Description

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.^1,2 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.

Aetiology

Fat embolism syndrome (FES) most often follows a closed fracture of a long bone but there are many other causes:³

• 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 replacements⁴
• Massive soft tissue injury
• Severe burns
• Bone marrow biopsy
• Nontraumatic settings occasionally lead to fat embolism. These include conditions associated with:
  • Liposuction⁵
  • Fatty liver
  • Prolonged corticosteroid therapy
  • Acute pancreatitis
  • Osteomyelitis
  • Conditions causing bone infarcts, especially sickle cell disease

Epidemiology

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%).⁶ 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.⁶

Presentation

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

Differential diagnosis

Dyspnoea, hypoxia and abnormal chest X-ray can occur with thromboembolism and pneumonia.

Investigations

• 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%).¹⁰
• 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.²
• Transoesophageal echocardiography (TEE) may be of value in detecting intraoperative release of marrow contents into the bloodstream during intramedullary reaming and nailing.³

Management

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.¹¹ 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.

Drugs

High-dose corticosteroids¹² have been effective in preventing development of FES in several trials but controversy on this issue still persists. Lower doses may also be effective.¹³ There is also dispute as to whether steroids are effective at all.

Surgical

Prompt surgical stabilisation of long bone fractures reduces the risk of the syndrome.

Prognosis

• 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.³

Prevention

Early immobilisation of fractures seems to be the most effective way of reducing the incidence of this condition.¹⁴

Historical

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.⁹

Document references

1. Fat Embolism Syndrome, Wheeless Online Textbook of Medicine
2. Buskens CJ, Gratama JW, Hogervorst M, et al; Encephalopathy and MRI abnormalities in fat embolism syndrome: a case report. Med Sci Monit. 2008 Nov;14(11):CS125-9. [abstract]
3. Kirkland L; Fat embolism. emedicine. 2009.
4. Taviloglu K, Yanar H; Fat embolism syndrome. Surg Today. 2007;37(1):5-8. Epub 2007 Jan 1. [abstract]
5. Wang HD, Zheng JH, Deng CL, et al; Fat embolism syndromes following liposuction. Aesthetic Plast Surg. 2008 Sep;32(5):731-6. Epub 2008 May 29. [abstract]
6. Stein PD, Yaekoub AY, Matta F, et al; Fat embolism syndrome. Am J Med Sci. 2008 Dec;336(6):472-7. [abstract]
7. Gurd AR; Fat embolism: an aid to diagnosis.; J Bone Joint Surg Br. 1970 Nov;52(4):732-7.
8. Gurd AR, Wilson RI; The fat embolism syndrome. J Bone Joint Surg Br. 1974 Aug;56B(3):408-16.
9. Shaikh N; Emergency management of fat embolism syndrome. J Emerg Trauma Shock. 2009 Jan;2(1):29-33. [abstract]
10. Wong MW, Tsui HF, Yung SH, et al; Continuous pulse oximeter monitoring for inapparent hypoxemia after long bone fractures.; J Trauma. 2004 Feb;56(2):356-62. [abstract]
11. McDermott ID, Culpan P, Clancy M, et al; The role of rehydration in the prevention of fat embolism syndrome.; Injury. 2002 Nov;33(9):757-9. [abstract]
12. Al-Khuwaitir TS, Al-Moghairi AM, Sherbeeni SM, et al; Traumatic fat embolism syndrome.; Saudi Med J. 2002 Dec;23(12):1532-6. [abstract]
13. Babalis GA, Yiannakopoulos CK, Karliaftis K, et al; Prevention of posttraumatic hypoxaemia in isolated lower limb long bone fractures with a minimal prophylactic dose of corticosteroids.; Injury. 2004 Mar;35(3):309-17. [abstract]
14. Robinson CM; Current concepts of respiratory insufficiency syndromes after fracture.; J Bone Joint Surg Br. 2001 Aug;83(6):781-91. [abstract]

Internet and further reading

• Levy D; The fat embolism syndrome. A review. Clin Orthop Relat Res. 1990 Dec;(261):281-6. [abstract]
• Shaikh N; Emergency management of fat embolism syndrome. J Emerg Trauma Shock. 2009 Jan;2(1):29-33. [abstract]

Acknowledgements