A 48-year-old woman comes to the emergency department due to a 4-hour history of acute-onset shortness of breath and chest pain. She has no fever and no history of similar symptoms. The patient is being evaluated as an outpatient for excessive menstrual bleeding and is scheduled to undergo endometrial biopsy and ultrasound. Her other medical problems include carpal tunnel syndrome, hypertension, hypercholesterolemia, and hypothyroidism. She is afebrile. Blood pressure is 130/80 mm Hg, pulse is 112/min, and respirations are 24/min. BMI is 36 kg/m². Heart sounds are normal. Bilateral wheezing is heard on auscultation. The patient's right leg is swollen. Which of the following is most likely present on further evaluation?

Question

Quizplus · Accepted Answer

This patient's acute-onset dyspnea and chest pain is most likely due to a pulmonary embolism (PE) in the setting of deep venous thrombosis (DVT), given her right leg swelling. Bilateral wheezing can occur in acute PE due to cytokine-induced bronchoconstriction in response to hypoxia and infarction. Her risk factors for DVT/PE include obesity (BMI 36 kg/m²) and possible endometrial cancer (abnormal uterine bleeding at her age). ² PE causes ventilation/perfusion (V/Q) mismatch, resulting in an increase from the expected alveolar-arterial (A-a) oxygen gradient. Alveolar oxygen (PAO₂) is calculated as follows: PAO₂ = (FiO₂ × [Patm − PH₂O]) − (PaCO₂/0.8)where FiO₂ = fraction of inspired oxygen, Patm = atmospheric pressure, PH₂O = water vapor pressure, and PaCO₂ = partial arterial pressure of carbon dioxide (obtained from arterial blood gas [ABG] results). PAO₂ = (FiO₂ × [Patm − PH₂O]) − (PaCO₂/0.8) where FiO₂ = fraction of inspired oxygen, Patm = atmospheric pressure, PH₂O = water vapor pressure, and PaCO₂ = partial arterial pressure of carbon dioxide (obtained from arterial blood gas [ABG] results). This simplifies to PAO₂ = 150 − (PaCO₂/0.8) for patients breathing room air at sea level. The A-a gradient is then calculated by subtracting PAO₂ - PaO₂, where PaO₂ = partial arterial pressure of oxygen (also from ABG results). The A-a gradient is elevated if it is higher than the expected A-a gradient on room air, estimated by (2.5 + [0.21 × patient age]) or (patient age/4 + 4). A-a gradient elevation occurs in processes that cause impaired gas exchange. (Choice A) Diffuse ST-segment elevation is consistent with acute pericarditis and in some cases massive myocardial infarction. This patient's right lower extremity swelling and possible malignancy is more suggestive of DVT and subsequent PE. (Choice C) Most patients with acute PE demonstrate decreased PaCO₂ due to hyperventilation. An elevated PaCO₂ would be concerning for developing respiratory failure. (Choice D) Pericardial effusion on echocardiogram is seen in pericardial tamponade. Pericardial tamponade can cause dyspnea and classically presents with the triad of hypotension, muffled heart sounds, and jugular venous distension. This patient has normal heart sounds, and the abrupt onset of symptoms and unilateral leg swelling make PE more likely. (Choice E) A widened mediastinum on chest x-ray may be seen in aortic dissection. A history of poorly controlled hypertension is often present, sharp chest pain (with radiation to the back) is classic, and a murmur of aortic regurgitation is sometimes heard on examination. Dyspnea is uncommon, and leg swelling would not be seen. Educational objective: Obesity and malignancy are important risk factors for deep venous thrombosis and pulmonary embolism (PE). Wheezing can occur in acute PE. An elevated alveolar-arterial oxygen gradient is commonly seen in patients with PE. References: Wheezing in patients with acute pulmonary embolism with and without previous cardiopulmonary disease. (http://www.ncbi.nlm.nih.gov/pubmed/14676506)

A 48-Year-Old Woman Comes to the Emergency Department Due to a 4-Hour