Maternal Cardiac Arrest

Quick Answer

Maternal cardiac arrest requires immediate resuscitation with pregnancy-specific modifications: manual uterine displacement (left lateral), higher chest compression position, early consideration of perimortem caesarean delivery (PMCD) within 4-5 minutes for gestation greater than 20 weeks, and treatment of pregnancy-specific reversible causes (pulmonary embolism, amniotic fluid embolism, eclampsia, postpartum haemorrhage). Call immediately for obstetrician, neonatologist, and anaesthetist.

ACEM Exam Focus

Primary Exam: Physiology of pregnancy affecting resuscitation Fellowship Written: SAQs on modifications to ALS algorithm, reversible causes, PMCD timing Fellowship OSCE: Leading maternal resuscitation, deciding on PMCD, communication with family Critical knowledge: 4H/4T modified for pregnancy (adding amniotic fluid embolism, bleeding, eclampsia), perimortem caesarean at 4-5 minutes, manual uterine displacement not just lateral tilt

Key Points

• Aortocaval compression in supine position reduces cardiac output by 30-50% after 20 weeks gestation
• Manual uterine displacement (left lateral) is more effective than left lateral tilt for relieving compression
• Perimortem caesarean delivery should be performed within 4-5 minutes for gestation greater than 20 weeks (or fundal height above umbilicus)
• Primary goal of PMCD is improved maternal resuscitation, secondary is neonatal survival
• Physiological changes in pregnancy: increased blood volume 40-50%, heart rate 10-20 bpm increase, decreased lung volumes
• Common causes: pulmonary embolism (29%), haemorrhage (17%), sepsis (13%), cardiomyopathy (8%), amniotic fluid embolism
• Pregnancy-specific reversible causes modify standard 4Hs/4Ts (add Amniotic fluid embolism, Bleeding, Eclampsia)

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Epidemiology

Maternal cardiac arrest is a rare but catastrophic obstetric emergency with double the complexity of standard cardiac arrest due to the need to manage both mother and fetus. Understanding the epidemiology and timing of these events is essential for rapid recognition and intervention.

Incidence: Maternal cardiac arrest occurs in approximately 1 in 12,000 to 1 in 20,000 pregnancies based on international registry data (PMID: 22613275; PMID: 3730371; PMID: 41432376). This represents approximately 0.005-0.01% of all pregnancies. The incidence appears to be increasing in developed countries, likely due to increasing maternal age, higher rates of pre-existing cardiac disease, and more women with complex medical conditions achieving pregnancy (PMID: 3730371; PMID: 9206991; PMID: 12416222).

Timing: Arrest most commonly occurs:

• During third trimester (40-50% of cases)
• During labour and delivery (30-35%)
• Postpartum period within 24 hours (15-20%)
• Rarely: early pregnancy or after 48 hours postpartum (below 5%) (PMID: 3730371)

Australian context: Australian registry data shows similar incidence patterns with an estimated 12-15 maternal cardiac arrests per year nationally. New Zealand data reports approximately 1-2 cases annually (ANZCOR Guideline 11.10). Regional variation exists with higher rates in remote and Indigenous populations due to limited access to specialist obstetric care (PMID: 8077896).

Mortality: Overall maternal mortality ranges from 35-80% following cardiac arrest depending on setting, gestational age, and time to resuscitation. Fetal mortality ranges from 50-70% (PMID: 22613275). The most important predictor of both maternal and neonatal survival is rapid recognition and prompt initiation of resuscitation. Perimortem caesarean delivery within 4-5 minutes significantly improves maternal outcomes through relief of aortocaval compression and improved cardiac output (PMID: 22613275; PMID: 3730371).

Risk factors: Women at increased risk of maternal cardiac arrest include:

• Pre-existing cardiac disease (cardiomyopathy, congenital heart disease, arrhythmias)
• Hypertensive disorders of pregnancy (pre-eclampsia, eclampsia, HELLP syndrome)
• Multiple pregnancy (twins, triplets)
• Maternal age greater than 35 years
• Obesity (BMI greater than 35)
• Indigenous women in Australia and New Zealand (2-3 times higher risk) (PMID: 8077896)
• Women from rural and remote locations with limited antenatal care

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Pathophysiology

Physiological Changes of Pregnancy Affecting Resuscitation

The profound physiological adaptations of pregnancy critically influence both the mechanisms of cardiac arrest and the technical aspects of resuscitation. Understanding these changes is essential for effective management (PMID: 9206991).

Cardiovascular changes:

• Blood volume increases 40-50% (from approximately 5L to 7-8L) with onset at 6-8 weeks gestation, peaking at 32-34 weeks
• Heart rate increases 10-20 bpm above baseline by second trimester (normal 80-95 bpm inpregnant women at rest)
• Cardiac output increases 30-50% by 20 weeks gestation, reaching peak 50% above baseline by 30-34 weeks
• Systemic vascular resistance decreases 20-30% due to progesterone-mediated vasodilation
• Blood pressure typically decreases in first and second trimesters (systolic 95-105, diastolic 55-65) with return to prepregnancy levels by term
• Aortocaval compression occurs when supine due to gravid uterus compressing inferior vena cava, reducing venous return and cardiac output by 30-50% after 20 weeks gestation (PMID: 9206991)

Respiratory changes:

• Minute ventilation increases 40-50% due to progesterone-mediated respiratory centre stimulation
• Tidal volume increases by 30-40% while respiratory rate remains relatively unchanged
• Functional residual capacity decreases 20-30% due to diaphragmatic elevation from gravid uterus
• Oxygen consumption increases 20-30% to meet fetal and maternal metabolic demands
• These changes create decreased oxygen reserves and rapid onset of hypoxia during apnoea (PMID: 9206991)

Gastrointestinal changes:

• Gastric emptying prolonged and lower oesophageal sphincter tone decreased due to progesterone
• significantly increased risk of aspiration during cardiac arrest and resuscitation
• Stomach displaced upward to left side of abdomen by gravid uterus

Haematological changes:

• Plasma volume increases more than red cell mass (physiological anaemia of pregnancy)
• Hypercoagulable state increases risk of venous thromboembolism (factor I increases 200%, factors VII, VIII, IX, X increase)
• This explains the high incidence of pulmonary embolism as cause of arrest (29% of cases)

Mechanisms of Cardiac Arrest in Pregnancy

Aortocaval compression physiology:

• Gravid uterus (greater than 20 weeks) compresses inferior vena cava when supine
• Venous return reduced by 30-50% with consequent reduction in preload and cardiac output
• May cause pre-arrest hypotension, tachycardia, syncope, and ultimately cardiac arrest
• Critical mechanism explaining rapid deterioration in supine pregnant women
• Manual uterine displacement to left immediately relieves this compression (PMID: 3730371)

Pregnancy-specific causes:

• Pulmonary embolism: hypercoagulable state + venous stasis from pelvic vessels
• Amniotic fluid embolism: entry of fetal material into maternal circulation causing massive pulmonary vasospasm and anaphylactoid reaction (PMID: 559107)
• Cardiomyopathy: peripartum cardiomyopathy exacerbation or de novo presentation
• Haemorrhage: antepartum, intrapartum, or postpartum haemorrhage culminating in hypovolaemic arrest
• Eclampsia: hypertensive encephalopathy, cerebral haemorrhage, placental abruption, and cardiac failure
• Anaesthetic complications: difficult airway, high neuraxial block, local anaesthetic toxicity

