A 42-year-old man comes to the emergency department due to several hours of dyspnea. He is a long-haul truck driver who became acutely short of breath during a 36-hour trip but previously had been healthy. The patient smokes a pack of cigarettes daily and drinks a 6-pack of beer on weekends. Pulmonary examination reveals vesicular breath sounds bilaterally with the overlying areas resonant to percussion. CT pulmonary angiogram shows a right lower lobe pulmonary artery occlusion consistent with pulmonary embolism but no evidence of pulmonary infarction. Which of the following is the most likely reason for the lack of lung tissue necrosis in this patient?

Question

A 42-year-old man comes to the emergency department due to several hours of dyspnea.  He is a long-haul truck driver who became acutely short of breath during a 36-hour trip but previously had been healthy.  The patient smokes a pack of cigarettes daily and drinks a 6-pack of beer on weekends.  Pulmonary examination reveals vesicular breath sounds bilaterally with the overlying areas resonant to percussion.  CT pulmonary angiogram shows a right lower lobe pulmonary artery occlusion consistent with pulmonary embolism but no evidence of pulmonary infarction.  Which of the following is the most likely reason for the lack of lung tissue necrosis in this patient?

Quizplus · Accepted Answer

11ec160b_3b4a_7744_9249_410145821720_MD0001_00 The lung is supplied by dual circulation from both the pulmonary arteries and bronchial arteries. This collateral circulation can help protect against lung infarction as a complication of pulmonary embolism (PE). The pulmonary arteries are the major suppliers of blood to the lungs, providing deoxygenated blood for gas exchange; the bronchial arteries supply nutrients, remove waste from the bronchi, and provide collateral blood flow to the remainder of the lung parenchyma. When a clot occludes the pulmonary system, the bronchial system continues to supply nutrients to pulmonary tissue and can even backfill the pulmonary capillaries to partially maintain gas exchange in the area of the thromboembolism. Distal PEs in small arteries (≤3 mm) are more likely to cause infarction as they may occlude areas distal to the pulmonary-bronchial anastomoses. When a pulmonary infarction does occur, it is typically hemorrhagic (red) rather than ischemic (white) due to the relatively low density of lung tissue and the dual blood supply. (Choice B) Alveolar inflammation triggered by PE can eventually lead to decreased surfactant and some degree of atelectasis. This process can take up to 2 days to develop, and the resulting intrapulmonary shunting makes a small contribution to the hypoxemia that occurs with PE. (Choice C) Recombinant tissue plasminogen activator (TPA) may be used to treat PE in patients who are hemodynamically unstable. However, endothelial-derived TPA is limited primarily to the bronchial circulation, and spontaneous recanalization of the pulmonary artery is a slow process. (Choice D) PE leads to increased pulmonary arterial pressure; however, the pulmonary venous pressure is unchanged or decreased as blood flow through the proximal pulmonary circulation is obstructed. Patients with an underlying elevation in pulmonary venous pressure (eg, decompensated heart failure) may be more likely to experience lung infarction with PE due to the high pulmonary venous pressure impairing collateral flow from the bronchial circulation. (Choice E) Intrapulmonary shunting occurs when an area of the lung is adequately perfused but poorly ventilated. PE causes intrapulmonary shunting due to redistribution of blood away from segments directly affected by the clot; the remaining accessible alveoli are unable to fully oxygenate all the blood passing through the pulmonary circulation, resulting in hypoxemia. In contrast, areas distal to the clot receive adequate ventilation but poor perfusion (ie, dead space ventilation). Educational objective: The lungs are supplied by dual circulation from both the pulmonary and bronchial arteries. This collateral circulation can help protect against lung infarction due to pulmonary artery occlusion (ie, pulmonary embolism), as the bronchial circulation can continue to provide blood to the lung parenchyma. __________ References: Pulmonary embolism and pulmonary infarction after lung transplantation. (http://www.ncbi.nlm.nih.gov/pubmed/20547546) Lung infarction following pulmonary embolism: a comparative study on clinical conditions and CT findings to identify predisposing factors. (http://www.ncbi.nlm.nih.gov/pubmed/25750111)

A 42-Year-Old Man Comes to the Emergency Department Due to Several