**Question:** Following pelvic gynecologic surgery, a 34-year-old woman becomes dyspneic, her peripheral arterial oxygen saturation falls from 94% to 81%, and her measured PaO2 is 52 on a 100% non-rebreather mask. She is hemodynamically stable. A CT angiogram is consistent with a right lower lobe pulmonary embolus. Which of the following is the next step in her management?

A. Initiate anticoagulation therapy
B. Administer thrombolytic therapy
C. Perform a pulmonary angiography
D. Respiratory support and close monitoring

**Correct Answer:** A. Initiate anticoagulation therapy

**Core Concept:** Pulmonary embolism is a life-threatening condition caused by the blockage of a pulmonary artery or its branches by a blood clot, leading to reduced blood flow and oxygenation in the affected lung. In this case, a right lower lobe pulmonary embolus is confirmed by a CT angiogram.

**Why the Correct Answer is Right:** Given the patient's history of dyspnea, decreased peripheral arterial oxygen saturation, and low PaO2 (arterial partial pressure of oxygen) on non-rebreather mask, it suggests a significant decrease in pulmonary perfusion and oxygenation. A pulmonary embolism is the most likely cause, given the patient's history of recent pelvic surgery, immobilization, and potential venous stasis, which are common risk factors.

**Why Each Wrong Option is Incorrect:**

**Option B (thrombolytic therapy):** This option suggests administering drugs to dissolve the blood clot directly. While thrombolytic therapy can be a viable treatment option, the patient's hemodynamic stability (stable vital signs) indicates that the pulmonary embolism is not causing hemodynamic compromise at this stage. In such cases, initiating anticoagulation therapy is a safer and more appropriate first step to prevent further clot formation and progression.

**Option C (perform a pulmonary angiography):** A pulmonary angiography is an invasive diagnostic procedure that involves injecting a contrast agent into the pulmonary artery to visualize the pulmonary vasculature. While it is essential for diagnosis, it is not a direct treatment for the patient's condition. Initiating anticoagulation therapy is more appropriate first-line management.

**Option D (respiratory support and close monitoring):** Providing respiratory support and close monitoring are essential components of the patient's care, but they do not address the primary cause of the patient's distress: a pulmonary embolism. Initiating anticoagulation therapy is the appropriate first step to address the underlying clot formation and prevent further embolization.

**Option A (initiating anticoagulation therapy):** Initiating anticoagulation therapy is crucial in this patient scenario. Anticoagulation therapy prevents further clot formation and embolization, which is essential for the patient's recovery. Ensuring the patient's oxygenation and ventilation remain stable while initiating anticoagulation therapy is crucial. Close monitoring of the patient's condition is essential for adjusting the treatment plan as needed.