A 32-year-old hospitalized man is evaluated for new-onset shortness of breath and confusion. The patient was admitted 3 days ago following a motor vehicle collision during which he sustained bilateral femur fractures, a pelvic fracture, and urethral injury. He underwent surgical repair with no operative complications. Temperature is 37.9 C (100.2 F), pulse is 110/min, respirations are 24/min, and oxygen saturation is 84% on room air. On physical examination, the patient appears agitated and disoriented. The lungs are clear to auscultation and there is no lower extremity edema. A petechial rash is present on the chest. ECG shows sinus tachycardia with no ischemic changes. Which of the following histologic changes has most likely taken place in this patient's lung tissue?

Question

A 32-year-old hospitalized man is evaluated for new-onset shortness of breath and confusion.  The patient was admitted 3 days ago following a motor vehicle collision during which he sustained bilateral femur fractures, a pelvic fracture, and urethral injury.  He underwent surgical repair with no operative complications.  Temperature is 37.9 C (100.2 F), pulse is 110/min, respirations are 24/min, and oxygen saturation is 84% on room air.  On physical examination, the patient appears agitated and disoriented.  The lungs are clear to auscultation and there is no lower extremity edema.  A petechial rash is present on the chest.  ECG shows sinus tachycardia with no ischemic changes.  Which of the following histologic changes has most likely taken place in this patient's lung tissue?

Quizplus · Accepted Answer

The clinical triad of acute-onset neurologic abnormalities, hypoxemia, and petechiae in a patient with traumatic bone fracture is strongly suggestive of fat embolism syndrome (FES). This condition most commonly occurs 24-72 hours following long-bone and/or pelvic fracture. Pathophysiologically, the traumatic event dislodges fat globules from the bone marrow and allows them to enter disrupted marrow venules, where they can then traverse the systemic veins and deposit in pulmonary microvessels. The pulmonary capillary occlusion impairs gas exchange and induces hypoxemia; release of free fatty acids from the fat globules also causes local toxic injury to the endothelium, potentially leading to acute respiratory distress syndrome. Some fat globules escape the lungs via precapillary arteriovenous shunts that open due to increased pulmonary artery pressure. This phenomenon appears to be responsible for the fat emboli-associated microvascular occlusion that can occur within the CNS, manifesting with confusion and neurologic impairment, and in the dermal capillaries, resulting in erythrocyte extravasation and a petechial rash. (Choices A, C, and D) A neutrophil-rich alveolar exudate is not an early histologic manifestation of FES but rather of acute bacterial or aspiration pneumonia. Mononuclear interstitial pulmonary infiltrates are found early in the course of a variety of interstitial lung diseases. A red thrombus lodged in the pulmonary artery is consistent with a thromboembolism from a deep venous source. None of these conditions would typically be associated with the neurologic impairment or petechial rash seen with FES. (Choice E) Focal necrosis of alveolar walls with associated intra-alveolar hemorrhage is often seen with pulmonary hemorrhage syndromes (eg, anti-glomerular basement membrane antibody disease, granulomatosis with polyangiitis). Educational objective: Fat embolism syndrome should be strongly suspected in a patient with severe long-bone and/or pelvic fractures who develops acute-onset neurologic abnormalities, hypoxemia, and a petechial rash. Occlusion of the pulmonary microvessels by fat globules is an early histologic finding of this syndrome.

A 32-Year-Old Hospitalized Man Is Evaluated for New-Onset Shortness of Breath