Fasting and IV Contrast. Let Them Eat?

So, I’m not sure how many of you are aware of this, but the American College of Radiology (ACR) has a contrast manual and they generally update it with something new every year. And the latest update, which came out in January 2021, was regarding the traditional habit of fasting prior to intravascular contrast media administration.

In the approximately “paragraph long” update with references, they cited a couple of studies from 2009, a meta-analysis from 2012 and a more recent study from 2020, looking at thousands of patients. And to get right to it, they determined that there really is no preventative effect of fasting prior to giving iodinated or gadolinium based contrast media. Specifically, they were commenting on the risk of nausea, vomiting and aspiration.

Now, I don’t know how many of you practice this way, but at my institution, we have been moving away from forcing patients to fast before a CT scan or MRI with contrast for years. Although we do rarely have patients that will vomit after getting the contrast, this hardly ever happens and ALWAYS goes away on its own without treatment. The real allergic-type contrast reactions are a different story, but we’re not talking about those today. Nausea and vomiting are in the physiologic category of contrast reactions, not the allergic-type. And a blanket policy of saying everybody must be fasting before a scan requiring contrast, assumes that there is no risk to fasting. OR maybe they are assuming the risk for vomiting and aspiration is greater than the risk of fasting.

Well, the ACR was kind enough to at least mention that there are problems with patients being forced to not eat anything before a study, such as concerning a delay of diagnosis, potential hypoglycemia in diabetic patients and overall general patient discomfort. So in my experience, over the past half decade or so, we saw this “real” risk and made changes to the way we practice years ago. But I’m happy that the ACR finally caught up with us and decided to at least make a statement addressing this in their 2021 updated manual.

So, now I have a question for you. How do you observe this practice at your institution? Do you require patients to fast before a scan with contrast? Or have you moved away from that years ago? It’s certainly something to keep in mind, as at least at my institution, I can say we safely moved away from requiring fasting and we believe our patients have benefited from this practice. And I would like to add, that this is primarily for outpatient studies. Inpatient exams are sometimes of a different flavor given their level of sickness, but our general rule for inpatients is that if they are already on a hospital diet, then there is no need to discontinue eating before the scan. Is a light meal a better option than 3 cheeseburgers, fries and a soda? Yes, of course. So, if we are asked, which happens occasionally, we usually say something like: #1 Take all your usual medications, and #2 No need to skip a meal before the exam, but a light meal is safer just in case the patient experiences some nausea. That’s about it. And let me tell you, patients hated not having their morning coffee before a scan. Now everyone is happier.

Obviously, if a patient needs conscious sedation or some sort of general anesthesia before one of these studies, well then you still have to follow safe practice for giving patients sedation which normally means fasting for at least 8 hours. This could be a vary an hour or two depending on the institution you’re working in and the anesthesiologists at your hospital.

Anyway, I just thought I’d bring this up as it is a new topic which was put out this year by the American College of Radiology in their famous contrast manual which pretty much everyone follows.

Now, if you would like to get a full rundown on the different types of allergic-like and physiologic contrast reactions that can occur and how to go about recognizing, treating and preventing these from happening, I have a fantastic course for you called the CT Contrast Course. This course not only deals with contrast reactions, but also covers many other important topics such as the patient’s kidney function, patients on dialysis, appropriate patient screening and the issues involved with giving contrast to children, pregnant women and women who are breast-feeding. If you’d like to learn more, please take a look here at the CT Contrast Course.