DIP Episode 478 - CT with contrast vs CT without contrast for the USMLEs

Welcome, my name is Devine. This is episode 478 of the Divine Intervention Podcast. And to this podcast I'm going to be discussing a topic that medical students have for the longest time struggled with. Really it's my hope that after you learn this topic it will give you a very nice useful framework for approaching a very common problem. So into this podcast I'm basically going to, and it's going to be a short podcast, and pretty much going to be discussing when you should use CT with contrast, and when you should not use CT with contrast. So when should you order CT with contrast, and when should you get CT without contrast? That's the big focus. And then at the end of the discussion today we will go ahead and talk about quick life lesson. There's a quick life lesson I have that we're going to discuss. So again this is going to be more conversational, but I think the very first thing you need to keep in mind is CT was the contrast we used for CT. Obviously the contrast we used for CT is iodine. They are iodine based for the most part. Most of the contrast we used for CT for the US Emily exam is iodine based. And again as I go and I'll try to make some integrations and pull in some classic scenarios and things you may see on your exams. So obviously right, there's a few problems with contrast that you want to be aware of. So for example they can give you a question about a person that gets contrast for an image in study.

The null of the sudden the person begins to have like shortness or breath, begins to have fevers, begins to have lipidema. Obviously this person has an allergic contrast reaction. And one easy thing they can easily test here is, oh what's the biggest risk factor for an allergic or contrast reaction? Well it's going to be a prior history of an allergic contrast reaction. If you've had a contrast reaction before chances are pretty good that you may have it again. That's actually the biggest risk factor. Another risk factor that's pretty high up there, but I would say it's probably the second one. It will be if you have like a history of atopic disease. So say for example you have a history of asthma and all those things. Yeah, you're pretty high risk for an allergic contrast reaction. And many times again I don't see the US Emily is asking you to treat an allergic contrast reaction. Well many times we're going to use first. We're going to straight up use a steroid. We're going to use like an IV steroid. And then many times we're going to give an anti-histamine as well. A steroid and an anti-histamine for the most part. Obviously if the person is having an anaphylaxis and they're always closing up, well how you're going to treat an anaphylaxis, you're going to be giving an epinephrine. And then what if they give you a question about a person? I've got an image in study with contrast and then you notice that man this person's baseline creatinine was 1.2, but now is like 2.7.

What happened there? Obviously that's going to be a contrast in use nephropathy. Many times when people have a contrast in use nephropathy, typically is going to present as an acute kidney injury. It's going to present as an intra-renol, acute renal failure, acute kidney injury. And they would ask which of the following interventions would have prevented this problem in the patient? Obviously you want to say fluids, given normal saline. Fluids, fluids are one of the best ways to prevent contrast in use nephropathy. And honestly when a person has contrast in use nephropathy, you probably should be giving them fluids as well. That's what I would go with first, honestly, over enacidocysteine. Many people know, oh yeah, enacidocysteine can help us deal with ferritical damage and all these things. Yes, it can help us with contrast in use nephropathy. But honestly the thing you want to be going for, the honesty you want to go for your exam is fluid. So I think those are kind of like the big things I want to delve into first about a CT contrast. So I think the next logical step here is then talking about situations where you should not use contrast when you're ordering a CT scan on your exams. Situations where you should not use contrast. I think that's kind of like an important topic to to go over. And again, I think if you're just going to have everything catalogged somewhere, I think you'll just make your life easier. So what's the very first one?

The first one is if a person has a stroke, if you're worried about a stroke and you want to order a first image in study, it should be a CT of the head without contrast. Because remember when you do a CT of the head without contrast, because blood will be its own contrast. Because remember when you get a CT head, if I lift a stroke, you're wondering, oh, is it an ischemic stroke or is it a hemorrhagic stroke? If you give contrast, then the contrast will obscure the blood. So you may not, it pretty much makes you not identify for stroke is a hemorrhagic. So the thing is generally when a person has a stroke, the first image test, you're going to order, it's going to be a CT of the head without contrast. And also, if you're so speculative, a person comes in with flunk pain, radiating to the growing, obviously that's a kidney stone. Kidney stones are pretty much never evaluated with contrast. I'm going to get a CT of the abdomen and pelvis, but in this case, it's going to be without contrast. It's going to be without contrast. And another one that also kind of makes sense is, honestly, I'm just telling you like a simple, right? If something is going to be like very, very bright or if something is already very, very dense at this line, chances are you probably should not be getting a contrast to look at that thing, right? Because that thing already contains a metal, right? Like calcium is a metal, right? Like bone. So in that case, it doesn't make sense to get contrast, right?

