Point-of-care ultrasound

To see contributor disclosures related to this article, hover over this reference: ^[1]

Physicians may earn CME/MOC credit by reading information in this article to address a clinical question, and then completing a brief evaluation, in which they will identify their question and report the impact of any information learned on their clinical practice.

AMBOSS designates this Internet point-of-care activity for a maximum of 0.5 AMA PRA Category 1 Credit(s)™. Physicians should claim only credit commensurate with the extent of their participation in the activity.

For answers to questions about AMBOSS CME, including how to redeem CME/MOC credit, see “Tips and Links” at the bottom of this article.

Point-of-care ultrasound (POCUS) is an imaging protocol performed at the patient's bedside by the treating clinician as an extension of the physical examination. It is a valuable diagnostic tool in the emergency department (ED) because it is noninvasive, rapidly deployed, does not necessitate moving the patient from the resuscitation area, and does not interrupt urgent management. Sonographic assessment at the bedside helps narrow differential diagnoses and guide urgent management decisions, as it permits immediate (real-time) correlation of clinical features to imaging findings. To perform an adequate POCUS, it is imperative to have a basic understanding of ultrasound transducers, knobology, and acoustic windows for the areas of interest. POCUS has several applications, including diagnostic, screening, and procedural applications. Examination is limited to the area(s) of interest and specific objectives, which are based on the pretest probability of the diagnoses being considered. This article introduces the most common emergency clinical applications of POCUS. Focused assessment with sonography for trauma (FAST) is used to assess for free fluid within three main areas of interest: the peritoneal, pericardial, and pleural cavities. Additionally, extended FAST (eFAST) includes evaluation of the thorax for a possible pneumothorax. POCUS for the abdominal aorta focuses on the maximal aortic diameter to rule out an abdominal aortic aneurysm. POCUS of the subcostal IVC focuses on the diameter and collapsibility of the IVC to help estimate the intravascular volume status. POCUS of the gallbladder and biliary tree is used to evaluate for signs of gallbladder inflammation and cholelithiasis. POCUS of the female pelvis is used to rule in an intrauterine pregnancy in women within the reproductive age group. Finally, it is important to remember that negative or inconclusive POCUS findings should not be used to definitively rule out a diagnosis because POCUS is not a comprehensive examination and the results are operator-dependent.

More advanced POCUS techniques (e.g., lung ultrasound, cardiac ultrasound) are beyond the scope of this article. See the “Ultrasound” article for more information on fundamental concepts applied to broader sonographic modalities, e.g., formal ultrasound, endoscopic ultrasound, contrast-enhanced ultrasound.

• Generating high-quality and reliably interpretable ultrasound images is essential for POCUS to aid clinical decision-making.
• Good image generation is reliant on the following:
  • An understanding of basic ultrasound principles
  • Proper transducer selection, placement, and manipulation techniques
  • Use of appropriate image optimization strategies
  • A patient-oriented approach that minimizes discomfort and enhances cooperation
• Once optimal images are generated, interpret POCUS findings alongside other clinical and diagnostic parameters according to each patient's individual context.

Proper transducer (or probe) selection, placement, and manipulation techniques are essential for image generation and should be guided by the clinical picture and area of interest.

Selection

Physical properties ^[2][3]

The ultrasound transducer emits ultrasound waves (via piezoelectric transducers) that are reflected back by organs or tissues, generating a two-dimensional image. The following features should be considered when selecting an appropriate transducer for POCUS:

• Frequency: The frequency of ultrasound waves emitted by the transducer determines the image quality and affects clinical applicability.
  • High ^[4]
    • Higher-resolution image
    • Low depth of penetration
    • Better to visualize superficial tissues
  • Low
    • Lower-resolution image
    • High depth of penetration
    • Better to visualize deeper tissue/organs
• Footprint: The surface of the probe from which the ultrasound waves are emitted
  • Small: preferred for narrow acoustic windows (e.g., intercostal spaces)
  • Wide: preferred for large acoustic window and/or scanning area (e.g., the abdominal cavity)

Transducer types

There are four types of transducers that are essential for POCUS. They differ in size, frequency, and footprint, and generate different image formats, all of which affect their clinical applications.

The frequency of ultrasound waves is inversely related to the depth of penetration and directly related to the quality of image resolution: High-frequency probes generate high-resolution images but only of superficial tissue; low-frequency probes enable visualization of deeper structures at a lower resolution.

Placement

To best visualize the area of interest, place properly oriented probes on an appropriate acoustic window that takes into account the ultrasound conductivity and acoustic impedance of the underlying tissues.

Orientation ^[8]

• Indicators (orientation markers): used to orient the transducer along the standard planes of view while scanning
  • On the probe: typically a groove or ridge on one side of the probe
  • On the monitor: typically appears as a white or green dot on one side of the screen
• Orientation conventions
  • By POCUS convention, the monitor indicator should be on the left side of the screen.
  • Standard planes of view
    • Sagittal plane: Orient the probe so that its indicator points cranially.
    • Transverse plane: Orient the probe so that its indicator points toward the patient's right side.
• Confirm probe-to-monitor orientation: Do this prior to scanning to ensure accurate interpretation of spatial relationships and relative location of findings.
  • Initially locate the probe indicator by inspection or palpation.
  • Next, verify that movement occurring on the indicator side of the probe corresponds to movement seen on the indicator side of the monitor.
    • Touch the indicator side of the probe surface with a gloved finger or apply gel to that side.
    • If movement is seen on the opposite side of the screen to the monitor indicator, this typically means the probe indicator was incorrectly identified and the probe needs to be rotated 180° before placement.

