (avoid cholinergic effects in presence of MgSO4)

Intraoperative management:

• Arterial line for beat-to-beat BP monitoring
• Maintain uterine displacement (left lateral tilt)
• Restricted fluid strategy (80-100 mL/hr)
• Oxytocin 5 units slow IV after delivery (avoid bolus in severe preeclampsia due to hypotension risk; consider infusion 10-20 units/hr)
• Second-line uterotonics: Ergometrine (avoid if hypertension), carboprost, misoprostol

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Complications and Special Considerations

Hepatic Complications

Hepatic rupture/hematoma:

• Rare (1-2% of HELLP) but life-threatening
• Presents with shock, severe RUQ pain, anemia
• Management: Resuscitation, embolization if hemodynamically stable, surgical packing/resection if unstable
• Delay hepatic surgery until coagulopathy corrected if possible

Cerebral Complications

Posterior reversible encephalopathy syndrome (PRES):

• Vasogenic edema preferentially affecting posterior circulation
• Symptoms: Headache, visual disturbances, altered consciousness, seizures
• MRI: T2 hyperintensity in parieto-occipital regions
• Treatment: BP control, magnesium; resolves with delivery

Stroke:

• Intracerebral hemorrhage (hypertension) or ischemic stroke
• Risk increased 3-5 fold in severe preeclampsia
• Management: Neurosurgical/stroke team involvement; control BP; delivery

Hematological Complications

Disseminated intravascular coagulation (DIC):

• Occurs in 10-20% of HELLP, 5-10% of severe preeclampsia
• Management: Blood products (RBC, FFP, cryoprecipitate, platelets), treat underlying cause (delivery)

Thrombotic microangiopathy (TMA) differential:

• Thrombotic thrombocytopenic purpura (TTP) - ADAMTS13 deficiency
• Atypical hemolytic uremic syndrome (aHUS) - complement dysregulation
• Differentiation important for treatment (plasma exchange for TTP, eculizumab for aHUS)

Long-term Complications

Maternal:

• Increased lifetime risk of cardiovascular disease (4-fold increased risk of hypertension, 2-fold increased risk of ischemic heart disease)
• Risk of recurrent preeclampsia in future pregnancies (16-25% if previous severe disease)
• Chronic hypertension (20-30% develop within 10 years)

Fetal/Neonatal:

• Growth restriction (30-40% of severe preeclampsia)
• Prematurity complications (if early delivery required)
• Long-term cardiovascular and metabolic risks

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Indigenous Health Considerations

Aboriginal and Torres Strait Islander Women:

Aboriginal and Torres Strait Islander women in Australia experience 2-3 times higher rates of hypertensive disorders in pregnancy compared to non-Indigenous women, with particularly elevated rates of severe preeclampsia and eclampsia. [16,17]

Contributing factors:

1. Pre-existing risk factors: Higher baseline prevalence of chronic hypertension, obesity, diabetes, and renal disease (likely related to higher rates of low birth weight and prematurity in previous generations creating intergenerational metabolic programming)
2. Access barriers: Geographic remoteness, limited specialist obstetric services in rural/remote communities, delayed presentation due to cultural/language barriers or previous negative healthcare experiences
3. Social determinants: Higher rates of smoking, nutritional challenges, and stress related to socioeconomic disadvantage and intergenerational trauma
4. Healthcare system factors: Institutional racism, lack of cultural safety, communication breakdowns

Clinical management considerations:

Culturally safe care:

• Engagement of Aboriginal Health Workers (AHWs) or Aboriginal Liaison Officers (ALOs) early in care pathway
• Provision of professional interpreter services for women with limited English proficiency
• Recognition of kinship obligations - family involvement in decision-making processes
• Understanding of "Sorry Business" and cultural protocols that may affect attendance at appointments or hospital stays

Remote/Regional considerations:

• Early identification and transfer to regional centers with appropriate obstetric/neonatal services
• Telemedicine consultations for specialist input when transfer delayed
• Retrieval services (RFDS) with specialized obstetric teams for inter-hospital transfer
• Clear protocols for magnesium administration and seizure management in facilities without resident obstetric anaesthetists

Communication strategies:

• Use of culturally appropriate educational materials and visual aids
• "Teach-back" method to confirm understanding of warning signs (headache, visual changes, RUQ pain)
• Involvement of community health workers for post-discharge follow-up and blood pressure monitoring
• Home blood pressure monitoring programs with telehealth follow-up

Māori Women (Aotearoa New Zealand):

Māori women experience similar disparities with higher rates of severe maternal morbidity including hypertensive disorders. [18,19]

