A 33-year-old postpartum woman is brought to the emergency department with sudden onset of severe dyspnea and right-sided chest pain that began 3 hours ago when getting up from breastfeeding her child. The patient was discharged from the hospital 4 days ago after an uneventful elective cesarean delivery. She does not use tobacco, alcohol, or illicit drugs. Temperature is 36.7 C (98 F), blood pressure is 100/70 mm Hg, pulse is 128/min, and respirations are 32/min. Pulse oximetry is 84% on room air. BMI is 34 kg/m². Examination shows a woman in moderate respiratory distress with evidence of accessory muscle use. She is alert and cooperative, without cyanosis or jaundice. Heart sounds are normal. The chest is clear to auscultation. Chest x-ray reveals no infiltrates and heart size is normal. ECG shows sinus tachycardia. Arterial blood gas analysis results are as follows: In addition to supplemental oxygen therapy, which of the following is the best initial step in management of this patient?

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11ec25c8_d4c5_9c91_bc81_5d3a40b18260_MD0003_00 The first step in managing patients with suspected pulmonary embolism (PE) is supportive care (eg, oxygen, intravenous fluids for hypotension). The next step is assessing absolute contraindications to anticoagulation (eg, active bleeding, hemorrhagic stroke). Patients with contraindications should undergo diagnostic testing for PE, with appropriate treatment (eg, inferior vena cava filter) if positive. Patients without contraindications can be assessed with the modified Wells criteria for PE pretest probability. In patients in whom PE is unlikely based on these criteria, diagnostic testing is performed before anticoagulation is considered. However, in patients with likely PE, especially if they are in moderate to severe distress, anticoagulation (eg, low-molecular-weight heparin or unfractionated heparin) should be given prior to diagnostic testing (patients in whom PE is unlikely or who do not have moderate to severe distress may proceed to diagnostic testing prior to anticoagulation). modified Wells criteria This postpartum patient likely has an acute PE (sudden-onset dyspnea, chest pain, tachypnea, hypoxemia). Her modified Wells score is 6 (absence of a more likely diagnosis = 3 points, tachycardia = 1.5 points, recent cesarean delivery = 1.5 points). She has some distress with increased work of breathing, significant hypoxia, and tachycardia. She has no absolute contraindications to anticoagulation (anticoagulation can be safely started within 6-12 hours of a cesarean delivery) and should be started on intravenous heparin before further diagnostic testing. Early and effective anticoagulation decreases mortality risk of acute PE from 30% to ~2%-8%. (Choices A and E) CT angiography (CTA) of the chest is the diagnostic test of choice for PE. Ventilation-perfusion scan is an alternate study for patients with significant renal impairment, morbid obesity, and/or contrast allergy. Transthoracic echocardiogram can identify right ventricular changes suggestive of PE in patients who are too unstable to undergo CTA. However, in this patient anticoagulation should be initiated prior to any diagnostic testing. (Choice B) D-dimer assays have good sensitivity and negative predictive value and can be useful to exclude PE in patients in whom PE is unlikely. However, a negative test result cannot be used to reliably exclude PE in patients with likely probability of PE. (Choice D) Lower extremity venous ultrasound is used to diagnose lower extremity deep venous thrombosis. However, a negative result does not rule out acute PE in a patient with high clinical suspicion (ie, dislodged clot). (Choice F) Troponin and CK-MB testing can be useful in the workup of acute chest pain; however, they should not delay initiation of anticoagulation in this patient. Educational objective: Early and effective anticoagulation decreases the mortality risk of acute pulmonary embolism (PE) and should be initiated prior to pursuing confirmatory diagnostic testing in patients with likely probability of acute PE, especially those in moderate to severe distress. References: Antithrombotic therapy for VTE disease: Antithrombotic therapy and prevention of thrombosis, 9th ed: American College of Chest Physicians evidence-based clinical practice guidelines. (http://www.ncbi.nlm.nih.gov/pubmed/22315268)

A 33-Year-Old Postpartum Woman Is Brought to the Emergency Department