If the probe indicator is identified correctly and the monitor is set to POCUS conventions, the left side of the screen should displays structures seen on the indicator side of the probe.

Adhere to orientation conventions as much as possible to avoid misinterpretation of findings and medical errors.

Acoustic windows ^[2][7]

• Description
  • Areas of the body that conduct ultrasound waves well and enable visualization of distal structures.
  • Must be accessible by the transducer or ultrasound beam for optimal visualization of areas of interest
• Ultrasound conductivity: The ability of a medium to conduct ultrasound waves; inversely related to its acoustic impedance. ^[8]

Choose acoustic windows with good ultrasound conductivity (e.g., fluid-filled or solid organs). Avoid areas with excessive intervening air, bone, or fat.

Manipulation ^[9]

There are five cardinal movements of the transducer that are required for most POCUS applications. These manipulations require movement of the transducer footprint in relation to the body and/or a change in the angle of insonation, which is the angle between the ultrasound beam and the area of interest.

Ultrasound machines are typically equipped with factory presets for certain applications (e.g., preset for abdominal examination). The factory presets serve as a good starting point to visualize the desired target tissue. Knobology refers to the manual adjustment of the following knobs or features on the ultrasound machine to enable further image optimization. ^{[3][5][8][10]}

Familiarize yourself with the ultrasound machine you will be using before conducting examinations.

Modes

• B-mode or brightness mode
  • Most commonly used mode for POCUS
  • Generates a grayscale 2D image
  • The image optimization settings described below refer primarily to those required for B-mode ultrasound.
• M-mode or motion mode: Used to evaluate tissue movement (e.g., in pneumothorax) ^[11]
• Doppler mode: Utilizes the Doppler effect to evaluate blood flow within an area of interest or differentiate static fluid collections (e.g., simple cyst) from dynamic fluid flow (e.g., aneurysm)
  • Based on the application, the following Doppler modes may be used:
    • CDI: color Doppler imaging
    • CW (CWD): continuous wave Doppler
    • PW (PWD): pulsed wave Doppler
  • Color duplex ultrasonography provides color-coding of flow direction.
    • Red: direction of flow is toward the transducer
    • Blue: direction of flow is away from the transducer

Depth penetration (sonography) ^[3]

• Background
  • Depth penetration is the distance traveled by ultrasound waves to visualize the target tissue/organs.
  • The depth traversed by ultrasound waves is depicted on the monitor, typically in centimeters.
• Action: Adjust the “Depth” or “Zoom” knob to optimize visibility and image quality.
  • An appropriate depth is one in which the image generated predominantly contains the area of interest.
  • As increasing the depth of penetration decreases the spatial resolution, select the least depth required to adequately visualize the target tissue/organs.
  • Increasing depth also decreases the frame rate.
• Examples
  • Assessment of superficial structures (e.g., thyroid ultrasound)
    • Select a high-frequency transducer (e.g., linear array transducer).
    • Decrease the depth penetration as needed.
  • Assessment of a deeper organ (e.g., pancreas)
    • Select a low-frequency transducer (e.g., curved array transducer)
    • Increase the depth penetration as needed.

The transducer frequency plays an important role in determining the depth penetration.

Gain (sonography) ^[3][8]

• Background
  • Gain is the magnitude of amplification of the ultrasound wave being reflected back to the transducer, and it determines the brightness of the image on the monitor.
  • Increasing gain:
    • Increases the reflected ultrasound wave and generates a brighter image
    • Decreases the contrast and spatial resolution of the image
• Action: Adjust the “Gain” knob to optimize the brightness and resolution of the image. ^[3]
  • Hypoechoic structures (e.g., fluid) should appear black.
  • Hyperechoic structures (e.g., bone) should appear white.
  • Adjoining structures should be distinguishable.

Avoid increasing gain too much, as overgained images result in poor contrast between adjacent structures.

Focal zone (sonography) ^[3][5][12]

• Background
  • The focal zone (or focal plane) refers to the part of the ultrasound beam with the narrowest diameter.
  • The lateral resolution of the image is best at the focal zone.
  • The location of the focal zone is depicted (e.g., with an arrowhead) on the lateral border of the image on the monitor.
  • Some machines have more than one focal zone.
• Action: Adjust the “Focus” knob so that the focal zone marker falls at the area of interest.

Image capture and analysis ^[3]

• Freezing images
  • Use the “Freeze” or “FRZ” button to pause the real-time image in order to:
    • Closely inspect the frame
    • Obtain measurements
    • Save and print the frame
  • With most devices, it is possible to rewind frames after freezing using the trackball or touchpad.
• Taking measurements
  • Areas of interest may need to be measured in various planes.
  • Use the “Caliper” button to obtain the straight-line measurement between two points and the “Trace” button to obtain curved line measurements.
  • Use the trackball or touchpad to maneuver the cursor to the desired point of measurement and set the points using the “Enter” or “Set” button.
  • Use the “Next” button to take another measurement.
  • Depending on the selected mode of examination, areas, volumes, angles, and more advanced measurements can also be calculated.
• Saving and recording images
  • Use the “Store” button to save paused frames.
  • Use the “Clips” button to obtain short recordings.
  • The “Print” button may be used if a physical copy of the ultrasound is desired.

• Turn the ultrasound machine on.
• Select an appropriate ultrasound transducer.
• Select “B-mode” or “2D mode” (appropriate for most POCUS applications).
• Select an application preset (e.g., abdominal, cardiac).
• Confirm the orientation of the transducer.
• Select an appropriate acoustic window to visualize the area of interest.
• Place adequate amounts of a low-impedance gel on the area to be scanned or on the transducer.
• Ensure firm and direct contact between the probe and skin to minimize air pockets.
• Adjust depth to maximize the visibility of the area of interest on the screen
• Adjust gain to optimize the contrast of structures
• Choose the optimal focal zone
• Manipulate the transducer (e.g., sliding, tilting) to visualize all areas of interest throughout the necessary planes.
• Document any necessary measurements.
• Record and save all relevant images.