Like what's the point? What are you going to, what's the contrast going to enhance in that circumstance? Although, again, there are exceptions to most rules. But, you know, if you're trying to evaluate for a musculoskeletal issue, like a fracture, doesn't make any sense to get a contrast, right? We said kidney stones. Many kidney stones contain like a metal, like calcium or magnesium or something. Doesn't make any sense to get a contrast in those circumstances. And also, if a person is a recent trauma victim, right? For a person who's a trauma victim, and the trauma is not penetrating, right? Or you don't suspect vascula injury, then in that case, you also should not be given contrast. You also should not be given contrast. And then if you're worried about interstitial lung disease, right? For a person who has ILD, right? Usually for that, you're going to do like a high resolution lung CT, right? Many times that's going to present as an old person with dry cough, fine cruckles in the lungs, right? I remember it's a business-like predominant disease. In that case, don't get any, don't get any contrast, right? And then, obviously, for a person is being screened for lung cancer. I remember lung cancer is screened with a Ludo CT scan. I talked about lung cancer screening in a previous podcast. I even made a correction actually at the bottom because guidelines change all the time.

But basically, in those circumstances where you also don't want to get a, you also don't want to get contrast, right? The Ludo CT that's done to screening lung cancer is not done with contrast. And also, if a person is getting like a CT colonography, remember that's one of the ways we can screen for colorectal cancer these days. You actually do not need contrast in those circumstances. So, again, just when do you not use contrast? Again, I kind of said, okay, again, if something is really, really bright already, like a bone, doesn't make sense to get contrast, right? If something already like contains a lot of metal, probably doesn't need contrast, right? So, again, just to summarize these real quick, again, if a person has an initial stroke, right? If you're evaluating for kidney stone, if you're evaluating a muscular skeletal structure, right? You're worried about fracture. For person who has trauma, right? And is not penetrating or you don't suspect vasculine injury. And then the screenings, right? You know, like CT colonography for colorectal cancer, Ludo CT for screening for lung cancer. And, you know, for person who has interstitial lung disease, right? Typically, you're going to do a high resolution CT of the lungs. Those things don't involve contrast, right? A higher CT is pretty, it's going to give you a pretty good visualisation. So, I think with that, let's go ahead and jump into when you use contrast. And again, this contrast I'm referring to is IV contrast.

And let me just say something. If you like the way I integrate things and whatnot, they may be interested in the review classes I offer. I have a bunch of classes coming up in the month of September. Starts with a test-taking course on the first of September. And then I, that's for step one to step three. And then all the courses have first step one to step three of the four hour bio stats class, the five hour social sciences, and quality improvement class, and effects, you know. And then I have a 25 hour step one class taking place in September, and a 20 hour step to step three class taking place in September. So, if you're interested in any of these classes, just shoot me an email through the website. I can give you more information, you know, the classes focus on really integrations, explaining pathophysiology, context. They are not like straight-up lectures. No, they're pretty much almost all these classes are essentially entirely all clinical scenarios. Again, many club taking these classes and don't vary, don't vary well on their exams. So the big question then is when do you do image in with contrast? When do you do a CT with IV contrast? When in the world should you do CT with IV contrast? Honestly, first big one is cancer. If you're worried about cancer, if you're worried about cancer, quite a get a CT of wherever the cancer is with contrast, with IV contrast, okay? With IV contrast.

You know, you may wonder in the drawing like, can you talk about oral rectal contrast? I'll talk about that towards the end. Those are pretty loyal. There's probably like one high-yield indication to know for your exams, and that'll be pretty much it. Right? But if you're worried about cancer, in general, you want to do CT, you generally want to do a CT with contrast. You know, one of the big exceptions here, again, I've kind of talked about some of these exceptions already. If you're screening for lung cancer, Ludo CT of the lungs, doesn't need contrast. Screen for correctal cancer in a CT colonography, doesn't need contrast. But also another unique example here, lymphomas. Lymphomas actually don't need contrast for lymphomas. If you're worried about lymphomas, you don't have to use contrast. Okay, another situation where you do need contrast is if you're ever worried about infection, this is one of these time-honored, very useful to no ones. If you're worried about infection, honestly, even inflammation, anywhere in the body, and you're getting a CT, you should get it with IV contrast. So, infection, inflammation. So if something has IDIS in the name, acute pancreatitis, you're going to get a CT, if you're ever getting many times, that's a clinical diagnosis, right? But if you're getting a CT of the abdomen with, with, you should get it with IV contrast, right? So, any time you're dealing with an IDIS, that'll have a particular IDIS, right?

