Amniotic Fluid Embolism

Entry of amniotic fluid into the maternal circulation was first described in 1926 by JR Meyer, however, the first recorded maternal death from amniotic fluid embolism was not until 1941.¹

Incidence

• Rare in UK, but the fifth commonest cause of perinatal mortality.
• The incidence has steadily declined over the last 40 years,² until the last triennial report where the mortality rate per 100,000 pregnancies had risen to 0.8 (from 0.25 the previous report).³
• A prospective, national study of amniotic fluid embolism is currently being undertaken by United Kingdom Obstetric Surveillance System (UKOSS) and has currently found an estimated incidence in the UK of 1.8 cases per 100,000 maternities.⁴

The improved quality of autopsy may have resulted in some increase in diagnosis.

Initial pulmonary symptoms may be minor. Amniotic fluid embolises to the pulmonary circulation, and the patient responds with collapse, shock, tachycardia, cardiac irregularity and arrest and sometimes death.

These may give a clue to diagnosis before collapse and haemorrhage occur.
The classical scenario of amniotic fluid embolism involves an older multiparous woman, in advanced labour who suddenly collapses.
It can occur following:

• Termination of pregnancy
• Amniocentesis
• Placental abruption
• Trauma
• During caesarean section
• Unexpectedly up to 30 minutes after delivery

There may be cardiotocographic abnormalities, uterine hypertonus and an obstetric intervention such as artificial rupture of the membranes.⁵

High index of suspicion on clinical criteria, as above.

• Symptoms occurring during delivery with high likelihood of collapse and incipient disseminated intravascular coagulation.
• CXR may show pulmonary oedema, acute respiratory distress syndrome (ARDS), right atrial enlargement and a prominent pulmonary artery.
• ECG and arterial blood gases are not helpful.
• Post-mortem will reveal fetal squamous cells and hair (lanugo) in the maternal pulmonary circulation.
• In the future, the measurement of complement, which may be activated following AFE, or the fetal antigen sialyl Tn may help diagnose the condition.⁶ The latter can be measured serologically or by immunocytochemistry on lung tissue but, as yet, is not widely available.

Women with symptoms suspicious of amniotic fluid embolism should be transferred to intensive care as soon as possible, as these women may have a better chance of survival.²Treatment is supportive.

General

• Resuscitation with oxygen to maintain normal oxygen saturation. Intubate if necessary.
• Fluids to maintain BP
• Consider pulmonary artery catheterisation in patients who are haemodynamically unstable.
• Initiate cardiopulmonary resuscitation (CPR) if the patient arrests. If she does not respond to resuscitation, perform a perimortem caesarean delivery. The Managing Obstetric Emergencies and Trauma (MOET) course recommends caesarean section delivery of the infant within five minutes of cardiac arrest to facilitate resuscitation.⁷
• Continuously monitor the fetus.

Pharmacological

• Dopamine if pulmonary artery catheter can be inserted (coagulopathy may prevent this).
• Otherwise rapid digitalisation needs to be considered.
• Management of coagulopathy with:⁸
  • FFP for a prolonged APTT
  • Cryoprecipitate for a fibrinogen level less than 100 mg/dL
  • Transfuse platelets for platelet counts less than 20 x 10⁹/L

Surgical

Uterine artery embolisation has been described in 2 cases, with excellent survival.⁹

The United Kingdom Amniotic Fluid Embolism Register was established to identify the incidence of the condition and examine any differences or common factors between survivors and fatalities.¹⁰ There is mandatory reporting of cases. In reported cases from 1997-2004 the mortality is 37%. Of those that die, a quarter are dead within the first hour and most of the remainder by nine hours after presentation.

Causes a high level of morbidity for mother and baby. If the patient survives, disseminated intravascular coagulation is a common complication. Typical findings among survivors include:¹¹

• Cardiac arrest
• Hysterectomy
• Further laparotomies
• Subglottic stenosis
• Persisting neurological impairment
• Admission to intensive care units

The majority of women will survive. Hypoxic ischaemic encephalopathy and cerebral palsy are found amongst surviving neonates.