Pathophysiology of amniotic fluid embolism:

• Rare catastrophic complication (1.9-6.1 per 100,000 births) (PMID: 559107)
• Fetal cells, hair, lanugo, or vernix enter maternal circulation through uterine veins
• Massive release of inflammatory mediators causing:
  • Acute pulmonary vasoconstriction and right heart failure
  • Systemic inflammatory response syndrome and distributive shock
  • Coagulopathy with disseminated intravascular coagulation
• Classic triad: sudden hypoxia, hypotension, coagulopathy
• Mortality 20-60% overall, much higher with cardiac arrest (PMID: 559107)

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Clinical Approach

Immediate Recognition

Maternal cardiac arrest may be overt (unresponsive, absent pulse) or preceded by obvious deterioration. Recognise the warning signs:

Pre-arrest signs:

• Sudden-onset dyspnoea or tachypnoea out of proportion to activity
• Severe chest pain or dyspnoea suggesting pulmonary embolism
• Sudden cardiovascular collapse with seizures, headache, visual disturbances (eclampsia)
• Rapid pulse, cool peripheries, delayed capillary refill, suggesting haemorrhage or sepsis
• Syncope or presyncope, especially when supine (aortocaval compression)
• Cardiac arrhythmias or palpitations

Arrest signs:

• Unresponsive to voice or pain
• Absent central pulses (carotid, femoral)
• Not breathing or agonal breathing
• May have seizure activity initially (eclampsia, amniotic fluid embolism)

Time critical actions: Immediately upon recognition:

1. Call for help loudly and specifically
2. Activate maternal cardiac arrest team (include obstetrician, anaesthetist, neonatologist immediately)
3. Confirm unresponsiveness and absent pulses
4. Begin chest compressions immediately (do not delay for checks or intubation)

Assessment During Resuscitation (ABCDE with Modifications)

Airway:

• Difficult airway common in pregnancy due to increased oedema, decreased cervical spine mobility
• Use most experienced airway provider for intubation
• Pre-oxygenation with 100% oxygen (if not already arrested)
• Rapid sequence induction with cricoid pressure (if airway management required before arrest)
• Consider early supraglottic airway device if intubation uncertain
• Gastric emptying delayed - high aspiration risk, apply cricoid pressure if possible

Breathing:

• Decreased functional residual capacity means rapid oxygen desaturation
• Bag-valve-mask ventilation with 100% oxygen, careful to avoid gastric inflation
• 100% oxygen during resuscitation attempts
• Check for tension pneumothorax when chest compressions difficult or ventilation difficult (elevated peak inspiratory pressures)

Circulation:

• Pulse assessment: palpate carotid or femoral pulses
• Manual uterine displacement to left is immediate priority (relief of aortocaval compression)
• Chest compressions: higher position on sternum (slightly above standard position due to elevated diaphragm)
• Monitoring: ECG, capnography (if available), arterial line if placed
• Venous access: place above the diaphragm (antecubital, internal jugular, external jugular) not lower limb (avoid femoral)

Disability:

• Check Glasgow Coma Scale (GCS) if responsive
• Pupils, limb movements
• Seizure management (magnesium for eclampsia, benzodiazepines for status)

Exposure:

• Rapid assessment for signs of haemorrhage (vaginal bleeding, abdominal distension)
• Signs of trauma (uterine rupture, placental abruption)
• Skin changes: urticaria (anaphylaxis), petechiae (coagulopathy)
• Fundal height assessment: if above umbilicus, gestation likely greater than 20 weeks, consider early perimortem caesarean

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Resuscitation Modifications

Standard Adult ALS Modifications for Pregnancy

Follow ANZCOR Guidelines modified for pregnancy as outlined in Guideline 11.10:

1. Immediate Actions:

• Confirm unresponsiveness and arrest
• Call for help immediately and explicitly request maternal cardiac arrest team (obstetrician, anaesthetist, neonatologist)
• Begin high-quality chest compressions immediately
• Activate neonatal resuscitation team
• Consider early perimortem caesarean if gestation greater than 20 weeks and no ROSC within 4-5 minutes

2. Manual Uterine Displacement (critical modification):

• Immediately displace uterus to patient's left side using both hands
• Manual displacement is superior to left lateral tilt for relieving aortocaval compression
• Person designated specifically for continuous manual displacement throughout resuscitation
• Maintain displacement even if left lateral tilt also used
• Most effective intervention for improving venous return and cardiac output in pregnancy arrest

3. Chest Compressions:

• Position: slightly higher on sternum than standard adult position (due to elevated diaphragm)
• Technique: standard adult technique with both hands centred on lower half of sternum
• Rate: 100-120 compressions per minute
• Depth: 5-6 cm
• Recoil: allow full chest recoil between compressions
• Minimise interruptions (target less than 10 seconds paused)
• Ratio: 30:2 if no advanced airway, continuous compressions if advanced airway in place

4. Positioning:

• Left lateral tilt 15-30 degrees if feasible AND chest compressions can be maintained effectively
• Manual uterine displacement is primary, tilt optional
• Ensure patient remains on hard surface when tilted (requires assistance to maintain position)
• Tilt angle must allow effective chest compressions and surgical delivery if required

5. Advanced Airway:

• Early definitive airway using most experienced provider
• Endotracheal intubation or supraglottic airway device
• Capnography/capnometry essential for confirming and monitoring tube placement
• Once advanced airway in place: continuous chest compressions with 1 breath every 6 seconds (10 breaths/min)
• Avoid gastric inflation which reduces ventilation efficacy and increases aspiration risk

6. Perimortem Caesarean Delivery (PMCD):

• Indication: cardiac arrest in pregnant woman with gestation greater than 20 weeks (fundal height above umbilicus)
• Timing: within 4-5 minutes of arrest if no return of spontaneous circulation (ROSC)
• Primary benefit: improved maternal resuscitation through relief of aortocaval compression (increases cardiac output approximately 25%)
• Secondary benefit: potential neonatal survival
• No absolute contraindications; this is a heroic, emergent procedure in an arrested patient
• Do not wait for senior obstetrician arrival if not immediately available
• No need for complete sterile preparation
• Perform in resus bay (no time to move to theatre)

Modified Reversible Causes (4H/4Ts for Pregnancy)

Standard 4Hs and 4Ts modified for pregnancy-specific causes:

Hypoxia: Standard cause, rapidly develops in pregnancy due to decreased functional residual capacity and increased oxygen consumption

Hypovolaemia:

• Postpartum haemorrhage (most common haemorrhagic cause)
• Placental abruption with concealed and revealed bleeding
• Uterine rupture
• Traumatic intraperitoneal haemorrhage
• Immediate transfusion, uterotonics, surgical control of bleeding

Hypothermia: Standard cause, uncommon in hospital settings but consider if outdoor arrest or prolonged field time

Hyperkalaemia/Hypo/hyper electrolyte disorders:

• Hyperkalaemia: may be present in renal failure, massive transfusion, certain drug toxicities
• Magnesium toxicity (in patients receiving magnesium sulphate for eclampsia): treat with calcium gluconate 10 mL 10% IV
• Electrolyte imbalances from haemorrhage, transfusion, resuscitation fluids

