Detecting Fluid

FAST is a helpful, very early investigation whenever free intraperitoneal, pleural or pericardial fluid is suspected. It is ideal in the complex trauma patient to clarify the source of haemorrhage. Distracting injuries (e.g. painful fractures) may result in abdominal pain being masked, and therefore use of FAST as part of the Advanced Trauma Life Support (ATLS) approach is recommended.

Always start with the RUQ view. The complete scan should be carried out rapidly and should never take any more than three minutes to be carried out. It can be started by a second clinician during the primary survey and certainly repeated during the secondary survey and subsequently. It is not unusual to carry out as many as three scans in a trauma patient.

Learning bite

Repeating the scan several times in a resuscitation setting may enable you to find fluid as it collects.

As there are only a limited number of places where bleeding occurs to produce hypovolaemic shock (i.e. pleural cavity, peritoneal cavity, retroperitoneum/pelvic, long bone and external), a hypovolaemic patient with no long bone fractures, no external haemorrhage and a normal pelvic xray, should be considered to be bleeding into the pleural cavity or peritoneal cavity. It is in these patients where repeated scans become valuable. This is even more the case in a patient with distracting injuries or those with a Glasgow Coma Scale (GCS) below 15.

Free intraperitoneal fluid in a shocked patient may be due to a bleed (e.g. from a ruptured spleen), but it may also be due to other causes such as a ruptured ectopic, a ruptured splenic artery aneurysm, simple ascites or leaked gastric/small bowel content. Hence, the history and clinical scenario are very important in determining the likely cause. The novice would do well to scan for trauma only.

Learning-bite

Do not assume free fluid is blood.