A standard protocol for all contrast enhanced studies is to ask patients to fast for 4-6 hours prior to the study. Over the years, the fasting is no longer rigorous and reasonable hydration has been recommended to prevent deleterious effects of intravenous contrast on the kidneys (thought that too is debatable).
Nevertheless, it has always been a paradox that while we talk about fasting, we also give 500-1000 cc of oral contrast prior to CT abdomen / pelvis studies.
The reason for people to be fasting has essentially been to reduce the risk of aspiration if there is nausea and vomiting. Given oral contrast in any case makes this reason redundant.
This nice recently published paper examines this issue and compares people who were asked to take a light meal prior to the study versus being asked to come fasting for 4 hours.
It actually finds that those who fast may land up with more problems due to issues with fasting (though their population was an oncology patient population) that those who don’t. Since the incidence of nausea and vomiting in the current era of iso-osmolar intravenous contrast media is low anyway, aspiration was just not an issue.
Perhaps it is time for all of us to examine this practice and to perhaps go easy on fasting instructions.