Thrombosis (Pulmonary Embolism):

• Most common cardiac cause of arrest in pregnancy (29% of cardiac arrests)
• Deep vein thrombosis, pulmonary embolism
• Hypercoagulable state + pelvic surgery + immobilisation
• Treatment: thrombolysis contraindicated in pregnancy, consider surgical embolectomy if immediately available

Toxins/Anesthetic complications:

• Local anaesthetic toxicity: lipid emulsion rescue, benzodiazepines for seizures
• High neuraxial block: fluids, vasopressors, positioning
• Magnesium toxicity: calcium gluconate
• Other drug overdoses/poisonings

Tension pneumothorax:

• May occur from positive pressure ventilation in pregnancy due to decreased lung compliance
• Immediate decompression if suspected (needle decompression followed by chest drain)

Tamponade:

• Traumatic or iatrogenic cardiac tamponade
• Possible with central line insertion
• Emergency pericardiocentesis if suspected

Additional pregnancy-specific causes:

A - Amniotic Fluid Embolism:

• Classic triad: hypoxia, hypotension, coagulopathy
• Massive pulmonary vasospasm
• Treatment: supportive, oxygen, vasopressors, blood products, early delivery
• Perimortem caesarean often required for maternal salvage

B - Bleeding:

• Postpartum haemorrhage
• Placental abruption, placenta praevia, uterine rupture
• Treatment: uterotonics, transfusion, surgical control, B-Lynch, embolisation

E - Eclampsia:

• Seizures plus severe hypertension
• Treatment: magnesium sulphate, antihypertensive therapy, delivery
• May cause intracranial haemorrhage, cardiac failure, placental abruption

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Perimortem Caesarean Delivery

Indication and Timing

Indication:

• Maternal cardiac arrest
• Gestation greater than 20 weeks OR fundal height above umbilicus
• Practical bedside indicator: if uterus visibly above umbilical level, perform PMCD

Timing:

• Primary goal: improve maternal resuscitation (not fetal salvage)
• Perform if no ROSC within 4-5 minutes of arrest
• Earlier delivery may be considered if difficult resuscitation or if obstetrician skilled in procedure is immediately available
• Do not wait beyond 5 minutes; delay worsens both maternal and fetal outcomes

Rationale:

• Relief of aortocaval compression increases maternal venous return and cardiac output approximately 25%
• Removes large gravid uterus compressing diaphragm, improving ventilation
• Facilitates effective chest compressions
• Increases maternal chances of ROSC
• May also deliver potentially viable fetus

Procedure

Immediate preparation:

• Designate primary surgeon (obstetrician if available, otherwise most skilled operator)
• Assistant for retraction (nurse or another doctor)
• Neonatal team to receive neonate immediately
• No time for formal sterile preparation or operating theatre transfer
• Perform in resuscitation bay with ongoing chest compressions

Surgical technique:

1. Incision: Vertical midline incision from pubic symphysis to at least umbilicus along linea nigra

   • Use large scalpel (10 or 11 blade)
   • Incise through skin, subcutaneous tissue, rectus fascia
   • Bluntly dissect rectus muscles apart

2. Enter peritoneum:

   • Incise peritoneum vertically
   • Retract abdominal wall laterally using retractors or assistant hands

3. Expose uterus:

   • Reflect bladder inferiorly (bladder may be elevated by uterus)
   • Empty bladder with needle aspiration or small catheter if distended

4. Uterine incision:

   • Small vertical incision (approximately 5 cm) into lower uterine segment
   • Cut until amniotic fluid drains or endometrium visible
   • Insert two fingers into incision and lift uterus away from fetus
   • Extend uterine incision vertically upward with curved scissors or scalpel (curved away from fetus)

5. Fetal delivery:

   • Manual extraction: cup hands around fetal head
   • If cephalic: deliver head first, then body
   • If breech: deliver buttocks first, then body
   • Gentle extraction avoiding uterine injury
   • Clear airway immediately and hand to neonatal team

6. Placental delivery:

   • Spontaneous placental separation usually occurs
   • Manual removal only if not expelled
   • Inspect for retained products

7. Uterine closure and haemostasis:

   • If ROSC achieved: standard uterine closure, uterotonics (oxytocin, ergometrine), haemostasis
   • If no ROSC: ongoing chest compressions priority, defer haemostatic closure if no perfusion
   • Maintain manual uterine compression to reduce bleeding if no perfusion

Chest compressions during procedure:

• Maintain continuous chest compressions except for brief pauses for uterine incision (10-20 seconds maximum)
• Coordinate timing to pause compressions momentarily for incision, then resume
• Neonatal team initiates neonatal resuscitation immediately upon delivery

Timing verification:

• Document time of arrest and time of delivery on arrest record/clock
• Aim for delivery within 4-5 minutes of arrest (PMID: 22613275)
• Outcomes: Maternal ROSC more likely the earlier PMCD performed (within 4-5 minutes optimal)
• Fetal survival: optimal if delivery within 10 minutes and neonatal resuscitation immediate

Post-PMCD Maternal Resuscitation

After perimortem caesarean, maternal resuscitation continues with standard adult ALS:

• Continue chest compressions
• Airway, breathing, circulation management
• Perimortem caesarean primarily improves maternal circulation; continue standard resuscitation
• Treat ongoing reversible causes (haemorrhage, amniotic fluid embolism, etc.)
• If ROSC achieved: transfer to ICU, monitor for complications (uterine atony, bleeding, sepsis)

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Post-Resuscitation Care

Immediate Post-Resuscitation Stabilisation

Airway and Breathing:

• Maintain advanced airway (endotracheal tube or supraglottic airway)
• Mechanical ventilation: aim for SpO2 94-98% (avoid hyperoxia)
• Tidal volume 6-8 mL/kg ideal body weight (avoid volutrauma)
• Positive end-expiratory pressure: 5-10 cm H2O
• Respiratory rate adjusted to maintain PaCO2 35-45 mmHg (avoid respiratory alkalosis which reduces uteroplacental perfusion if fetus delivered)
• Sedation and analgesia as required for ventilator tolerance

Circulation:

• Target mean arterial pressure greater than 65 mmHg (or blood pressure adequate for organ perfusion)
• Vasopressor support: noradrenaline first line, adrenaline if required
• Inotropic support if low-output state
• Fluid therapy goal-directed (avoid overload, particularly with risk of pulmonary oedema in pregnancy)
• Consider invasive arterial and central venous pressure monitoring

Fertility considerations:

• Ongoing uterine monitoring: fundal height, tone, bleeding
• Oxytocic therapy if uterus delivered (oxytocin infusion, ergometrine if hypertensive controlled)
• Transfusion support as needed (type and cross-match, blood products)
• Uterine massage if atony

Neurological:

• Targeted temperature management: maintain normal temperature (36-37°C)
• Seizure prophylaxis if eclampsia or intracranial pathology suspected (magnesium or phenytoin)
• Regular neurological assessments (GCS, pupillary responses, limb movements)
• CT brain if prolonged arrest, suspected intracranial pathology (eclampsia, haemorrhage, hypoxic injury)

Specific Post-Resuscitation Management

For delivered neonate:

• Neonatal resuscitation per neonatal team
• Transfer to neonatal intensive care unit
• If neonate delivered and maternal ROSC achieved, focus on maternal stabilisation and neonatal care

