24.2 Obstetric Emergencies: Maternal Collapse, Amniotic Fluid Embolism, Uterine Inversion and Resuscitative Hysterotomy

24.2 Obstetric Emergencies: Maternal Collapse, Amniotic Fluid Embolism, Uterine Inversion and Resuscitative Hysterotomy

Maternal Collapse

Maternal collapse is an acute event involving the cardiorespiratory system and/or brain, with reduced consciousness, at any stage of pregnancy or up to 6 weeks after delivery.

Causes (the "4 Hs and 4 Ts" plus Obstetric Causes)

Physiological Changes That Affect Resuscitation

• Aortocaval compression from about 20 weeks (uterine fundus at or above the umbilicus) reduces venous return and cardiac output in the supine position.
• Reduced FRC and increased oxygen consumption cause rapid desaturation.
• Airway oedema, enlarged breasts and full stomach make intubation more difficult and aspiration more likely.
• Increased blood volume can mask haemorrhage until it is advanced.

Adapted Advanced Life Support

1. Call for help, including the obstetric, neonatal and anaesthetic teams; note the time.
2. Manual left uterine displacement (pushing the uterus up and to the left) while the woman is supine, which allows effective chest compressions; a left lateral tilt of about 15-30° on a firm surface is an alternative.
3. Standard chest compressions and defibrillation (energy levels are unchanged; remove fetal monitors if possible).
4. Early tracheal intubation by an experienced operator to protect the airway and improve oxygenation; use a smaller tube.
5. Intravenous access above the diaphragm.
6. Treat the cause: for example, intravenous lipid for local anaesthetic toxicity, calcium for magnesium toxicity, blood products and uterotonics for haemorrhage.

Resuscitative Hysterotomy (Perimortem Caesarean Delivery)

If there is no return of spontaneous circulation within 4 minutes of cardiac arrest in a woman with a uterus at or above the umbilicus, perform resuscitative hysterotomy, aiming for delivery within 5 minutes of collapse.

• The main purpose is maternal resuscitation: emptying the uterus relieves aortocaval compression and improves venous return and the effectiveness of CPR.
• It should be performed where the arrest occurs without moving the woman to theatre, with a scalpel and minimal equipment; continue CPR throughout.

Amniotic Fluid Embolism (AFE)

AFE is rare (about 2 per 100,000 maternities in UK data) but carries high mortality. Fetal material entering the maternal circulation triggers an anaphylactoid-type reaction with complement activation.

Typical features: sudden hypoxia, hypotension or cardiac arrest, altered consciousness or seizures, and disseminated intravascular coagulation with massive bleeding, during labour, Caesarean section or within about 30 minutes of delivery. An initial phase of pulmonary hypertension and right ventricular failure is followed by left ventricular failure.

Management is supportive: resuscitation, oxygenation and ventilation, inotropes and vasopressors, early correction of coagulopathy (fibrinogen, plasma, platelets, guided by viscoelastic testing), delivery of the baby if undelivered, and consideration of extracorporeal support. The diagnosis is clinical and of exclusion.

Acute Uterine Inversion

The uterine fundus inverts into the uterine cavity or through the cervix, usually during the third stage of labour (excessive cord traction with a fundal placenta).

• Features: severe pain, haemorrhage and shock out of proportion to visible blood loss (vagal stimulation from traction on the ovarian and uterine ligaments causes bradycardia), and a mass in the vagina.
• Management: call for help, resuscitate, stop oxytocic infusions, attempt immediate manual replacement (pushing the fundus up through the cervix). If the cervical ring has contracted, give uterine relaxation with glyceryl trinitrate (intravenous boluses of about 50-100 $\mu\text{g}$ or sublingual), terbutaline, or general anaesthesia with a volatile agent. Hydrostatic replacement (O'Sullivan technique) or surgery may be needed. Once replaced, give uterotonics to prevent recurrence and treat haemorrhage.

Placenta Accreta Spectrum

Abnormal placental invasion into (accreta), into the myometrium (increta) or through it (percreta). The main risk factors are previous Caesarean section and placenta praevia; risk rises with each previous Caesarean.

• Diagnosed antenatally by ultrasound and MRI.
• Planned delivery in a specialist centre, often by Caesarean hysterectomy, with large-bore access, cell salvage, blood products, a massive haemorrhage protocol and sometimes interventional radiology (balloon occlusion).
• Neuraxial anaesthesia may be used initially, with conversion to general anaesthesia for prolonged surgery or massive haemorrhage.

Uterine Rupture

Usually associated with a previous uterine scar during labour, especially with induction or augmentation. Signs include fetal heart rate abnormalities (the most consistent early sign), abdominal pain (which may break through epidural analgesia), vaginal bleeding, loss of fetal station and maternal shock. Management is immediate laparotomy and resuscitation.

Umbilical Cord Prolapse

Cord prolapse with fetal bradycardia is an obstetric emergency. Relieve cord compression (manual elevation of the presenting part, knee-chest position or bladder filling) and deliver by category 1 Caesarean section, usually under general anaesthesia unless a working epidural can be extended quickly.

Urgency of Caesarean Section

Spinal anaesthesia can often be achieved quickly for category 1 delivery if performed by an experienced anaesthetist, but general anaesthesia remains appropriate when there is no time or neuraxial anaesthesia is contraindicated. An existing labour epidural can be extended with a rapid-onset solution (for example lidocaine 2% with adrenaline and bicarbonate, or 0.5% levobupivacaine).

Other Obstetric Anaesthetic Emergencies

• High or total spinal block: hypotension, bradycardia, breathing difficulty, upper limb weakness and loss of consciousness; support ventilation and circulation, intubate if needed, and maintain uterine displacement.
• Magnesium toxicity: loss of reflexes, respiratory depression, cardiac arrest; stop the infusion and give calcium gluconate 1 g intravenously.
• Failed intubation: follow the obstetric difficult airway guideline, prioritising oxygenation and considering whether to wake the woman or proceed with a supraglottic airway.