All views

• Apply gel liberally to fill any spaces or crevices between the probe and skin, e.g., skin folds, umbilicus.
• Ensure firm and direct contact between the probe and skin to minimize air pockets.

Abdominal and subxiphoid views

• Consider applying sustained pressure, if tolerated, to allow bowel gas to slowly displace from the field of view.
• To reduce discomfort and resistance from pressure applied, consider asking the patient to flex the hips and knees to relax the abdominal muscles.
• Ask patients to take a deep breath and hold it, if tolerated, to inferiorly displace subdiaphragmatic abdominal organs that are obscured by rib and lung shadows.
• Consider alternative imaging techniques for patients with:
  • Uncontrolled abdominal pain
  • Excessive gaseous bowel distension
  • Obese body habitus

Pelvic views

• If using a transabdominal approach, consider asking patients to defer urination until after the scan, if tolerated.
• If an empty bladder impairs visualization, consider the following:
  • Repeat the examination after a period of hydration.
  • For catheterized patients, consider temporarily clamping the catheter or instilling a small amount (e.g., 50 mL) of normal saline into the bladder.
• Switch to an endocavitary probe if appropriate and tolerated, e.g., during POCUS for early pregnancy.

Thoracic views

• Place the probe within the intercostal space to visualize thoracic structures whenever possible, and consider switching to a probe with a smaller footprint.
• To better visualize the heart, consider asking the patient to turn towards the left-lateral decubitus position if tolerated.
• Consider comparing lung findings with the contralateral lung at the same intercostal level to help determine if they are pathological.

Artifacts

• Distortion or attenuation of the ultrasound beam can result in artifacts, such as acoustic shadow, acoustic enhancement, and reverberation artifacts.
  • Some of these can be useful for the interpretation of images (e.g., gallstones producing acoustic shadows).
  • Others can lead to false-positive, false-negative, or indeterminate findings
• Anticipate and recognize artifacts based on the acoustic impedance of overlying structures.
• Adjust gain or change transducer placement to minimize interference of artifacts with visualization.

FAST and eFAST are abbreviated scans that help with decision-making in select patients with acute traumatic injuries. They do not replace clinical judgment or other imaging modalities in trauma (e.g., CT scanning, radiography). Always interpret results along with other diagnostic and clinical findings within the individual patient context. ^[6]

Definitions ^{[6][7][13][14]}

• Focused assessment with sonography for trauma (FAST): a rapid, point-of-care sonographic assessment of the abdomen and thorax of trauma patients to detect free fluid within the peritoneal, pericardial, and pleural cavities.
• Extended FAST (eFAST): an extension of the FAST scan that includes evaluation for pneumothorax

Indications

FAST and eFAST can be performed by nonradiologist clinicians with appropriate training and experience.

• Initial evaluation of patients with blunt or penetrating trauma to the torso.
  • Recommended for all hemodynamically unstable patients (as an adjunct to primary survey) ^[15]
  • Can be considered in hemodynamically stable patients prior to CT ^[16]
• Reassessment of stable trauma patients who are being managed conservatively

Limitations ^[17]

• Sensitivity low for the detection of:
  • Hemorrhage < 500 mL
  • Injuries to the bowel, mesentery, retroperitoneum, or diaphragm
• Intervening air (e.g., bowel gas, subcutaneous emphysema) and fat (due to obese body habitus) can limit visualization.
• High false-negative rate, especially in hemodynamically stable patients ^[17][18]
• False positives are possible in patients with comorbid nontraumatic pleural, pericardial, or peritoneal effusions.

A negative FAST does not rule out an intraabdominal or intrathoracic injury!

General technique ^[7][17][19]

• Patient position
  • Typically supine (may be the only feasible position in unstable or critically ill patients)
  • Trendelenburg position improves the likelihood of identifying free fluid in the upper quadrants.
  • Reverse Trendelenburg or a seated position improves the likelihood of identifying free fluid in the pelvic view.
• Preferred transducers:
  • Cardiac and abdominal (FAST): curvilinear transducer or phased array transducer ^[7]
  • Lung (added for eFAST): linear transducer or curvilinear transducer
• Sequence ^[6]
  • Can be guided by clinical features (e.g., external evidence of trauma, area of maximum tenderness) and/or mechanism of injury
  • The RUQ is often assessed first followed by a clockwise sequence through the subxiphoid, LUQ, and pelvic views.
  • For advanced trauma life support (ATLS), the American College of Surgeons suggests starting with the subxiphoid area and then moving through the RUQ, LUQ, and pelvis. ^[19]

If possible, obtain two planes of view for each area to avoid missing small fluid collections.

Subxiphoid view ^[6][7][19]

• Areas of interest: pericardial space
• Acoustic window: left lobe of liver
• Technique
  • Start in the transverse plane (indicator pointing towards the patient's right side).
  • Place the transducer on the subxiphoid space in the midline.
  • Apply firm pressure posteriorly to direct the ultrasound beam behind the ribs.
  • To bring the heart into view, tilt the transducer anteriorly and toward the left shoulder, while maintaining posterior pressure to avoid losing contact with the skin.
  • Identify the pericardium in relation to the diaphragm and the beating cardiac chambers.
  • Scan the entire heart from base to apex and anterior to posterior by tilting and rocking the transducer through the planes of section.
• Troubleshooting
  • Adjust gain so that the fluid within the cardiac chambers appears black.
  • Use more of the liver as an acoustic window: slide the probe towards the patient's right while rocking it towards the patient's left.
  • Ask the patient to bend their knees or take a deep breath and hold it (see “General troubleshooting”).
• Findings: An anechoic (black) area between the hyperechoic pericardium and the myocardium represents a pericardial effusion.

