Rosen donne des idées intéressantes sur ce sujet: How can I rule out pulmonary embolism in a pregnant patient without use of ionizing radiation? PE is the most common nontraumatic cause of death in pregnant women, so clinicians are justified to adopt a liberal rule-out PE approach to all pregnant women with dyspnea. Pulmonary V/Q scanning is safe in pregnancy and provides almost no risk to the fetus. A chest CT scan delivers about 250 mrad of energy, whereas the common threshold at which fetomaternal experts believe fetal teratogenicity becomes a concern is about 5 rad. The mother's abdomen can be shielded, but the fetus will still receive a small fraction of the 250 mrad. There is a rapidly growing body of literature that suggests that exposure of the young brain to even small amounts of radiation can produce subtle cognitive deficits later in life, and at present the long-term consequences of CT scanning of pregnant patients are unknown. It seems logical to try to rule out PE with the D-dimer in pregnant patients; if D-dimer is negative in a patient believed to be at low pretest probability, this excludes the diagnosis. Coagulation systems are hyperactive in pregnancy, elevating the circulating D-dimer concentration. The D-dimer concentration increases linearly with duration of normal pregnancy, and about 75% of all pregnant patients evaluated for PE have a D-dimer concentration greater than the abnormal cutoff of 500 ng/mL.[46 <http://www.mdconsult.com/das/book/body/85842565-2/0/1365/252.html#4-u1.0-B0 -323-02845-4..50092-5--bib46> ] About 60% of healthy pregnant patients have a D-dimer less than 1000 ng/mL, however, and virtually all pregnant patients with a PE have a D-dimer greater than 1000 ng/mL. A reasonable interpretation of these data suggests the following approach. If the D-dimer concentration is less than 1000 ng/mL, and the patient meets the criteria in Box <http://www.mdconsult.com/das/book/body/85842565-2/0/1365/250.html#4-u1.0-B0 -323-02845-4..50092-5--cetextbox2> 87-2 , the diagnosis of PE may be considered reasonably excluded, and pulmonary vascular imaging is not necessary. As an additional margin of safety, a negative venous ultrasound of the lower extremities excludes DVT and helps reduce the probability of PE by about half. V/Q scanning, if normal, excludes the diagnosis. A high-probability V/Q scan establishes the diagnosis, and heparin (which does not cross the placental barrier) can be initiated. If neither normal nor high probability, the V/Q scan is nondiagnostic, and further imaging (perhaps beginning with venous duplex ultrasound of the legs) is indicated.
Alain Vadeboncoeur
