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Pathophysiology
Clinical meaning
Fat embolism syndrome (FES) results from both mechanical embolization and biochemical inflammatory cascade. Mechanically, intramedullary fat and marrow particles enter the venous circulation through torn medullary venous sinusoids after long bone fracture or intramedullary instrumentation. These particles lodge in pulmonary capillaries, causing V/Q mismatch. Particles <20 micrometers can traverse the pulmonary capillary bed to reach the systemic circulation (paradoxical embolization through pulmonary microvasculature or patent foramen ovale), causing cerebral and cutaneous manifestations. Biochemically, pulmonary lipase hydrolyzes neutral fat into free fatty acids that are directly cytotoxic to capillary endothelium, activating the complement cascade, causing platelet aggregation and consumption (thrombocytopenia), increasing capillary permeability (non-cardiogenic pulmonary edema), and triggering DIC. The clinician must apply Gurd's diagnostic criteria, manage respiratory failure, order advanced diagnostics, prescribe supportive therapy, and coordinate surgical fixation to prevent further embolization.
Diagnostics & workup:
- Apply Gurd's diagnostic criteria systematically: ≥1 major criterion + ≥4 minor criteria
- Major criteria: petechial rash, respiratory insufficiency (PaO2 <60 mmHg), cerebral involvement (not attributable to other causes)
- Minor criteria: tachycardia >110, pyrexia >38.5°C, retinal fat emboli on fundoscopy, fat in urine, unexplained drop in Hgb, elevated ESR, thrombocytopenia, fat macroglobulinemia
- Order ABG: progressive type I respiratory failure (low PaO2, normal or low PaCO2, increased A-a gradient)
- Order CT head if cerebral involvement: may show petechial hemorrhages in white matter (starfield pattern on MRI DWI)
- Order bronchoscopy with BAL if diagnosis uncertain: >5% alveolar macrophages with fat-laden inclusions (fat staining with Oil Red O) supports diagnosis
- Order serial CBC: falling platelets (consumption) and hemoglobin (mechanical hemolysis)
- Order lipase, triglycerides, and urine for fat globules (lipiduria)
Risk factors:
- Bilateral femur fractures (highest risk: up to 33% incidence of FES)
- Closed long bone fractures (higher risk than open fractures due to intact marrow cavity)
- Delayed fracture fixation beyond 24 hours
- Reaming during intramedullary nailing
- Multiple fractures and polytrauma
- Young males (demographic most often affected due to trauma pattern)
- Total joint arthroplasty with cemented prostheses
- Severe burns and liposuction (non-orthopedic causes)
Management
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Prescribing & monitoring
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Takeaways
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