Which clinical manifestation can a client experience during a fat embolism syndrome FES )?

Fat embolism syndrome occurs when fat enters the blood stream [fat embolism] and results in symptoms.[1] Symptoms generally begin within a day.[1] This may include a petechial rash, decreased level of consciousness, and shortness of breath.[1] Other symptoms may include fever and decreased urine output.[2] The risk of death is about 10%.[2]

Fat embolism most commonly occurs as a result of fractures of bones such as the femur or pelvis.[3][1] Other potential causes include pancreatitis, orthopedic surgery, bone marrow transplant, and liposuction.[3][2] The underlying mechanism involved widespread inflammation.[3] Diagnosis is based on symptoms.[2]

Treatment is mostly supportive care.[4] This may involve oxygen therapy, intravenous fluids, albumin, and mechanical ventilation.[2] While small amounts of fat commonly occur in the blood after a bone fracture,[3] fat embolism syndrome is rare.[4] The condition was first diagnosed in 1862 by Zenker.[1]

Signs and symptoms[edit]

Symptoms of fat embolism syndrome [FES] can start from 12 hours to 3 days after diagnosis of the underlying clinical disease. The three most characteristic features are: respiratory distress, neurological features, and skin petechiae.[5] Respiratory distress [present in 75% of the cases] can vary from mild distress which requires supplemental oxygen to severe distress which requires mechanical ventilation. For neurologic features, those who have FES may become lethargic, restless, with a drop in Glasgow Coma Scale [GCS] due to cerebral oedema rather than cerebral ischaemia. Therefore, neurological signs are not lateralised to one side of the body. In the severe form of cerebral odema, a person may become unresponsive. Petechiae rash usually happens in 50% of the patients. Such skin manifestation is temporary and can disappear within one day.[6] The fat embolism syndrome can be divided into three types:[5]

• Subclinical FES - It manifests as reduced partial pressure of oxygen [PaO2] on arterial blood gas [ABG] with deranged blood parameters[5] [reduced haemoglobin or thrombocytopenia][6] associated with fever, pain, discomfort, tachypnoea, tachycardia. However, there is no respiratory distress. However, it is often confused with post-operative symptoms of fever, pain, and discomfort.[5]
• Subacute FES [non-fulminant FES] - The three characteristic features of fat embolism are present: respiratory distress, neurological signs, and skin petechiae. Petechiae are seen on the chest, axilla, shoulder, and mouth.[5] Occulsion of dermal capillaries by the fat emboli result in petechial rash. Petechiae rash occurs in 50 to 60% of the cases.[7] Neurologic signs such as confusion, stupor, and coma may be present. These are usually temporary and do not happen on one side of the body. Respiratory distress can be mild and tends to improve on the third day. Retinal changes similar to Purtscher's retinopathy may also be present.[5] Retinal changes happens in 50% of the patients with FES. These are the cotton wool exudates and small haemorrhages along the retinal vessels and macula.[7]
• Fulminant FES - This type of FES is much rarer than the above two types. It usually happens within the first few hours of the injury. The three characteristics of FES existed in the most severe form. Cause of death is usually due to acute right heart failure.[5]

Causes[edit]

Orthopaedic injuries especially fractures of the long bones are the most common cause of fat embolism syndrome [FES]. The rates of fat embolism in long bone fractures vary from 1% to 30%. The mortality rate of fat-embolism syndrome is approximately 10–20%.[7] However, fat globules have been detected in 67% of those with orthopaedic trauma and can reach as high as 95% if the blood is sampled near the fracture site. As the early operative fixation of long bone fractures became a common practice, the incidence of FES has been reduced to between 0.9% and 11%.[6]

Other rare causes of fat embolism syndrome are:[7][6]

• Severe burns
• Liver injury
• Closed chest cardiac massage [during cardiopulmonary resuscitation]
• Bone marrow transplantation
• Liposuction
• Parenteral lipid infusion
• Decompression sickness
• Extracorporeal circulation
• Acute haemorrhagic pancreatitis
• Alcoholic liver disease
• Prolonged corticosteriod therapy
• Sickle cell disease
• Carbon tetrachloride poisoning
• Osteomyelitis

Pathophysiology[edit]

Histopathology of a pulmonary artery with fat embolism [seen as multiple empty globular spaces on this H&E stain since its processing dissolves fat]. There is a bone marrow fragment in the middle, and multiple single hematopoietic cells in the blood, being evidence of fracture as the source of the embolism.

Once fat emboli enter the blood circulation, they can lodge at various sites of the body, most commonly in the lungs [up to 75% of cases]. However, it can also enter the brain, skin, eyes, kidneys, liver, and heart circulation, causing capillary damage, and subsequently cause organ damage in these areas. There are two theories that describe the formation of a fat embolus:[6]

• Mechanical theory - Following trauma, fat is released directly from the bone marrow into the circulation. This is because after trauma, an elevated pressure in the medullary cavity [central cavity of the bone where the bone marrow are stored] causes the release of fat globules into the venous system supplying the bone. Since venous blood returns to the right heart and is pumped to the lungs for reoxygenation, the fat globules often get lodged in the pulmonary circulation. Fat globules may also pass through lung circulation back into the left ventricle of the heart to be pumped throughout the body in the systemic circulation.[8] They may also reach the systemic circulation through a patent foramen ovale [a hole communicating the right atrium directly to the left atrium of the heart].[6] If fat globules obstruct 80% of the lung capillary network, the resulting back pressure on the right heart increases workload and causes right heart dilatation through cor pulmonale, leading to acute right heart failure.[5]
• Biochemical theory - Following trauma, an inflammation causes bone marrow to liberate fatty acids into the venous circulation.[6] This is achieved through the increased activity of lipoprotein lipase which break down triglycerides into free fatty acids.[7] Both the release of fatty acids and the inflammation causes damage to the capillary beds[6] of the lungs and other organs, causing interstitial lung disease, chemical pneumonitis,[7] and acute respiratory distress syndrome [ARDS].[6] This theory can help to explain non-traumatic causes of fat embolism.[7]

Diagnosis[edit]

Fat embolism is presence of fat particles in the micro-circulation of the body. Meanwhile, fat embolism syndrome is the clinical manifestation as the result of fat particles lodging in the body micro-circulation.[6] There are three major diagnostic criteria proposed for fat embolism syndrome, however, none of them are validated and accepted universally.[6] However, Gurd and Wilson's criteria for fat embolism become more commonly used when compared to the other two diagnostic criteria.[9]

Gurd and Wilson's criteria[edit]

Major criteria[6][7][9]

• Axillary or subconjunctival petechiae
• Hypoxaemia PaO2