Fat Embolism Syndrome

How fat embolism happens

When a large bone such as the femur breaks, fat from the bone marrow can be forced into torn veins. Fat droplets travel to the lungs and block small vessels. Some pass through to the arterial circulation, reaching the brain, skin, eyes and kidneys. Fat is then broken down into free fatty acids, which inflame and damage blood vessel walls, causing the delayed lung injury typical of the syndrome.

Small amounts of fat enter the circulation in most long-bone fractures, but only a small proportion of patients develop the full syndrome, estimated at a few percent of isolated femur fractures and higher with multiple fractures.

Causes and risk factors

• fractures of the femur, tibia or pelvis, especially closed fractures
• multiple fractures and polytrauma
• young adult age (more common in 10 to 40 year olds)
• delayed fixation of fractures
• orthopedic procedures: reaming the femur for nailing, hip and knee replacement
• rarely: liposuction, bone marrow procedures, pancreatitis, sickle cell crisis with bone marrow infarction, burns

Symptoms

Symptoms usually begin 24 to 72 hours after injury:

Lungs (most common)

• shortness of breath and rapid breathing
• low oxygen levels
• in severe cases, acute respiratory distress syndrome needing a ventilator

Brain

• confusion, agitation or drowsiness
• headache
• seizures, weakness or coma in severe cases

Skin

• a petechial rash: tiny red-brown dots that do not fade when pressed, on the upper chest, armpits, neck, and inside the eyelids and mouth. It appears in a third to half of patients and fades within a week.

Other

• fast heart rate and fever
• retinal changes, fat droplets in urine, low platelets and anemia

Diagnosis

There is no single test. Diagnosis is clinical, based on the typical symptoms after a known risk event, and on ruling out other causes such as pulmonary embolism from a blood clot, pneumonia, head injury or infection. Doctors may use criteria such as Gurd's criteria, which combine major features (breathing problems, brain symptoms, petechial rash) with minor ones (fever, fast heart rate, retinal changes, low platelets, anemia, fat in urine).

Supporting tests:

• oxygen levels and arterial blood gas
• chest X-ray or CT, which may show patchy changes
• brain MRI showing a typical "starfield" pattern of small spots
• blood count for low platelets and anemia

Treatment

There is no specific treatment to remove fat emboli. Care is supportive:

• oxygen therapy, and noninvasive or mechanical ventilation if needed
• fluids and careful circulation support
• early stabilization of fractures, ideally within 24 hours, to reduce ongoing fat release
• prevention of other complications such as blood clots and pressure sores
• steroids have been studied for prevention in high-risk patients, but evidence is mixed and they are not routinely recommended

Outlook

Most patients recover fully with supportive care, often within days to weeks. Mortality is estimated at under 10%, mainly from severe respiratory failure. Neurological symptoms usually resolve, although some people have lasting cognitive effects after severe cases.

Prevention

• early surgical fixation of long-bone fractures
• careful surgical techniques during reaming and joint replacement
• splinting fractures promptly to limit movement before surgery
• close monitoring of oxygen levels and mental status in the first 72 hours after injury

Frequently asked questions

What are the symptoms of fat embolism syndrome?

The classic signs are breathing difficulty with low oxygen, confusion or drowsiness, and a pinpoint rash on the chest, armpits and eyes. They usually appear 1 to 3 days after a long-bone or pelvic fracture.

What causes fat embolism?

Most cases follow fractures of large bones such as the femur, tibia or pelvis, when fat from the bone marrow enters the bloodstream. It can also follow orthopedic surgery, such as joint replacement or reaming of the femur, and rarely other conditions.

How is fat embolism treated?

Treatment is supportive. It includes oxygen, breathing support with a ventilator if needed, fluids, and early surgical stabilization of fractures. Most people recover as the fat is cleared and the inflammation settles.

Is fat embolism the same as a blood clot?

No. A pulmonary embolism is usually a blood clot from the leg veins. Fat embolism involves fat droplets from bone marrow. Both can cause breathlessness after a fracture, so doctors use imaging and other tests to tell them apart.