Beware of false positives for free pericardial fluid: A hypoechoic area limited to the anterior apex that does not extend posteriorly to dependent regions of the pericardial space may represent periapical fat. Fluid in the pleural and peritoneal spaces may also be mistaken for pericardial fluid.

RUQ view ^[6][7][19]

• Main areas of interest (craniocaudally)
  • Right costodiaphragmatic recess
  • Right subphrenic space
  • Hepatorenal space
• Additional areas of interest for free fluid
  • Right paracolic gutter
  • Inferior renal pole
• Acoustic window: liver
• Technique
  • Begin in the sagittal plane (indicator pointing towards the patient's head)
  • Place the transducer subcostally or in one of the inferior intercostal spaces over the right anterior axillary line.
  • Rotate the transducer so that it is parallel to the ribs, with the orientation marker pointing toward the vertebral end of the rib.
  • Slide the transducer in an anteroposterior and/or cephalocaudal direction to locate and center the hepatorenal interface.
  • Once it is identified, tilt and rock the transducer to assess for free fluid (anechoic areas) within all areas of interest
    • Angle the transducer superiorly to assess the right costodiaphragmatic recess and right subphrenic space.
    • Angle the transducer inferiorly to assess the right paracolic gutter and inferior pole of the kidney.
• Troubleshooting: To improve image generation and visualization
  • Adjust gain so that the diaphragm and renal sinus fat appear white and fluid-filled structures such as the IVC or gallbladder appear black.
  • If possible, ask the patient to take a deep breath and hold it.
• Findings: Anechoic or hypoechoic fluid collections within the areas of interest should be considered pathological in the setting of trauma.

LUQ view ^[6][7][19]

• Main areas of interest (craniocaudally)
  • Left costodiaphragmatic recess
  • Left subphrenic space
  • Splenorenal space
• Additional areas of interest for free fluid
  • Left paracolic gutter
  • Inferior renal pole
• Acoustic window: spleen
• Ideal patient position: Trendelenburg position
• Technique
  • Begin in the sagittal plane (indicator pointing towards the patient's head)
  • Place the transducer in one of the inferior intercostal spaces over the left midaxillary line.
  • Rotate the transducer so that it is parallel to the ribs, with the orientation marker pointing toward the vertebral end of the rib.
  • Slide the transducer in an anteroposterior and/or cephalocaudal direction to locate and center the splenorenal interface.
  • Once it is identified, tilt and rock the transducer to assess for free fluid (anechoic areas) within all areas of interest
    • Angle the transducer superiorly to assess the left costodiaphragmatic recess and left subphrenic space. It is generally considered a complete study if at least
    • Angle the transducer inferiorly to assess the left paracolic gutter and inferior pole of the kidney.
• Troubleshooting: To improve image generation and visualization
  • Adjust gain so that the diaphragm and renal sinus fat appear white and fluid-filled structures such as the aorta appear black.
  • If possible, ask the patient to take a deep breath and hold it.
• Findings: Anechoic or hypoechoic fluid collections within the areas of interest should be considered pathological in the setting of trauma.

To assess the LUQ, place the transducer more cranially and more posteriorly than for the RUQ.

Beware of false positives for free fluid in the LUQ: contained fluid collections (e.g., abscesses, cysts, loculations, or accessory organs) or pleural fluid collections can be mistaken for intraperitoneal free fluid. ^[6]

Pelvic view ^{[6][7][17][19]}

• Areas of interest
  • ♂: rectovesical space
  • ♀: rectouterine space
• Acoustic window: bladder (ideally, fluid-distended)
• Technique
  • Begin in the transverse position (indicator pointing towards the patient's right side)
  • Place the probe just superior to the pubic bone.
  • Rock the probe caudally to identify the bladder, if not immediately visible.
  • Tilt the probe cephalocaudally to scan through the areas of interest in the transverse planes.
  • Rotate the probe 90° clockwise so that the orientation marker points cranially, and tilt the probe laterally to scan through the sagittal planes.
• Troubleshooting
  • Adjust gain settings as needed.
  • If genitourinary trauma is suspected, avoid urethral catheterization or instilling saline into the bladder to improve visualization until urethral or bladder injury has been ruled out.
  • Avoid applying pressure to the pubic bone if pelvic fracture is suspected.
• Findings
  • Anechoic or hypoechoic fluid collections within the pouch of Douglas should be considered pathological in the setting of trauma.
  • Free fluid is most likely to be seen behind or above the bladder or uterus.
  • Any free fluid within the pouch of Douglas in male patients is considered pathological.

Following ovulation and menstruation in women of reproductive age, a small amount (e.g., < 50 mL or ≤ 1 cm diameter) of anechoic free fluid in the pouch of Douglas may be physiological. Clinical correlation is essential.

Limited lung ultrasound ^[6][7][19]

Views to screen for pneumothorax in both lungs are added to the FAST components to make up the eFAST protocol.

