Focused Assessment with Sonography for Trauma (FAST)

Why Use

FAST is a rapid, non-invasive, and repeatable imaging modality that can guide the surgeon in the decision to operate. Performed in trauma bay (does not require patient transport out of the emergency department, which is risky in unstable patients).

When to Use

FAST should be used liberally in the evaluation of trauma patients. Especially useful in patients with penetrating thoracic trauma and in unstable patients after blunt abdominal trauma.

Formula

Pearls / Pitfalls

Assesses for fluid in the pericardium or abdomen (hemopericardium or hemoperitoneum, respectively). The traditional four views consist of a subxiphoid view of the heart and pericardium, right and left upper quadrant windows, and the pelvis. More recently, the extended FAST (eFAST) has entered into clinical practice with the addition of bilateral thoracic views to assess for pneumo- and hemothoraces. Negative FAST does not exclude injury. Ultrasound is user dependent; therefore, clinicians should be cautious in interpretation of negative FAST. Sensitivities of abdominal and suprapubic views in FAST vary widely, with ranges of 22–98% reported in recent literature ( Richards 2017 , Carter 2015 ). In penetrating thoracic trauma, pericardial view sensitivity approaches 100% ( Matsushima 2017 , Ball 2009 , Rozycki 1999 ) but can miss cardiac injury if there is concomitant pericardial laceration allowing decompression into the left chest ( Ball 2009 ). If clinical suspicion for injury persists despite negative FAST, FAST should be repeated, additional investigations should be performed, or intervention should be pursued, depending on patient’s clinical condition. For tips on ultrasound technique, see Next Steps > Advice.

Management

Suggested management (clinician must consider additional clinical information including hemodynamic stability and clinical suspicion for injury): Pericardial FAST (penetrating thoracic trauma) Positive: emergent surgical intervention recommended. Median sternotomy preferred if the patient is stable; otherwise, use left anterolateral thoracotomy. Equivocal: pericardial window or formal transthoracic echocardiography (TTE) recommended. Negative: close clinical monitoring or discharge recommended, according to clinical suspicion for injury. Abdominal FAST (blunt abdominal trauma) Positive: in the unstable patient, emergent exploratory laparotomy is recommended. In the stable patient, cross-sectional imaging (CT scan) in recommended. Equivocal: in the unstable patient, diagnostic peritoneal aspiration (DPA) is recommended. In the stable patient, cross-sectional imaging (CT scan) is recommended. Negative : in the unstable patient, diagnostic peritoneal aspiration (DPA) is recommended if clinical suspicion for intra-abdominal bleeding exists. In the stable patient, CT scan, close clinical monitoring, or discharge is recommended, according to clinical suspicion for injury.

Critical Actions

Repeating FAST while preparing to perform diagnostic peritoneal aspiration is useful to quickly reassess unstable patients with blunt abdominal trauma with initially negative FAST. Intra-abdominal hemorrhage may not be significant enough on presentation to be FAST-positive initially. Be cautious if pericardial FAST is negative in patients with penetrating thoracic trauma, especially if unstable. Cardiac injuries can decompress through the injured pericardium, most commonly into the left hemithorax, resulting in negative pericardial FAST ( Ball 2009 ). Therefore, unstable patients with this mechanism of injury and FAST finding should undergo a chest x-ray. If it reveals a hemothorax, a chest tube must be placed. Ongoing or high-volume chest tube output in this clinical context may be from cardiac injury.

Advice

FAST results alone should not determine the decision to operate. However, FAST can be a helpful adjunct in clinical decision making, particularly in an unstable blunt trauma patient in order to rapidly assess the chest and abdomen for potential causes of hypotension. Most clinicians use the low frequency phased array ultrasound probe (a.k.a. cardiac probe), to obtain all windows in FAST. Pericardial: place probe in the subxiphoid area and orient towards patient’s left shoulder. Apply downward pressure to look under the costal margin and towards the heart. The heart and pericardium will come into view, allowing inspection for hemopericardium and ultrasound findings of cardiac tamponade. Right upper quadrant: place probe in right anterior to mid axillary line (between 11th–12th ribs). Visualization of the hepatorenal recess (Morison’s pouch) allows the assessment for hemoperitoneum in the right upper quadrant. Blood most likely accumulates here if hemoperitoneum is present. Left upper quadrant : apply transducer firmly onto the skin in left posterior axillary line (between the 9th–10th ribs) to visualize splenorenal and subphrenic spaces. In practice, it is important to remember that the right and left upper quadrant views are often more posterior than anticipated. It can be helpful to bring the probe all the way down to the stretcher in order to best visualize these windows. Suprapubic: place transducer superior to pubic symphysis and fan probe inferiorly to visualize the bladder.

More Information

Interpretation: If pericardial fluid is seen in the subxiphoid view, surgical intervention is warranted. If intra-abdominal fluid is seen in any of the three abdominal views, emergent laparotomy is indicated in unstable patients. Stable patients with intra-abdominal fluid should proceed to cross-sectional imaging. See Next Steps > Management for suggested algorithm.