Medical School · Year 3 · Emergency Medicine · includes a quiz and discussion video

Seminar 17: Point-of-Care Ultrasound

Emergency Medicine Clerkship

Learning Objectives

By the end of this seminar, students will be able to:

1. Select the appropriate ultrasound transducer and optimize image acquisition using fundamental knobology and orientation conventions
2. Perform a complete FAST and extended FAST examination and accurately interpret findings in the trauma patient
3. Obtain standard cardiac ultrasound views and identify pericardial effusion, cardiac tamponade, and right ventricular strain
4. Recognize sonographic signs of pulmonary pathology including pneumothorax, pleural effusion, pulmonary edema, and consolidation
5. Evaluate the abdominal aorta, biliary system, kidneys, and vascular structures using bedside ultrasound for emergent diagnosis
6. Apply ultrasound guidance for procedural applications including vascular access, thoracentesis, paracentesis, and abscess evaluation

Seminar Outline

Section 1: Ultrasound Fundamentals

Point-of-care ultrasound relies on three primary transducer types, each optimized for specific clinical applications based on frequency, footprint, and imaging characteristics. The curvilinear (convex) transducer operates at 2 to 5 MHz, providing a wide field of view with moderate resolution that makes it ideal for abdominal, pelvic, and FAST examinations. The phased array (sector) transducer operates at 1 to 5 MHz with a small footprint that allows imaging between ribs, making it the primary probe for cardiac and lung applications. The linear transducer operates at 5 to 15 MHz, providing the highest resolution with a narrow field of view, optimized for superficial structures including vascular access, soft tissue evaluation, and procedural guidance. Selection of the appropriate transducer is the first step in any ultrasound examination and directly determines image quality and diagnostic accuracy.

Basic ultrasound terminology describes how tissues interact with sound waves and appear on the display. Echogenic structures appear white on the screen because they strongly reflect sound waves back to the transducer; examples include bone cortex, calcifications, and air interfaces. Anechoic structures appear black because they transmit sound waves without reflection; simple fluid collections such as urine, ascites, and pericardial effusion are characteristically anechoic. Hyperechoic structures are brighter than surrounding tissue, hypoechoic structures are darker than surrounding tissue, and isoechoic structures are the same brightness as surrounding tissue. Understanding this terminology allows the clinician to systematically describe sonographic findings and communicate them to colleagues, and recognizing characteristic echogenicity patterns is fundamental to identifying both normal anatomy and pathologic conditions.

Ultrasound orientation follows standardized conventions that ensure consistency in image acquisition and interpretation. In abdominal scanning, the screen left corresponds to the patient's right, with the probe indicator (marker) directed toward the patient's right or cephalad. The top of the screen represents the structure closest to the transducer (most superficial), while the bottom of the screen represents deeper structures. Cardiac ultrasound follows a different convention, with the probe marker directed toward the patient's right shoulder in parasternal views and toward the left axilla in apical views. Depth is adjusted to ensure the structure of interest occupies the majority of the screen, and gain is adjusted to optimize brightness without obscuring detail. Proper orientation and optimization are essential for acquiring diagnostic-quality images and avoiding misinterpretation of anatomy.

Ultrasound artifacts are predictable image distortions that arise from the physical properties of sound wave propagation, and understanding them is critical because some artifacts provide important diagnostic information. Posterior acoustic enhancement occurs when sound waves pass through a fluid-filled structure with minimal attenuation, causing the tissue immediately deep to the fluid to appear abnormally bright; this artifact confirms the fluid nature of anechoic collections. Acoustic shadowing is the opposite phenomenon, occurring when sound waves are completely reflected or absorbed by dense structures such as bone and gallstones, creating a dark shadow deep to the structure. Mirror image artifact occurs at the diaphragm, where the highly reflective surface can create a duplicated image of subdiaphragmatic structures appearing above the diaphragm. In lung ultrasound, A-lines are horizontal reverberation artifacts arising from the pleural line that indicate normal aeration, while B-lines are vertical hyperechoic artifacts arising from the pleural line and extending to the bottom of the screen that indicate interstitial pathology when present in excess of three per intercostal space.

<image>Panel A: Three primary ultrasound transducers displayed with their frequency ranges and clinical applications: curvilinear probe (2-5 MHz, abdomen/FAST), phased array probe (1-5 MHz, cardiac/lung), and linear probe (5-15 MHz, vascular/superficial/procedures). Panel B: Ultrasound echogenicity scale showing anechoic (black, fluid), hypoechoic (dark gray, muscle), isoechoic (same as reference tissue), hyperechoic (bright, fascia), and echogenic (white, bone/air) structures with corresponding example images. Panel C: Ultrasound orientation diagram showing probe marker position relative to the screen indicator dot, depth adjustment demonstrating structures of interest centered on screen, and gain optimization comparison with undergained, properly gained, and overgained images. Panel D: Common ultrasound artifacts illustrated: posterior acoustic enhancement behind a simple cyst, acoustic shadowing behind a gallstone, mirror image artifact at the diaphragm, horizontal A-lines indicating normal lung, and vertical B-lines indicating interstitial edema.</image>

Section 2: FAST Examination

The Focused Assessment with Sonography in Trauma (FAST) examination is one of the most important point-of-care ultrasound applications in emergency medicine, designed to rapidly detect free fluid in the peritoneal and pericardial spaces of trauma patients. The primary indication is blunt abdominal trauma in a hemodynamically unstable patient, where a positive FAST can direct the patient immediately to the operating room without the delay of CT imaging. In penetrating trauma, the FAST is particularly useful for detecting pericardial effusion that may indicate cardiac injury. The FAST is also valuable as a serial examination, repeated when clinical status changes, because free fluid may not be immediately apparent if the bleeding is ongoing and the volume has not yet accumulated sufficiently. The entire examination can be completed in less than one minute by a trained operator, making it an ideal tool for rapid assessment during the primary and secondary trauma surveys.