• Area of interest: pleural line
• Acoustic window: intercostal space
• Transducer
  • A high-frequency linear transducer is best suited to detect pneumothorax.
  • Higher frequency (i.e., > 5 MHz) curvilinear transducers can be used if linear transducers are not available or if there is no time to change transducers.
• Technique
  • Place the transducer in the sagittal plane over the 2^nd or 3^rd intercostal space at the midclavicular line.
  • Adjust focal zone, gain, and depth as needed.
• Findings
  • Normally, the visceral and parietal pleura slide over each other easily during respiration and B-lines are visible.
  • Sonographic signs of pneumothorax
    • Absence of pleural sliding
    • Lung point
    • Absence of B-lines with or without prominent A-lines
    • On M-mode: barcode sign (instead of seashore sign )

In hemodynamically unstable patients, an abbreviated scan as described here is acceptable to detect a large pneumothorax. In stable patients, multiple areas of the chest should ideally be scanned to detect a pneumothorax. ^[6]

Further management

• Pericardial free fluid: See “Management of cardiac tamponade.”
• Free fluid in any of the other spaces in a trauma patient: Obtain immediate surgical consult.
  • Depending on hemodynamic stability, further diagnostic evaluation may be considered.
  • Unstable patients should undergo emergency laparotomy.
  • See also “Management of trauma patients,” “Approach to blunt abdominal trauma,” and “Approach to penetrating abdominal trauma.”
• Signs of pneumothorax on eFAST: See “Management of traumatic pneumothorax.”

In trauma patients, it should be assumed that free fluid within any of the potential spaces is pathological.

POCUS is a key diagnostic tool in the acute evaluation of patients with suspected AAA. Although it has high accuracy, it does not replace clinical judgment, formal ultrasound, or CT scanning, especially if performed by an inexperienced practitioner. Always interpret results along with other diagnostic and clinical findings within the individual patient context. ^[6][20]

Indications ^[4][21]

• Urgent
  • Palpable pulsatile midline abdominal mass
  • Abdominal bruit
  • Unexplained acute abdominal, lower back, or flank pain
  • Sudden abdominal, back, or flank pain in a patient with known AAA
  • Undifferentiated shock
• Nonurgent: See “Screening for AAA.”

Technique ^[4][6][21]

Initial steps

• Patient position: supine
• Preferred transducer: curvilinear or phased array
• Ultrasound preset: abdomen

Identifying the area of interest

The area of interest is the abdominal aorta lying just anterior to the hyperechoic vertebral body and its acoustic shadow.

• Place the transducer in the subxiphoid region.
• Start in the transverse plane (indicator pointing towards the patient's right side)
• Press down firmly but gently until the area of interest is in view.
• Adjust depth so that the hyperechoic vertebral bodies are visible at the bottom of the monitor.
• Distinguish the aorta from the IVC using POCUS.
• Center the aorta on the screen.

Scanning the aorta

• Slide the transducer from the xiphoid to the umbilicus to visualize the entire abdominal aorta from the celiac artery to the iliac bifurcation.
  • Proximal aorta (corresponds to the subxiphoid): subphrenic region, near the celiac artery
  • Mid aorta: adjacent to the level of the renal arteries
  • Distal aorta: below the renal arteries, up to the iliac bifurcation (typically found at the level of the umbilicus)
• Evaluate for any positive POCUS findings of AAA.

Inability to visualize the entire aorta from celiac artery to iliac bifurcation, e.g., due to overlying bowel gas, results in an indeterminate study.

Measurements

• Measure from outer wall to outer wall at the greatest width of the aorta.
• Ensure that the transducer is accurately aligned along or perpendicular to the aorta to avoid over- or underestimating the aortic diameter.
• Ideally, both anteroposterior and transverse diameters should be measured.

As an intraluminal clot may mimic the aortic wall, measuring only the inner lumen of the aorta may underestimate the size of the aorta.

Troubleshooting

• Consider asking the patient to bend their knees to help relax the abdominal muscles.
• If bowel gas obstructs the view
  • Attempt to displace it: Rock the transducer back and forth while applying firm but gentle pressure over the area of interest.
  • If attempted displacement is unsuccessful, consider obtaining lateral views.
• Consider additional color Doppler imaging for the following:
  • Evaluating for luminal patency
  • Distinguishing the aorta from adjacent structures (i.e., lymph nodes) ^[6][22]

Findings

• Normal: A normal abdominal aorta should have a uniform appearance without thrombi or wall irregularities and a diameter < 3 cm from the celiac artery to the iliac bifurcation. ^[20]
• POCUS findings of AAA ^[20]
  • A diameter either ≥ 3 cm or ≥ 50% greater than the aortic diameter proximal to the dilation indicates an AAA. ^[21]
    • Document the maximal size, shape, and location of the AAA.
    • Note the location of the aneurysm in relation to the renal arteries and aortic bifurcation.
    • If an aneurysm is present, assess for free fluid using the FAST technique.
  • The presence of a luminal flap indicates aortic dissection.

POCUS may miss small or saccular AAAs (e.g., due to intervening bowel gas).

Paraaortic lymph nodes and retroperitoneal masses can have a similar appearance to AAA.

Further management

• For a negative study: Consider other causes of symptoms (see “Acute abdomen”).
• For confirmed AAA: See “Acute management checklist for AAA.”
  • Stable patients, no sign of rupture: CT angiography with IV contrast of abdomen and pelvis, vascular surgery consult
  • Unstable patients and/or rupture: immediate vascular surgery consult for endovascular or surgical repair

AAA may not be the cause of the presenting features. Corroborate imaging findings with clinical features and consider alternate diagnoses. ^[6]

In patients with negative or indeterminate POCUS findings, consider CT angiography if the pretest probability for AAA is high. ^[4][6]

POCUS of the subcostal IVC is widely used as part of the assessment of volume status and prediction of fluid responsiveness, however, its accuracy and utility remain unclear. ^{[23][24][25][26]}

Clinical applications ^[17][25][27]

• Part of the multimodal assessment of intravascular volume status in patients with suspected hypovolemia (e.g., shock, dehydration), hypervolemia (i.e., fluid overload), or congestive heart failure ^[23]
• Estimation of fluid responsiveness in patients requiring fluid resuscitation (e.g., after a fluid challenge or passive leg raise test) ^{[24][25][28][29][30]}
• Noninvasive estimation of central venous pressure (CVP) in spontaneously breathing patients (e.g., to guide fluid management in critically ill patients) ^[29][31]

Interpret IVC ultrasound alongside other diagnostic and clinical parameters of volume status. Avoid using it in isolation to predict fluid responsiveness.

