Point-of-care gastric ultrasound: how to proceed when the exam is inconclusive

Key takeaways for faster decision-making#

If you cannot see it confidently, do not classify it as "empty"

• If the antrum is not visualized, it may mean a small, empty antrum; however, if neither the antrum nor its contents can be confidently identified, the stomach should not be classified as empty.
• It should be reported as an inconclusive exam, and decisions should rely on the clinical context.

Return to the basics of anatomy and image acquisition before interpreting content

• Return to the basics of anatomy: the antrum lies next to the left hepatic lobe, with the pancreas posteriorly and the aorta further posterior.
• Confirm you are at the "aorta level" (avoid measuring/interpreting when at the pylorus with the IVC posteriorly).
• If the "IVC behind the antrum" appears: slide the probe slightly to the left, use a transverse plane and/or Doppler as needed.

Rule out mimickers and use image patterns for "empty vs solid"

• If the image looks like the "antrum" but something does not add up: rule out mimickers (GEJ, colon, small bowel, gallbladder) using topography, peristalsis, and gas patterns.
• If the question is empty vs solid: look for the "ground-glass pattern" and apply zoom + dynamic right-to-left sweep.

If the antrum "disappears," use alternative windows with realistic expectations

• If the antrum is not visible (gas/dressing/incision): try alternative windows (transsplenic for the gastric fundus or subcostal for the body), keeping in mind they are only qualitative.
• If uncertainty persists: report as inconclusive and decide based on the clinical context, not on an "assumed" normality.

Why this topic matters in the perioperative setting#

Point-of-care gastric ultrasound (gastric PoCUS) has gained prominence in the perioperative setting, especially when fasting status is uncertain and in scenarios of potentially delayed gastric emptying (e.g., growing use of GLP-1 agonists).

Nevertheless, a non-negligible fraction of exams (2% to 5%) ends with indeterminate findings, usually due to window/acoustic limitations, complex anatomy, intestinal gas, and interpretive difficulties.

The educational article from Regional Anesthesia & Pain Medicine (RAPM) organizes these "pitfalls" into two major domains: (1) acquisition/anatomical identification failures and (2) content interpretation errors, while also proposing maneuvers and alternative windows when the antrum is not assessable.

The antrum is the standard target, and this explains some of the errors#

The gastric antrum is the recommended structure for gastric PoCUS for three reasons: it is the most recognizable portion on ultrasound, it typically has less air than the body/fundus (making it easier to see the circumference and contents), and in the right lateral decubitus (RLD) position, it becomes the most dependent portion, with good correlation between cross-sectional area (CSA) and volume.

Basic technique

• Low-frequency curvilinear transducer, sagittal plane in the epigastrium, just distal to the xiphoid process, with the marker oriented cephalad.
• The antrum appears adjacent to the tip of the left hepatic lobe, anterior to the pancreas and at the level of the aorta, which appears posterior to the pancreas and antrum.

Shape variations of the empty stomach (where many get lost)

• "Bull's-eye" pattern near the edge of the left hepatic lobe.
• Alternatively, it may appear as an elongated, flat structure ("finger of glove") near the hepatic edge.
• It can also be seen posterior to the anterior abdominal wall and caudal to the liver tip.

Two populations in which the window "disappears" more often

• Significant obesity: the antrum is more posterior due to increased intraperitoneal fat.
• Pregnancy (3rd trimester): the gravid uterus displaces the antrum superiorly and to the right.

In both cases, asking for a deep inspiration can bring the antrum to a more anterior plane and improve visualization.

Critical anatomical clue: regardless of shape, the antrum displays a multilayered wall, including a thick anechoic layer corresponding to the muscularis propria.

Pitfall #1: you found the antrum, but you are at the wrong level#

Confirming the antrum at the aorta level is particularly important when:

• there is clear fluid (to measure CSA validly) and
• the stomach appears empty (to support the absence of content).

If, instead of the aorta, you see the inferior vena cava (IVC) posterior to the "antrum," the structure is likely the pylorus/gastroduodenal junction, not the antral cavity, with the risk of grossly underestimating content.

How to differentiate aorta vs IVC (practical solutions from the article)

Pitfall #2: look-alike structures that mimic the antrum#

The article emphasizes that operator experience is key to avoiding false positives and describes the main mimickers.

