Maternal Cardiac Arrest

Cardiac arrest in a pregnant woman, occurring in approximately 1 in 12000 admissions for delivery. It requires standard resuscitation plus a set of specific modifications, and a single time critical obstetric intervention that has no equivalent in any other resuscitation.

Physiological changes that make resuscitation different

• Aortocaval compression: from around 20 weeks, or whenever the uterus is clinically large enough, the gravid uterus compresses the inferior vena cava and aorta in the supine position, reducing venous return by up to 30 to 40 percent. Chest compressions in this state generate a fraction of the already limited output achievable, and this is the single most important mechanical obstacle to effective resuscitation.
• Reduced functional residual capacity by 20 to 25 percent with increased oxygen consumption by 20 to 30 percent, so desaturation occurs within seconds rather than minutes and preoxygenation is both more essential and less effective.
• Airway oedema, capillary engorgement, weight gain, large breasts and full dentition make intubation substantially more difficult, with a failure rate several times that of the non pregnant population.
• Delayed gastric emptying with a relaxed lower oesophageal sphincter, so aspiration risk is high.
• Increased plasma volume and cardiac output by 30 to 50 percent, so large volumes of blood may be lost before hypotension appears, and haemorrhage is dramatically under recognised.
• The diaphragm is displaced upward, which is why hand position for compressions is moved slightly higher on the sternum than usual.

Resuscitative hysterotomy

Emergency caesarean section during arrest, historically termed perimortem caesarean section, is performed primarily to save the mother, not the fetus. Delivering the uterus relieves aortocaval compression, returns a substantial autotransfusion to the circulation, reduces oxygen consumption and improves the mechanics of compressions, and it frequently produces return of spontaneous circulation that was unobtainable before.

The target is delivery within 5 minutes of arrest, which means the decision is made at around 4 minutes and the procedure is started where the patient lies, without moving her to theatre, without waiting for a surgeon to scrub, and without anaesthesia, since an arrested patient does not require it. The commonest reasons this is not done are hesitation, an attempt to move the patient, and waiting for someone more senior. All three cost the mother her life.

The decision is made on the basis that the uterus is obviously gravid, meaning clinically large enough to cause aortocaval compression, which corresponds roughly to a fundus at or above the umbilicus or a gestation of around 20 weeks. Do not delay for an ultrasound to date the pregnancy.

• Unresponsive, not breathing or only gasping, no pulse, in a pregnant woman.
• The uterus is assessed immediately for size, since this determines whether the obstetric modifications apply.

Aetiology, which differs substantially from the general population

• Anaesthetic complications: failed intubation, high spinal or epidural block, local anaesthetic systemic toxicity, aspiration.
• Bleeding: uterine atony, placental abruption, placenta praevia and accreta, ruptured uterus, ruptured ectopic pregnancy, and disseminated intravascular coagulation. Haemorrhage is the leading cause in most settings and is frequently underestimated because young women compensate until they collapse.
• Cardiac disease: myocardial infarction, ischaemia, aortic dissection, peripartum cardiomyopathy, and pre existing congenital or valvular disease, which is now the leading cause of maternal death in several high income settings.
• Drugs: magnesium toxicity, oxytocin, opioids, illicit drugs, anaphylaxis to antibiotics.
• Embolism: pulmonary thromboembolism, amniotic fluid embolism, coronary and air embolism.
• Fever, that is sepsis, from chorioamnionitis, endometritis, genital tract infection and pneumonia, and in endemic areas severe malaria.
• General non obstetric causes, that is the standard reversible causes.
• Hypertensive disease: preeclampsia, eclampsia and intracranial haemorrhage.

Magnesium toxicity deserves particular emphasis, since a woman receiving magnesium for preeclampsia who arrests should be assumed to have magnesium toxicity until proven otherwise, and the antidote is immediately available.

• Clinical, in under 10 seconds, exactly as for any arrest.
• Note and announce the time of arrest, since the 5 minute target for delivery cannot be met if nobody knows when the clock started. Assign a timekeeper explicitly.
• Determine whether the uterus is obviously gravid by palpation.
• Establish the likely cause from the immediately available history: gestation, mode of delivery or ongoing labour, blood loss, magnesium infusion, recent anaesthetic intervention, hypertension, known cardiac disease, and the events immediately preceding collapse.
• Point of care ultrasound during the rhythm check for tamponade, right ventricular strain, free intraperitoneal fluid and cardiac activity, without extending the compression pause. Do not use ultrasound to assess fetal viability during the arrest, since it does not change the decision and it wastes time.
• Blood for full blood count, crossmatch, coagulation screen, fibrinogen, magnesium, calcium, potassium, glucose and lactate.
• Post resuscitation imaging and investigation according to the suspected cause.