Technique ^[4][17][32]

Initial steps

• Patient position: supine
• Preferred transducer: curvilinear
• Ultrasound preset: abdomen
• Acoustic window: liver

Identifying the area of interest

The area of interest is the intrahepatic IVC as it flows into the right atrium (RA).

• Suggested starting point
  • Start in the transverse plane (indicator pointing towards the patient's right).
  • Place the transducer in the subxiphoid region at the patient's midline.
  • Press down firmly but gently until the area of interest is in view: i.e., the intraabdominal vessels can be seen anterior to the hyperechoic vertebral body and its acoustic shadow.
  • Adjust depth so that the hyperechoic vertebral bodies are visible at the bottom of the monitor.
  • Distinguish the IVC from the aorta using POCUS and center it in the image.
  • While keeping the IVC centered, rotate the transducer 90° clockwise (with the indicator now pointing cranially) to view the IVC in the sagittal plane.
• Alternative starting point
  • Start in the sagittal plane (indicator pointing towards the patient's head).
  • Place the transducer in the subxiphoid region at the patient's midline.
  • Slide and/or angle the transducer toward the patient's right side until the IVC is at the center of the image, taking care to distinguish the IVC from the aorta using POCUS.
• Common endpoint
  • Once the IVC is visible in the sagittal plane, rock the transducer cranially until the IVC-RA junction can be seen on the indicator side of the screen.
  • Slide and/or angle the transducer to capture the IVC in the longitudinal section where it appears widest (i.e., the midline of the vessel).

Measurements

• If possible, follow the IVC in a cephalad direction to visualize the site at which it drains into the right atrium (RA) and the liver veins.
• Measure the IVC diameter at peak inspiration and expiration, ideally at either of the following sites:
  • Just distal to the IVC-RA junction
  • 2 cm caudal to the IVC-hepatic vein junction

Troubleshooting

• Consider rewinding the image after hitting “Freeze” to select images with both the widest and narrowest diameter of the IVC during the respiratory cycle.
• If visualization of the IVC is difficult, e.g., because of interposed bowel gas, consider obtaining lateral views:
  • Turn the patient in the left lateral decubitus position
  • Place the transducer at the right midaxillary line and visualize the IVC through the liver.
• Consider switching to M-mode, as this may help to obtain precise measurements.

Findings ^[27][29][33]

• Normal maximal IVC diameter: ∼ 1.5–2.5 cm ^[17][34]
• IVC diameter variation (caval index): percentage of change in the IVC diameter over the respiratory cycle
  • For spontaneously breathing patients : IVC collapsibility index (IVCc) = ([maximal venous diameter during expiration - minimal venous diameter during inspiration]/maximal vessel diameter) × 100% ^[27][35]
  • For mechanically ventilated patients : IVC distensibility index (IVCd) = ([maximal venous diameter during inspiration - minimal venous diameter during expiration]/minimal venous diameter during expiration) × 100% ^[36]
  • Conditions that limit the reliability of caval indices to predict fluid responsiveness include: ^[17][37]
    • Reduced venous return
      • Increased intrathoracic pressure: e.g., dynamic hyperinflation, obstructive lung disease, mechanical ventilation with high PEEP
      • Cardiac dysfunction: e.g., chronic right heart failure, cardiac tamponade, right-sided MI, tricuspid valve regurgitation
    • Unpredictable respiratory pattern: e.g., variation in patient respiratory effort, use of mixed ventilator modes
    • Others: increased intraabdominal pressure, vascular disease involving the IVC (e.g., stenosis, thrombosis, external obstruction)

The absence of IVC diameter variability on respiration is suggestive of elevated central venous pressure (e.g., due to volume overload or right heart failure), while total IVC collapse suggests volume depletion. ^[6][32]

Ensure IVC measurements are taken in the midline of the vessel to avoid underestimating the diameter.

Further management

Management of patients with volume overload or depletion is based on the underlying etiology.

• The management of acute heart failure, immediate hemodynamic support of patients in shock, and initial fluids for dehydration and hypovolemia are covered in detail elsewhere.
• See also “Strategies for parenteral fluid therapy” for an overview of fluid management.

Biliary POCUS does not replace clinical judgment or formal ultrasound. Always interpret results along with other diagnostic and clinical findings within the individual patient context. ^[6]

Indications ^[4][6]

• RUQ abdominal pain and/or mass
• Unexplained jaundice, ascites, or altered liver chemistries
• Fever of unknown origin

Technique ^[4][6]

Initial steps

• Patient position: supine; alternatively, left lateral decubitus position
• Preferred transducer: curvilinear
• Ultrasound preset: abdomen
• Acoustic window: liver

Although biliary ultrasound is best performed in the fasting state, do not delay examination if the patient presents with acute symptoms.

Identifying the area of interest ^[6]

The main area of interest is the gallbladder body and contents.

• Start in the sagittal plane (indicator pointing toward the patient's head).
• Place the transducer in the subxiphoid region at or slightly to the right of the patient's midline.
• Optimize depth and gain as needed.
• Locate the gallbladder by sliding the transducer along the right costal margin (subcostal sweep).

