Focussed Assessment Sonography for Trauma (FAST) scan is a rapid, non-invasive technique for assessing abdominal trauma. Haemodynamic instability and a positive FAST result are significantly associated. Sensitivities and specificities of FAST scans for blunt and penetrating trauma, reported by Smith and Wood (2013), are 93.1% and 100%, and 90.0% and 100%, respectively.

Haemorrhage is the most common cause of tissue hypoperfusion (shock) in trauma patients. Haemorrhagic shock may be caused by 1) Haemothorax 2) intra-abdominal bleeding 3) haemorrhage associated with pelvic fracture 4) haemorrhage associated with long bone fractures and 5) external blood loss.