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fat embolism
Etiology:
1) blunt trauma (90%)
- most commonly long bone & pelvic fractures [2]
2) acute pancreatitis
3) diabetes mellitus
4) burns
5) joint reconstruction
6) liposuction
7) cardiopulmonary bypass
8) decompression sickness
9) parenteral lipid infusion
10) sickle cell crisis
11) pathologic fractures
12) osteomyelitis [2]
Pathology:
- 2 theories exist
a) 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
b) 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:
1) Bergman's triad
a) mental status changes
b) petechiae (often in the axilla/thorax)
c) dyspnea
2) tachycardia
3) fever with high-spiking temperatures
4) tachypneic, dyspnea, hypoxia due to ventilation-perfusion
5) 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}
6) subconjunctival and oral hemorrhages and petechiae also appear.
7) agitated delirium but may progress to stupor, seizures, or coma, frequently is unresponsive to correction of hypoxia
8) retinal hemorrhages with intra-arterial fat globules are visible upon funduscopic examination
Laboratory:
1) arterial blood gas: hypoxia results from ventilation-perfusion mismatch
2) complete blood count (CBC) thrombocytopenia, anemia common but non-specific
3) low plasma fibrinogen common but not specific
4) urinary fat stains not sensitive or specific
Special laboratory:
- bronchoalveolar lavage (BAL) with staining of alveolar macrophages for fat is controversial
Radiology:
1) chest X-ray: diffuse bilateral pulmonary infiltrates within 12-72 hours of onset of clinical findings
2) noncontrast head CT: may be normal or may reveal diffuse white-matter petechial hemorrhages consistent with microvascular injury
3) nuclear medicine ventilation/perfusion imaging of the lungs to rule out pulmonary embolism
- may be normal or may show subsegmental perfusion defects
4) 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:
1) treatment is supportive
a) maintenance of adequate oxygenation & ventilation,
b) stable hemodynamics, hydration
c) prophylaxis for DVT & stress-ulcers
d) nutrition
2) continuous pulse oximetry monitoring in at-risk patients
3) surgery
- early stabilization of long bone fractures is recommended to minimize bone marrow embolization into the venous system
4) prophylactic placement of inferior vena cava filters may help reduce the volume of fat reaching the heart
General
embolism
References
- eMedicine: Fat embolism
http://www.emedicine.com/med/TOPIC652.HTM
- Medical Knowledge Self Assessment Program (MKSAP) 19
American College of Physicians, Philadelphia 2022