Avoid confusing the gallbladder with other fluid-filled structures in the area, e.g., portal vein, IVC, liver or kidney cysts, abscesses. Scan in multiple planes or use color doppler if there is doubt. ^[6]

Troubleshooting

• Ask the patient to breathe deeply and hold their breath in inspiration, if feasible.
• If the lower liver margin cannot be visualized, use an intercostal approach.
  • Place the transducer in one of the inferior intercostal spaces, parallel to the ribs.
  • Ensure that the orientation marker points toward the vertebral end of the rib.
  • Slide the transducer from the sternal border toward the patient's right side to locate the gallbladder.

The gallbladder may be difficult to identify because it contracts in the postprandial state and its position is variable. If the gallbladder cannot be identified or adequately assessed on POCUS, rescan the patient after 6–8 hours of fasting in nonurgent cases or obtain a formal abdominal ultrasound.

Scanning the gallbladder ^[6]

• Longitudinal plane (long axis)
  • Rotate the transducer to align with the long axis of the gallbladder so that the fundus appears on the right side of the screen.
  • Tilt and/or slide the transducer to visualize the entire gallbladder.
• Transverse plane (short axis)
  • Rotate the transducer so that the orientation marker points toward the patient's right side.
  • Tilt and/or slide the transducer to visualize the entire gallbladder, from fundus to neck.
• Examination
  • Assess for gallstones, gallbladder wall thickening, pericholecystic fluid, and sonographic Murphy sign (see “Pathological findings and further management” for details).
  • If cholelithiasis is suspected, change the patient's position and evaluate for movement of the intraluminal echogenic foci.

Measurements ^[4][6]

• Gallbladder wall thickness
  • Measure the thickest portion of the anterior gallbladder wall.
  • Gallbladder wall thickness is normally ∼ 3 mm in the fasting state and ∼ 1 mm in the distended state. ^[38]
• Gallbladder diameter
  • Consider measuring the anteroposterior diameter of the gallbladder in the transverse plane.
  • Measurements of the gallbladder diameter are of limited value because the size of the gallbladder is highly variable.
  • Gross distension (anteroposterior diameter > 4–5 cm) may indicate biliary outflow obstruction (e.g., due to acute cholecystitis or choledocholithiasis).

Pathological findings and further management ^[6]

Cholelithiasis ^[39]

• Findings
  • Highly echogenic intraluminal foci
  • Strong posterior acoustic shadowing
  • Movement of the echogenic foci on repositioning the patient (rolling stone sign)
• Further management: See “Acute management checklist for biliary colic.”

Biliary sludge, which can cause biliary colic, is seen on ultrasound as low-level echogenic material in the dependent portion of the gallbladder. Biliary sludge moves slowly on repositioning the patient and does not cause posterior acoustic shadowing. ^[40][41][42]

A gallbladder polyp can be differentiated from a gallstone as it does not cast a posterior acoustic shadow and does not move on repositioning the patient. ^[6]

Acute cholecystitis ^[6][43]

• Findings
  • Gallbladder wall thickening > 3–5 mm ^[6][44]
  • Gallbladder distension (8–10 x 4–5 cm) ^[43][45]
  • Gallbladder wall edema (sometimes referred to as the double-wall sign): The innermost and outermost layers appear hyperechoic, while edematous tissue between these layers appears as a hypoechoic layer.
  • Sonographic Murphy sign
  • Pericholecystic free fluid: hypoechoic region around the gallbladder
  • Intraluminal gallstones and/or biliary sludge may be present.
• Further management: See “Acute management checklist for acute cholecystitis.”

Do not forget to rule out other life-threatening causes of epigastric pain (e.g., AAA, MI) even in patients with POCUS findings consistent with acute cholecystitis. ^[6]

Basic POCUS for early pregnancy is a limited study focused on the presence of an intrauterine pregnancy (IUP). It does not replace clinical judgment or formal ultrasound. Always interpret results along with other diagnostic and clinical findings within the individual patient context. ^[6]

Indications ^[6][46]

• To confirm the presence of, i.e., rule in, an IUP in first-trimester patients with any of the following symptoms suggestive of ectopic pregnancy:
  • Acute lower abdominal pain
  • Abnormal vaginal bleeding
  • Syncope
  • Signs of hemodynamic instability of no obvious etiology
• Identification of an IUP significantly reduces the likelihood of ectopic pregnancy, unless the patient has risk factors for heterotopic pregnancy, e.g., in vitro fertilization, previous ectopic pregnancy, or tubal disease. ^[6]
• See “Diagnostics for ectopic pregnancy.”

Obtain β-HCG in symptomatic patients at risk of early pregnancy, regardless of contraception use, followed by sonographic evaluation for IUP if positive.

Limitations

• It is beyond the scope of basic POCUS to assess other pelvic organs (e.g. ovaries, adnexa, uterus) or pregnancy viability beyond the presence of fetal heart activity.
• POCUS is not sensitive enough to rule out IUP or ectopic pregnancy.
• Accuracy is further limited in patients who have had pelvic surgery involving the vaginal canal or the rectum.
• If the diagnosis is uncertain or other structures need evaluation, obtain a formal ultrasound.

