FIGURE 52-6 Axial image of the chest from a four-channel multidetector spiral computed tomographic scan performed ater administration of intravenous contrast. There is enhancement of the pulmonary artery with a large thrombus on the right (arrow) consistent with pulmonary embolism. (Reproduced with permission from Dr. Michael Landay.) shown in Figure 52-6. The estimated fetal radiation exposure averages 0.45 to 0.6 mGy. he estimated maternal breast dose is 10 to 70 mGy (Waksmonski, 2014).
Bourjeily and colleagues (2012) performed a follow-up study of 318 pregnant women who had a negative CTP A performed for a suspected pulmonary embolism. All were seen 3 months following their initial presentation or at 6 weeks postpartum. None of these women were subsequently diagnosed with a thromboembolism.
CTP A has many advantages, but we find that the higher resolution allows detection of previously inaccessible smaller distal emboli that have uncertain clinical significance. Similar observations have been reported by others (Anderson, 2007; Hall, 2009). Also, the hyperdynamic circulation and augmented plasma volume associated with pregnancy leads to a higher number of nondiagnostic studies compared with nonpregnant patients (Ridge, 2011; Scarsbrook, 2006).
his technique involves a small dose of radiotracer such as intravenously administered technetium-99m-macroaggregated albumin. There is negligible fetal and maternal breast radiation exposure-0.1 to 0.4 mGy. The scan may not provide a deinite diagnosis because many other conditions can cause perfusion defects. Examples are pneumonia or local bronchospasm. Chan and coworkers (2002) found that a fourth of ventilationperfusion scans in pregnant women were nondiagnostic. In these instances, CTPA is preferred (T romeur, 2017).
To compare the performance of lung scintigraphy and CTPA, Revel and colleagues (201a1) evaluated 137 pregnant women with suspected pulmonary embolism. he two modalities performed comparably and had no signiicant diferences between the proportions of positive, negative, or indeterminate results. Speciically, the proportion of indeterminate results for both approximated 20 percent. By way of comparison, about a fourth of the nonpregnant population had indeterminate studies. The investigators attributed this diference to the younger age of the pregnant patients. Similarly, one systematic review concluded that both CTP A and lung scintigraphy seem appropriate for exclusion of pulmonary embolism during pregnancy (van Mens, 2017).
his requires catheterization of the right side of the heart and is considered the reference test for pulmonary embolism. With newer generation multidetector CT scanners, however, the role of invasive pulmonary angiography has been questioned. his is especially true given the higher radiation exposure for the fetus (Konstantinides, 2014; Kuriakose, 2010). Other detractions are that it can be time consuming, uncomfortable, and associated with dye-induced allergy and renal failure. Indeed, the procedure-related mortality rate approximates 1 in 200 (Stein, 1992). It is reserved for confirmation when less invasive tests are equivocal.
Immediate treatment for pulmonary embolism is full anticoagulation similar to that for deep-vein thrombosis as discussed on page 1012. Several complementary procedures may be indicated.