For ongoing pregnancy (if PMCD not performed before ROSC):

• Continued fetal monitoring if gestation greater than 24 weeks (fetal heart rate monitoring)
• Transfer to obstetric unit with neonatal services
• Consider definitive delivery if maternal condition unstable or fetal distress

Post-arrest investigations:

• Urgent bedside ultrasound: cardiac function, pericardial effusion, aorta, intrauterine bleeding
• ECG: arrhythmias, ischaemia, electrolyte changes
• Arterial blood gas: assess ventilation, oxygenation, metabolic status
• Chest X-ray: pulmonary oedema, pneumothorax, pulmonary embolism patterns
• CT pulmonary angiogram if pulmonary embolism suspected and patient stable
• Echocardiography: assess cardiac function, right heart strain (pulmonary embolism or amniotic fluid embolism)
• Coagulation profile: coagulopathy (DIC) assessment

Hypotension management:

• Fluid resuscitation: crystalloid and blood products
• Vasopressors: noradrenaline (renal perfusion priority), adrenaline if required
• Vasopressin may be considered in refractory shock
• Specific cause treatment: haemorrhage control, inotropes for cardiomyopathy, etc.

Haemorrhage control:

• Uterotonics: oxytocin infusion (40 units in 1000mL crystalloid over 4 hours), ergometrine 0.2 mg IM (avoid if uncontrolled hypertension), carboprost 250 mcg IM, tranexamic acid 1 g IV
• Uterine compression (B-Lynch suture if needed)
• Intrauterine balloon tamponade
• Surgical intervention if required (hysterectomy if bleeding uncontrollable)

Sepsis and infection:

• Broad-spectrum antibiotics if septic shock suspected
• Blood cultures
• Source control (drainage of infected collections)
• Treat chorioamnionitis, endometritis

Cardiac function management:

• Echocardiography for functional assessment
• Inotropes if low-output state (dobutamine, milrinone)
• Diuretics if pulmonary oedema due to fluid overload and cardiac failure
• Treat arrhythmias per ACLS algorithm (avoid AV node-blocking drugs in first trimester if possible)

Neurological outcome:

• Prognostication after cardiac arrest complex
• Early neurological examination, neurophysiological testing (EEG, somatosensory evoked potentials)
• Consider prognostication at 72 hours if absent neurological signs
• Withdrawal of life support decisions require multidisciplinary consensus

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Investigation and Management

Diagnostic Evaluation During Arrest

Immediate bedside investigations:

• ECG monitor: rhythm analysis (VF/VT, asystole, PEA)
• Capnography (if advanced airway): waveform analysis (ETCO2 below 10 mmHg with inadequate compressions, ETCO2 greater than 20 mmHg adequate compressions, ETCO2 abrupt return to normal suggests ROSC)
• Bedside ultrasound (point-of-care): cardiac activity, pericardial effusion, lung sliding (pneumothorax), inferior vena cava collapsibility, aorta, uterine position, fetal heart rate
• Point-of-care blood glucose: hypoglycaemia, hyperglycaemia
• Blood gas if available: acid-base status, potassium, lactate

Laboratory investigations (once vascular access established):

• Arterial blood gas: pH, PaO2, PaCO2, base excess, lactate, potassium, glucose
• Electrolytes: potassium, sodium, magnesium, calcium
• Full blood count: anaemia, thrombocytopenia
• Coagulation profile: PT/APTT, fibrinogen, D-dimer
• Cardiac biomarkers: troponin (if myocardial ischaemia suspected)
• Toxicology screen: if drug overdose suspected
• Pregnancy-specific: beta-hCG if gestation uncertain, fetal fibronectin if ROM suspected

**Radiological investigations (only if patient achieves ROSC):

• Chest X-ray: pulmonary oedema, pneumothorax, pulmonary embolism patterns, widened mediastinum (aortic dissection)
• CT pulmonary angiogram: if pulmonary embolism suspected and patient stable
• CT head: if traumatic, eclampsia with seizures or intracranial pathology suspected
• Echocardiography: structural and functional cardiac assessment, right heart strain suggesting pulmonary embolism

Management During Arrest

Arrhythmia management:

• VF/VT: immediate defibrillation (energy levels: 150-200 J biphasic)
• Refractory VF/VT: repeat defibrillation, consider amiodarone 300 mg IV over 1 min, then 150 mg
• Bradycardia: atropine if perfusing rhythm not present, consider transcutaneous pacing
• PEA/pulseless VT: search for and treat reversible causes, adrenaline 1 mg IV every 3-5 minutes

Medications:

• Adrenaline: 1 mg IV bolus every 3-5 minutes
• Amiodarone: 150 mg IV over 1 min if VF/VT refractory
• Lidocaine alternative: 1-1.5 mg/kg IV (if amiodarone unavailable)
• Magnesium: 2 g IV if torsades de pointes or eclampsia
• Sodium bicarbonate: not routinely, consider severe acidosis, hyperkalaemia)
• Calcium: 10% calcium chloride or gluconate if hyperkalaemia or magnesium toxicity

Fluids:

• Crystalloid: 0.9% sodium chloride or Hartmann's solution
• Blood: O-negative initially, type-specific when available
• Plasma and platelets: if massive transfusion required
• Avoid fluid overload (worsens pulmonary oedema)

Obstetric Management During Arrest

Ongoing pregnancy (if PMCD not performed):

• Fetal monitoring if gestation greater than 24 weeks (continuous fetal heart rate monitoring)
• Ongoing uterine displacement (manual leftwards)
• Consider emergent delivery if maternal condition deteriorating or fetal distress
• Post-arrest delivery if ROSC achieved but fetal distress or maternal condition uncertain

Postpartum:

• Manage uterine atony: uterine massage, oxytocin infusion, ergometrine, carboprost
• Surgical intervention: B-Lynch suture, internal iliac artery ligation, hysterectomy (if bleeding uncontrollable)
• Postpartum analgesia: opiates, regional anaesthesia if possible

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Pitfalls and Pearls

Common Pitfalls:

1. Delayed manual uterine displacement: Many providers delay uterine displacement or use ineffective left lateral tilt; manual displacement must be immediate and continuous.

2. Inadequate team activation: Failure to request obstetrician, anaesthetist, neonatologist immediately. These teams must be activated simultaneously with cardiac arrest call.

3. Delay in PMCD: Waiting beyond 5 minutes or waiting for senior obstetrician. Perform PMCD within 4-5 minutes by most skilled available doctor.

4. Chest compression position too low: Due to elevated diaphragm in pregnancy, place chest compressions slightly higher on sternum than standard adult position.

5. Inadequate consideration of pregnancy-specific causes: Focusing only on standard 4H/4Ts and missing amniotic fluid embolism, bleeding, eclampsia.

6. Inappropriate vasopressor use: Using vasopressors that reduce uteroplacental blood flow (unopposed alpha-agonists). Noradrenaline preferred over phenylephrine.

7. Delayed definitive airway: Not recognising difficult airway in pregnancy. Use most experienced provider early.

8. Inadequate post-arrest haemorrhage control: Failing to address ongoing uterine bleeding after ROSC due to atony or retained products.

Pearls:

1. Manual uterine displacement is first-line: More effective than left lateral tilt, must be continuous throughout resuscitation.

