US is also commonly used to evaluate patients presenting
with abdominal trauma in the acute setting. The FAST
(focused assessment with sonography for trauma) examination
is a rapid examination that is proven to accurately
identify major abnormalities such as intraperitoneal hemorrhage
and free air as well as identify specific injury patterns
[25]. US determination of IVC diameter has been shown to
be an acceptable measure of blood loss and can be rapidly
performed as an additional parameter in FAST scans [24].
In a study conducted by Lyon et al [26] that involved
31 volunteer blood donors, US was capable of accurately
detecting losses of 450 mL of blood [26]. In clinically stable
patients who present without symptoms of shock, a finding of
an IVC diameter 9 mm should raise suspicion for hypovolemia
and a preshock state [23]. Although the IVC
diameter fluctuates in correspondence with changes in
intrathoracic pressure during breathing, both IVC calibres on
expiration and on inspiration are significantly lower in shock
patients [24]. General advantages of US include its portability,
accessibility, and lack of ionizing radiation, but wellrecognized
limitations such as interoperator variability,
poor imaging of patients with obesity, and those with an
increased volume of abdominal bowel gas also apply to the
assessment of the trauma patient [25].