Or you have inflammation going also in the body, right? You have an infection, like an abscess or whatever, you generally should be getting CT with, with contrast, right? And then, you know, if a person has trauma and they spend treating injury, right? If a person has been treating trauma, although many times, especially like in the abdomen, if a person has been treating trauma to the abdomen, you're going to go ahead and take them straight to the, to the OR. You're going to go ahead and do X-lap. That's one of the indications for X-lap. But if you're trying to get your peak image on your exams, and it's been treating trauma anywhere in the body, or you're worried about a vasculine injury, you want to get a CT with IV contrast. In those circumstances, you definitely want to get a CT with IV contrast. That's actually very, very important and very high, you know, you want to get a CT with IV contrast, right? And then, if you suspect a person to have, like, some kind of infarction or a schemia, somewhere in the body, again, with the exception of the, of the brain, right, with the exception of the brain, generally, you want to get a CT with IV contrast. So if you suspect in functional ischemia, anywhere in the body, except the brain, remember, we said that, oh, infarction ischemia in the brain, obviously, it's going to be like a stroke. You're going to be getting a CT without contrast.

But if you suspect in infarction ischemia, pretty much anywhere else in the body, again, it's not about I get to get a CT with IV, with IV contrast, right? And then, in general, if you have any kind of vascular issue, honestly, if you literally have any kind of vascular issue, any kind of vascular issue, right, dissection, embolose, blah, blah, blah, blah, blah. In those circumstances, you're going to get a CT with IV contrast, right? In fact, if you ever see the word and geography in any kind of imaging, you can pretty much assume that that image involves contrast. Again, these roles, I'm sure you can dig up some rare exception, but honestly, these roles and giving you will generally net you those easy points on your exams, right? It's just, again, I think, more of having a useful framework to think about these things. And then, the only times I will say you should use oral, because so far, I've been talking about IV contrast, the only times you really should be using oral or rectal contrast is, if, for example, you suspect that a part of the GI tract, so the tube that runs from your mouth to your inus has exploded literally, right? So, in a way, suspect that, this person has preferethed as something from the GI tract, then you probably should get some kind of oral or rectal contrast. Many times the right answer is going to be an oral contrast.

And again, remember, though, if it's oral contrast, we usually want to try to give gastro-graphing, this I'm going to be saying, I think, quite a number of podcasts, you generally want to give gastro-graphing instead of burium, or you usually prefer gastro-graphing. If you only pick burium if gastro-graphing is not available, or gastro-graphing doesn't show you anything, but generally, you want to use gastro-graphing. Another name for gastro-graphing is hearing your exams, is a water soluble contrast, animal, water soluble contrast, animal. Okay, so that's kind of like a smart way to think about that. You know, the one of the few times you should use rectal contrast, is if, for example, you suspect that, oh, maybe this person is sigmoid colon, or a person's rectum has a perforated. You may see that in a person that has like herchprom's disease, for example, a person that has like really, really bad crows disease, really, really bad, all-shrieff colitis. In those circumstances, that's absolutely fine. You can do a CT with rectal contrast. Now, one thing I should definitely say, once in a few moments, you should never, ever, ever use oral contrast, is when a patient is woman, right? It kind of makes logical sense. For a person who is woman, it maybe doesn't seem like the best time to be pouring contrast down during, down your throats. Okay, doesn't seem like it's best time to be pouring contrast down your, down your throats.

