Thromboembolic disorders of pregnancy are the number one cause of maternal mortality in the United States, accounting for approximately 20% of all deaths. While hemorrhage still accounts for the most maternal deaths in developing countries, embolic disorders are gaining ground worldwide.
The anesthesiologist must rapidly diagnose the etiology of embolism and initiate supportive management that focuses on cardiopulmonary resuscitation:
Intubation and mechanical ventilation;
Cardiopulmonary resuscitation if necessary;
Support of maternal circulation with inotropic drugs and intravascular fluid replacement;
Fetal monitoring and emergency Caesarean section if indicated;
End-organ shock management (e.g., cardiac failure, pulmonary edema/acute respiratory distress syndrome (ARDS), renal/hepatic failure, neurologic sequelae);
Anticipation of intensive care unit (ICU) level care.
Venous thromboembolisms consist of deep vein thromboses (DVT) and pulmonary emboli (PE). Hypercoagulability, stasis, and endothelial injury (Virchow’s Triad) are thought to be the factors that contribute to formation of thromboemboli. In the case of pregnancy, all three factors are met through increased coagulation factors II, VII, VIII, X (hypercoagulability), aortocaval compression (stasis), and vaginal/operative delivery (endothelial injury).
Pregnancy is a hypercoagulable state, resulting in a 5–10× increase risk of DVT/PE, with an incidence of up to 2 per 1000 pregnancies. The risk continues up to 6 weeks postdelivery. Approximately, 25% of patients with a DVT develop pulmonary embolisms, resulting in a 15% mortality rate in those with a PE.
The main risk factors for developing a venous thromboembolism are maternal age greater than 35 years, multiple gestation, higher parity, pre-eclampsia, previous thromboembolism/family history, surgery during pregnancy (including Caesarean section), immobility, pelvic trauma, smoking, heart disease, obesity, and thrombophilias. Caesarean sections alone have been attributed with an 8× higher risk of thromboembolism. Approximately, half of all pregnant patients with a thrombophilia will develop a thromboembolism during pregnancy.
A DVT presents with signs of lower extremity edema, calf discomfort, and pain on dorsiflexion during initial assessment. Pertinent clinical manifestations of a PE include a sudden onset oxygen desaturation, dyspnea, tachypnea, tachycardia, and pleuritic chest pain.
Aside from supportive management, patients with hemodynamically stable venous thromboembolism may be started on therapeutic unfractionated heparin for secondary prevention of further clot development. For unstable patients, thrombolysis with tissue plasminogen activator may be indicated. Embolectomy is rarely necessary during pregnancy. Patients without current venous thromboembolism but with several risk factors may be started on prophylactic unfractionated heparin or low molecular weight heparin (LMWH).
For the anesthesiologist, therapeutic anticoagulation is usually stopped when active labor begins. Neuraxial analgesia placement should be withheld until a normal partial thromboplastin time (PTT) results if unfractionated heparin is used. Enoxaparin is a commonly used LMWH and must be discontinued for 24 hours prior to neuraxial analgesia placement when therapeutic dosing (1 mg/kg every 12 hours) is being used.