Cause:Fat globules, from bony fractures, via the circulation to the pulmonary arteries and other vessels? Often seen w total hip replacement (94%—Clin Orthoped Related Res 1999;355:23)
Pathophys:Fat from marrow or from tissue enter veins to inferior vena cava, or enter the lymphatics and from there go to the thoracic duct via the superior vena cava to the lungs and beyond to the systemic circulation; there the fat emboli are broken down by lipoprotein lipase into triglycerides and free fatty acids, which are toxic molecules
Symptomatic emboli in 3% of all femoral shaft trauma; they are the cause of death in 5% of all trauma deaths; but 90% of emboli cause no sx or are undetected
Sx:24-48 h latent period after femoral, pelvic, tibial, humeral, or other trauma; then nonlateralizing CNS sx’s of confusion/acute brain syndrome; dyspnea and respiratory distress
Si:Fever; tachycardia; skin petechiae (85%), mantle distribution over chest, neck, and conjunctiva; cyanosis; confusion
of those with sx, 10-20% mortality if no coma; 85% mortality if coma present
Lab:
Chem:Lipase elevated in 3-5 d, peaks at 5-8 d
Hem:Thrombocytopenia
Noninv:Transesophageal cardiac echo shows emboli themselves during fx repair (Clin Orthoped Related Res 1999;355:23)
Path:Bx of petechiae or kidney show fat in capillaries with platelets about them; use frozen section, which avoids formalin dissolution of the fat. Sputum stained for fat, 80% false negative; bronchial lavage shows intracellular fat in >33% of cells (8/8 patients—Ann IM 1990;113:583)
Urine:Fat stain positive in 60% with acid-washed glass
Xray:
Chest shows bilateral fluffy infiltrates, ARDS
Lung scans show mismatched V/Q defects
Rx:
Methylprednisolone 1+ mg/kg q 6 h × 3 d at first si in likely patient; prevents without complications (Ann IM 1983;99:439)
Supportive rx of ARDS (Acute Respiratory Distress Syndrome (Shock Lung))