fat embolism

Etiology

• blunt trauma (90%)
  • most commonly long bone & pelvic fractures
• acute pancreatitis
• diabetes mellitus
• burns
• joint reconstruction
• liposuction
• cardiopulmonary bypass
• decompression sickness
• parenteral lipid infusion
• sickle cell crisis
• pathologic fractures
• osteomyelitis

Pathology

• 2 theories exist
  • mechanical theory:
    • large fat droplets are released into the venous system
    • droplets are deposited in the pulmonary capillary beds & travel through arteriovenous shunts to the brain
    • microvascular lodging of droplets produces local ischemia & inflammation, with concomitant release of inflammatory mediators, platelet aggregation, & vasoactive amines
  • biochemical theory
    • hormonal changes caused by trauma &/or sepsis induce systemic release of free fatty acids as chylomicrons
    • acute-phase reactants, such as C-reactive proteins, cause chylomicrons to coalesce & create the physiologic reactions described above

Clinical manifestations

• Bergman's triad
  • mental status changes
  • petechiae (often in the axilla/thorax)
  • dyspnea
• tachycardia
• fever with high-spiking temperatures
• tachypneic, dyspnea, hypoxia due to ventilation-perfusion
• reddish-brown nonpalpable petechiae developing over the upper body, particularly in the axillae, within 12-72 hours of insult or injury (20-50% & may resolve quickly) {virtually diagnostic in the right clinical setting}
• subconjunctival and oral hemorrhages and petechiae also appear.
• agitated delirium but may progress to stupor, seizures, or coma, frequently is unresponsive to correction of hypoxia
• retinal hemorrhages with intra-arterial fat globules are visible upon funduscopic examination

Laboratory

• arterial blood gas: hypoxia results from ventilation-perfusion mismatch
• complete blood count (CBC) thrombocytopenia, anemia common but non-specific
• low plasma fibrinogen common but not specific
• urinary fat stains not sensitive or specific

Diagnostic procedures

• bronchoalveolar lavage (BAL) with staining of alveolar macrophages for fat is controversial

Radiology

• chest X-ray: diffuse bilateral pulmonary infiltrates within 12-72 hours of onset of clinical findings
• noncontrast head CT: may be normal or may reveal diffuse white-matter petechial hemorrhages consistent with microvascular injury
• nuclear medicine ventilation/perfusion imaging of the lungs to rule out pulmonary embolism
  • may be normal or may show subsegmental perfusion defects
• helical chest CT for pulmonary embolism:
  • may be normal or may show parenchymal changes consistent with lung contusion, acute lung injury, or ARDS
  • nodular or ground glass opacities in the setting of trauma suggest fat embolism

Complications

• mortality rate is 10-20%

Differential diagnosis

• pulmonary embolism
• thrombotic thrombocytopenic purpura

Management

• treatment is supportive
  • maintenance of adequate oxygenation & ventilation,
  • stable hemodynamics, hydration
  • prophylaxis for DVT & stress-ulcers
  • nutrition
• continuous pulse oximetry monitoring in at-risk patients
• surgery
  • early stabilization of long bone fractures is recommended to minimize bone marrow embolization into the venous system
• prophylactic placement of inferior vena cava filters may help reduce the volume of fat reaching the heart

More general terms

• embolism