So, I think with these general rules, I think it should be in pretty good shape with this stuff on, on exams. Now, the thing I'm just going to say, before I discuss my life lesson, again, I have these podcasts on the major apps, Apple Google and Spotify, I have a You Tube channel, Divine Intervention, USML podcast and videos. And I offer tutoring for one-on-one tutoring for many of the USML exams. I also have a review courses that I offer. Most people really benefit a lot from the review courses. And then I also help with applications and whatnot. And also, if you are interested in some of these life lessons I have, I actually got lots of emails from Blue Dent. Wow, I love your life lessons. So, I have a new website called Divine Intervention Life Lessons.com. I post two life lessons a week from a biblical perspective, you know, addressing a common problem is that people face. Actually, I have almost a, actually more than 200 podcasts on them. There's actually an Apple podcast associated with that. So, real quick, the life lesson I just want to give today is to stop wasting the opportunities that you have. Stop wasting the opportunities that you have. That's one thing that I think is just very important for many people. Many people just wake up and they feel like the day has nothing for them. What they feel like, man, my background, you know, I'm a failure whatever. You don't have to think of yourself like that. There is actually a reason why you're on earth. That's the truth.

Whether you like it or not, there are patients that you need to tend to. There are people that you have to affect positively. So, just wake up every day with a mission mindset. Don't waste your day. Approach your day with some more income of Western. Because again, many people, I feel like they just go through the day and just kind of mosey through the day, but that's not the way you should really take your life. Your life is pretty important. And honestly, let me tell you this. If you feel hopeless or you feel like, man, like I've failed so many times, no one likes me. People are always finding fault with me. Looking at the word, but don't waste the opportunity that you're having life. Study day with a mission mindset that, you know what, I have something great I'm going to achieve today. I'm going to affect a life positively today. I'm going to do something to help someone's destiny today. I'm going to improve my life in some way today. Just have a goal for your days because I'm telling you this, many people you'll be surprised that they go through days, weeks, months with no goals. And then they wonder, man, I've not made any progress in my life. Well, hello, you have the answer there, right? And the solution is not to commit suicide. The solution is not to start acting out. No, that's not the solution. I've actually made a pretty comprehensive podcast on suicide in medicine, I'm back in the actually a few weeks ago. But honestly, like, just get up, right?

Even if you've made mistakes, but you can start taking good decisions from today, right? The mistake is continuing to make a series of bad decisions. But if you get a few more and say, you know what, I'm going to start making better decisions from now, you can create a much better future for yourself than is your present. I'm telling you, that's one of the smartest things to do. And don't don't turn making a good decision. Don't keep postponing it. Good decisions are one of those things you generally don't want to postpone. You want to make that decision now, right? Now is the time to make that change, right? Today, if you're listening to this message, listen to this like, listen, and you know that man, there is an area of my life I need to change. Go ahead and make that change. I think that's just generally a smart thing to do. Because that change you don't make today, that positive change you don't make today, you're just creating a bigger problem in the future, right? A person that smokes today, you know, let's say they smoke a pack of secrets. They've smoked a pack of secrets every day, say for the last five years, you know, they have a five pack here smoking history. If they quit today, they're smoking history of the five pack years. But if they say okay, I'll quit in five years, they're smoking history doubles to 10 pack years, right? So you kind of get the job. So just be be wise with your life and start making good decisions.

Don't waste opportunities you have like today. The today you have standing in front of you is literally an opportunity to make a change. Okay, so thank you for listening to me today. I'll see you in episode 479. God bless you and all. Bye for now.

Iodine-based contrast.

IV contrast, because it can obscure the identification of hemorrhage.

Stroke evaluation (head), kidney stones/urology, musculoskeletal fractures, or screening procedures like low-dose lung CT.

Suspected infection, inflammation, or vascular injury (e.g., abscess, pancreatitis).

Oral contrast, specifically gastro-graphing (preferred over barium) if possible.

It is generally advised against due to potential discomfort or risk during administration.

CT Head without IV contrast.

Aggressive intravenous hydration with normal saline fluids.

Vascular dissection or embolism (any kind of suspected vascular issue).

Lung cancer screening.

Gastro-graphing; it is a water-soluble contrast medium (preferred over barium).

If there is suspicion of vascular injury or if the patient has generalized abdominal trauma.

CT Head without IV contrast.

Aggressive intravenous hydration with normal saline fluids.

Vascular dissection or embolism (any kind of suspected vascular issue).

Lung cancer screening.

Gastro-graphing; it is a water-soluble contrast medium (preferred over barium).

If there is suspicion of vascular injury or if the patient has generalized abdominal trauma.