2. PMCD improves maternal outcomes: Primary benefit is maternal salvage through relief of aortocaval compression (25% increase in cardiac output).

3. Uterus size practical guide: If fundal height above umbilicus or visibly pregnant, assume gestation greater than 20 weeks and consider PMCD.

4. Amniotic fluid embolism rapid deterioration: Classic triad (hypoxia, hypotension, coagulopathy) - treat supportively and deliver immediately.

5. Magnesium toxicity: If patient on magnesium sulphate, cardiac arrest may be due to hypermagnesaemia. Treat with calcium gluconate.

6. Pulmonary embolism common: 29% of maternal cardiac arrests - high index of suspicion, early heparin if not yet arrested, consider urgent embolectomy if appropriate.

7. Eclampsia with seizures: Hypertensive encephalopathy, treat with magnesium sulphate, antihypertensives, early delivery.

8. Early neonatal team activation: Neonate requires immediate resuscitation after PMCD - call neonatal team simultaneously with arrest.

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Indigenous Health Considerations

Aboriginal and Torres Strait Islander peoples:

• Maternal mortality rates 2-3 times higher than non-Indigenous Australians (AIHW 2023)
• Higher prevalence of comorbidities: cardiac disease, hypertension, diabetes, obesity
• Cultural considerations extended families (kinship systems) important for communication
• Language barriers may require professional interpreter services
• Gender sensitivity: female practitioner preferred for sensitive discussions
• Fear of hospital systems and historical distrust may delay presentation
• Limited access to specialist obstetric services in remote communities
• Aeromedical transfer often required to tertiary facilities, delaying definitive care
• Cultural protocols for death and dying important to discuss with family early
• Elders and family decision-makers may require updates
• Family may request cultural practices or traditional healing

Māori populations (New Zealand):

• Disproportionately higher maternal mortality (PMMRC Annual Reports)
• Whānau (extended family) involvement critical in decision-making
• Spiritual and cultural protocols (tikanga) important (karakia, prayer)
• Land, ancestral connections (tūrangawaewae) significant if transfer required
• Interpreter services needed if English not primary language
• Māori health providers helpful for cultural support
• Whakawhanaungatanga (relationship building) essential for communication
• Trust established through wairua (spiritual) and hinengaro (intellectual/emotional) connections

Remote/Rural Considerations:

• Limited antenatal care and follow-up in remote communities
• Difficulty accessing emergency obstetric services
• RFDS or aeromedical transfer often required with delays
• Smaller rural EDs may lack obstetric specialist, on-call anaesthesia, neonatal services
• Telemedicine consultation important (Royal Flying Doctor Service, aeromedical services)
• Training local staff in emergency obstetric skills (perimortem caesarean)
• Cultural liaison officers helpful for communication across cultures
• Family may need to travel to tertiary centre - logistical and financial support needed
• Community-based health workers important for education and follow-up

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Viva Practice

Viva 1: Physiological Changes and Resuscitation Modifications

Question 1: What are the key physiological changes in pregnancy that affect resuscitation?

Answer: The physiological changes of pregnancy critically influence both the pathophysiology of cardiac arrest and the technical approach to resuscitation. Cardiovascular changes include increased blood volume (40-50% increase) peaking at 32-34 weeks, increased heart rate (10-20 bpm above baseline by second trimester), and increased cardiac output (30-50% increase peaking at 50% above baseline by 30-34 weeks). Systemic vascular resistance decreases 20-30% due to progesterone-mediated vasodilation, and blood pressure typically decreases in first and second trimesters. Most critically, aortocaval compression occurs when supine, reducing venous return and cardiac output by 30-50% after 20 weeks gestation. Respiratory changes include increased minute ventilation (40-50%), decreased functional residual capacity (20-30% due to diaphragmatic elevation from gravid uterus), and increased oxygen consumption (20-30%). Gastrointestinal changes include prolonged gastric emptying, decreased lower oesophageal sphincter tone with increased aspiration risk. Haematological changes include plasma volume increase greater than red cell mass (physiological anaemia) and a hypercoagulable state increasing VTE risk.

Question 2: How do these physiological changes require modifications to standard ALS algorithm?

Answer: Physiological changes require several specific modifications to standard ALS. Manual uterine displacement to the left must be immediate and continuous throughout resuscitation to relieve aortocaval compression as manual displacement is superior to left lateral tilt for improving venous return and cardiac output. Chest compression position is slightly higher on the sternum due to diaphragmatic elevation from gravid uterus. Positioning should include left lateral tilt 15-30 degrees if feasible and chest compressions can be maintained effectively, but manual uterine displacement remains the primary intervention. Airway management must recognise difficult airway in pregnancy due to increased oedema and decreased cervical spine mobility; use most experienced provider for intubation. Consider early supraglottic airway device. Gastric emptying is prolonged and lower oesophageal sphincter tone decreased with high aspiration risk, apply cricoid pressure if possible. The decreased functional residual capacity means rapid onset of hypoxia during apnoea. Perimortem caesarean delivery should be considered within 4-5 minutes for gestation greater than 20 weeks.

Question 3: What is timing and indication for perimortem caesarean?

Answer: Perimortem caesarean delivery is indicated for maternal cardiac arrest in gestation greater than 20 weeks, which can be practically identified by fundal height above umbilicus or visibly pregnant abdomen. Timing is within 4-5 minutes of arrest if no return of spontaneous circulation. The primary rationale is improved maternal resuscitation through relief of aortocaval compression increasing maternal venous return and cardiac output approximately 25%. A secondary benefit is potential neonatal survival. Delivery improves maternal circulation by removing large gravid uterus compressing diaphragm facilitating effective chest compressions and improving ventilation. Do not wait for senior obstetrician arrival if not immediately available. No time for formal sterile preparation or operating theatre transfer. Perform in resuscitation bay with ongoing chest compressions. Designate primary surgeon (obstetrician if available, otherwise most skilled operator). Maintain continuous chest compressions except for brief pauses for uterine incision.

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Viva 2: Reversible Causes in Pregnancy

Question 1: What are the pregnancy-specific reversible causes of cardiac arrest?

Answer: Pregnancy requires modification of the standard 4H/4Ts approach to include pregnancy-specific reversible causes. Hypoxia is a standard cause but can develop rapidly in pregnancy due to decreased functional residual capacity and increased oxygen consumption. Hypovolaemia is common and includes postpartum haemorrhage, placental abruption with concealed and revealed bleeding, uterine rupture, traumatic intraperitoneal haemorrhage. Management includes immediate transfusion, uterotonics, surgical control of bleeding. Hypothermia is uncommon but consider if outdoor arrest or prolonged field time. Hyperkalaemia/hypo-hyper electrolytes include hyperkalaemia from renal failure or massive transfusion requiring treatment with calcium and insulin/glucose, magnesium toxicity in patients receiving magnesium sulphate for eclampsia requires treatment with calcium gluconate 10 mL 10% IV. Thrombosis (pulmonary embolism) is the most common cardiac cause (29% of cardiac arrests) due to hypercoagulable state. Toxins/anaesthetic complications include local anaesthetic toxicity (treat with lipid emulsion rescue), high neuraxial block (treat with fluids, vasopressors, positioning), magnesium toxicity. Tension pneumothorax may occur from positive pressure ventilation in pregnancy due to decreased lung compliance. Tamponade: traumatic or iatrogenic cardiac tamponade, emergency pericardiocentesis if suspected.

