On postpartum day 2 after a vaginal delivery, a 32-year-old G2P2 develops acute shortness of breath and chest pain. Her vital signs are: blood pressure 120/80 mm Hg, pulse 130 beats per minute, respiratory rate 32 breaths per minute, and temperature 37.6°C (99.8°F). She has new onset of cough. She appears to be in mild distress. Lung examination reveals clear bases with no rales or rhonchi. The chest pain is reproducible with deep inspiration. Cardiac examination reveals tachycardia with 2/6 systolic ejection murmur. Pulse oximetry shows an oxygen saturation of 88% on room air, and oxygen supplementation is initiated.
Which of the following is the best diagnostic tool to confirm the diagnosis?A) Arterial blood gas
The patient most likely has a pulmonary embolism (PE). All three components of Virchow’s triad are present during pregnancy and the postpartum period: venous stasis, endothelial injury, and a hypercoaguable state. The reported incidence of venous thromboembolism during pregnancy is 1 in 500 to 1 in 2000. PE is the seventh leading cause of maternal mortality, responsible for 9% of maternal deaths, and therefore, rapid diagnosis and treatment are critical. The classic triad—hemoptysis, pleuritic chest pain, and dyspnea—appears in only 20% of cases. The most common sign on physical examination is tachypnea (> 16 breaths/min). Ventilationperfusion scans with large perfusion defects and ventilation mismatches support the putative diagnosis of PE, but this finding can also be seen with atelectasis or other disorders of lung aeration. Conversely, a normal ventilation-perfusion scan suggests that massive PE is not the etiology of the clinical symptoms. To confirm the diagnosis, a CT pulmonary angiography is the best diagnostic tool in this setting, and has high sensitivity and specificity for the diagnosis of PE. An arterial blood gas will confirm hypoxia, but not confirm PE as the cause. A chest x-ray could be done to rule out other causes such as pulmonary edema or pneumonia, but will not make the diagnosis of PE.