The FAST examination consists of four standard views that evaluate the most dependent areas of the peritoneal and pericardial cavities where fluid is most likely to accumulate. The right upper quadrant (RUQ) view evaluates Morison's pouch (hepatorenal space), which is the most dependent area of the peritoneal cavity in the supine patient and therefore the most sensitive location for detecting free fluid. The left upper quadrant (LUQ) view evaluates the splenorenal space and the perisplenic region for free fluid. The pelvic (suprapubic) view evaluates the retrovesical space in males and the rectouterine space (pouch of Douglas) in females, which is the most dependent area when the patient is upright. The cardiac (subxiphoid) view evaluates for pericardial effusion, which appears as an anechoic stripe surrounding the heart and must be distinguished from pericardial fat pad, which is typically anterior only and more echogenic.

Proper technique for each FAST view ensures accurate and reproducible examinations. The RUQ view is obtained by placing the curvilinear probe at the right ninth to eleventh intercostal space at the midaxillary line with the probe indicator directed cephalad, fanning through the hepatorenal interface and the subdiaphragmatic space. The LUQ view is obtained similarly on the left side, at the ninth to eleventh intercostal space at the posterior axillary line, with particular attention to scanning superior and posterior to the spleen, as the splenorenal space is more posteriorly located than the hepatorenal space. The pelvic view is obtained with the probe placed transversely and then sagittally just above the pubic symphysis, using the full bladder as an acoustic window to visualize the space posterior to the bladder. The subxiphoid cardiac view is obtained by placing the probe below the xiphoid process, angled toward the left shoulder, with the liver serving as the acoustic window to the pericardium and heart.

Interpretation of the FAST requires understanding the significance of both positive and negative results. A positive FAST is defined by the presence of an anechoic stripe (representing free fluid) in one or more of the dependent peritoneal spaces or pericardial space. In the context of trauma, free peritoneal fluid is presumed to be blood (hemoperitoneum) and, when combined with hemodynamic instability, typically indicates the need for emergent laparotomy. A negative FAST does not rule out intra-abdominal injury, as the sensitivity of the examination is approximately 85 percent for hemoperitoneum, meaning that 15 percent of patients with significant intra-abdominal bleeding may have a falsely negative study, particularly early in the course before significant fluid has accumulated or in patients with isolated solid organ injury without free rupture. For this reason, a negative FAST in a patient whose clinical picture suggests intra-abdominal injury should be followed by CT imaging if the patient is hemodynamically stable, or by serial FAST examinations if clinical deterioration occurs.

<image>Panel A: Four standard FAST examination views shown on a body diagram with probe positions marked: right upper quadrant at the right midaxillary line, left upper quadrant at the left posterior axillary line, pelvis above the pubic symphysis, and subxiphoid with probe angled toward the left shoulder. Panel B: Normal and positive RUQ FAST views side by side, with normal showing the liver and kidney in direct apposition at Morison's pouch, and the positive view showing an anechoic stripe of free fluid separating the liver from the kidney. Panel C: Technique for each FAST view showing proper hand position, probe orientation with marker direction, and corresponding ultrasound image for the RUQ, LUQ, pelvic, and subxiphoid views. Panel D: Interpretation algorithm showing positive FAST in an unstable patient directing to the operating room, negative FAST with high clinical suspicion directing to CT scan, and the role of serial FAST with clinical change over time.</image>

Section 3: Extended FAST (eFAST)

The extended FAST (eFAST) adds bilateral lung assessments to the standard four-view FAST examination, enabling detection of pneumothorax and hemothorax in addition to free peritoneal and pericardial fluid. The anterior chest is evaluated at the second to fourth intercostal spaces at the midclavicular line, which is the most sensitive location for detecting pneumothorax because free air rises to the least dependent area in the supine patient. The lateral chest is evaluated at the fourth to sixth intercostal spaces at the midaxillary line to assess for hemothorax and pleural effusion. Both sides are examined and compared, as many of the findings are assessed by identifying asymmetry between the two hemithoraces. The eFAST has been shown to be more sensitive than supine chest radiography for detection of pneumothorax, making it particularly valuable in the acute trauma setting.

Normal lung ultrasound findings provide the baseline against which pathologic conditions are identified. Lung sliding is the most important normal finding, visualized as a shimmering or sliding motion at the pleural line that represents the visceral pleura gliding against the parietal pleura with respiration. A-lines are horizontal reverberation artifacts that appear as regularly spaced bright lines equidistant below the pleural line, representing normal sound wave reflection from the air-filled lung surface. When viewed in M-mode, normal lung demonstrates the seashore sign, in which the static chest wall layers above the pleural line appear as parallel horizontal lines (the ocean) and the dynamic lung tissue below appears as a granular, sandy pattern (the beach). Comet-tail artifacts, which are short vertical lines arising from the pleural line, may be seen in normal lungs in small numbers, with fewer than three per intercostal space considered normal.

The sonographic diagnosis of pneumothorax relies on the absence of findings that require visceral-parietal pleural contact. Absent lung sliding is the most sensitive finding, indicating that the visceral pleura is no longer in contact with the parietal pleura because air has accumulated between them. The absence of comet-tail artifacts and B-lines supports the diagnosis, as these artifacts require pleural apposition to be generated. In M-mode, the normal seashore sign is replaced by the barcode sign (stratosphere sign), in which parallel horizontal lines extend throughout the entire image because the static chest wall pattern continues below the pleural line where no dynamic lung tissue is present. The most specific finding for pneumothorax is the lung point, which is the transition point where lung sliding is present on one side (where the lung remains opposed to the chest wall) and absent on the other (where the pneumothorax separates the pleural surfaces). Identification of the lung point is essentially diagnostic of pneumothorax and can also help estimate its size based on how laterally the transition point is located.

Hemothorax on ultrasound appears as an anechoic or hypoechoic fluid collection above the diaphragm in the dependent portions of the thorax. The spine sign is a key finding: normally, the thoracic spine is not visible above the diaphragm because air-filled lung reflects the sound waves before they reach the spine, but when fluid replaces the air in the pleural space, the spine becomes visible as a continuous hyperechoic line extending above the diaphragm. The fluid collection is dynamic, changing with respiration as the lung tissue moves within or floats upon the effusion. Quantification of hemothorax volume by ultrasound is imprecise, but the presence of a significant collection in a trauma patient with hemodynamic instability, combined with the clinical context, guides the decision for tube thoracostomy. The eFAST views for hemothorax are often obtained simultaneously with the RUQ and LUQ FAST views, as the probe is already positioned at the diaphragmatic interface where pleural fluid accumulates.

