Blunt Abdominal Trauma
Haemodynamically unstable patients

FAST is indicated in the patient who has sustained blunt abdominal trauma who may or may not be haemodynamically unstable. Ultrasound is poor at identifying and grading solid organ injury, bowel injury and retroperitoneal trauma. The FAST examination is directed purely at detecting free intra-peritoneal fluid or the presence of cardiac tamponade.

Trauma Ultrasonography

Introduction
FAST
-  Perihepatic
-  Perisplenic
-  Pelvis
-  Pericardium
Indications
How good is FAST?
Thoracic Ultrasound
References
 

Haemodynamic instability and free intra-peritoneal fluid mandates a laparotomy for intra-abdominal haemorrhage. In the presence of haemorrhagic shock but a negative FAST examination, other sites of haemorrhage must be sought and controlled. Serial FAST examinations may be required. Thoracic haemorrhage may require thoracotomy, pelvic haemorrhage angiographic embolisation. Retroperitoneal haemorrhage from vascular injury remains a possibility with a negative FAST.

Non-haemorrhagic shock is also a possibility. FAST can detect a pericardial collection causing cardiac tamponade, but profound hypoxia, tension pneumothorax and blunt myocardial injury must also be excluded.

There is a significant false-negative rate for the FAST examination (see next page). This is in part due to the FAST examination being carried out early in the resuscitation phase - when only a small amount of free fluid may be visualised in the peritoneal cavity. Serial physical examination, repeat FAST examinations or Diagnostic Peritoneal Lavage (DPL) should be considered when there is on-going haemorrhagic shock despite an initially negative FAST.

Indeterminate FAST examinations do occur. Patients who are obese, or who have subcutaneous emphysema may have suboptimal, and therefore inconclusive, scans. In the haemodynamically unstable patient with an indeterminate scan, a judgement will have to be made based on mechanism of injury, clinical signs, injury pattern and phsyiological response. A diagnostic peritoneal lavage may be necessary to exclude intraperitoneal injury.

Haemodynamically stable patients

Ultrasound is also useful in haemodynamically stable patients where physical examination of the abdomen is inadequate or compromised. A negative FAST will exclude significant intraperitoneal fluid collections and can therefore be used as a screening tool. A negative examination is highly suggestive, but does not exclude, significant intra-abdominal injury. Hollow-organ injury may be missed on ultrasound examination if there has not been leakage of enough gut contents to detect free fluid. Retroperitoneal injuries are also difficult or impossible to detect with ultrasonography.

If the FAST is positive or indeterminate, and the patient is haemodynamically stable a CT scan of the abdomen and pelvis is indicated.

How Good is the FAST?
Alex Ng,trauma.org 6:12, December 2001