First responder actions

• Activate the resuscitation team and, simultaneously, the obstetric and neonatal teams. Maternal arrest requires three teams and calling them sequentially loses minutes.
• Document and announce the time of onset of arrest.
• Place the patient supine on a firm surface. Do not use left lateral tilt for compressions, since tilting substantially reduces the force that can be applied and produces ineffective compressions. Relieve aortocaval compression instead by manual left uterine displacement.
• Start resuscitation as for adult cardiac arrest, with hand position slightly higher on the sternum to account for upward displacement of the diaphragm and heart.

Manual left uterine displacement

Performed continuously from the moment the arrest is recognised until the uterus is delivered. An assistant stands on the patient's left and uses two hands to pull the uterus leftward and upward, or stands on the right and pushes it leftward with one or two hands. This relieves caval compression while allowing full force compressions on a flat patient, and it is the correct alternative to tilting.

Maternal resuscitation, unmodified

• Do not delay defibrillation. Energy levels are unchanged and defibrillation is safe in pregnancy. Fetal monitors should be removed before shock delivery but their presence must not delay it.
• Give the standard advanced life support drugs at standard doses. Adrenaline 1 mg every 3 to 5 minutes and amiodarone 300 mg for refractory ventricular fibrillation. There is no evidence that dose modification is required and no drug is withheld out of concern for the fetus, since the fetus cannot survive a dead mother.
• Ventilate with 100 percent oxygen.
• Monitor waveform capnography and compression quality.
• Continue all maternal resuscitative interventions during and after the caesarean section without interruption. Compressions do not stop for the operation.

Maternal modifications

• Establish intravenous access above the diaphragm, that is in the upper limbs or neck, since drugs given below the diaphragm may not reach the heart because of caval compression.
• Assess for hypovolaemia and give a fluid bolus, with a very low threshold given that haemorrhage is the commonest cause and is concealed in abruption, uterine rupture and ruptured ectopic pregnancy. Activate the massive haemorrhage protocol early and give blood rather than crystalloid where haemorrhage is likely.
• Anticipate a difficult airway. The most experienced available provider should manage the airway, using a smaller endotracheal tube of 6.0 to 7.0 mm, video laryngoscopy where available, and with a plan for failure prepared before the first attempt. Apply cricoid pressure with awareness that it may worsen the view.
• If magnesium was being infused before the arrest, stop it immediately and give calcium chloride 10 mL of a 10 percent solution, or calcium gluconate 30 mL of a 10 percent solution, intravenously or intraosseously. This is the specific antidote for magnesium toxicity and it should be given empirically in any woman who arrests while receiving magnesium.
• For local anaesthetic systemic toxicity, give intravenous lipid emulsion 20 percent as a 1.5 mL/kg bolus followed by an infusion.
• For amniotic fluid embolism, which presents with sudden cardiovascular collapse, hypoxia and profound coagulopathy, provide supportive resuscitation, early and aggressive blood product replacement with fibrinogen and cryoprecipitate, and consider extracorporeal support in centres where available.
• Suspect and treat pulmonary embolism, considering thrombolysis, which is not absolutely contraindicated in maternal arrest.

Obstetric intervention

• The obstetric and neonatal teams prepare immediately for emergency caesarean section where the uterus is obviously gravid.
• If there is no return of spontaneous circulation by 4 minutes of arrest, begin the hysterotomy, aiming for delivery by 5 minutes.
• Perform it at the site of the resuscitation. Do not transfer to theatre.
• A midline vertical incision from just below the umbilicus to the symphysis gives the fastest access and the best exposure, though a transverse incision is acceptable for an operator more familiar with it. Speed matters more than the choice of incision.
• Anaesthesia is not required in a patient in arrest, though anaesthesia must be provided immediately if circulation returns during the procedure.
• Bleeding is minimal in true arrest and becomes brisk when circulation returns, which requires prompt haemostasis.
• After delivery, continue compressions, give uterotonics to control atony, and close or pack as circumstances allow.
• Do not delay the procedure to determine fetal viability. The primary indication is maternal survival, and the procedure is performed even where the fetus is known to be dead if the uterus is large enough to compress the cava.
• The neonatal team receives the infant and resuscitates it separately.

After return of spontaneous circulation

• Standard post arrest care with attention to oxygenation and blood pressure targets.
• Continue left uterine displacement if the patient remains undelivered.
• Ongoing obstetric management: control of haemorrhage, uterotonics, surgical haemostasis, and management of coagulopathy with blood products guided by fibrinogen and viscoelastic testing.
• Transfer to a critical care setting with obstetric input.
• Temperature management as for other arrests, with fetal monitoring if the pregnancy continues.

Team and system preparation

Maternal arrest is rare, so it is managed badly unless it has been rehearsed. Every unit caring for pregnant women should have a maternal arrest drill, a scalpel available in the resuscitation trolley on the labour ward, and a clear escalation pathway that summons obstetric and neonatal teams simultaneously with the resuscitation team. Debrief afterwards, and provide psychological support for staff, which is frequently overlooked after these events.