<image>Panel A: eFAST lung scanning positions on the anterior and lateral chest showing probe placement at the second to fourth intercostal spaces midclavicular for pneumothorax detection and fourth to sixth intercostal spaces midaxillary for hemothorax evaluation, with bilateral comparison. Panel B: Normal lung ultrasound findings showing lung sliding as a shimmering pleural line, A-line reverberation pattern with equally spaced horizontal bright lines, seashore sign in M-mode with sandy granular pattern below the pleural line, and fewer than three comet-tail artifacts per field. Panel C: Pneumothorax ultrasound findings showing absent lung sliding at the pleural line, barcode sign in M-mode with continuous parallel horizontal lines throughout the image, and the lung point transition where sliding resumes marking the edge of the pneumothorax. Panel D: Hemothorax ultrasound showing an anechoic fluid collection above the diaphragm, the spine sign with thoracic vertebral bodies visible extending above the diaphragm through the pleural fluid, and comparison of normal lung-diaphragm interface where the spine is not visible above the diaphragm.</image>

Section 4: Cardiac Ultrasound

Bedside cardiac ultrasound in the emergency department employs four standard views that together provide a comprehensive assessment of cardiac structure and function. The parasternal long-axis view is obtained by placing the phased array probe at the left sternal border at the third to fourth intercostal space with the marker directed toward the right shoulder, revealing the left ventricle, mitral valve, aortic valve, left atrium, and proximal aorta in a sagittal plane. The parasternal short-axis view is obtained from the same position by rotating the probe 90 degrees with the marker toward the left shoulder, producing a cross-sectional view of the left ventricle that allows assessment of wall motion in specific coronary territories. The apical four-chamber view is obtained by placing the probe at the cardiac apex (point of maximum impulse) with the marker toward the left axilla, displaying all four cardiac chambers and both atrioventricular valves simultaneously and permitting assessment of relative chamber sizes. The subxiphoid view is the same as the FAST cardiac view, with the probe placed below the xiphoid directed toward the left shoulder, and is particularly useful in patients with hyperinflated lungs or mechanical ventilation where parasternal windows are limited.

Pericardial effusion appears as an anechoic space surrounding the heart on any of the four standard cardiac views. Small effusions (less than 1 cm in diastole) typically accumulate posteriorly and may be seen only in the parasternal long-axis or subxiphoid views. Moderate effusions (1 to 2 cm) are circumferential, and large effusions (greater than 2 cm) surround the heart completely and may demonstrate a swinging heart motion. Cardiac tamponade is the hemodynamic consequence of a pericardial effusion that has accumulated rapidly enough or in sufficient volume to impair diastolic filling, and the sonographic signs include right ventricular diastolic collapse, right atrial systolic collapse, and a dilated inferior vena cava that does not collapse with respiration. The distinction between pericardial effusion and pericardial fat pad is clinically important: pericardial fat is typically confined to the anterior surface, appears more echogenic than fluid, and does not extend posteriorly, whereas true effusion is anechoic and circumferential.

Right ventricular strain on bedside echocardiography is a critical finding that suggests acute right heart pressure overload, most commonly from massive pulmonary embolism or severe pulmonary hypertension. The key finding is right ventricular dilation with an RV to LV ratio greater than 1:1 in the apical four-chamber view, where the normal right ventricle is approximately two-thirds the size of the left ventricle. Interventricular septal flattening, known as the D-sign, occurs when elevated right ventricular pressure pushes the septum leftward, causing the left ventricle to assume a D-shape rather than its normal circular cross-section in the parasternal short-axis view. McConnell's sign is characterized by right ventricular free wall hypokinesis with preserved apical contractility, a finding that is relatively specific for acute pulmonary embolism. While these findings support the diagnosis of massive PE, they are not specific and can also be seen in chronic pulmonary hypertension and right ventricular infarction, requiring integration with the clinical presentation and additional diagnostic testing.

Assessment of left ventricular function on bedside echocardiography provides immediately actionable information in the undifferentiated critically ill patient. Visual estimation of ejection fraction, while subjective, correlates well with formal echocardiographic measurements when performed by experienced operators, categorizing function as hyperdynamic, normal, mildly reduced, moderately reduced, or severely reduced. The E-point septal separation (EPSS), measured in the parasternal long-axis view as the distance between the anterior mitral valve leaflet at its maximal opening and the interventricular septum, provides a semi-quantitative assessment of ejection fraction: a distance greater than 7 mm suggests a reduced ejection fraction. Global ventricular dysfunction with diffuse hypokinesis suggests cardiomyopathy, septic cardiomyopathy, or severe metabolic derangement, while focal wall motion abnormalities localized to a specific coronary artery territory suggest acute myocardial infarction or ischemia. This information guides immediate decisions regarding fluid administration, vasopressor selection, and the need for mechanical circulatory support or cardiology consultation.

<image>Panel A: Four standard cardiac ultrasound views showing probe positions on the chest and corresponding ultrasound images: parasternal long axis showing LV, LA, aortic root, and mitral valve; parasternal short axis showing the circular LV cross-section; apical four-chamber showing all four chambers and both AV valves; and subxiphoid showing the heart through the hepatic acoustic window. Panel B: Pericardial effusion spectrum from small posterior effusion to large circumferential effusion with swinging heart, and tamponade physiology showing RV diastolic collapse and RA systolic collapse with a plethoric IVC that does not collapse with respiration. Panel C: Right ventricular strain findings including apical four-chamber view with RV dilation showing RV:LV ratio greater than 1:1, parasternal short-axis view demonstrating the D-sign with septal flattening, and McConnell's sign with free wall akinesis and preserved apical motion highlighted. Panel D: Left ventricular function assessment showing visual estimation comparison of normal versus severely reduced ejection fraction, EPSS measurement technique in the parasternal long-axis view with the distance between the mitral valve leaflet and septum measured, and wall motion abnormality patterns mapped to coronary artery territories.</image>

Section 5: Pulmonary Ultrasound

B-lines are the hallmark ultrasound finding of interstitial lung pathology and represent one of the most clinically useful sonographic signs in emergency medicine. Each B-line is a discrete, vertical, hyperechoic line that originates from the pleural line, extends to the bottom of the screen without fading, moves synchronously with lung sliding, and erases any underlying A-lines in its path. The physical basis for B-lines is the reverberation artifact created when ultrasound waves bounce between thickened interlobular septa or fluid-filled alveolar walls, which are spaced at intervals that generate these characteristic vertical lines. Fewer than three B-lines per intercostal space in a given lung zone is considered normal, as isolated B-lines can be found in healthy individuals. When three or more B-lines are present in two or more lung zones bilaterally, the finding is considered pathologic and indicates interstitial syndrome, a term encompassing any condition that causes thickening or fluid accumulation in the pulmonary interstitium or alveoli.

