Amniotic fluid embolism

Amniotic fluid embolism (AFE) is a rare and incompletely understood obstetric emergency in which amniotic fluid, fetal cells, hair or other debris enters the mother's blood stream via the placental bed of the uterus and triggers an allergic reaction. This reaction then results in cardiorespiratory (heart and lung) collapse and coagulopathy. It was first formally characterized in 1941.

Presentation

The condition is so rare (between 1 in 8000 and 1 in 80,000 deliveries) that most doctors will never encounter it in their professional careers, and as a result the exact process is poorly understood. However, it is believed that once the fluid and fetal cells enter the maternal pulmonary circulation a two-phase process occurs:

First phase

The patient experiences acute shortness of breath and hypotension. This rapidly progresses to cardiac arrest as the chambers of the heart fail to dilate and there is a reduction of oxygen to the heart and lungs. Not long after this stage the patient will lapse into a coma. 50% die within the first hour of symptoms.

Second phase

Although many women do not survive beyond the first stage, about 40 per cent of the initial survivors will pass onto the second phase. This is known as the hemorrhagic phase and may be accompanied by severe shivering, coughing, vomiting and the sensation of a bad taste in the mouth. This is also accompanied by excessive bleeding as the blood loses its ability to clot. Collapse of the cardiovascular system leads to fetal distress and death unless the child is delivered swiftly.

Causes

It is mostly agreed that this condition results from amniotic fluid entering the uterine veins and in order for this to occur there are three prerequisites:

• Ruptured membranes (a term used to define the rupture of the amniotic sac)
• Ruptured uterine or cervical veins
• A pressure gradient from uterus to vein

Although exposure to fetal tissue is common and thus finding fetal tissue within the maternal circulation is not significant, in a small percentage of women this exposure leads to a complex chain of events resulting in collapse and death.

There is some evidence that it can be associated with abdominal trauma.

Treatment

One approach which has been used is an immediate caesarean section.