Specific considerations:

1. Whānau-centered care: Recognition that decision-making involves extended family; ensure whānau involvement in care planning and informed consent processes
2. Cultural safety: Training for healthcare providers in Tikanga Māori (customs and protocols)
3. Māori Health Workers: Integration of Māori Health Workers into multidisciplinary teams
4. Kaupapa Māori services: Where available, preference for Māori-led maternity services that provide culturally safe care
5. Addressing institutional racism: Active efforts to address unconscious bias and systemic barriers in healthcare delivery

Key principle: Indigenous women with preeclampsia require not only clinical excellence but culturally safe care that addresses access barriers, respects cultural protocols, and actively works to eliminate the disparities in maternal outcomes.

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ANZCA Exam Focus

High-Yield Topics

Written Examination:

• Pharmacology of magnesium sulfate (mechanism, dosing, toxicity, antidote)
• Antihypertensive agents in pregnancy (contraindications, fetal effects)
• Coagulation thresholds for neuraxial anesthesia in thrombocytopenia
• Fluid management strategies (restricted vs. liberal)
• Differential diagnosis of thrombocytopenia in pregnancy

Viva Voce:

• Management algorithm for severe preeclampsia (BP control, magnesium, delivery timing)
• Anesthetic technique selection (regional vs. general) based on clinical scenario
• Airway management in the eclamptic patient (seizing, full stomach, potential difficult airway)
• Troubleshooting: Refractory hypertension, recurrent seizures, coagulopathy
• Ethical scenario: Delivery timing in extreme prematurity (<28 weeks) with severe preeclampsia

Common Exam Scenarios

Scenario 1: Severe Preeclampsia for Emergency Cesarean

• 32-year-old G2P1 at 34 weeks
• BP 175/115 mmHg, platelets 65 × 10⁹/L
• Headache, visual disturbances, epigastric pain
• Fetal bradycardia on CTG

Key discussion points:

• Immediate management: BP control (labetalol), magnesium loading, fluid restriction
• Anesthetic choice: GA vs. regional (platelets 65 × 10⁹/L generally acceptable for neuraxial at experienced centers, but GA may be preferred given urgency and coagulation trend)
• Intraoperative: Arterial line, uterine displacement, controlled delivery of baby and placenta, uterotonic strategy

Scenario 2: HELLP Syndrome

• 28-year-old primigravida at 36 weeks
• BP 155/105 mmHg, platelets 45 × 10⁹/L
• Hb 85 g/L (was 105 g/L 3 days ago), LDH 850 U/L
• AST 180 U/L, ALT 220 U/L
• RUQ pain, nausea

Key discussion points:

• HELLP diagnosis and classification (Class I: platelets <50)
• Management priorities: Stabilization, corticosteroids for fetus, platelet transfusion threshold for neuraxial vs. GA
• Complications: Hepatic rupture risk, DIC monitoring, postoperative ICU admission

Scenario 3: Eclampsia

• 24-year-old primigravida at 38 weeks
• Witnessed tonic-clonic seizure in emergency department
• BP 190/120 mmHg post-ictal
• Confused, agitated

Key discussion points:

• Immediate seizure management: Left lateral position, airway protection, oxygen, magnesium sulfate loading
• BP control while avoiding oversedation
• Timing of delivery after stabilization (usually within 12-24 hours)
• Anesthetic technique for emergency delivery

Key Pharmacology

Magnesium Sulfate:

• Mechanism: CNS depressant, blocks NMDA receptors, reduces acetylcholine release at neuromuscular junction, vasodilator, neuroprotective
• Elimination: Renal (require dose reduction if creatinine clearance impaired)
• Interactions: Potentiates neuromuscular blockers (both depolarizing and non-depolarizing), calcium channel blockers, general anesthetics
• Monitoring: Clinical (reflexes, respiratory rate, urine output) ± serum levels
• Toxicity: Sequential loss of reflexes → respiratory depression → cardiac arrest; calcium gluconate antidote

Antihypertensives:

• Labetalol: Combined α1 and non-selective β antagonism; reduces BP without reflex tachycardia; minimal placental transfer
• Hydralazine: Direct arteriolar vasodilation; reflex tachycardia and headache common
• Nifedipine: Calcium channel blocker; avoid sublingual (erratic absorption); oral preferred

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Assessment Content

SAQ 1: Severe Preeclampsia Management (20 marks)

Question:

A 30-year-old primigravida at 35 weeks gestation presents to the emergency department with severe headache, visual disturbances ("spots in vision"), and epigastric pain. Her blood pressure is 185/118 mmHg. On examination, she has brisk reflexes with ankle clonus. Her blood results show:

