Fat Embolism Syndrome
Fat embolism syndrome (FES) occurs when embolic fat macroglobules pass into the small vessels of the lung and other sites, producing endothelial damage and resulting respiratory failure (ARDS-like picture), cerebral dysfunction and a petechial rash. It can be difficult to diagnose.The initial symptoms are probably caused by mechanical occlusion of multiple blood vessels with fat globules that are too large to pass through the capillaries. The vascular occlusion in fat embolism is often temporary or incomplete, as fat globules do not obstruct capillary blood flow completely because of their fluidity and deformability. The late presentation is thought to be a result of hydrolysis of the fat to more irritating free fatty acids which then migrate to other organs via the systemic circulation. It has also been suggested that paradoxical embolism occurs from shunting.
Fat embolism syndrome (FES) most often follows a closed fracture of a long bone but there are many other causes:
Fractures - closed fractures produce more emboli than open fractures. Long bones, pelvis and ribs cause more emboli. Sternum and clavicle furnish less. Multiple fractures produce more emboli
Orthopaedic procedures - most commonly intramedullary nailing of the long bones, hip or knee replacements
Massive soft tissue injury
Bone marrow biopsy
Nontraumatic settings occasionally lead to fat embolism. These include conditions associated with:
Prolonged corticosteroid therapy
Conditions causing bone infarcts, especially sickle cell disease
The given incidence of this complication ranges from less than 2% to 22% in different studies. It varies considerably according to the cause. One large study found that patients with multiple fractures of the femur (excluding neck) were more likely to have fat embolism syndrome (FES) than those with isolated fractures (1.29% versus 0.54%). Patients with isolated fractures of the tibia and fibula had a lower incidence (0.30%) and patients with isolated fractures of the neck of the femur were even lower (0.06%). Minimal incidence was seen in isolated fractures of the pelvis, ribs, humerus, radius and ulna. Nonorthopaedic conditions rarely, if ever, were accompanied by FES.Men were more likely to develop the condition than women and it was rare in children aged 0 to 9 years. The age range most commonly affected was 10 to 39 years.
There is usually a latent period of 24 to 72 hours between injury and onset. The onset is then sudden, with:
Breathlessness ± vague pains in the chest. Depending on severity this can progress to respiratory failure with tachypnoea, increasing breathlessness and hypoxia.
Fever - often in excess of 38.3°C with a disproportionately high pulse rate.
Petechial rash -commonly over the upper anterior part of the trunk, arm and neck, buccal mucosa and conjunctivae. The rash may be transient, disappearing after 24 hours.
Central nervous system symptoms, varying from a mild headache to significant cerebral dysfunction (restlessness, disorientation, confusion, seizures, stupor or coma).
Renal - oliguria, haematuria, anuria.
Drowsiness with oliguria is almost pathognomonic.
There is a fulminant form which presents as acute cor pulmonale, respiratory failure and/or embolic phenomena leading to death within a few hours of injury.4
Diagnostic criteria (combined from various sources)
Diagnostic criteria were first devised by Gurd and have been modified several times since. Major criteria
Pyrexia (usually >39°C)
Sustained pO2 <8 kPa
Sustained respiratory rate >35/minute, in spite of sedation
Retinal changes - cotton wool exudates and small haemorrhages, occasionally fat globules seen in retinal vessels
Diffuse alveolar infiltrates 'snow storm appearance' on chest X-ray
Dyspnoea, hypoxia and abnormal chest X-ray can occur with thromboembolism and pneumonia.
Cytological examination of urine, blood and sputum may detect fat globules that are either free or in macrophages. This test has low sensitivity and a negative result does not exclude fat embolism.
The chest X-ray may show evenly distributed, fleck-like pulmonary shadows (snow storm appearance), increased pulmonary markings and dilatation of the right side of the heart.
Blood gases will show hypoxia, pO2 usually less than 8 kPa (60 mmHg) and hypocapnia. Continuous pulse oximeter monitoring may enable hypoxia from fat embolism to be detected in at-risk patients before it is clinically apparent (suggested by recurrent desaturations below 90%).
Platelets are reduced. Decreased haematocrit occurs within 24 to 48 hours and is attributed to intra-alveolar haemorrhage. Lipase is elevated but this is not pathognomonic, as it occurs in any bone trauma. Calcium is reduced.
Brain MRI scan may help in the diagnosis of cerebral fat embolism.
Transoesophageal echocardiograph (TEE) may be of value in detecting intraoperative release of marrow contents into the bloodstream during intramedullary reaming and nailing.
Management of fat embolism syndrome (FES) is supportive and consists primarily of ensuring good arterial oxygenation. High flow rate of oxygen is given to maintain the arterial oxygen tension in the normal range. Restriction of fluid intake and the use of diuretics can minimise fluid accumulation in the lungs so long as circulation is maintained.On the other hand, maintenance of intravascular volume is important because shock can exacerbate the lung injury caused by FES. Albumin has been recommended for volume resuscitation in addition to balanced electrolyte solution, because it not only restores blood volume but also binds fatty acids and may decrease the extent of lung injury.Mechanical ventilation and positive end-expiratory pressure (PEEP) may be required to maintain arterial oxygenation.
High-dose corticosteroids have been effective in preventing development of FES in several trials but controversy on this issue still persists. Lower doses may also be effective There is also dispute as to whether steroids are effective at all.
Prompt surgical stabilisation of long bone fractures reduces the risk of the syndrome.
The mortality rate from fat embolism syndrome (FES) is 5 to 15%. Even severe respiratory failure associated with fat embolism seldom leads to death.
Neurological deficit and coma may last for days or weeks. Residual deficits may include personality changes, memory loss and cognitive dysfunction.
Pulmonary sequelae usually resolve completely within a year, although residual diffusion capacity deficits may exist.
Early immobilisation of fractures seems to be the most effective way of reducing the incidence of this condition.
Fat embolism was first described as an autopsy finding by Zenker in 1862. In 1873 von Bergmann described it as a clinical syndrome for the first time.