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
If the FAST is positive or indeterminate,
and the patient is haemodynamically stable a CT scan
of the abdomen and pelvis is indicated.
6:12, December 2001