The pattern and distribution of B-lines helps differentiate among the multiple causes of interstitial syndrome. Cardiogenic pulmonary edema produces diffuse, bilateral, symmetric B-lines that are homogeneously distributed across all lung zones and typically increase in density from apex to base, corresponding to the gravity-dependent distribution of hydrostatic edema. Pneumonia produces focal B-lines concentrated in the affected lobe or segment, often accompanied by subpleural consolidations, air bronchograms, and a pleural effusion. Pulmonary contusion in the trauma setting produces focal B-lines at the site of chest wall impact, which may evolve over the first 24 to 48 hours. Acute respiratory distress syndrome (ARDS) produces diffuse bilateral B-lines with an irregular, inhomogeneous distribution that spares some areas while heavily involving others, and the pleural line often appears thickened and irregular. Interstitial lung disease produces diffuse bilateral B-lines with a distribution that depends on the specific disease pattern.

Lung consolidation on ultrasound has a characteristic appearance that reflects the replacement of air-filled alveoli with fluid, inflammatory cells, or atelectatic tissue. The consolidated lung takes on a tissue-like echotexture referred to as hepatization because it resembles the parenchyma of the liver. Dynamic air bronchograms, seen as hyperechoic punctate or linear foci within the consolidated tissue that move with respiration, indicate that the bronchi contain air but the surrounding alveoli are fluid-filled, a pattern most consistent with pneumonia. Static air bronchograms that do not move with respiration suggest obstructive atelectasis. Consolidation is most commonly found in the posterior and dependent lung zones, reflecting the gravitational distribution of both pneumonic infiltrate and atelectasis. The causes of consolidation include pneumonia, atelectasis, pulmonary hemorrhage, and tumor, and the clinical context guides the differential diagnosis.

Pleural effusion on ultrasound appears as an anechoic space between the visceral and parietal pleura, most readily visualized in the dependent portions of the thorax when the patient is upright or semi-recumbent. The spine sign, as described in the eFAST section, is a reliable indicator of pleural effusion in which the thoracic spine is visualized above the diaphragm through the fluid that replaces the normally air-filled lung base. Within the effusion, the collapsed or partially aerated lung may be seen floating or undulating with respiration, a dynamic finding that confirms the fluid nature of the collection. The echogenicity of the effusion can provide diagnostic clues: simple transudative effusions are typically anechoic, while complex effusions with internal echoes, septations, or heterogeneous echotexture suggest exudate, hemorrhage, or empyema. Ultrasound is also used to guide thoracentesis by identifying the largest fluid pocket, marking the optimal insertion site, and confirming that the lung and diaphragm are not in the needle path, substantially reducing procedural complications.

<image>Panel A: B-line ultrasound appearance showing multiple discrete vertical hyperechoic lines originating from the pleural line, extending to the bottom of the screen, erasing underlying A-lines, and moving with lung sliding, with a comparison of normal lung (A-lines) versus pathologic B-line pattern (three or more per intercostal space). Panel B: Distribution patterns of B-lines for different pathologies: diffuse bilateral symmetric pattern in cardiogenic pulmonary edema, focal unilateral pattern in pneumonia, focal pattern at the impact site in pulmonary contusion, and inhomogeneous bilateral pattern with pleural irregularity in ARDS. Panel C: Lung consolidation showing tissue-like hepatized lung parenchyma with dynamic air bronchograms visible as bright punctate foci within the consolidated tissue, compared with normal aerated lung, and a shred sign at the boundary between aerated and consolidated lung. Panel D: Pleural effusion demonstrated with an anechoic collection above the diaphragm, the spine sign showing vertebral bodies visible through the fluid, a compressed lung floating within the effusion, and comparison of anechoic simple transudative effusion versus complex effusion with internal echoes and septations.</image>

Section 6: Abdominal Ultrasound

Aortic ultrasound is a critical emergency application used to evaluate for abdominal aortic aneurysm (AAA) in patients presenting with abdominal or back pain, syncope, or hypotension. The aorta is imaged using the curvilinear probe in both sagittal and transverse planes, starting at the xiphoid and scanning inferiorly to the aortic bifurcation at approximately the level of the umbilicus. The aortic diameter is measured from outer wall to outer wall in the transverse plane at multiple levels, as aneurysms may be focal. A normal abdominal aorta measures less than 3 cm in diameter, and a measurement of 3 cm or greater defines an aneurysm. The iliac arteries are normal up to 1.5 cm. Bedside ultrasound can rapidly identify an AAA in the unstable patient, guiding the decision for emergent surgical or endovascular repair. It is important to note that ultrasound cannot reliably distinguish between a contained and a ruptured AAA; therefore, any patient with a known or newly discovered AAA who presents with symptoms suggestive of rupture should receive immediate vascular surgery consultation regardless of the ultrasound findings.

Biliary ultrasound evaluates the gallbladder and biliary tree for evidence of acute cholecystitis, cholelithiasis, and biliary obstruction. The gallbladder wall is normally less than 3 mm in thickness; wall thickening beyond this threshold suggests inflammation, though it can also be seen in ascites, hypoalbuminemia, hepatitis, and heart failure. The common bile duct is measured in its short axis and is normally less than 6 mm in diameter, with an allowance of up to 10 mm in patients who have undergone previous cholecystectomy or are elderly. Gallstones appear as echogenic foci within the gallbladder that produce posterior acoustic shadowing and are mobile, moving with changes in patient position. Sludge appears as layering echogenic material in the dependent portion of the gallbladder without discrete shadowing. The sonographic Murphy's sign, defined as maximal tenderness elicited by pressing the ultrasound probe directly over the gallbladder, is a highly specific finding for acute cholecystitis when combined with gallstones. The combination of gallstones, gallbladder wall thickening, and a positive sonographic Murphy's sign has a positive predictive value exceeding 90 percent for acute cholecystitis.

