What is a fat embolism?
Fat embolism is where large globules of fat travel in the bloodstream. Since fat cannot dissolve in blood on its own, it remains in a solid form and there is a risk that it may block a smaller blood vessel. It is more likely to obstruct a blood vessel that is already narrowed (stenosis) with conditions like atherosclerosis. However, even healthy blood vessels that are not narrowed in any way may become obstructed with these fat globules.
Fat is not the only type of solid material that can form and travel in the bloodstream. More commonly, a blood clot forms at one site, breaks away and travels through the blood to lodge elsewhere. A fat embolism tends to occur after injury that either leads to a fracture or is extensive. It can sometimes arise with other diseases despite there being no trauma or fracture of a bone. In severe cases where medical treatment is not forthcoming, fat embolism can be fatal.
Fat embolism syndrome
Fat embolism syndrome (FES) is when macroglobule of fat (emboli) lodges in the small blood vessels of the lung, brain and other sites. This causes acute respiratory failure, brain injury and spots of bleeding under the skin (petechial rash). It tends to occur within 1 to 3 days after an injury like a fracture of a large bone. Here fat or even bone marrow may enter the bloodstream. There is sometimes confusion over similar terms like a thrombus and embolus. Thrombus is a blood clot that forms at a point in the blood vessel and remains there. If it breaks away then it is known as an embolus. However, any other solid material in the bloodstream is known as an embolus, including fat, plastic from catheters, parasites and cancer cells. Even though the fat emboli may cause an incomplete obstruction and this blockage can be temporary, fat embolism syndrome is a serious condition that requires medical intervention.
Fat embolism reasons
It is not clear exactly how large fat globules enter the bloodstream in every instance . There are possibly two ways by which this occurs.
- Large droplets of fat are released into the bloodstream as a result of injury dislodging it from its original site or with the biochemical changes that arise with severe trauma. This possibly explains the development of fat emboli with trauma.
- Fatty acids that normally travel in the blood attached to chylomicrons coalesce due to the effects of certain hormones in diseased states. This possibly explains the reason for fat emboli that occurs in non-traumatic cases.
The fat emboli may then break down (hydrolysis) into smaller free fatty acids and travel via the bloodstream to all parts of the body where it causes inflammation at multiple sites.
Fat embolism causes
Most cases of fat embolism arise after some form of trauma. However, there are various non-traumatic causes as well.
Blunt trauma is the most common way that a fat embolism arises. It may be associated with various tissue injuries. Fat emboli with trauma may arise after :
- Fractures, more likely with simple than compound fractures.
- Extensive soft tissue injury following car accidents or assault.
- Surgery, and in particular orthopedic procedures and liposuction.
- Severe burns
- Bone marrow biopsy
These causes are less likely to lead to fat emboli.
- Acute pancreatitis
- Corticostroid use over a prolonged period.
- Diabetes mellitus
- Decompression sickness
- Fatty liver disease
- Sickle cell disease
Fat embolism symptoms
Fat emboli on its own is usually asymptomatic until the fatty globules lodge in a blood vessel and block it. The blood vessels of the lungs and the brain are more commonly affected by fat emboli, a condition known as fat embolism syndrome. However, it is possible for any organ or structure in the body to be affected. Furthermore free fatty acids that may break away from the fat globule can cause irritation of tissue even if its blood vessels are not blocked.
Lungs and Heart
- Rapid heart rate (tachycardia)
- Rapid breathing (tachypnea)
- Chest pains
The characteristic skin rash seen in fat embolism syndrome is a petechial rash. It appears as tiny red, brown to purple spots due to small hemorrhaging (blood loss) under the skin. Typically the rash is non-palplable meaning that it does not feel any different from the surrounding normal skin. These hemorrhages may also be seen in the eye (subconjunctival hemorrhage) and inner lining of the mouth (oral purpura).
- Little or no urine (oliguria or anuria)
- Blood in the urine (hematuria)
- Headache from low blood oxygen levels (hypoxia) or injury to the vessels or linings of the brain.
- Fever with high spiking temperatures.
Fat embolism diagnosis
A diagnosis of fat embolism syndrome may be made by the presence of certain clinical features. This is divided into major and minor criteria. A positive diagnosis is made if there is at least one major criteria and four minor criteria in addition to the presence of fat microglobulinemia.
- Respiratory failure
- Brain dysfunction
- Petechial rash
- Rapid heart rate (tachycardia)
- Rapid breathing rate (tachypnea) above 35 breaths per minute
- Fever above 39°C
- Low blood oxygen levels
- Abnormalities visible in the retina such as cotton wool exudates and small hemorrhages and sometimes even fat globules seen in retinal vessels.
- Kidney dysfunction
- Low platelet count (thrombocytopenia)
- Low hemoglobin (anemia)
- Elevated ESR (erythrocyte sedimentation rate)
- Chest X-ray abnormalities (diffuse alveolar infiltrates)
- Fat macroglobulinemia
Diagnostic investigations help with confirming the diagnosis and assessing the extent of the condition.
- Blood tests like arterial blood gas, ESR and hematocrit.
- Urine analysis
- Sputum examination
- Chest x-ray
- Computed tomography (CT) scan
- Brain MRI (magnetic resonance imaging)
- Transcranial Doppler ultrasonography
- Transesophageal echocardiography (TEE)
Fat embolism treatment
Treatment for a fat embolism is largely supportive. This means that different treatment measures are initiated to :
- Improve blood oxygen levels by providing oxygen and even mechanical ventilation.
- Stabilize heart rate and blood pressure as is necessary.
- Limit or even restrict fluid intake to minimize fluid accumulation in the lungs.
Corticosteroids are the only drugs that are used for a fat embolism. High doses may prevent fat embolism syndrome while lower doses may be effective in minimizing inflammation. However, there is some controversy over its use in the treatment and manage of fat embolism syndrome. There is no significant evidence to support the use of one corticosteroid over another. Methylpredisolone is the most commonly used steroid for fat embolism syndrome.
Surgery is not necessary for treating fat embolism syndrome. However, early surgical intervention for stabilizing long bone fractures can help to reduce the risk of developing fat embolism syndrome. Reaming or nailing the marrow can help to reduce the quantity of fat embolization. A filter placed within the inferior vena cava (IVC) may reduce the fat volume in the bloodstream from reaching the heart and entering the general circulation again.