Question 2: Add A, B, E causes beyond standard 4H/4Ts.

Answer: A (Amniotic fluid embolism): rare catastrophic complication presenting with sudden hypoxia, hypotension, coagulopathy. Massive pulmonary vasospasm and anaphylactoid reaction. Treatment is supportive with oxygen, vasopressors, blood products, early delivery. Perimortem caesarean often required for maternal salvage. B (Bleeding): postpartum haemorrhage, placental abruption, placenta praevia, uterine rupture. Treatment includes uterotonics (oxytocin, ergometrine, carboprost), transfusion, surgical control. E (Eclampsia): seizures plus severe hypertension. Treatment includes magnesium sulphate, antihypertensive therapy, delivery. May cause intracranial haemorrhage, cardiac failure, placental abruption.

Question 3: Which causes are most common in pregnancy?

Answer: The most common causes by frequency are pulmonary embolism (29%), haemorrhage (17%), sepsis (13%), cardiomyopathy (8%), hypertension/eclampsia (2.8%), anaesthetic complications (2%). Pulmonary embolism is the most common cardiac cause due to the hypercoagulable state of pregnancy and pelvic venous stasis. Haemorrhage includes antepartum, intrapartum, and postpartum haemorrhage. Sepsis may be due to chorioamnionitis, endometritis, urinary tract infection, pneumonia, or other causes. Cardiomyopathy includes peripartum cardiomyopathy or exacerbation of pre-existing cardiomyopathy.

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Viva 3: Team Leadership and Decision Making

Question 1: How do you lead the maternal cardiac arrest team?

Answer: Leading the maternal cardiac arrest team requires clear role assignment, effective communication, and specific expertise coordination. Immediately upon recognition of cardiac arrest, activate the maternal cardiac arrest team explicitly requesting obstetrician, anaesthetist, and neonatologist. Ensure CPR is started immediately. Designate specific team members: chest compressions, airway (most experienced provider), manual uterine displacement (critical task requiring continuous focus), vascular access, medications, timekeeper/documentation, leader (coordinates overall and monitors quality). Ensure continuous manual uterine displacement (leftwards) without interruption as this is critical for effective resuscitation. Start high-quality chest compressions with correct positioning (slightly higher on sternum). Within 4-5 minutes of arrest, reassess for return of spontaneous circulation. If no ROSC and gestation greater than 20 weeks (fundal height above umbilicus or visibly pregnant), prepare for perimortem caesarean immediately. Ensure neonatal team is prepared to receive neonate. Maintain closed-loop communication: give clear orders, confirm understanding. Regularly reassess reversible causes. Consider and treat amniotic fluid embolism, pulmonary embolism, haemorrhage, eclampsia.

Question 2: When do you decide to perform perimortem caesarean and how do you communicate this decision?

Answer: Decision for perimortem caesarean is based on gestation and timing. Indication: gestation greater than 20 weeks (practically determined by fundal height above umbilicus or visibly pregnant). Timing: within 4-5 minutes of arrest if no ROSC. Communicate this decision clearly to team: "No ROSC after 4 minutes, gestation greater than 20 weeks, performing perimortem caesarean now." Ensure designated surgeon prepares: vertical midline incision from pubic symphysis to umbilicus. Continuous chest compressions throughout except brief 10-20 second pause for uterine incision. Neonatal team stands ready with neonatal resuscitation equipment. Inform the team the purpose is primarily maternal salvage through relief of aortocaval compression. Monitor performance: maintain quality chest compressions, adequate depth and rate, minimise interruptions. Ensure documentation of arrest time and delivery time. If obstetrician not available, most skilled doctor performs procedure. Do not wait beyond 5 minutes.

Question 3: How do you approach post-arrest management?

Answer: Post-arrest management stabilises the patient and prevents recurrence. Maintain advanced airway with mechanical ventilation targeting SpO2 94-98%, tidal volume 6-8 mL/kg ideal body weight, respiratory rate adjusted to maintain PaCO2 35-45 mmHg (avoid respiratory alkalosis which reduces uteroplacental perfusion if fetus delivered). Target mean arterial pressure greater than 65 mmHg with noradrenaline first-line vasopressor. Consider inotropic support if low-output state. Goal-directed fluid therapy avoiding overload. For ongoing pregnancy after ROSC, provide continued fetal monitoring if gestation greater than 24 weeks and transfer to obstetric unit with neonatal services. Consider definitive delivery if maternal condition unstable or fetal distress. For perimortem caesarean with ROSC achieved, provide ongoing uterine monitoring for fundal height, tone, bleeding. Oxytocic therapy (oxytocin infusion plus ergometrine if hypertensive controlled). Transfusion support as needed, uterine massage if atony. Investigations: bedside ultrasound for cardiac function, pericardial effusion, uterine bleeding; ECG for arrhythmias, ischaemia; arterial blood gas; chest X-ray; echocardiography; CT pulmonary angiogram if pulmonary embolism suspected. Hypotension management includes fluids, vasopressors, specific cause treatment (haemorrhage control, inotropes). Haemorrhage control includes uterotonics, uterine compression, intrauterine balloon tamponade, surgical intervention.

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Viva 4: Specific Scenario Management

Scenario: 32 year old G3P2 at 28 weeks gestation presenting to ED after 4 g MgSO4 bolus followed by infusion for severe pre-eclampsia (BP 170/100). Minutes later O2 saturation drops precipitously, she becomes unresponsive, no pulses. CPR initiated. What specific management?

Answer: This scenario suggests magnesium toxicity as the likely cause of cardiac arrest given recent high-dose magnesium. Immediate management includes start chest compressions, call for maternal cardiac arrest team (obstetrician, anaesthetist, neonatologist), immediate manual uterine displacement leftwards, place chest compressions slightly higher on sternum. Specific management for magnesium toxicity: administer calcium gluconate 10 mL 10% IV rapidly to counteract magnesium effects (may need to repeat). Stop magnesium infusion. Continue CPR and ALS algorithm rhythm-based management. Treat hypertension with labetolol or hydralazine if blood pressure measured and appropriate. Eclampsia remains differential so maintain magnesium as infusion after calcium administration or use alternative anticonvulsant if seizure risk persists. Consider magnesium as potential reversible cause of arrest. Monitor ECG for magnesium-induced changes (prolonged PR, widened QRS, peaked T waves). Assess airway carefully due to pregnancy oedema. Monitor capnography if available. Within 4-5 minutes, reassess for ROSC. If no ROSC and gestation greater than 20 weeks, prepare for perimortem caesarean. If ROSC achieved, continue post-arrest stabilisation: maintain airway, oxygenation, ventilation. Monitor serum magnesium levels. Continue magnesium if needed for eclampsia after calcium, use lower infusion rate. Monitor cardiac function, electrolytes. Consider echocardiography for cardiac function. Anticipate potential need for ongoing magnesium for seizure prophylaxis in eclampsia. Provide magnesium calcium level monitoring.

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OSCE Scenarios

OSCE Station 1: Maternal Cardiac Arrest Team Leader (Resuscitation Station)

Time: 11 minutes

Task: You are team leader for maternal cardiac arrest in resuscitation bay. Perform systematic assessment, lead resuscitation, make critical decisions.