Main antrum mimickers and how to differentiate

Pitfall #3: "empty" vs "solid" when intraluminal air is present#

One of the most common challenges (especially for beginners) is differentiating an empty antrum (no liquid/solid content) but with air present.

The key point: not all intraluminal air means solid content; a completely empty stomach usually has some visible air.

How air "deceives"

Air can appear hyperechogenic between the anterior/posterior walls and generate "comet-tail" artifacts, resembling "B-lines" from lung ultrasound, obscuring the posterior wall.

Patterns that help with interpretation

Management of indeterminate cases

• Zoom to improve resolution and discern intragastric material.
• Dynamic sweep of the stomach from right to left to identify the nature of the content, especially when clear liquid mixes with solid material.

When the antrum does not appear: alternative windows#

There are scenarios in which the antrum is not identifiable by the standard approach due to poor visualization, such as intestinal gas interference or a recent midline incision with dressings.

In these cases, the article proposes alternative scanning planes to assess regions of the stomach beyond the antrum.

Central limitation: these alternative approaches provide qualitative information only; no validated volume models exist for them to date.

Transsplenic window for the gastric fundus

• Uses the spleen as an acoustic window to visualize the fundus (in close relationship with the spleen).
• Position: supine or slight right lateral decubitus.
• Low-frequency curvilinear probe on the left posterior/mid-axillary line, at the 9th-11th intercostal space, oblique orientation with the marker anterior.
• The gastric wall is recognized by its multilayered pattern; the presence of content (liquid/solid) facilitates visualization, while an empty stomach may be harder to see.
• Useful for identifying solids or mixed content; utility for quantifying clear fluid is not established.

Subcostal window for the gastric body

• Probe in the epigastrium, transverse orientation, slightly to the left, marker toward the patient's right.
• Visualizes the gastric body between the left hepatic lobe (anterior) and the pancreas (posterior).
• Can be complementary when there is doubt about the nature of the content (e.g., liquid with solid particles) or when the antrum is not identifiable by the traditional technique.
• A practical limitation highlighted: overlying intestinal gas (especially from the transverse colon) can hinder the gastric body window.

Situations in which the exam may be unreliable and how to report safely#

The article points out scenarios in which gastric PoCUS is not currently recommended, such as in patients with altered gastric anatomy (e.g., hiatal hernia or prior gastric surgery).

It also discusses early data on adjusted formulas for patients who have undergone sleeve gastrectomy, but emphasizes the need for more evidence before robust recommendations can be made.

And here is a critical clinical point (often overlooked in practice):

A "full stomach" is usually easy to recognize.

A small/empty antrum can be difficult to find, especially for beginners.

If the antrum is not visualized, it may mean a small, empty antrum; however, if neither the antrum nor its contents can be confidently identified, the stomach should not be classified as empty. It should be reported as an inconclusive exam, and decisions should rely on the clinical context.

A 90-second troubleshooting algorithm#

• Return to the basics of anatomy: the antrum lies next to the left hepatic lobe, with the pancreas posteriorly and the aorta further posterior.
• Confirm you are at the "aorta level" (avoid measuring/interpreting when at the pylorus with the IVC posteriorly).
• If the "IVC behind the antrum" appears: slide slightly to the left, use a transverse plane and/or Doppler as needed.
• If the image looks like the "antrum" but something does not add up: rule out mimickers (GEJ, colon, small bowel, gallbladder) using topography, peristalsis, and gas patterns.
• If the question is empty vs solid: look for the "ground-glass pattern" and apply zoom + dynamic right-to-left sweep.
• If the antrum does not appear (gas/dressing/incision): try alternative windows (transsplenic for the gastric fundus or subcostal for the body), keeping in mind they are only qualitative.
• If uncertainty persists: report as inconclusive and decide based on the clinical context, not on an "assumed" normality.

Learning curve and standardization#

The article reinforces that mastering gastric PoCUS is a gradual process, combining acquisition and interpretation skills.

After adequate training and supervision, anesthesiologists can achieve approximately 95% success in qualitative assessment after about 33 exams.

Canadian guidelines suggest 20 or more supervised complete exams, and the ASRA expert panel recommends 30 or more supervised studies performed and interpreted.

Where AnestCopilot fits in#

If you need to review anatomical landmarks and gastric volume calculation formulas, Anestcopilot is the reliable tool for this task.