Focused Assessment with Sonography for Trauma (FAST) Exam: Image Acquisition

The FAST Exam is designed to screen for several kinds of life-threatening pathology most relevant to the care of trauma patients. Hemopericardium, pneumothorax, hemothorax, and free peritoneal fluid. This FAST protocol emphasizes several key concepts that, in our experience, are underappreciated.

One, the utility of the parasternal long axis view as an adjunct. Two, the pattern of free peritoneal fluid in the left upper quadrant. And three, the importance of adding a sagittal to the traditional transverse pelvic view.

To begin, position the patient supine with the chest and abdomen exposed. For scanning, apply gel to the ultrasound probe. To examine the right upper quadrant window, place the probe on the patient's right side along the mid to posterior axillary line in the seventh to ninth intracoastal space.

Then, adjust the probe positioning until a view containing the liver, right kidney, and hepato-renal interface, or Morison's pouch, becomes visible. Next, adjust the screen depth such that the hepato-renal interface occupies the middle third of the screen. Adjust the gain until the liver and kidney appear slightly hyperechoic, but not too dark or too bright that they are indistinguishable from their hyperecoic capsules.

Then click on Acquire. During acquisition, fan across the hepato-renal interface anteriorly to posteriorly, examining the free fluid around the caudal-most tip of the liver and between the liver and the kidney. To examine the left upper quadrant window, place the probe on the patient's left flank along the mid to posterior axillary line in the fifth to seventh intracoastal space.

Then, adjust the probe positioning until a view containing the spleen, diaphragm, and spleno-renal interface becomes visible. Adjust the screen depth to bring the spleno-diaphragmatic interface to the middle third of the screen. Then adjust the gain as demonstrated to visualize the spleen and kidney distinguishable from their capsules.

Now, click on Acquire. While recording, fan across the spleen and diaphragm front to back, inspecting the hypoechoic or anechoic stripe between the spleen and diaphragm, and the spleen and left kidney. If the spleno-renal interface is inadequately visualized, slide the probe caudily until the spleno-renal interface is visualized and inspected for a hypoechoic or anechoic stripe between the kidney and spleen.

To examine the suprapubic window, place the probe cranially to the pubic synthesis. And angle the ultrasound beam 10 to 20 degrees caudily into the pelvis, with the indicator mark pointing to the patient's right side. Next, adjust the probe positioning to obtain a view containing the sex-specific structures.

Adjust the screen depth so that the bladder is focused on the screen. Then, adjust the screen gain to visualize the urine in the bladder as anechoic, and the space below the bladder is distinct from the posterior bladder wall. After clicking on Acquire, fan across the pelvis posteriorly to anteriorly to inspect the view for an anechoic stripe.

To examine the sagittal suprapubic window starting with the transverse view, rotate the probe 90 degrees clockwise to align it in the sagittal plane. Next, adjust the probe positioning to obtain a view containing the sex-specific structures. Adjust the screen depth as demonstrated previously.

And screen gain until urine in the bladder appears anechoic, and the space below the bladder is distinct from the posterior bladder wall. Click on Acquire. And fan across the pelvis left to right and back to inspect the view for an anechoic stripe.

The right upper quadrant view is considered negative when there's an absence of free peritoneal fluid, while a positive exam shows the presence of free fluid around the caudal tip of the liver. The upper left quadrant view is termed negative when it reveals no peritoneal fluid in the perisplenic space. In contrast, a left upper quadrant view is termed positive when it shows fluid between the spleen and diaphragm, or between the spleen and kidney.

The female pelvic views are considered negative when no free peritoneal fluid is observed. And positive when the free fluid is observed in the rectouterine space and spaces lateral to the uterus. Similarly, the male pelvic views are considered negative when no free peritoneal fluid was observed.

And positive when the free fluid was observed in the rectal vesicle space posterior to the bladder. Although the FAST exam is most clearly validated to triage unstable blunt trauma patients, the exam has emerging utility in other settings such as perioperative or peripartum hemodynamic instability, screening for intraperitoneal bladder rupture, and as part of the preoperative assessment of patients with liver disease. Beginners often struggle by mistaking an epicardial fat pad for hemopericardium, or by missing fluid in the left upper quadrant or pelvis.

These errors can be ameliorated respectively by one, adding a parasternal long view. Two, visualizing the spleno-diaphragmatic interface. And three, by obtaining both a transverse and sagittal view of the pelvis.