ventricle of the heart to be pumped throughout the body in the systemic circulation. 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). 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. Biochemical theory - Following trauma, an inflammation causes bone marrow to liberate fatty acids into the venous circulation. This is achieved through the increased activity of lipoprotein lipase which break down triglycerides into free fatty acids. Both the release of fatty acids and the inflammation causes damage to the capillary beds of the lungs and other organs, causing interstitial lung disease, chemical pneumonitis, and acute respiratory distress syndrome (ARDS). This theory can help to explain non-traumatic causes of fat embolism. Diagnosis 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. There are three major diagnostic criteria proposed for fat embolism syndrome, however, none of them are validated and accepted universally. However, Gurd and Wilson's criteria for fat embolism become more commonly used when compared to the other two diagnostic criteria. Gurd and Wilson's criteria Major criteria Axillary or subconjunctival petechiae Hypoxaemia PaO2 <60 mm Hg, FIO2 = 0.4 Central nervous system depression disproportionate to hypoxaemia Pulmonary oedema Minor criteria Tachycardia more than 110 beats per minute Pyrexia more than 38.5 °C Fat globules present in urine Changes in renal function (reduced urine output) Drop in haemoglobin values (more than 20% of the value upon admission) Drop in haematocrit values Drop in platelet values (more than 50% of the value upon admission) Increasing erythrocyte sedimentation rate (ESR) (greater than 71 mm per hour) Fat globules present in the sputum Emboli present in the retina on fundoscopy A least two positive major criteria plus one minor criteria or four positive minor criteria are suggestive of fat embolism syndrome. Fat embolism syndrome is a clinical diagnosis. There are no laboratory tests sensitive or specific enough to diagnose FES. Such laboratory tests are only used to support the clinical diagnosis only. Chest X-ray may show diffuse interstitial infiltrates while chest CT scan will show diffuse vascular congestion