FAST Exam in Blunt Abdominal Trauma
Andrew Matella DO
1 year old male presents to the ED after being struck in the abdomen with a baseball bat several times just prior to arrival. Patient complaining of right sided abdominal pain.
Vitals: HR 110 BP 145/89 RR 24 Spo2 99% on RA Temp 98.6
Whats the plan?
Morphine for pain, basic labs, slap a lidocaine patch on there
Norco prescription with incentive spirometer and send home
Patient complains of worsening pain!
HR 122 BP 115/75 RR 25 Spo2 98% on RA Temp 98
Did we miss a diagnosis?
Let's look at the FAST scan criteria!
How do we stratify risk within in our patient's with the FAST Scan?
The Unstable Patient
In hemodynamically unstable patients (SBP <90 mm Hg) with blunt abdominal trauma, bedside ultrasound, when available, should be initial diagnostic modality performed to identify the need for emergent laparotomy (B level recommendations per ACEP)
Multiple large studies have found that the specificity of a positive FAST exam in an unstable patient approaches 100% [1,4,6]
Keep looking for signs of shock
Resuscitate and reevaluate with FAST Exam or CT if stable enough
Sensitivity varies (anywhere from 79-100% [1,4])
In order to cause hypotension from intraperitoneal bleed, you need to lose close to ~2L of blood and usually only require 150-200cc of blood in abdomen to be seen on FAST
The Stable Patient
If positive, current recommendations from ACEP/UTD/EMRAP/Tintinelli’s is to obtain a CT scan to further evaluate the specific location and severity of injury
If negative ,FAST in HDS patient DOES NOT rule out intra-abdominal injury
FAST + has about 99% specificity based off of several large studies146, sensitivity varied. Retrospective cohort study with 421 patients demonstrated sensitivity of 67% in this group .
Large prospective study of 2100 patients demonstrated sensitivity of 41%6.
Patient has a negative FAST, but you're still suspicious of injury. Let's take a look at some other signs:
HDS patient with negative FAST but increased likelihood of intraabdominal injury :
-The presence of a seat belt sign (LR+ 5.6-9.9).
-Abdominal rebound tenderness (LR+ 6.5, 95% CI: 1.8-24).
-Abdominal distension (LR+ 3.8, 95% CI: 1.9-7.6).
-Abdominal guarding (LR+ 3.7, 95% CI: 2.3-5.9).
-Concomitant femur fracture (LR+ 5.2, 95% CI: 2.1-4.1).
-Abdominal tenderness on exam or ecchymosis
-Pelvic or lower rib fractures
-Costal margin tenderness
-Hematocrit less than 30%
-Hematuria (>25 RBCs/hpf)
-Mechanism of injury
In the end...
Gold Standard: CT Scan
If the CT is negative:
Level B Recommendations
Clinically stable patients with isolated blunt abdominal trauma can be safely discharged after a negative result for abdominal CT with intravenous (IV) contrast (with or without oral contrast).
Level C Recommendations
Further observation, close follow-up, and/or imaging may be warranted in select patients based on clinical judgment.
Limitations of Ultrasound:
Need at least 150-200cc of fluid in order to detect on US
Unable to differentiate blood from ascitic fluid, urine and peritoneal dialysate
Inability to determine exact source of the bleed
US unable to visualize retroperitoneal structures and solid organ subcapsular injuries
Can miss hollow viscus injuries
Image quality can be limited due to body habitus or bowel gas
Take Away Points:
1) In the unstable patient, the US is the gold standard in blunt abdominal trauma. If positive, they should be going to the OR.
2) Specificity of the FAST exam near 100%.
3) You cannot reliably exclude intraabdominal injury in the HDS patient with negative FAST. A negative FAST on these patient’s basically means nothing.
4) Just like everything in medicine, clinical gestalt/physical exam extremely important in next steps for the HDS patient with a negative FAST.