Causes

The definition of disseminated intravascular coagulation (DIC) is a systemic thrombohaemorrhagic disorder found in association with well-defined clinical situations and laboratory evidence of procoagulant activation, fibrinolytic activation, inhibitor consumption and biochemical evidence of end-organ damage or failure. DIC is always secondary to another condition that provokes clotting within the vascular compartment. There are three main mechanisms by which obstetric conditions may activate the coagulation system:

• 1.
  

  Release of thromboplastins from placental and decidual tissue into the maternal circulation. This may happen with dramatic suddenness in cases of amniotic fluid embolism and abruptio placentae. It can occur at the time of surgical intervention for placenta praevia accreta, ruptured uterus and trophoblastic disease. In patients with intrauterine fetal death or missed abortion, release of thromboplastins into the maternal circulation is delayed and less consistent. In such cases about 25% will develop DIC some 5–6 weeks after fetal demise. Fetal death and missed abortion are now rare causes of DIC because, with ultrasound, the diagnosis is usually made early and the pregnancy terminated before DIC can develop.

  
  
• 2.
  

  Endothelial damage exposes the underlying collagen to plasma and procoagulants. Such endothelial damage may be caused insidiously by pre-eclampsia/eclampsia, HELLP (Haemolysis, elevated liver enzymes and low platelets) syndrome, acute fatty liver or by sepsis. Another cause of endothelial hypoxia and damage is haemorrhagic shock with delayed restoration of the circulating intravascular volume. This is now one of the commonest causes of DIC in obstetrics.

  
  
• 3.
  

  Red blood cell/platelet injury may occur with incompatible blood transfusion reactions leading to the release of phospholipids and initiation of the coagulation cascade.

Pathophysiology

Normal haemostasis is a complex and dynamic balance between coagulation, which leads to fibrin formation, and the fibrinolytic system, which disposes of fibrin once its haemostatic function has been fulfilled. In DIC there is excessive and widespread coagulation which leads to consumption and depletion of the coagulation factors, resulting in haemorrhage. In response to this widespread coagulation and deposition of fibrin in the microvasculature the fibrinolytic system is activated. As plasminogen is converted to plasmin it breaks down the fibrin to form fibrin degradation products (FDP). FDP have anticoagulant properties as they inhibit both platelet function and the action of thrombin, serving to aggravate the coagulopathy. While the haemorrhagic diathesis is the dominant pathology in most cases, extensive microvascular thrombosis can also occur, leading to organ ischaemia and infarction. This can be a secondary factor, along with hypovolaemic shock, in the causation of renal cortical necrosis, lung damage and Sheehan’s syndrome. The causes and pathophysiological features of DIC are outlined in Figure 25-1 .

Causes and pathophysiology of disseminated intravascular coagulation.

(Adapted from Baskett TF. Essential management of obstetric emergencies. 4th ed. Bristol: Clinical Press Ltd, 2004, with permission of Clinical Press Ltd.)

Clinical Presentation

It is common for the main clinical features to be those of the obstetric complication that has triggered the DIC. Clinical manifestations of the DIC per se will depend upon its severity. These will range across the spectrum from no clinical manifestations with only haematological changes of DIC (↓ platelets, ↑ FDP); relatively subtle clinical signs such as bruising, epistaxis, purpuric rash, and oozing from venepuncture sites; to the dramatic torrential postpartum haemorrhage (PPH) and bleeding from all operative sites.

Diagnosis

Diagnosis is aided by recognition of the obstetric initiating causes of DIC. Certain haematological tests are useful in the diagnosis and, if available, it is appropriate to enlist the aid of a haematologist. Depending upon the level of sophistication of the hospital laboratory some tests may be unavailable. In addition, the process of DIC is so dynamic that results, as they become available, may not reflect the current status. Bedside whole-blood clotting tests are not helpful as their accuracy is limited unless controlled laboratory conditions are applied.

The most rapid and useful screening tests are the platelet count (low and falling), activated partial thromboplastin time (which is usually prolonged when clotting factors are severely depleted), prothrombin time (usually prolonged) and the thrombin time, which is usually prolonged and is one of the more valuable tests. Fibrinogen levels are increased in normal pregnancy to 400–650 mg/dl; with DIC this level falls but may still be in the normal non-pregnant range. In severe DIC the fibrinogen levels usually fall below 150 mg/dl. Fibrin degradation products such as D-dimer can be unreliable for diagnosis in pregnant women as their levels are often increased in normal pregnancy.

The diagnosis of DIC in pregnancy is therefore primarily clinical, supported by the coagulation profile. Letsky has suggested a three-stage severity system based on the degree of haemostatic compensation allied to the blood levels of coagulation factors.