Fat embolism syndrome.

A 49-year-old man with a history of prostate cancer metastatic to bone suffered a pathological fracture to the left femur while hospitalized (Figure 1A). Eighteen hours after the fracture, he developed hypoxemia and hypotension followed by confusion and a petechial rash in the left axilla. Chest X-ray obtained after intubation demonstrated new diffuse bilateral patchy infiltrates (Figure 1B). Urgent transthoracic echocardiogram showed right ventricular dilation and free wall hypokinesis with preserved con-tractility of the right ventricular apex (McConnell's Sign; Figure 2, Movie I in the online-only Data Supplement). Based on the clinical presentation and supportive imaging, the patient was diagnosed with fat embolism syndrome. He was transferred to the intensive care unit for further management. Overview Although it was observed centuries ago that intravenous injection of oil resulted in mechanical obstruction of small vessels, 1 the exact pathophysiol-ogy of fat embolism syndrome (FES) remains uncertain. Fat embolism (FE) is defined by the presence of fat glob-ules in the pulmonary microcirculation regardless of clinical significance. FES describes a characteristic pattern of clinical findings that follow an insult associated with the release of fat into the circulation. FES is most commonly associated with orthopedic trauma, with highest incidence in closed, long bone fractures of the lower extremities, particularly the femur. 2 The risk of FES complicating orthopedic trauma is highest in ages 10 to 40 years and occurs in men more frequently than women. 3 Nonorthopedic causes of FES are exceedingly rare and include pan-creatitis, sickle cell crisis, alcoholic liver disease, bone marrow harvest or transplant, and liposuction. 4 In the orthopedic and trauma literature , the incidence of FES has ranged from <1% to >30% of cases. The wide range of incidence likely reflects the heterogeneity of diagnostic criteria. Recent population level data from the National Hospital Discharge Survey found an FES incidence of 0.17% in patients with isolated or multiple orthopedic fractures. 3 The incidence increased to 0.54% in isolated femo-ral fractures and 1.29% if multiple fractures including the femur were present. 3 Although FES remains a relatively rare entity, subclinical FE in the trauma population is highly prevalent , with an autopsy series finding fat emboli in the pulmonary circulation of 82% of trauma patients and 88% of patients who received cardiopulmo-nary resuscitation. 5 Pathophysiology The pathophysiologic mechanisms of FES have yet to be fully elucidated. End organ pathology is thought to be mediated by 2 main processes: mechanical …