Emergency Ultrasound: FAST and Focused Echo Overview

Point-of-care ultrasound (POCUS) has established itself as an indispensable tool in emergency medicine. What previously required time-consuming imaging in the radiology department is now available to you directly at the bedside – in seconds. Whether in the trauma bay, on the emergency physician response vehicle, or during a resuscitation: emergency ultrasound provides critical information that immediately influences therapeutic decisions. Two protocols are at the center: the FAST protocol for detecting free fluid and the focused echo for cardiac assessment. Both complement each other and can be seamlessly integrated into existing algorithms – provided you master the technique and know when to apply the probe.

The FAST Protocol: Systematic Search for Free Fluid

Basic Principle and Indications

FAST stands for Focused Assessment with Sonography in Trauma. The protocol was developed to rapidly detect free fluid in the abdomen and pericardium in trauma patients. The central clinical question is not "What is injured?" but rather "Is there free fluid – yes or no?" This binary question is what makes the protocol so efficient.

The indication is broad: every patient with blunt or penetrating thoracic or abdominal trauma benefits from a FAST examination. Beyond that, the protocol has also proven valuable in non-traumatic settings – such as in cases of unclear abdominal pathology, suspected ascites, or hemodynamic instability of unknown origin.

The Four Classic Views

The FAST protocol comprises four standardized probe positions:

1. Right upper quadrant (Morrison's pouch): The curvilinear probe is placed in the mid-axillary line at the level of the 10th–12th ribs on the right. You are looking for the hepatorenal recess – the most dependent point between the liver and the right kidney in the supine position. Free fluid appears as an anechoic (black) stripe between the organ capsules. This view has the highest sensitivity of all FAST positions.

2. Left upper quadrant (Koller's pouch): The probe is positioned in the posterior axillary line on the left, slightly more cranial than on the right (8th–11th ribs). Here you assess the splenorenal recess. Caution: this view is technically more challenging because the spleen is smaller and the stomach can cause artifacts. Don't forget to also inspect the tip of the spleen and the subdiaphragmatic space.

3. Suprapubic view: Transverse and longitudinal views above the symphysis. The filled urinary bladder serves as an acoustic window. Free fluid collects in the rectovesical pouch (Douglas pouch) in men and in the pouch of Douglas (between the uterus and rectum) in women. An empty bladder – for example after catheterization – significantly limits the assessment.

4. Subxiphoid (pericardial effusion): The probe is placed flat beneath the xiphoid process, angled cranially. The goal is to visualize the heart with the pericardium. A pericardial effusion appears as an anechoic rim around the heart. This view simultaneously serves as the bridge to the focused echo.

eFAST: The Extended Variant

The extended FAST (eFAST) supplements the four classic views with bilateral thoracic ultrasound for detecting pneumothorax. The probe is placed anteriorly in the 2nd–3rd intercostal space at the midclavicular line. You are looking for lung sliding – the respiratory-synchronous sliding of the visceral pleura against the parietal pleura.

• Lung sliding present: Pneumothorax at this location is virtually excluded (negative predictive value >99%)
• Lung sliding absent: Highly suspicious for pneumothorax – in M-mode, the stratosphere sign (barcode sign) appears instead of the normal seashore sign
• Lung point: The location where lung sliding transitions to absent sliding is pathognomonic for pneumothorax and allows a rough estimation of its extent

Additionally, the eFAST can be used to search for pleural effusions – identifiable as an anechoic zone above the diaphragm in the lateral views.

Limitations and Pitfalls

The FAST examination is a screening tool, not definitive diagnostics. You need to be aware of the following limitations:

• Sensitivity with small volumes: FAST only becomes reliably positive starting at approximately 200–500 ml of free fluid. Small amounts – especially in the early phase – are missed.
• Retroperitoneal hemorrhage: The FAST protocol does not detect retroperitoneal hematomas (kidneys, pelvis, aorta). A negative FAST does not rule out a significant intra-abdominal injury.
• Hollow organ injuries: Bowel and bladder perforations are not reliably detected.
• Obesity and subcutaneous emphysema: Significantly impair image quality.
• Serial FAST: If the initial exam is negative but clinical suspicion persists, the examination should be repeated after 15–30 minutes. Serial application significantly increases sensitivity.

A negative FAST with unstable hemodynamics after trauma never replaces CT imaging, provided it is available and the patient is stable enough for transport.

Focused Echo: The Heart in Focus

Indications and Clinical Questions

Focused echocardiography goes beyond the simple pericardial effusion assessment of the FAST protocol. It answers targeted, binary questions about cardiac function in hemodynamically unstable patients:

• Pericardial effusion / cardiac tamponade?
• Right ventricular dilatation (suggesting pulmonary embolism or right heart failure)?
• Grossly reduced left ventricular function?
• Hypovolemia (hyperdynamic, small ventricles – "kissing walls")?
• Wall motion abnormalities (regional akinesia suggesting acute coronary syndrome)?

Standard Views of the Focused Echo

Four views form the backbone of focused echocardiography:

1. Subcostal four-chamber view: Identical to the FAST pericardial view, but with an expanded scope of assessment. Ideal for pericardial effusion diagnosis and gross evaluation of chamber size relationships. Advantage: can be performed even during ongoing chest compressions, as the probe is not in the compression zone.

2. Parasternal long axis (PLAX): Probe placed left parasternal in the 3rd–4th intercostal space, indicator directed toward the right shoulder. Shows the left ventricle, mitral valve, aortic valve, and the proximal aorta. Allows assessment of LV function (fractional shortening), pericardial effusion, and differentiation of pericardial effusion vs. pleural effusion (the descending aorta serves as an anatomical landmark: fluid between the aorta and heart = pericardial effusion; fluid posterior to the aorta = pleural effusion).

