Amniotic fluid embolism
Encyclopedia
Amniotic fluid embolism (AFE) is a rare and incompletely understood obstetric emergency in which amniotic fluid
Amniotic fluid
Amniotic fluid or liquor amnii is the nourishing and protecting liquid contained by the amniotic sac of a pregnant woman.- Development of amniotic fluid :...

, fetal cells, hair, or other debris enters the mother's blood stream via the placenta
Placenta
The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. "True" placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and...

l bed of the uterus and triggers an allergic reaction. This reaction then results in cardiorespiratory (heart and lung) collapse and coagulopathy
Coagulopathy
Coagulopathy is a condition in which the blood’s ability to clot is impaired. This condition can cause prolonged or excessive bleeding, which may occur spontaneously or following an injury or medical and dental procedures.The normal clotting process depends on the interplay of various proteins in...

. It was first formally characterized in 1941. It is the fifth leading cause of maternal mortality.

Presentation

The condition is so rare (between 1 in 8000 and 1 in 80,000 deliveries, although more recent studies show 1 in 20,464 deliveries for a more precise number) that most doctors will never encounter it in their professional careers, and as a result the exact process is poorly understood.

It is believed however that once the fluid and fetal cells enter the maternal pulmonary circulation in general terms there will be profound respiratory failure with deep cyanosis
Cyanosis
Cyanosis is the appearance of a blue or purple coloration of the skin or mucous membranes due to the tissues near the skin surface being low on oxygen. The onset of cyanosis is 2.5 g/dL of deoxyhemoglobin. The bluish color is more readily apparent in those with high hemoglobin counts than it is...

 and cardiovascular shock followed by convulsions and profound coma
Coma
In medicine, a coma is a state of unconsciousness, lasting more than 6 hours in which a person cannot be awakened, fails to respond normally to painful stimuli, light or sound, lacks a normal sleep-wake cycle and does not initiate voluntary actions. A person in a state of coma is described as...

, however this does occur in two phases detailed below:

First phase

The patient experiences acute shortness of breath and hypotension
Hypotension
In physiology and medicine, hypotension is abnormally low blood pressure, especially in the arteries of the systemic circulation. It is best understood as a physiologic state, rather than a disease. It is often associated with shock, though not necessarily indicative of it. Hypotension is the...

. This rapidly progresses to cardiac arrest
Cardiac arrest
Cardiac arrest, is the cessation of normal circulation of the blood due to failure of the heart to contract effectively...

 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
Coma
In medicine, a coma is a state of unconsciousness, lasting more than 6 hours in which a person cannot be awakened, fails to respond normally to painful stimuli, light or sound, lacks a normal sleep-wake cycle and does not initiate voluntary actions. A person in a state of coma is described as...

. While previously believed to have a maternal mortality rate of 60-80%, more recently it has been reported at 26.4%.

Second phase

Although many women do not survive beyond the first stage, about 40 percent 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
Uterine
The word uterine can refer to different meanings:* relating to or near the uterus or womb* having the same mother, but different fathers, see matrilineality...

 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
    Amniotic sac
    The amniotic sac is the sac in which the fetus develops in amniotes. It is a tough but thin transparent pair of membranes, which hold a developing embryo until shortly before birth. The inner membrane, the amnion, contains the amniotic fluid and the fetus. The outer membrane, the Chorion,...

    )
  • Ruptured uterine or cervical
    Cervix
    The cervix is the lower, narrow portion of the uterus where it joins with the top end of the vagina. It is cylindrical or conical in shape and protrudes through the upper anterior vaginal wall...

     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 AFE may be associated with abdominal trauma
Physical trauma
Trauma refers to "a body wound or shock produced by sudden physical injury, as from violence or accident." It can also be described as "a physical wound or injury, such as a fracture or blow." Major trauma can result in secondary complications such as circulatory shock, respiratory failure and death...

  or amniocentesis
Amniocentesis
Amniocentesis is a medical procedure used in prenatal diagnosis of chromosomal abnormalities and fetal infections, in which a small amount of amniotic fluid, which contains fetal tissues, is sampled from the amnion or amniotic sac surrounding a developing fetus, and the fetal DNA is examined for...

. A 2006 study showed that the use of drugs to induce labor, such as misoprostol
Misoprostol
Misoprostol is a drug that is used for the prevention of non steroidal anti inflammatory drug induced gastric ulcers, for early abortion, to treat missed miscarriage, and to induce labor. The latter use is controversial in the United States. Misoprostol was invented and marketed by G.D...

, nearly doubled the risk of AFE. A maternal age of 35 years or older, caesarean or instrumental vaginal delivery, polyhydramnios
Polyhydramnios
Polyhydramnios is a medical condition describing an excess of amniotic fluid in the amniotic sac. It is seen in 0.2 to 1.6% of pregnancies,,...

, cervical laceration or uterine rupture
Uterine rupture
Uterine rupture is a potentially catastrophic event during childbirth by which the integrity of the myometrial wall is breached. In an incomplete rupture the peritoneum is still intact. With a complete rupture the contents of the uterus may spill into the peritoneal cavity or the broad ligament...

, placenta previa or abruption, eclampsia
Eclampsia
Eclampsia , an acute and life-threatening complication of pregnancy, is characterized by the appearance of tonic-clonic seizures, usually in a patient who had developed pre-eclampsia...

, and fetal distress
Fetal distress
In medicine , the term fetal distress refers to the presence of signs in a pregnant woman—before or during childbirth—that suggest that the fetus may not be well...

 were also associated with an increased risk.

Treatment

One emergency intervention which has been applied is an immediate caesarean section
Caesarean section
A Caesarean section, is a surgical procedure in which one or more incisions are made through a mother's abdomen and uterus to deliver one or more babies, or, rarely, to remove a dead fetus...

.

External links

  • Histology at University of Utah
    University of Utah
    The University of Utah, also known as the U or the U of U, is a public, coeducational research university in Salt Lake City, Utah, United States. The university was established in 1850 as the University of Deseret by the General Assembly of the provisional State of Deseret, making it Utah's oldest...

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