Page created on December 15, 2021. Last updated on January 17, 2022 at 19:05

Amniotic fluid embolism

Definition and epidemiology

Amniotic fluid embolism (AFE) refers to the entry of amniotic fluid (which contains foetal cells or hair) into the maternal circulation, which then embolise. It causes a systemic inflammatory response syndrome (SIRS)-like syndrome and is an obstetrical emergency which is often lethal. It occurs during labour or within 30 minutes postpartum. Thankfully, it is rare (1 – 10 per 100 000 deliveries).

Etiology

Risk factors for AFE are not well known. As such, it’s difficult to predict who will develop the complication. Complicated labour, placental abruption, and preeclampsia may be risk factors.

Pathomechanism

Amniotic fluid enters the maternal circulation through a breach in the maternal/foetal circulation interface. However, how this leads to the clinical syndrome is not well known, but it is likely that foetal components activate hormonal and immunological processes which free vasoactive and procoagulant substances. Pulmonary pressures increase, causing RV and subsequently LV failure, as well as pulmonary oedema and respiratory failure. Activation of coagulation factors and platelets causes DIC, potentially causing multi organ failure.

Clinical features

The clinical presentation of AFE occurs abruptly, catastrophically, and progresses rapidly. Hypotension, dyspnoea, cyanosis occurs initially, with DIC, acute heart failure, haemorrhage, and ARDS following.

Diagnosis and evaluation

The diagnosis is clinical and made when other differential diagnoses (PE, anaphylaxis, sepsis, AMI, haemorrhagic shock, air embolism, eclampsia, etc.) are excluded. Clinical investigations must be performed while the patient is treated.

Treatment

All cases require emergency intensive care and stabilisation. Failing organ systems must be supported, and the patient may require fluids, ventilation, vasopressors, dialysis, transfusion, ECMO, etc. If the child has not yet been delivered, C-section should be initiated urgently.

Complications and prognosis

The maternal death rate is high, approximately 20%. Survivors often sustain permanent neurological injury due to cerebral hypoxia.

HELLP syndrome

Definition and epidemiology

HELLP syndrome is an abbreviation of Haemolysis, Elevated Liver enzymes, and Low Platelet count. It’s one of the hypertensive pregnancy disorders (together with preeclampsia and eclampsia). Its name describes its characteristics. It can lead to DIC, liver failure, acute kidney injury, ARDS, and even death. However, the outcome is usually good for both the mother and the foetus.

It occurs in 0,1 – 1% of pregnancies. Most cases present in weeks 28 – 36.

Etiology

See topic B17.

Pathomechanism

The liver enzymes are elevated due to liver damage, but the pathomechanism which leads to haemolysis, liver injury, and thrombocytopaenia is not well known.

Classification

The severity is classified according to the Mississippi classification and is based on the degree of thrombocytopaenia.

• Class I – Platelet count < 50 000 cells/µL
• Class II – Platelet count 50 – 100 000 cells/µL
• Class III – Platelet count 100 – 150 000 cells/µL

Yes, class I is the worst. That’s not a mistake.

Clinical features

Patients present abruptly with progressively worsening abdominal pain, and nausea/vomiting and other viral infection-like symptoms. Organ failure may develop rapidly thereafter, including DIC, placental abruption, acute kidney injury, pulmonary oedema, liver rupture, and acute liver failure.

Diagnosis and evaluation

Haemolysis is determined with the presence of schistocytes on blood smear, elevated bilirubin or LDH, and decreased haptoglobin. As a hypertensive pregnancy disorder, there is often hypertension and proteinuria.

Treatment

If there is foetal or maternal distress, delivery is initiated. If there is no foetal or maternal distress, the management depends on the gestational age:

• Gestational age is > 34 weeks -> delivery is initiated
• Gestational age is < 34 weeks -> administer RDS prophylaxis (dexa- or betamethasone) -> initiate delivery 1 – 2 days later

The lecture mentions giving dexamethasone routinely in all cases of HELLP, but this is not recommended according to UpToDate and current guidelines.

DIC

Definition

Disseminated intravascular coagulation (DIC) is what occurs when something causes an uncontrolled activation of coagulation and fibrinolysis. It’s characterised by both thrombosis and haemorrhage. It’s a rare complication in pregnancy overall, but common in the setting of certain pregnancy complications, like amniotic fluid embolism and placental abruption.

Etiology

In obstetrics, DIC is mostly a consequence of either of these:

• Severe hypertensive pregnancy disorder (preeclampsia with severe features, eclampsia, HELLP syndrome)
• Amniotic fluid embolism
• Placental abruption
• Septic abortion

Pathomechanism

In general, DIC occurs because something triggers excessive activation of the clotting cascade. This causes widespread formation of microthrombi, while also depleting coagulation factors and platelets, leading to widespread haemorrhage. Formation of microthrombi and the presence of haemorrhage often leads to organ failure. For more background, see this topic from pathophysiology.

To limit bleeding during placental separation during the third stage of labour, the coagulation/fibrinolysis equilibrium in pregnancy is always shifted toward coagulation, making pregnancy a physiological hypercoagulable state. This makes pregnancy a predisposition to DIC.

In DIC, there’s always a primary driver of clot formation. In pregnancy, this is usually the release of tissue factor (TF) from the diseased placenta or foetus, which overactivates the extrinsic pathway of the coagulation cascade.

Clinical features

Patients may present with severe uterine bleeding, bleeding from the mucosa, bleeding from sites of IV catheters, or signs of organ failure or shock. However, bleeding may be retroplacental and therefore concealed.

Diagnosis and evaluation

The diagnosis is based on clinical suspicion and typical laboratory features, and when there is a suspected cause of it. DIC always occurs in the context of another disorder. Laboratory findings show abnormal coagulation studies and thrombocytopaenia.

Treatment

Treatment involves treating the underlying condition as well as transfusions of fresh frozen plasma and platelets to replenish clotting factors and platelets.