Venous thromboembolism

The primary goals of therapy should be directed toward maintenance of oxygenation and cardiac output for both mother and fetus. This is achieved by traditional critical care support. The promotion of thrombus resolution and the prevention of thrombus extension and dislodgement are further therapeutic priorities, pending a complete diagnostic work-up.

Heparin is the safest anticoagulant in pregnancy because, unlike Coumadin (warfarin), its high molecular weight prevents it from crossing the placenta. Coumadin should be avoided throughout pregnancy as a characteristic embryopathy has been associated with its use in the first trimester. Central nervous system and ophthalmological abnormalities may result from exposure to these drugs in any trimester. In addition, fetal and neonatal hemorrhage and placental abruption are potential side-effects. Because of immature liver enzyme systems, the effect of oral anticoagulants on the fetus is much greater and lasts for much longer than the effect on the mother.

Women with venous thromboembolism presenting during pregnancy or the puerperium should initially be treated with a continuous intravenous infusion of heparin for 5 to 10 days according to current protocols for non-pregnant patients. If the thromboembolic event occurs antepartum, subcutaneous concentrated heparin (20 000 lU/ml) should be given into the lateral abdominal wall every 12 h until delivery. The regimen should be dose adjusted to prolong the activated partial thromboplastin time measured 6 h after the injection to a value 1.5 times greater than control. To minimize the risk of recurrence, Coumadin is then administrated postpartum for at least 6 weeks (3 months if thromboembolism complicates the puerperium). Neither heparin nor Coumadin therapy is a contraindication to breast feeding. Postpartum suppression of lactation with estrogen markedly increases the incidence of thromboembolism and is contraindicated.

A separate entity from deep vein thrombosis is septic pelvic and puerperal ovarian vein thrombophlebitis. This is encountered in patients with endometritis who do not respond to antibiotics. A continuous intravenous infusion of heparin should be added to the antibiotic regimen for 10 to 20 days and then stopped.

Low-molecular-weight heparin does not cross the placenta. Limited experience with this agent has been gained during pregnancy, but its use is attractive because its longer half-life allows a once-daily regimen and because it lowers the risk of heparin-induced osteoporosis and thrombocytopenia.

Anticoagulant therapy usually does not affect vaginal delivery significantly. The risk of maternal hemorrhage is minimal if protamine sulfate is administered to patients with markedly prolonged activated partial thromboplastin times and to those subjected to Cesarean section. Regional anesthesia is usually contraindicated because of the risk of epidural hematoma.

Recurrence of pulmonary embolism in adequately anticoagulated patients, any absolute contraindication to anticoagulant therapy, and any serious complication of anticoagulation such as heparin-induced thrombocytopenia are potential indications for transvenous insertion of a permanent inferior vena cava filter in women with venous thromboembolism. These filters have the ability to trap emboli without significantly reducing flow in the inferior vena cava. Recurrence of pulmonary embolism after filter insertion is less than 5 per cent. If possible, anticoagulation should be continued for 3 months after filter insertion to allow lysis of initial thrombosis or any clot trapped by the filter. Apart from leg swelling, no serious fetal and maternal side-effects (e.g. perforation of the inferior vena cava wall) have been reported. However, there is a risk of dislodgement due to the dilated venous system and pressure effects during labor. Radiographic follow-up is mandatory to check for migration, angulation of the device, or perforation of the vein wall.

The use of thrombolytic agents should be restricted to life-threatening situations, such as impending or established acute cor pulmonale, because of the risk of maternal bleeding at the time of delivery and immediately postpartum.

Surgical or transvenous catheter embolectomy/fragmentation may occasionally be lifesaving in the expeditious management of massive pulmonary embolism with cardiovascular collapse in patients who are severely hemodynamically compromised and/or in whom thrombolytic therapy is inadvisable.

The therapeutic strategy for obstetric emboli should also encompass antepartum prophylaxis for women with a known hypercoagulable state, with any condition normally requiring long-term anticoagulant therapy, or with a history of previous venous thromboembolism related or not to pregnancy. The incidence of thromboembolism during pregnancy ranges from 5 to 70 per cent in these patients. Adjusted (1.5 times control value) rather than fixed-dose subcutaneous heparin should be started as early as possible in pregnancy and continued up to delivery. Coumadin should be given immediately postpartum for 6 weeks.

An adjusted-dose regimen is essential for effective prophylaxis or treatment during pregnancy to offset the physiological increases in plasma volume, renal clearance, and plasma levels of clotting factors.

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