Renal ultrasound in the emergency department is primarily used to evaluate for hydronephrosis, which is the dilation of the renal collecting system resulting from downstream urinary obstruction. Normal kidneys measure 9 to 12 cm in length and have a cortical thickness that should be preserved; a thinned cortex suggests chronic kidney disease. Hydronephrosis appears as anechoic dilation of the renal pelvis and calyces, graded as mild (dilation of the renal pelvis alone), moderate (dilation of the pelvis and calyces), or severe (dilation with cortical thinning). In the context of acute flank pain, hydronephrosis suggests ureteral obstruction from urolithiasis, though the stone itself is often not visible on bedside ultrasound unless it is located at the ureteropelvic or ureterovesical junction. Renal stones that are visible appear as echogenic foci with posterior acoustic shadowing. Perinephric fluid (free fluid surrounding the kidney outside the renal capsule) in the trauma setting suggests renal injury and hemoperitoneum, while in the medical patient it may indicate forniceal rupture from severe ureteral obstruction.

Evaluation for intraperitoneal free fluid outside the trauma context uses the same views as the FAST examination but with a broader differential diagnosis. In the RUQ, Morison's pouch is the most sensitive location for detecting free fluid in the supine patient. In the LUQ, the splenorenal recess and perisplenic region are evaluated. In the pelvis, the retrovesical or rectouterine space (pouch of Douglas) is assessed. The paracolic gutters along the lateral abdominal flanks represent additional locations where fluid may accumulate. The differential diagnosis of free intraperitoneal fluid depends on the clinical context: in the trauma patient it is presumed to be blood, in the patient with known liver disease it suggests ascites, in the febrile patient with abdominal pain it may represent peritonitis or ruptured viscus, and in the reproductive-age female with pelvic pain and a positive pregnancy test it may indicate ruptured ectopic pregnancy. The echogenicity of the fluid can provide clues, as simple ascites is anechoic while hemorrhage, pus, and proteinaceous fluid may demonstrate internal echoes.

<image>Panel A: Abdominal aorta ultrasound showing the sagittal view from the xiphoid to the bifurcation with the celiac and superior mesenteric artery branches visible, transverse view at multiple levels with outer-wall-to-outer-wall measurement technique, and comparison of a normal aorta (less than 3 cm) with an abdominal aortic aneurysm (greater than 3 cm with intraluminal thrombus). Panel B: Biliary ultrasound showing a normal gallbladder with thin wall and anechoic bile, gallstones with posterior acoustic shadowing, gallbladder wall thickening measured greater than 3 mm, and the sonographic Murphy's sign performed by pressing the probe over the gallbladder while observing the patient's facial expression for tenderness. Panel C: Renal ultrasound showing normal kidney anatomy with cortex, medullary pyramids, and central sinus echoes, grading of hydronephrosis from mild (pelvis dilation only) to moderate (pelvis and calyceal dilation) to severe (cortical thinning), and a renal stone at the ureterovesical junction with posterior acoustic shadowing. Panel D: Free fluid evaluation showing anechoic fluid in Morison's pouch, the splenorenal recess, the rectouterine pouch of Douglas, and a paracolic gutter, with comparison of simple anechoic ascites versus echogenic hemorrhagic fluid.</image>

Section 7: Vascular Ultrasound

Deep vein thrombosis (DVT) evaluation by compression ultrasound is a highly accurate bedside diagnostic technique that can be performed rapidly in the emergency department. The technique involves placing the high-frequency linear probe in the transverse plane over the common femoral vein at the inguinal ligament and applying firm downward pressure to assess compressibility, then advancing distally every 1 to 2 cm through the femoral vein, pausing at each level to compress. The normal vein completely collapses under probe pressure, demonstrating full wall apposition. The three critical compression points are the common femoral vein at the saphenofemoral junction, the superficial (now termed femoral) vein at the adductor canal, and the popliteal vein in the popliteal fossa. A two-point compression study at the common femoral and popliteal veins has a sensitivity exceeding 95 percent for proximal DVT and is the standard emergency department approach. Augmentation, in which distal calf compression produces a surge of blood flow through the vein visualized on Doppler, provides additional evidence of venous patency.

A positive DVT finding is defined by incomplete compressibility of the vein, meaning the anterior and posterior walls do not fully coapt when downward probe pressure is applied. In some cases, the thrombus itself may be directly visualized as echogenic material within the vein lumen, though acute thrombus is often hypoechoic or anechoic and may be difficult to distinguish from flowing blood without compression testing. Absent blood flow on color Doppler within the vein supports the diagnosis of complete occlusion. The distinction between acute and chronic DVT has clinical implications: acute thrombus tends to be more anechoic (darker), homogeneous, and causes vein distention, while chronic thrombus is more echogenic (brighter), heterogeneous, and may be associated with a thickened, non-distensible vein wall from post-thrombotic changes. Chronic DVT may produce a vein that does not fully compress but has a different clinical significance and treatment approach than acute DVT.

Arterial ultrasound applications in the emergency department include locating peripheral pulses for vascular access, evaluating pseudoaneurysms, and assessing the abdominal aorta for aneurysm. Ultrasound-guided arterial line placement in the radial or femoral artery uses the linear probe to visualize the pulsatile artery and guide needle insertion in real time. Pseudoaneurysms, which may occur as a complication of arterial catheterization or percutaneous procedures, appear on ultrasound as a pulsatile mass adjacent to the artery with a characteristic "yin-yang" or swirling flow pattern on color Doppler, connected to the native artery through a narrow communication neck. The abdominal aorta evaluation for aneurysm has been discussed in the abdominal ultrasound section and remains one of the highest-impact emergency ultrasound applications. Carotid artery ultrasound has a limited role in the emergency department, though it may be used to rapidly identify carotid dissection or to confirm the pulsatile nature of a neck mass.

