Gastric Ultrasound

1

How to Scan

Probe

Curvilinear 2–5 MHz, abdominal preset
Under 30 kg: high-frequency linear
Probe marker cephalad
Severe obesity: set depth to about 7 cm

Curvilinear

Linear

Patient position

1 · Supine, head up 45°

2 · Right lateral (RLD)

1 · Semi-recumbent 45°

2 · Right lateral (RLD)

Both positions

Scan supine first, then RLD. The antrum cannot be called empty until it has been scanned in RLD, because fundal contents move into the antrum in this position.

Optimising views in pregnancy

Slight manual displacement of the gravid uterus
Ask for a slow deep breath, then hold at end-expiration

2

Probe Placement

Scan plane

L LiverS StomachA AntrumP PancreasAo AortaSma SMA

L LiverS StomachA AntrumP PancreasAo AortaU Gravid uterus

Dashed grey outline: usual stomach position. The stomach is pushed cephalad and to the right.

Sagittal plane, just below the xiphisternum
Find the left liver lobe edge; the antrum lies deep to it
Slide until the aorta or IVC is seen behind the antrum
Set depth so the vessels and spine sit at the bottom
Rotate until the antrum looks round; oval means oblique and overestimates content

Why it is harder in pregnancy

Gravid uterus and a moving fetus
Stomach displaced cephalad and to the right
Fast, shallow breathing
Hyperdynamic circulation
Steep angle between xiphisternum and abdomen makes probe placement harder

Recognising the antrum

Tap the image to hide or show the labels.

Sagittal epigastric scan showing liver, antrum, pancreas, SMA and aorta

A AntrumL LiverP PancreasSma SMAAo AortaR RectusD Diaphragm

Sagittal epigastric scan in late pregnancy showing liver, antrum and fetus

A AntrumL LiverF Fetus

Round structure deep to the liver edge
Thick hypoechoic rim from the muscularis propria, which persists even when distended
Liver anterior; pancreas and aorta or IVC posterior
Assess the antrum at the level of the aorta, as the volume formulas were validated in this view
The antrum cannot be seen in 4–14% of patients; the scan is then inconclusive

3

Identify the Content

Tap an image to see its key features. Sample images are from non-pregnant adults.

In pregnancy

Qualitative assessment accurately identifies the content as empty, clear fluid or solid. It is most sensitive for solid compared with fluid or empty.

4

Patient

Age

yrs

Months

mo

Weight

kg

Formula –

5

Antral Content

Both positions scanned?

Antrum scanned in supine and in right lateral decubitus

6

Antral Measurement (RLD)

Watch the antrum for 10–15 seconds first. Take 3 measurements between contractions and enter the average for best results. Measure at the aorta level; the IVC level underestimates volume.

Clear fluid antrum with AP and CC diameters marked

In RLD, at the level of the aorta
AP: anterior to posterior serosa, at right angles to CC
CC: the widest craniocaudal diameter
Full wall thickness, serosa to serosa

AP diameter

cm

CC diameter

cm

CSA = π × AP × CC ÷ 4 –

Clinical Context

When to scan in pregnancy (ASRA 2026)

Active labour
Urgent caesarean with uncertain fasting status
Drugs that delay gastric emptying
Hyperemesis gravidarum
Pre-eclampsia or eclampsia
Gestational diabetes

Potential delay in gastric emptying

Pregnancy or labour
Diabetes (higher risk with retinopathy, neuropathy, long duration or HbA1c > 7%)
Severe liver or kidney dysfunction
Neuromuscular disorders
Critical illness
Severe obesity
GLP-1 receptor agonists

Limitations

Any decision on aspiration prophylaxis must include a thorough patient assessment and the many factors besides gastric content that influence aspiration risk. Findings may be inaccurate with abnormal gastric anatomy, such as previous gastric resection, bypass or sleeve, a gastric band in situ, previous fundoplication or a large hiatus hernia.