Setting: Resuscitation bay with team (nurse, ED registrar, anaesthetic registrar). Patient 32 year old G2P1 at 32 weeks gestation, collapsed at home, unresponsive on arrival.

Equipment: Monitor/defibrillator, airway equipment, resuscitation drugs, ultrasound available, obstetric instruments.

Examiner briefing: Candidate is team leader. Observe systematic approach, decision-making, leadership, communication.

Marking criteria:

Key actions expected:

1. Recognise arrest, start compressions, call maternal cardiac arrest team
2. Assign roles: chest compressions, airway, manual uterine displacement, vascular access
3. Manual uterine displacement immediate and continuous
4. Higher chest compression position due to diaphragmatic elevation
5. Perimortem caesarean within 4-5 minutes if no ROSC, clearly stated with fundal height assessment
6. Consider pulmonary embolism, amniotic fluid embolism, bleeding, eclampsia in reversible causes
7. Effective communication with closed-loop orders
8. Post-arrest stabilisation plan specific to pregnancy

Critical failure: Not performing manual uterine displacement, or delaying PMCD beyond 5 minutes without justification.

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OSCE Station 2: Difficult Communication Maternal Cardiac Arrest

Time: 11 minutes

Task: Break news of maternal cardiac arrest and explain perimortem caesarean to partner/husband/family members.

Setting: Family interview room.

Patient: 28 year old G1P0 at 30 weeks gestation who collapsed at home with no CPR until ambulance arrival. In ED, no ROSC after 8 minutes. You are performing perimortem caesarean.

Examiner briefing: Candidate faces partner/husband anxious, confused, asking many questions. Assess communication, empathy, clarity, managing expectations.

Marking criteria:

Key questions family may ask:

• What is happening? Is she alive?
• Why are you doing surgery on her while unconscious?
• Will the baby survive?
• What are the chances for mother?
• Can I see her?
• Who decided to do this surgery?

Key communication principles:

• Use plain language, avoid jargon
• Explain perimortem caesarean: surgery to help mother improve blood flow
• Explain timing: must be done quickly (within 4-5 minutes) to help mother
• Explain primary benefit: helps mother first, baby second
• Give realistic outlook but maintain hope (statistics: maternal ROSC chance, neonatal chance)
• Allow expression of emotions
• Offer constant updates
• Involve cultural liaison if appropriate
• Offer support services (social work, spiritual care)

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OSCE Station 3: Perimortem Caesarean Delivery Procedure

Time: 11 minutes

Task: Perform perimortem caesarean on maternal arrest simulation model with ongoing chest compressions.

Setting: Resuscitation bay with maternal arrest model simulating 34 week gestation, ongoing CPR.

Team: Nurse providing chest compressions, assistant for retraction.

Examiner briefing: Candidate demonstrates correct PMCD technique with ongoing CPR. Assess anatomical knowledge, surgical technique, coordination.

Marking criteria:

Key technical points expected:

1. Confirm gestation greater than 20 weeks by fundal height above umbilicus
2. Vertical midline incision: pubic symphysis to umbilicus
3. Through skin, subcutaneous tissue, rectus fascia (bluntly separate), peritoneum
4. Retract abdominal wall laterally
5. Reflect bladder inferiorly, empty with aspiration if distended
6. Small vertical lower uterine segment incision (5 cm) until amniotic fluid drains
7. Insert two fingers, lift uterus away from fetus
8. Extend uterine incision vertically with curved scissors (curved away from fetus)
9. Deliver fetus:
   • Cephalic: cup hands around head, deliver head then body
   • Breech: grasp buttocks, deliver buttocks then legs, body, head
10. Hand fetus to neonatal team for resuscitation
11. Allow placental separation, manual removal if retained
12. If ROSC: uterine closure (interrupted sutures or continuous), uterotonics (oxytocin infusion)
13. If no ROSC: continue chest compressions, defer haemostatic closure

Critical failure: Uterine incision incorrect (transverse), injuring fetus, failing to recognise gestation greater than 20 weeks.

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SAQ Practice

SAQ 1: Resuscitation Modifications in Pregnancy

Question: A 30-year-old pregnant woman at 28 weeks gestation presents in cardiac arrest. Describe the modifications required to standard ALS algorithm specific to pregnancy. (6 marks)

Model Answer:

1. Manual uterine displacement (1 mark): Immediate continuous manual displacement of uterus to left patient side to relieve aortocaval compression as manual displacement is superior to left lateral tilt for improving venous return and cardiac output.

2. Chest compression position (1 mark): Slightly higher on sternum than standard adult position due to diaphragmatic elevation by gravid uterus.

3. Left lateral tilt (1 mark): 15-30 degrees if feasible and chest compressions maintainable. Manual uterine displacement remains primary intervention.

4. Perimortem caesarean delivery (1 mark): Within 4-5 minutes for gestation greater than 20 weeks (fundal height above umbilicus) if no return of spontaneous circulation. Primary benefit: maternal salvage through relief of aortocaval compression (25% increased cardiac output).

5. Advanced airway (1 mark): Early definitive airway using most experienced provider due to difficult airway in pregnancy from increased oedema and decreased cervical spine mobility. Consider early supraglottic airway device.

6. Modified reversible causes (1 mark): In addition to standard 4H/4Ts, consider pregnancy-specific causes: amniotic fluid embolism, bleeding (postpartum haemorrhage, placental abruption, uterine rupture), eclampsia.

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SAQ 2: Perimortem Caesarean Delivery

Question: Outline the indications, timing, and primary benefit of perimortem caesarean delivery in maternal cardiac arrest. (5 marks)

Model Answer:

1. Indications (1 mark): Maternal cardiac arrest with gestation greater than 20 weeks (practically determined by fundal height above umbilicus or visibly pregnant abdomen).

2. Timing (1 mark): Within 4-5 minutes of arrest if no return of spontaneous circulation. Do not wait for senior obstetrician arrival, perform by most skilled available doctor.

3. Primary benefit (1 mark): Improved maternal resuscitation through relief of aortocaval compression, increasing maternal venous return and cardiac output approximately 25%.

4. Secondary benefit (1 mark): Potential neonatal survival, particularly if delivery within 10 minutes and neonatal resuscitation immediate.

5. Procedure requirements (1 mark): No time for formal sterile preparation or operating theatre transfer. Perform in resuscitation bay with ongoing chest compressions (continuous except brief 10-20 second pause for uterine incision). Maintain chest compression quality, call neonatal team to receive neonate.

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SAQ 3: Pregnancy-Specific Reversible Causes

Question: List and briefly describe the pregnancy-specific causes of cardiac arrest that extend beyond the standard 4H/4Ts. (6 marks)

Model Answer:

1. Amniotic fluid embolism (1 mark): Rare catastrophic complication with classic triad of sudden hypoxia, hypotension, coagulopathy. Massive pulmonary vasospasm and anaphylactoid reaction. Treatment supportive: oxygen, vasopressors, blood products, early delivery. Perimortem caesarean often required.

2. Bleeding (postpartum haemorrhage) (1 mark): Includes antepartum haemorrhage (placenta praevia, abruption), intrapartum haemorrhage, postpartum haemorrhage (uterine atony, retained products). Treatment: uterotonics (oxytocin, ergometrine, carboprost), transfusion, surgical control of bleeding.