Inferior vena cava (IVC) assessment provides a rapid bedside estimate of volume status and fluid responsiveness. The IVC is imaged in the sagittal plane using the curvilinear or phased array probe placed in the subxiphoid region, with measurement taken just distal to the hepatic vein confluence. A collapsing IVC that demonstrates greater than 50 percent diameter reduction with respiration (or with a sniff maneuver in the spontaneously breathing patient) suggests intravascular volume depletion and a likely positive response to intravenous fluid administration. A plethoric (distended) IVC that shows minimal respiratory variation suggests volume overload, cardiac tamponade, tension pneumothorax, or right heart failure. The IVC diameter correlates with central venous pressure, with a small collapsible IVC corresponding to low CVP and a large non-collapsible IVC corresponding to elevated CVP. While IVC assessment is a useful adjunct in the resuscitation of undifferentiated shock, it should be interpreted in the context of the complete clinical picture, as conditions such as mechanical ventilation, elevated intra-abdominal pressure, and chronic pulmonary hypertension can affect IVC dynamics independent of volume status.

<image>Panel A: DVT compression ultrasound technique showing the linear probe positioned transversely over the femoral vein, compression sequence demonstrating a normal vein that completely collapses and an abnormal vein with thrombus that does not compress, and the three critical compression points at the common femoral, femoral, and popliteal veins mapped on a leg diagram. Panel B: DVT ultrasound findings including a non-compressible vein with visible echogenic thrombus in the lumen, absent color Doppler flow within the occluded vein compared to normal flow in the adjacent artery, and comparison of acute (anechoic, distended) versus chronic (echogenic, thickened wall) thrombus appearance. Panel C: Arterial ultrasound applications showing ultrasound-guided radial arterial line placement, a femoral artery pseudoaneurysm with yin-yang color Doppler flow pattern and the communication neck with the native artery visible, and abdominal aorta transverse view for aneurysm measurement. Panel D: IVC assessment in the sagittal subxiphoid view showing measurement just distal to the hepatic vein confluence, a collapsing IVC with greater than 50 percent respiratory variation indicating volume responsiveness, and a plethoric non-collapsing IVC indicating volume overload or obstructive physiology, with corresponding CVP estimates.</image>

Section 8: Procedural Guidance

Ultrasound-guided vascular access has become the standard of care in emergency medicine, substantially improving first-pass success rates and reducing complications compared to landmark-based techniques. For peripheral intravenous access in patients with difficult veins, the linear probe is used to identify a suitable vein in either short-axis (transverse) or long-axis (sagittal) orientation, with the needle advanced under real-time visualization. The short-axis approach is more intuitive for beginners and allows visualization of surrounding structures, but requires careful attention to keep the needle tip in view as only a cross-section of the needle is seen. The long-axis approach allows visualization of the entire needle shaft and tip as it enters the vein, but the narrow ultrasound beam makes it challenging to keep the needle in the imaging plane. For central venous access, the internal jugular vein is the preferred site for ultrasound guidance, as the vein and adjacent carotid artery are clearly visualized, and real-time guidance allows the operator to confirm needle entry into the vein rather than the artery.

The technique for ultrasound-guided central line placement follows a systematic approach that maximizes safety. The initial scout scan identifies the target vein and its relationship to the adjacent artery, confirms patency by demonstrating compressibility and the absence of thrombus, and identifies anatomic variants. The probe is oriented in either short-axis or long-axis relative to the vessel, and the needle is advanced under real-time visualization. In-plane technique (long-axis) allows visualization of the entire needle as it enters the vessel, while out-of-plane technique (short-axis) shows the needle as a bright dot with characteristic tissue movement artifact. After the needle enters the vein, the guide wire is threaded and its position within the vein is confirmed by ultrasound before dilating and placing the catheter. Post-procedure ultrasound is used to check for complications, particularly pneumothorax following internal jugular or subclavian line placement, by evaluating for bilateral lung sliding.

Ultrasound guidance enhances the safety and success of multiple non-vascular procedures commonly performed in the emergency department. For paracentesis, ultrasound identifies the largest pocket of ascitic fluid and marks the optimal insertion site, confirms the absence of bowel loops in the needle path, and can be used for real-time guidance during needle insertion. Thoracentesis benefits from ultrasound guidance that confirms the location and depth of the pleural effusion, identifies the diaphragm to avoid subdiaphragmatic insertion, and marks the safest insertion point above the level of the effusion. Pericardiocentesis, previously performed using a blind subxiphoid approach, is now routinely ultrasound-guided to identify the largest fluid pocket, optimize the needle trajectory, and visualize the needle tip in real time as it enters the pericardial space. Lumbar puncture can be facilitated by ultrasound identification of the midline, spinous processes, and intervertebral spaces, particularly valuable in obese patients where landmarks are difficult to palpate. Abscess evaluation with ultrasound confirms the presence of a drainable fluid collection, distinguishes abscess from cellulitis (which appears as cobblestoning without a defined collection), and marks the point of maximal fluctuance for incision.

The evidence supporting ultrasound guidance for procedures consistently demonstrates improved patient outcomes. Ultrasound-guided central venous access reduces the rate of pneumothorax, arterial puncture, hematoma formation, and catheter malposition compared to landmark-based techniques. First-pass success rates are significantly higher with ultrasound guidance across all vascular access types. The number of needle passes is reduced, decreasing patient discomfort and tissue trauma. Procedure time may be equivalent or decreased in experienced operators, though it may initially increase during the learning curve. Multiple professional organizations and clinical practice guidelines now recommend ultrasound guidance as the standard of care for central venous access and strongly recommend it for peripheral difficult access, thoracentesis, paracentesis, and pericardiocentesis. The integration of procedural ultrasound into emergency medicine training has become a core competency, reflecting its established role in improving the safety and efficacy of bedside procedures.

