Fig. 11

The stomach. Left Empty state (low aspiration risk). The empty antrum (Ant) appears as a small round or oval structure. It may resemble a “bull’s eye target”. When the antrum is empty, all you can see is gastric wall. What appears to be a small amount of content is actually the thickness of all the layers of the gastric wall. The gastric wall has five distinct sonographic layers. The most prominent layer can be clearly seen in this figure as a hypoechoic “ring” and it corresponds histologically to the muscularis propriae of the stomach. The antrum is located immediately posterior to the left lobe of the liver (L); the pancreas (P); splenic vein (SV); aorta (Ao); spine (S). Middle: Solid content (high aspiration risk) Solid content in the stomach appears as non-homogeneous, mostly hyperechoic content. There is usually some amount of air mixed with the solid meal, and this produces multiple “ring down artefacts” that obscure the posterior wall. We call this type of image a “frosted glass pattern”, and we can see some degree of this type of artefact in this image. Right Clear fluid content. Clear fluid in the stomach (such as water, tea or normal gastric secretions) can be seen as a homogeneous hypoechoic content within the antrum. When clear fluid is seen, it may be useful to do a volume estimation to better assess aspiration risk. (Courtesy of Anahi Perlas, University of Toronto and Toronto Western Hospital, Toronto, Canada)