Fat Embolism Syndrome

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- Discussion:
    - FES results when embolic marrow fat macroglobules damage small vessel perfusion leading to endothelial
            damage in pulmonary capillary beds leading to respiratory failure and ARDS like picture;
    - risk factors for FES:
            - long bone frx (esp femoral shaft);
                  - note that the risk is especially high with femoral shaft fracture and concomitant head injury;
                  - risk is higher w/ non-operative therapy but is also higher w/ over-zealous reaming of femoral canal;
                  - multiple trauma w/ major visceral injuries and blood loss (incidence may be as high as 5-10%);
                  - see timing of orthopaedic surgery with concomitant head injury;    
    - controversies: Is the method of frx fixation relevant?
            - as noted by EH Schemitsch et al in an experimental animal study, the amount of embolized fat measured at 24 hours after
                  pressurization of the IM canal was not affected by the method fixation;
                  - frx fixation was not associated w/ evidence of acute accumulation, nor did it have any effect on pulmonary artery pressure;
                  - concluded that pulmonary dysfunction from fat emboli depends on addtional factors, and the method of frx fixation was not a significant factor;
    - references:
            - 1990 Proceedings of The Hip Society--Basic Science and Pathology: The Fat Embolism Syndrome: A Review.
            - Fatal fat embolism following total condylar knee arthroplasty.
            - The fat embolism syndrome. A review.
            - Fat embolism, intravascular coagulation, and osteonecrosis.
            - Fat emboli syndrome in isolated fractures of the tibia and femur.
            - Fat embolism syndrome: history, definition, epidemiology.
            - Fat embolism: the reaming controversy.
            - Physical and technical aspects of intramedullary reaming.
            - Fat embolism: special situations Bilateral femoral fractures and pathologic femoral fractures.

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- gurd's criteria for diagnosis:
            - pulse ox monitoring for subclinical hypoxemia may also be beneficial;
            - ref: Clinically inapparent hypoxemia after skeletal injury. The use of the pulse oximeter as a screening method.

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- Labs:
      - hypoxia on ABG;
      - fallen hemoglobin (3-5 g)
      - early thrombocytopenia;
      - fat demonstrated in blood clots

- CXR: nonspecific serial chest roentgenograms;

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- Prevention:
      - immediate frx fixation may lower incidence of FES (ref)
      - consider prophylactic steroids for prevention of FES in patients w/ isolated long bone trauma;
            - references:          
                    - Fat embolism prophylaxis with corticosteroids. A prospective study in high-risk patients.
                    - Low-dose corticosteroid prophylaxis against fat embolism.
                    - Fat embolism and the fat embolism syndrome. A double-blind therapeutic study.
                    - The use of methylprednisolone and hypertonic glucose in the prophylaxis of fat embolism syndrome.
      - role of intramedullary instrumentation:
            - references:
                    Intramedullary Pressure Changes and Fat Intravasation During Intramedullary Nailing: An Experimental Study in Sheep.
                    Pulmonary damage after intramedullary femoral nailing in traumatized sheep--is there an effect from different nailing methods?
                    Fat embolism syndrome following the intramedullary alignment guide in total knee arthroplasty.
                    Influences of Different Methods of Intramedullary Femoral Nailing on Lung Function in Patients With Multiple Trauma.
                    Pulmonary effects of fixation of a fracture with a plate compared with IM nailing. A canine model of fat embolism and fracture fixation.
                            EH Schemitsch MD et al.   JBJS Vol 79-A. 1997. No 7 Jul. p 984.
                    Femoral canal reaming in the polytrauma patient with chest injury. A clinical perspective.
                    Intramedullary nailing and reaming for delayed union or nonunion of the femoral shaft. A report of 105 consecutive cases.
                    ARDS, Pneumonia and Mortality following Thoracic Injury and a Femoral Fracture Treated Either with IM Nailing with Reaming or with a Plate.
                            MJ Bosse MD et al.   JBJS Vol 79-A, No 6. June 1997. p 799.
                    Fat embolism prophylaxis with corticosteroids. A prospective study in high-risk patients.
                    Low-dose corticosteroid prophylaxis against fat embolism.
                    Fat embolism and the fat embolism syndrome. A double-blind therapeutic study.
                    Prevention of fat embolism syndrome.
                    The use of methylprednisolone and hypertonic glucose in the prophylaxis of fat embolism syndrome.

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- Treatment:
      - once FES occurs, it is mandatory that perfusion be maintained, especially in older patients;
      - to adequately treat FES patients, must take a "pro-active" intervention statedgy to ensure that perfusion is maintained as soon as FES is diagnosed;
      - specific requirements include:
            - SG monitoring (w/ continuous mixed VO2 monitoring);
            - arterial line for monitorying blood pressure and ABG;
            - metabolic acidosis or suboptimal mixed VO2 indicates sub-optimal perfusion;
            - maintenance of perfusion by optimizing:
                - cardiac output - influenced by preload, afterload, and thru use of inotropic agents;
                - hematocrit: must be aggressively be kept above 30% w/ pRBC;
            - most pts will require mechanical ventilation as they enter respiratory failure;
            - ref: Therapeutic aspects of fat embolism syndrome.

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Bone marrow fat in the circulation: clinical entities and pathophysiological mechanisms.