Obstetric anaesthesia13 / 17
Mechanical mitral valve on LMWH for induction of labour32-year-old woman, 70 kg, at 37 weeks with a mechanical mitral valve
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Know this first
- Mechanical valve is mWHO class III: significantly raised maternal risk.
- Therapeutic LMWH: 24 hours before neuraxial. IV heparin: stop 4–6 hours, normal aPTT.
- Endocarditis prophylaxis is reasonable at membrane rupture with a prosthetic valve.
- Unstable AF in pregnancy: electrical cardioversion, first shock 200 J biphasic.
- Large oxytocin boluses (over 10 units) cause haemodynamic compromise.
The patient
32-year-old woman, 70 kg, at 37 weeks with a mechanical mitral valve, for planned induction of labour.
Switched from warfarin to enoxaparin 70 mg SC 12-hourly with anti-Xa monitoring; paroxysmal AF; NYHA class I.
Drugs: enoxaparin, bisoprolol.
Vitals: BP 112/68, HR 76, SpO2 98% on air, RR 16.
The examiner asks
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Consider
What are the issues?
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- A 32-year-old with a mechanical mitral valve and paroxysmal AF, for induction at 37 weeks. Patient
- Pregnancy raises her output and volume, peaking in labour and just after delivery.
- A mechanical valve is mWHO class III: high risk, needing expert shared care. Disease
- Heparins anticoagulate less well than warfarin; valve thrombosis in pregnancy can be catastrophic.
Prepare
How do you manage her anticoagulation?
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- Cardiology, haematology and obstetrics agree the plan with me before induction. Patient
- Anti-Xa peaks and troughs while she stays on LMWH, as her needs shift. Disease
- Before delivery she moves to IV unfractionated heparin, which can be measured and reversed.
- Neuraxial: 24 hours after therapeutic LMWH; heparin infusion off 4–6 hours with a normal aPTT.
- Endocarditis prophylaxis is reasonable at membrane rupture with her prosthetic valve.
Plan
How do you manage her labour and delivery?
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- Early epidural, dosed slowly, to stop pain-driven tachycardia and output surges. Disease
- Any drop in pressure gets a carefully titrated alpha agonist, avoiding tachycardia.
- Passive descent and an assisted second stage spare her repeated Valsalva. Surgery
- Oxytocin as a slow infusion, no large bolus; methylergonovine avoided. After surgery
- Anticoagulation restarts after delivery by the agreed plan, once bleeding allows and the catheter is out.
Crisis
In the second stage she develops AF at 170/min; BP 76/44 and she feels faint. What do you do?
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- Tachycardia algorithm: unstable AF at 170 with hypotension, so synchronised cardioversion. Crisis
- Awake with a full stomach: brief sedation, with suction and airway kit ready.
- Left uterine displacement and oxygen throughout.
- Synchronised shock at 200 J biphasic, increased if it fails.
- Fetal heart watched; the obstetrician ready to expedite delivery once she's stable.
- Then rate control with her beta-blocker, and heparin continued for her valve. After surgery
Fatal mistakes
- Neuraxial block inside the heparin window.
- Drug-only treatment of unstable AF.
- Stopping anticoagulation with no bridging plan.
Checked against: Stoelting 8e · Barash 9e · Miller 10e
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