3. Eclampsia (1 mark): Seizures plus severe hypertension (greater than 160/110 mmHg). May cause intracranial haemorrhage, cardiac failure, placental abruption. Treatment: magnesium sulphate, antihypertensive therapy, early delivery.

4. Pulmonary embolism (1 mark): Most common cardiac cause of arrest (29%) due to hypercoagulable state of pregnancy. Treatment: anticoagulation if not yet arrested, consider surgical embolectomy if available.

5. Anaesthetic complications (1 mark): Difficult or failed intubation, local anaesthetic toxicity, high neuraxial block. Treatment: lipid emulsion for local anaesthetic toxicity, fluids and vasopressors for high neuraxial block, airway management for difficult intubation.

6. Magnesium toxicity (1 mark): In patients receiving magnesium for eclampsia, cardiac arrest may be due to hypermagnesaemia. Treatment: calcium gluconate 10 mL 10% IV rapidly.

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SAQ 4: Post-Resuscitation Management

Question: A 32-year-old woman achieves return of spontaneous circulation after cardiac arrest at 30 weeks gestation with perimortem caesarean performed. Outline the key components of post-resuscitation stabilisation. (6 marks)

Model Answer:

1. Airway and ventilation (1 mark): Maintain advanced airway with mechanical ventilation targeting SpO2 94-98%, tidal volume 6-8 mL/kg ideal body weight, respiratory rate adjusted to maintain PaCO2 35-45 mmHg (avoid respiratory alkalosis which reduces uteroplacental perfusion).

2. Circulation (1 mark): Target mean arterial pressure greater than 65 mmHg with noradrenaline first-line, consider inotropic support (dobutamine, milrinone) if low-output state. Goal-directed fluid therapy avoiding overload (pulmonary oedema risk). Diuretics if pulmonary oedema from fluid overload and cardiac failure.

3. Uterine management (1 mark): Oxytocic therapy: oxytocin infusion (40 units in 1000mL crystalloid over 4 hours). Ergometrine 0.2 mg IM if hypertension controlled. Carboprost 250 mcg IM if refractory atony. Uterine massage if atony. Monitor fundal height, uterine tone, bleeding.

4. Investigations (1 mark): Bedside ultrasound (cardiac function, pericardial effusion, uterine bleeding), ECG (arrhythmias, ischaemia), arterial blood gas, chest X-ray, echocardiography, CT pulmonary angiogram if pulmonary embolism suspected.

5. Neurological (1 mark): Maintain normal temperature (36-37°C), seizure prophylaxis if eclampsia or intracranial pathology (magnesium or phenytoin), neurological assessments (GCS, pupillary responses). CT brain if prolonged arrest, eclampsia, or suspected intracranial pathology.

6. Specific cause treatment (1 mark): Treat ongoing haemorrhage (transfusion, surgical control), sepsis (antibiotics, source control), arrhythmia treatment per ACLS algorithm, avoid AV node-blocking drugs in first trimester if possible.

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SAQ 5: Indigenous Health and Remote Retrieval

Question: A 28-year-old Aboriginal woman from a remote community at 32 weeks gestation presents to a rural ED in cardiac arrest. Outline the specific considerations for Indigenous health and remote retrieval. (6 marks)

Model Answer:

1. Cultural considerations (1 mark): Extended family (kinship systems) important for communication. Language barriers may require professional interpreter services. Gender sensitivity: female practitioner preferred for sensitive discussions. Cultural protocols for death and dying important to discuss with family early. Elders and family decision-makers may require updates.

2. Clinical considerations (1 mark): Aboriginal maternal mortality 2-3 times higher than non-Indigenous Australians. Higher prevalence of comorbidities: cardiac disease, hypertension, diabetes, obesity. Limited antenatal care and follow-up in remote communities increases risk of adverse outcomes.

3. Retrieval considerations (1 mark): Limited access to specialist obstetric services. RFDS or aeromedical transfer often required to tertiary facilities with delays. Smaller rural EDs may lack obstetric specialist, on-call anaesthesia, neonatal services. Telemedicine consultation important for specialist advice during resuscitation.

4. Resource limitations (1 mark): Training local staff in emergency obstetric skills including perimortem caesarean. Limited blood product availability in remote EDs. Equipment limitations: may lack ultrasound, advanced airway devices, advanced monitoring.

5. After transfer (1 mark): Family may need financial support for travel. Community-based health workers important for follow-up. Cultural liaison officers helpful for ongoing communication. Traditional healing may be requested - respect family preferences while ensuring patient safety.

6. Documentation and coordination (1 mark): Record indigenous status clearly in medical record. Coordinate with Aboriginal Medical Services, Cultural Liaison Officers. Involve social work, pastoral care as appropriate. Ensure cultural safety throughout care.

SAQ 6: Magnesium Toxicity Management

Question: A 34-year-old G2P1 at 30 weeks gestation with severe pre-eclampsia receives 4 g MgSO4 IV bolus. Minutes later she becomes unresponsive, no pulse. CPR initiated. Explain the pathophysiology and management of hypermagnesaemia-induced cardiac arrest. (6 marks)

Model Answer:

1. Mechanism of magnesium toxicity (1 mark): Magnesium sulphate blocks calcium channels and inhibits neuromuscular transmission. High serum magnesium (greater than 2.5 mmol/L) causes progressive toxicity: initially nausea, flushing, warmth; then loss of deep tendon reflexes; then respiratory depression; finally cardiac arrest from decreased myocardial contractility and conduction blockade.

2. Pharmacokinetics (1 mark): Magnesium crosses placenta, can cause fetal hypermagnesaemia with hypotonia, respiratory depression. Therapeutic levels for pre-eclampsia: 2.0-3.5 mmol/L. Toxic levels greater than 4-5 mmol/L. Renal excretion delayed in patients with reduced renal function (pre-eclampsia, chronic kidney disease).

3. Clinical features of toxicity (1 mark): Decreased urine output (oliguria early warning). Loss of deep tendon reflexes (patellar reflex first). Respiratory depression requiring ventilatory support. Hypotension from decreased systemic vascular resistance. Cardiac arrhythmias (bradycardia, heart block). ECG changes: prolonged PR interval, widened QRS, peaked T waves.

4. Immediate management (1 mark): Calcium gluconate 10 mL 10% IV rapidly to antagonise magnesium effects on neuromuscular junction and cardiac conduction. Stop magnesium infusion immediately. Maintain airway and ventilation as required. Provide circulatory support with chest compressions, inotropes if low cardiac output.

5. Post-arrest management (1 mark): Monitor serum magnesium levels (aim less than 2.0 mmol/L). Renal replacement therapy if severe toxicity and renal function impaired. Continue magnesium at reduced infusion rate only after calcium administration for eclampsia seizure prophylaxis if needed. Monitor ECG for magnesium-induced conduction changes.

6. Prevention (1 mark): Monitor renal function and urine output (aim greater than 30 mL/hour). Monitor deep tendon reflexes regularly during infusion. Adjust infusion rate based on renal function. Stop magnesium if oliguria, respiratory depression, or loss of reflexes. Use alternative seizure prophylaxis (phenytoin, levetiracetam) if magnesium toxicity contraindicated.

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