<image>Panel A: Ultrasound-guided vascular access showing short-axis (transverse) view of a peripheral vein with the needle tip visible as a bright dot within the vessel lumen, and long-axis (sagittal) view showing the entire needle shaft entering the vein, with comparison of the two approaches side by side. Panel B: Central line ultrasound guidance technique showing the scout scan identifying the internal jugular vein and carotid artery, the compressibility test distinguishing vein from artery, in-plane needle visualization with the full needle visible entering the vein, and guide wire confirmation within the vessel lumen. Panel C: Non-vascular procedural ultrasound applications showing paracentesis with fluid pocket identification and bowel avoidance, thoracentesis with effusion depth measurement and diaphragm identification, pericardiocentesis with needle tip visible entering the pericardial space, and lumbar puncture with spinous process and interspace identification. Panel D: Evidence-based benefits of ultrasound guidance displayed as a comparison showing reduced complication rates, higher first-pass success rates, fewer needle passes, and the evolution from landmark to ultrasound-guided techniques over time for central venous access.</image>

Section 9: OB/GYN Ultrasound

Emergency obstetric ultrasound in the first trimester focuses on confirming or excluding intrauterine pregnancy, a critical determination in the evaluation of any reproductive-age female presenting with abdominal pain, vaginal bleeding, or hemodynamic instability. The earliest sonographic finding of pregnancy is the gestational sac, visible at approximately 5 weeks of gestational age as a round, anechoic structure within the uterine cavity surrounded by a hyperechoic decidual ring. The yolk sac, a round echogenic ring within the gestational sac, appears at approximately 5.5 weeks and is the first structure that definitively confirms an intrauterine pregnancy, as a pseudosac (decidual reaction without a true gestational sac) associated with ectopic pregnancy does not contain a yolk sac. The fetal pole becomes visible at approximately 6 weeks, and cardiac activity is typically detectable by 6 to 7 weeks. The discriminatory zone is the beta-hCG level (typically 1,500 to 3,000 mIU/mL for transvaginal ultrasound) above which an intrauterine pregnancy should be visible if present; an empty uterus above the discriminatory zone is highly concerning for ectopic pregnancy.

Ectopic pregnancy is the most dangerous diagnosis that emergency obstetric ultrasound is designed to identify, as ruptured ectopic pregnancy remains a leading cause of maternal mortality in the first trimester. The classic sonographic finding is an empty uterus in a patient with a positive beta-hCG above the discriminatory zone, though this finding alone is not diagnostic and may also represent a very early intrauterine pregnancy or a recent complete miscarriage. Direct visualization of an extrauterine gestational sac, known as the tubal ring sign, is a more specific finding but is seen in only a minority of cases. Free fluid in the pelvis (particularly in the pouch of Douglas) in the context of a positive pregnancy test and an empty uterus suggests ruptured ectopic pregnancy with hemoperitoneum and warrants emergent gynecologic consultation. The most specific finding is a live ectopic pregnancy with cardiac activity detected outside the uterus, though this is uncommon. A pseudosac, representing decidual reaction within the uterine cavity without a true gestational sac or yolk sac, can be mistaken for an early intrauterine pregnancy and must be carefully distinguished by the absence of the double decidual sign and yolk sac.

The choice between transabdominal and transvaginal approaches depends on the clinical situation and the information needed. Transabdominal ultrasound is the initial survey approach, providing a wide field of view of the pelvis and lower abdomen, and is the primary modality for evaluating later pregnancies and for detecting free fluid. A full bladder is required for transabdominal scanning, as it serves as an acoustic window to the pelvic structures. Transvaginal ultrasound provides significantly higher resolution of the uterus, adnexa, and early gestational structures because the high-frequency endocavitary probe is placed in close proximity to the structures of interest. An empty bladder is preferred for transvaginal scanning to bring the uterus closer to the probe. In early pregnancy, transvaginal ultrasound can detect gestational structures approximately one week earlier than transabdominal ultrasound and should be performed whenever the transabdominal examination is indeterminate and ectopic pregnancy remains in the differential diagnosis.

Fetal heart rate assessment is an important component of the emergency obstetric ultrasound examination and provides information about fetal viability and well-being. M-mode is the preferred method for measuring fetal heart rate, as it allows precise identification of cardiac motion without the potential bioeffects of spectral Doppler in early pregnancy. The normal fetal heart rate ranges from 120 to 160 beats per minute. Fetal bradycardia, defined as a heart rate below 120 bpm, is a concerning finding that may indicate fetal distress, and in the early first trimester (less than 8 weeks), a heart rate below 100 bpm is associated with a high rate of subsequent pregnancy loss. Fetal tachycardia, defined as a heart rate above 180 bpm, warrants further investigation for maternal fever, medication effects, fetal arrhythmia, or other underlying pathology. The presence of fetal cardiac activity does not exclude the possibility of an ectopic pregnancy if the cardiac activity is observed outside the uterus, nor does it guarantee a viable pregnancy, as subsequent pregnancy loss may still occur despite documented cardiac activity.

<image>Panel A: Early pregnancy ultrasound landmarks in chronologic sequence: gestational sac at 5 weeks (round anechoic structure with decidual ring), yolk sac at 5.5 weeks (echogenic ring confirming IUP), fetal pole at 6 weeks, and cardiac activity at 6-7 weeks, with corresponding beta-hCG levels and discriminatory zone threshold marked. Panel B: Ectopic pregnancy findings showing an empty uterus with thickened endometrium, a tubal ring sign with an extrauterine gestational sac in the adnexa, free fluid in the pouch of Douglas suggesting rupture, and comparison of a true gestational sac with double decidual sign versus a pseudosac without internal structures. Panel C: Comparison of transabdominal and transvaginal approaches showing probe positions, the full bladder acoustic window for transabdominal scanning versus the empty bladder preference for transvaginal, and resolution comparison of the same early gestational sac imaged by both approaches demonstrating the superior detail of transvaginal imaging. Panel D: Fetal heart rate assessment using M-mode showing the cursor placed across the fetal heart, the M-mode tracing with cardiac motion measured for rate calculation, and examples of normal heart rate (120-160 bpm), bradycardia (below 120 bpm), and tachycardia (above 180 bpm) tracings.</image>

Section 10: Soft Tissue and Musculoskeletal Ultrasound

Soft tissue ultrasound for abscess evaluation is a common and high-value emergency department application that improves diagnostic accuracy and procedural success. An abscess appears as a hypoechoic or anechoic fluid collection with irregular walls, internal echoes representing debris or purulent material, and posterior acoustic enhancement confirming the fluid-filled nature of the collection. Surrounding tissue inflammation manifests as hyperechoic fat stranding and edematous soft tissue. Cellulitis without abscess appears on ultrasound as cobblestoning, a characteristic pattern of subcutaneous edema with hyperechoic fat lobules separated by hypoechoic fluid tracking along fascial planes, without a discrete fluid collection amenable to drainage. This distinction is clinically important because cellulitis is treated with antibiotics alone, while an abscess requires incision and drainage as the primary treatment. Ultrasound has been shown to change clinical management in a significant proportion of patients with suspected soft tissue infections, either by identifying occult abscesses that would have been missed on clinical examination or by confirming the absence of a drainable collection in patients who might have otherwise undergone unnecessary incision.