• Hemoglobin: 112 g/L
• Platelets: 78 × 10⁹/L (trend: 145 → 120 → 95 → 78 over past 72 hours)
• Creatinine: 98 μmol/L
• Urate: 0.42 mmol/L
• AST: 156 U/L, ALT: 198 U/L
• LDH: 620 U/L

a) Outline your immediate management priorities for this patient. (8 marks)

b) Discuss the role of magnesium sulfate in this patient, including indications, dosing, monitoring, and potential toxicity. (6 marks)

c) She requires delivery. Discuss the factors influencing your choice of anesthetic technique and outline your management if she requires general anesthesia. (6 marks)

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Model Answer:

a) Immediate management priorities (8 marks):

Diagnosis: Severe preeclampsia with HELLP syndrome (Class II: platelets 50-100 × 10⁹/L, elevated transaminases, hemolysis [elevated LDH, falling Hb])

b) Magnesium sulfate (6 marks):

Indications in this patient:

• Severe preeclampsia with severe features (BP >160/110, thrombocytopenia, hepatic dysfunction, cerebral symptoms)
• HELLP syndrome (benefit for seizure prophylaxis and neuroprotection)
• Reduces seizure risk by approximately 50% and maternal mortality by 40%

Dosing:

• Loading dose: 4 g IV over 15-20 minutes (diluted in 100 mL normal saline)
• Maintenance infusion: 1-2 g/hr continuous IV
• Duration: Continue for 24 hours postpartum or for 24 hours after last seizure if eclampsia develops

Monitoring:

• Patellar reflexes (discontinue if absent)
• Respiratory rate (discontinue if <12 breaths/min)
• Urine output (reduce dose if <25-30 mL/hr)
• Serum magnesium levels 6-hourly if renal impairment (therapeutic 2-3.5 mmol/L)

Toxicity (sequential):

• Loss of deep tendon reflexes (first sign, levels 3.5-5 mmol/L)
• Respiratory depression (levels 5-7.5 mmol/L)
• Respiratory paralysis and cardiac arrest (levels >7.5 mmol/L)

Antidote: Calcium gluconate 1 g IV over 10 minutes reverses magnesium-induced cardiac and neuromuscular effects

c) Anesthetic technique and GA management (6 marks):

Factors influencing anesthetic choice:

If general anesthesia required:

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SAQ 2: HELLP Syndrome and Hepatic Complications (15 marks)

Question:

A 26-year-old woman at 34 weeks gestation is diagnosed with HELLP syndrome. Her laboratory values are:

• Hemoglobin: 88 g/L (was 105 g/L 48 hours ago)
• Platelets: 28 × 10⁹/L
• PT: 16 seconds (control 12), APTT: 48 seconds (control 32)
• Fibrinogen: 1.2 g/L
• Bilirubin: 42 μmol/L (conjugated 12, unconjugated 30)
• LDH: 950 U/L
• AST: 245 U/L, ALT: 320 U/L
• Creatinine: 112 μmol/L

She complains of severe right upper quadrant pain that radiates to the right shoulder.

a) What is the significance of her RUQ pain and shoulder pain? What investigation would you order to evaluate this? (3 marks)

b) Outline your management of this patient including blood product administration. (7 marks)

c) What are the potential complications of HELLP syndrome that may require ICU admission? (5 marks)

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Model Answer:

a) RUQ pain significance and investigation (3 marks):

Significance:

• RUQ pain in HELLP indicates hepatic involvement - specifically hepatic distension from sinusoidal fibrin deposition and periportal necrosis
• Pain radiating to right shoulder (Kehr's sign equivalent) suggests diaphragmatic irritation from:
  • Subcapsular hepatic hematoma (most concerning)
  • Hepatic capsule distension
  • impending hepatic rupture

Investigation:

• Urgent abdominal ultrasound with Doppler (liver, kidneys, spleen)
• Look for: Subcapsular hematoma (hypoechoic collection), intrahepatic hematoma, free fluid
• CT abdomen if ultrasound inconclusive and hemodynamically stable (contrast risk in pregnancy acceptable if clinical indication strong)
• Bedside FAST exam if hemodynamically unstable

b) Management including blood products (7 marks):

Immediate priorities:

1. Large-bore IV access, type and crossmatch 4-6 units blood
2. Arterial line for monitoring
3. URGENT delivery once stabilized (definitive treatment)

Blood product strategy:

Hepatic management:

• Hematology/hepatology consultation
• If subcapsular hematoma confirmed:
  • Conservative if <50% surface area, hemodynamically stable: close monitoring, avoid trauma/hepatomegaly
  • Arterial embolization if bleeding source identified
  • Surgical packing only if rupture/hemodynamic instability
• Avoid hepatotoxic drugs (acetaminophen within safe limits, avoid NSAIDs)

Delivery:

• General anesthesia (contraindications to neuraxial: platelets 28 × 10⁹/L, coagulopathy)
• Platelet transfusion preoperatively if active bleeding
• ICU admission postoperatively

c) Complications requiring ICU admission (5 marks):

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Viva Scenario: Magnesium Toxicity

Setting: Clinical viva (10 minutes)

Scenario:

"You are the anaesthetic registrar on call. You are called to the obstetric HDU where a 32-year-old woman with severe preeclampsia has received magnesium sulfate for 4 hours. The midwife is concerned because the patient is increasingly drowsy and her respiratory rate has decreased to 8 breaths per minute. The patellar reflexes are absent."

Examiner-Candidate Dialogue:

Examiner: "What are your immediate concerns and actions?"

Candidate: "My immediate concern is magnesium toxicity given the clinical picture - drowsiness, respiratory depression, and absent reflexes in the context of magnesium therapy. My actions would be:"

1. Immediate assessment:

   • Check ABC: airway patency, breathing adequacy, circulation
   • Check vital signs: BP, heart rate, oxygen saturation
   • Call for help - senior anaesthetic colleague, resuscitation team if needed

2. Stop magnesium infusion immediately - disconnect the infusion to prevent further magnesium administration

3. Airway management:

   • Given respiratory rate of 8 and drowsiness, she is at high risk of respiratory failure
   • Prepare for potential intubation: difficult airway equipment (obese, edematous airway), pre-oxygenation
   • Position left lateral with head-up if possible
   • High-flow oxygen via facemask

4. Specific antidote:

   • Administer calcium gluconate 1 g (10 mL of 10% solution) IV over 10 minutes
   • This competitively antagonizes magnesium at the neuromuscular junction and cardiac conduction system
   • Can repeat if necessary

5. Supportive care:

   • If respiratory failure progresses: RSI with thiopental/propofol and suxamethonium (short-acting given potential for prolonged blockade)
   • Mechanical ventilation if intubated
   • Hemodynamic support if hypotension develops

Examiner: "What magnesium level would you expect, and what are the specific manifestations at different levels?"

Candidate:

This patient likely has a magnesium level between 5-7.5 mmol/L based on absent reflexes and respiratory depression.

Examiner: "How would you monitor her going forward?"

Candidate:

• Continuous observation in high dependency setting
• Cardiac monitoring for arrhythmias and conduction abnormalities
• Serial calcium levels if repeated calcium administration required
• Monitor urine output - magnesium is renally excreted; ensure adequate output to clear accumulated magnesium
• Recheck deep tendon reflexes hourly until return (sign of falling magnesium levels)
• Avoid further magnesium exposure until levels normalize and symptoms resolve
• Consider hemodialysis if renal impairment present and toxicity severe/refractory

Examiner: "What factors predispose to magnesium toxicity?"

Candidate:

• Renal impairment - reduced excretion (most common)
• Excessive dosing - too rapid loading or excessive maintenance dose
• Drug interactions - potentiation by calcium channel blockers, neuromuscular blockers
• Dehydration - reduced renal perfusion
• Concomitant use of other CNS depressants - opioids, benzodiazepines
• Monitoring failure - inadequate clinical monitoring or failure to adjust dose for reduced urine output

Examiner: "How does magnesium sulfate work as an anticonvulsant?"

Candidate: Magnesium sulfate exerts its anticonvulsant effects through multiple mechanisms:

1. NMDA receptor antagonism - Blocks N-methyl-D-aspartate glutamate receptors in the CNS, reducing neuronal excitability and seizure propagation

2. Calcium channel blockade - Acts as a physiological calcium antagonist at voltage-gated calcium channels, reducing calcium influx and neurotransmitter release

3. Peripheral neuromuscular blockade - Reduces acetylcholine release at the neuromuscular junction and decreases motor end-plate sensitivity to acetylcholine, reducing seizure-induced muscle contractions and trauma

4. Cerebral vasodilation - Causes mild vasodilation of cerebral vessels, potentially improving blood flow and reducing ischemia

5. Membrane stabilization - General stabilizing effect on excitable membranes including neurons and cardiac myocytes

The combination of CNS depression and peripheral neuromuscular blockade effectively terminates and prevents seizure activity while minimizing maternal and fetal complications compared to traditional anticonvulsants like diazepam or phenytoin.

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