Determining Gastric Volume With Ultrasound

Gastric ultrasound is a non-invasive, fast, bedside imaging technique that can estimate gastric volume. Placing a curvilinear ultrasound probe (oriented cephalad-caudad) in the epigastric region shows the gastric antrum (A) adjacent to the left lobe of the liver and superficial to the superior mesenteric artery (SMA), abdominal aorta (Ao), and spine.

Gastric ultrasound showing an empty antrum and the relevant surrounding anatomy.

Measuring the anteroposterior (AP) and craniocaudal (CC) diameters, we can calculate a cross-sectional area (CSA). CSA = (π x CC x AP) / 4. In the adult population, this can then be used to estimate the gastric volume by the Bolondi formula: 27 + (14.6 * CSA) – (1.28 * age). Gastric volumes < 1.5 cc/kg are considered low risk for aspiration with the induction of general anesthesia.

The craniocaudal (CC) diameter and the anteroposterior (AP) diameter (both in centimeters) are used to calculate the cross-sectional area (CSA) of the gastric antrum.

Additionally, gastric ultrasound can provide real-time information about the stomach’s contents, making it useful for monitoring the progression of digestive processes. This information can also be used to diagnose and monitor various gastrointestinal disorders, such as gastroparesis or functional dyspepsia, which can affect gastric emptying and lead to symptoms such as nausea, vomiting, and bloating.

In the following video, water intake shows dilation of the gastric antrum with the characteristic “starry sky” appearance associated with clear liquids. Solid food would appear more echogenic with air creating reverberations and a “frosted glass” appearance of the antrum.

Gastric ultrasound showing distention of the antrum after consuming water giving the characteristic “starry sky” appearance.

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