Foreign body detection is another valuable application of soft tissue ultrasound, particularly for radiolucent objects that are not visible on conventional radiography. The high-frequency linear probe provides excellent resolution of superficial structures, and most foreign bodies regardless of composition (wood, glass, metal, plastic) appear as hyperechoic structures with a variable degree of posterior acoustic shadowing depending on their density and composition. Dense objects such as metal and glass produce strong posterior shadowing, while less dense objects such as wood produce minimal shadowing but are still distinctly hyperechoic against the surrounding soft tissue. The surrounding tissue often demonstrates a hypoechoic halo representing the inflammatory reaction and granulation tissue that forms around the foreign body. Ultrasound can be used not only to detect and localize the foreign body but also to guide its removal in real time, with the probe used to visualize the instrument approaching the foreign body and confirm complete extraction.

Tendon evaluation by ultrasound is useful in the emergency department for evaluating suspected tendon injuries, particularly when the physical examination is equivocal or limited by pain and swelling. Normal tendons display a characteristic fibrillar pattern of alternating hyperechoic and hypoechoic parallel lines that represents the organized collagen fiber bundles. A complete tendon tear appears as a discontinuity in the tendon substance, with retraction of the torn ends creating a hypoechoic gap filled with hematoma, and the diagnosis can be confirmed by demonstrating that the gap widens with passive or active motion. Partial tears appear as focal hypoechoic areas within the tendon without complete disruption. Tendinosis (chronic tendon degeneration) manifests as diffuse tendon thickening with loss of the normal fibrillar pattern and a hypoechoic, heterogeneous echotexture. Tenosynovitis, inflammation of the tendon sheath, appears as anechoic or hypoechoic fluid surrounding the tendon within its sheath. Common tendons evaluated in the emergency department include the Achilles, patellar, rotator cuff (supraspinatus), and extensor tendons of the wrist.

Fracture evaluation by ultrasound is an emerging application that can complement radiographic imaging and detect fractures that may be occult on initial radiographs. The cortical surface of bone appears on ultrasound as a bright, continuous hyperechoic line with posterior acoustic shadowing. A fracture disrupts this cortical continuity, appearing as a step-off, gap, or irregularity in the hyperechoic cortical line, often with associated soft tissue hematoma visible as a hypoechoic collection overlying the fracture site. Rib fractures are a particularly valuable application, as ultrasound has been demonstrated to be more sensitive than plain radiography for detecting rib fractures, and the findings directly correlate with the patient's point of maximal tenderness. In pediatric patients, ultrasound can detect occult fractures that may be missed on radiographs, including toddler fractures of the tibia, buckle fractures of the distal radius, and clavicle fractures in neonates. The limitations of musculoskeletal ultrasound include inability to visualize deep bone structures, operator dependence, and the fact that it provides a focused evaluation of the area of concern rather than the comprehensive anatomic survey provided by radiography or CT.

<image>Panel A: Soft tissue abscess ultrasound showing a well-defined hypoechoic fluid collection with irregular walls, internal echoes representing purulent material, posterior acoustic enhancement, and surrounding inflammatory changes, compared with cellulitis showing the cobblestoning pattern of edematous fat lobules separated by hypoechoic fluid without a discrete collection. Panel B: Foreign body detection showing a wooden splinter as a hyperechoic linear structure with minimal posterior shadowing and a surrounding hypoechoic inflammatory halo, a glass fragment with strong posterior shadowing, and real-time ultrasound-guided foreign body removal with a hemostat approaching the object under direct visualization. Panel C: Tendon ultrasound showing normal fibrillar pattern of a healthy tendon, complete tear with retracted ends and hypoechoic gap, partial tear as a focal hypoechoic area within the tendon substance, and tenosynovitis with anechoic fluid surrounding the tendon within its sheath. Panel D: Fracture ultrasound showing a normal continuous hyperechoic cortical line, a rib fracture with cortical step-off and overlying hematoma at the patient's point of maximal tenderness, and a pediatric distal radius buckle fracture with subtle cortical irregularity visible on ultrasound but not apparent on the corresponding radiograph.</image>

Summary

• FAST examines RUQ (Morison's pouch), LUQ (splenorenal), pelvis (retrovesical/rectouterine), and subxiphoid (pericardial) views to detect free fluid in trauma
• eFAST adds bilateral anterior and lateral lung views for pneumothorax and hemothorax detection, with greater sensitivity than supine chest radiography
• Pneumothorax is identified by absent lung sliding, barcode sign on M-mode, and the lung point, which is the most specific diagnostic finding
• Cardiac tamponade is diagnosed by pericardial effusion with right ventricular diastolic collapse and a plethoric, non-collapsing IVC
• Right ventricular strain suggesting massive PE is indicated by RV:LV ratio greater than 1:1, D-sign from septal flattening, and McConnell's sign
• B-lines exceeding three per intercostal space indicate interstitial pathology, with distribution pattern differentiating pulmonary edema, pneumonia, contusion, and ARDS
• DVT is diagnosed by non-compressibility of the vein at the common femoral, femoral, or popliteal compression points
• IVC collapsibility greater than 50 percent suggests volume responsiveness, while a plethoric IVC suggests overload or obstructive pathology
• Ultrasound-guided procedures improve first-pass success and reduce complications for vascular access, thoracentesis, paracentesis, and pericardiocentesis
• An empty uterus with a positive beta-hCG above the discriminatory zone is highly concerning for ectopic pregnancy

Key Terms

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