Technique: transabdominal approach ^[6]

Initial steps

• Patient position: supine
• Preferred transducer: curvilinear
• Ultrasound preset: abdomen
• Acoustic window: full bladder

Identifying the areas of interest

• Start in the sagittal plane (indicator pointing toward the patient's head).
• Place the transducer at the midline, just above the pubic symphysis.
• Identify the fluid-distended bladder and optimize depth and gain as needed.
• Locate the uterus posterior and inferior to the bladder.
  • The vaginal mucosa appears as a hyperechoic stripe (vaginal stripe) surrounded by hypoechoic walls.
  • Follow the vagina in a cephalad direction to identify the uterus, which appears as a pear-shaped organ.
  • Identify the endometrial stripe, which appears as :
    • A central hyperechoic line toward the end of the cycle
    • A central hypoechoic line during the early cycle
  • The thick-walled hypoechoic myometrium surrounds the endometrium.

The endometrial stripe is the initial area of interest for POCUS to rule in an IUP.

Scanning the uterus

• Longitudinal plane
  • Rotate the transducer so that it is aligned with the long axis of the uterus.
  • Tilt and/or slide the transducer laterally on either side to obtain sagittal planes of the entire uterus.
• Transverse plane
  • Rotate the transducer counterclockwise so that the orientation marker points toward the patient's right side.
  • Tilt and/or slide the transducer cranially then caudally to obtain transverse planes of the uterus.
• Examination
  • Look for sonographic signs of IUP.
  • Evaluate for free fluid within the pouch of Douglas.

Following ovulation and menstruation, a small amount (≤ 1 cm in diameter) of anechoic free fluid in the pouch of Douglas is considered physiological. ^[22]

Technique: transvaginal approach ^[6]

The field of view on a transvaginal ultrasound is limited, and specialized training is required to adequately perform and interpret a transvaginal ultrasound.

• Patient position
  • Lithotomy position
  • Alternatively, supine with flexed hips and knees
• Transducer: endocavitary
• Initial steps
  • Ideally, the bladder should be empty.
  • Apply the low-impedance ultrasound gel inside the disposable sleeve for the transvaginal transducer.
  • Apply lubricant liberally outside the sleeve.
• Scanning technique: Scan the uterus in longitudinal and coronal planes.
  • Slowly insert the transducer (with the indicator pointing ventrally) using gentle pressure
  • Advance until the probe tip makes contact with the cervix and uterine tissue can be seen on the monitor.
  • Sweep the transducer to each side to obtain longitudinal views.
  • Gently rotate the transducer 90° counterclockwise (indicator pointing towards patient right) and tilt anteroposteriorly to obtain additional coronal views.
  • Once the endometrial stripe is identified, look for sonographic signs of IUP throughout the planes of interest.
  • Evaluate for free fluid within the pouch of Douglas.

Patients undergoing transvaginal ultrasound should have a chaperone present. ^[6]

Avoid color doppler ultrasound in the first trimester because of possible risks to the fetus. ^[47]

Troubleshooting

See also “Pelvic views” in “General troubleshooting.”

• Transabdominal approach
  • Ensure the bladder is full
  • If the bladder cannot be filled, or structures are not visible despite a full bladder, switch to an endocavitary probe if available and tolerated by the patient.
• Transvaginal approach
  • Use lubricant liberally.
  • Ensure no air pockets are present between the probe and the sleeve.
  • Patients may be more comfortable inserting the probe themselves.
  • For patients in the supine position with flexed legs in whom anterior visualization is difficult, consider placing a pillow under the patient's sacrum.

Sonographic signs of IUP ^[47]

In chronological order of appearance:

1. Gestational sac: the earliest sign of a possible IUP
   • A small, anechoic spherical structure within the endometrial cavity (varies in size depending on gestational age)
   • Identifiable by 4.5–5 weeks of gestational age (may only be 2–3 mm in size)
   • Not a definite sign of IUP if seen in isolation ^[47]
   • Endometrial thickening around the gestational sac (decidual reaction) may be visible.
   • Double decidual sac sign
     • A hypoechogenic center surrounded by two concentric echogenic rings within the uterine cavity
     • Increases the likelihood of an IUP, but may be absent in up to a third of patients
2. Yolk sac: the earliest definitive sign of an IUP
   • A 3–5 mm spherical structure with an echogenic rim eccentrically located within the gestational sac
   • Identifiable by ∼ 5.5 weeks of gestational age
3. Fetal pole (embryo): a definitive sign of an IUP
   • An echogenic thickening attached to the inner wall of the yolk sac
   • First visible at ∼ 6 weeks of gestational age when it has reached a size of ∼ 1–2 mm ^[47]
4. Fetal heart activity: a definitive sign of a viable IUP
   • May be identifiable as early as ∼ 6 weeks of gestational age
   • Best evaluated in M-mode

Only confirm IUP if definitive signs are present, i.e., gestational sac PLUS either yolk sac, fetal pole, or fetal heart activity, and that these can be seen implanted within normal endometrium and myometrium. If the diagnosis is uncertain, obtain a formal ultrasound.

The inability to visualize an IUP on both transabdominal and transvaginal ultrasound at the β-hCG discriminatory level strongly suggests ectopic pregnancy.

The absence of IUP in a pregnant patient with hemodynamic instability and/or POCUS evidence of intraperitoneal free fluid strongly suggests ruptured ectopic pregnancy. This is a medical emergency requiring acute stabilization and definitive surgical treatment without delay.

Further management

• IUP confirmed: Consider other causes acute symptoms besides ectopic pregnancy unless risk factors for heterotopic pregnancy are present
• Positive pregnancy test and no sonographic signs of IUP
  • Hemodynamically stable patients: formal ultrasound to confirm POCUS findings
  • Hemodynamically unstable patients
    • Urgent obstetric and gynecology consult for emergency surgery
    • Do not delay stabilization for formal ultrasound.
  • See “Acute management checklist for ectopic pregnancy” and “Management of ruptured ectopic pregnancy.”