3. Parasternal short axis (PSAX): Rotation of the probe 90° from the PLAX position. Shows the LV in cross-section at the papillary muscle level. Ideal for assessing regional wall motion and septal behavior. In right heart strain, the typical D-sign appears: the septum is pushed to the left, and the LV appears D-shaped instead of round.

4. Apical four-chamber view (A4C): Probe at the cardiac apex (5th intercostal space, midclavicular line), indicator pointing to the left. Shows all four chambers. Allows direct size comparison of RV and LV. Normally, the RV is significantly smaller than the LV (RV:LV ratio <0.6:1). An RV:LV ratio >1:1 indicates significant right heart strain.

Recognizing Cardiac Tamponade

Cardiac tamponade is one of the most important sonographically diagnosable emergency conditions because it requires immediate intervention. The diagnosis is based on the following findings:

• Anechoic rim circumferentially around the heart (>2 cm in diastole suggests a hemodynamically significant effusion)
• Diastolic collapse of the right atrium (early sign)
• Diastolic collapse of the right ventricle (specific sign)
• Dilated inferior vena cava without respiratory variability (>2.1 cm, collapsibility <50%)
• Clinical findings: Hypotension, jugular venous distension, muffled heart sounds (the classic Beck's triad is rarely complete in practice)

Ultrasound-guided pericardiocentesis via the subxiphoid approach is the therapeutic gold standard in the acute setting. Aspiration of as little as 20–30 ml can produce dramatic hemodynamic improvement in tamponade.

Inferior Vena Cava Assessment

As a supplement to the focused echo, assessment of the inferior vena cava (IVC) provides valuable information about volume status:

• IVC <2.1 cm with >50% inspiratory collapse: Suggests low CVP, indicates hypovolemia
• IVC >2.1 cm without inspiratory collapse: Suggests elevated CVP (right heart failure, tamponade, tension pneumothorax, volume overload)

Important: IVC assessment is one component of the overall clinical picture and should never be used in isolation to guide therapy. Different interpretation rules apply in mechanically ventilated patients.

Integration into Resuscitation Algorithms

POCUS During CPR

The AHA guidelines recommend the use of point-of-care ultrasound during resuscitation, provided it does not prolong interruptions to chest compressions. In practice, this means:

• Sonography only during planned rhythm analysis pauses (<10 seconds)
• Pre-position the probe subxiphoidally before the pause begins
• One team member is exclusively responsible for sonography and reviews the saved loop after CPR resumes
• No additional pauses for imaging

Identifying Reversible Causes

Emergency ultrasound is the fastest tool for identifying the 4Hs and 4Ts – the reversible causes of cardiac arrest:

Reversible Cause	Sonographic Finding
Hypovolemia	Empty chambers, collapsed IVC, free abdominal fluid (FAST)
Cardiac tamponade	Pericardial effusion with chamber collapse
Thromboembolism (PE)	RV dilatation, D-sign, possible thrombus in right heart chambers
Tension pneumothorax	Absent lung sliding, absent lung pulse

When one of these causes is identified, causal therapy can be initiated immediately: pericardiocentesis for tamponade, chest tube for tension pneumothorax, thrombolysis for massive pulmonary embolism, volume resuscitation for hypovolemia.

Prognostic Significance

Sonographic findings during resuscitation also have prognostic relevance. The detection of organized cardiac activity (recognizable wall motion) in pulseless electrical activity (PEA) is associated with a significantly higher probability of survival compared to the finding of cardiac standstill (complete absence of any wall motion). The latter correlates with a very poor prognosis but cannot be used in isolation as the sole criterion for terminating resuscitation efforts.

Practical Tips

Image Optimization and Common Errors

• Gel selection: Use plenty of gel. In an emergency, sterile gloves filled with water can serve as a standoff pad.
• Probe selection: Curvilinear probe (3.5–5 MHz) for FAST and subxiphoid echo. Sector probe (phased array, 1–5 MHz) for transthoracic echocardiography – it fits between the ribs.
• Set the depth correctly: The most common source of error is insufficient penetration depth. For FAST, you need to see the posterior kidney and the entire organ. For echo, the entire left ventricle should be visualized.
• Confusing pericardial effusion with pleural effusion: The descending aorta in the PLAX is your reference structure (see above).
• Confusing free fluid with fat tissue: Perirenal fat can appear hypoechoic and mimic free fluid. However, fat is usually more echogenic than simple fluid and does not shift with changes in patient positioning.

Structured Documentation

Document every POCUS finding in a standardized manner:

• Clinical question
• Finding (positive/negative, semi-quantitative if applicable)
• Consequence (therapeutic decision)
• Image archiving (save loop or still image)

Clean documentation is not only medicolegal protection but also improves team communication and follow-up assessment.

Regular Training

Emergency ultrasound is a psychomotor skill. Like any manual competency, quality declines without regular practice. Studies show that after an initial course, examination quality significantly decreases within six months if not practiced regularly. Integration into daily clinical routine – for example through systematic POCUS during every trauma bay activation – is the most effective way to maintain competency.

Hands-On Training

Emergency ultrasound thrives on practical application under realistic conditions. Knowing the algorithms is one thing – correctly positioning the probe under stress, interpreting images in seconds, and drawing the right therapeutic conclusions is another. In the Emergency Physician Refresher Course by Simulation Tirol, you train these skills in realistic scenarios, including the integration of POCUS into resuscitation and trauma bay algorithms. Hands-on training with structured feedback offers the opportunity to build confidence in decision-making situations where every second counts.