Apr 3, 2013
There are times when the safety of IV contrast can be a confusing quagmire. We know that iodinated contrast for CT scans can hurt the kidneys. But is it harmful for someone who already has renal failure and is on dialysis? What about the breastfeeding mother? Will IV contrast harm her infant? How should we pretreat patients who have had a previous reaction to IV contrast? These questions and more answered on this episode of ERCast.
If you want to be uber-educated, check out The American College of Radiology’s (ACR) Manual on Contrast Media. As this type of document goes, it’s actually pretty concise, and something you may want to keep as a reference.
Q: Is it safe to give iodinated contrast to a breastfeeding mother?
Less than 1% of contrast is excreted in the breast milk and less than 1% of that is absorbed by the child’s gut. If the patient is concerned about even this level of exposure, she can always discard the next 24 hours of breast milk (the so-called ‘pump and dump’), but the ACR feels it’s safe for breastfeeding to continue without interruption after administration of iodinated contrast.
Q: If we give iodinated contrast to a dialysis patient, do they need to be dialyzed immediately, or can they wait until their next regularly scheduled dialysis?
A: Most patients can wait until their next regularly scheduled dialysis. If a patient has severe underlying cardiac disease and the small osmotic load of contrast will potentially send them into pulmonary edema, then urgent dialysis may be indicated. Does a potential risk warrant a default of immediate - post contrast dialysis? Probably not. I think a more reasoned approach is to assess the patient after they have received contrast. If there are signs of volume overload, then dialyze. If not, then dialysis can wait.
There is also a theoretical risk of making an oliguric patient anuric, but limited evidence to give a clear answer. Bottom line from the American College of Radiology:
“Unless an unusually large volume of contrast medium is administered or there is substantial underlying cardiac dysfunction, there is no need for urgent dialysis after intravascular iodinated contrast medium administration.” For a specialty that defines itself by beating around that bush, that is a pretty clear statement. No clinical correlation recommended, nothing in the differential diagnosis includes that this patient who you just sent home is going to die from this incidentaloma.
The Renal Fellow Network has an excellent synopsis on dialysis post CT contrast. Worth a read
Q: What is the best way to pretreat patients who have had a previous reaction to iodinated contrast?
A: Many EDs give a two pronged pretreatment: steroids and antihistamines with a one hour delay between treatment and injection of contrast.
The steroid studies have shown that pretreatment several hours before contrast decreases the incidence of reactions. The limited data on a single steroid dose two hours before contrast injection shows no benefit. This goes along with our current thinking about steroids - they take several hours to work.
H1 blockers: Probably useful when given one hour before contrast injection.
H2 blockers: Unclear if they have beneficial effect. There is little downside to giving an H2 blocker along with an H1 blocker, but it should not be used as a substitute.
For a deep dive review of pretreatment, check out this 2006 article from the British Medical Journal
Q: Is there a role for pre-treatment to decrease the chance of contrast induced nephrotoxicity (CIN)?
A: A bigger question is: why does CIN happen in the first place? No one really knows. There are theories ranging from direct renal tubular toxicity to vasoconstriction. Since the cause isn’t clear, treatment is somewhat a patchwork of guesswork.
There is no evidence that gives a clear creatinine cutoff as to when we should or should not give contrast. The ACR feels that a creatinine of less than 2 mg/dL is safe for IV contrast, but that’s a fuzzy line. Is a creatinine of 1.9 mg/dL safer than 2.1? I’ll put it this way: clinical correlation recommended.
How should we pretreat patients we’re worried about CIN? Hydration is a good bet. There is decent evidence that pretreating with IV 0.9% NS decreases the incidence of CIN. How much, how long, how fast to infuse? Unknown.
The bigger mystery lies in pretreatment with sodium bicarbonate and N-acetylcystine (NAC). These have both fallen in and out and then in and then back out of vogue. Where they are now in the sphere of medical thinking is a mystery to me.
Bicarb: there is some evidence to say it decreases CIN and other evidence that it makes no difference.
Does it work? Conflicting evidence.
NAC: here is what the ACR has to say about NAC pretreatment:
The efficacy of N-acetylcysteine to reduce the incidence of CIN is controversial. Multiple studies and a number of meta-analyses have disagreed as to whether this agent reduces the risk of CIN. There is evidence that it reduces serum creatinine in normal volunteers without changing cystatin-C (cystatin-C is reported to be a better marker of GFR than serum creatinine). This raises the possibility that N-acetylcysteine might be simply lowering serum creatinine without actually preventing renal injury. There is insufficient evidence of its efficacy to make a definitive recommendation. N-acetylcysteine should not be considered a substitute for appropriate pre-procedural patient screening and adequate hydration.
Does it work: The jury is still out.
Q: Who should have their creatinine checked before IV contrast?
A: Some of this is evidence based, some is OGSAR based (old guys sitting around a room). Below are the ACR consensus recommendations taken directly from the document.
Patients who are scheduled for a routine intravascular study but do not have one of the above risk factors do not require a baseline serum creatinine determination before intravascular iodinated contrast medium administration.
*Metformin does not confer an increased risk of CIN. However, metformin can very rarely lead to lactic acidosis in patients with renal failure. Therefore, patients who develop CIN while taking metformin are susceptible to the development of lactic acidosis. To assess the risk of lactic acidosis, it is probably prudent to stratify the risk of CIN in patients taking metformin who will be exposed to intravascular iodinated contrast medium .
We’ve been talking about safety of iodinated contrast for CT scans, but what about gadolinium - the contrast used for MRI? It’s much less common for us to order an MRI than CT and even less common to give gadolinium, but it occasionally comes up. Is there a problem with Gadolinium and the kidneys? We used to think, and not that long ago, that gadolinium was safe for the kidneys. About as safe as injecting saline. The risk of direct nephrotoxicity is indeed extremely low - there have been some cases of gadolinium related kidney injury, but for the most part, it’s not directly nephrotoxic. The problem is something called Nephrogenic Systemic Fibrosis or NSF. NSF is a condition of progressive fibrosis throughout the body. It usually starts with skin thickening and pruritis but can involve several organs including the heart, lungs, esophagus, skeletal muscles. It can even be fatal. Not so good. The exact mechanism is unclear, but the primary risk factor for developing NSF is renal insufficiency. The screening for who is a risk for NSF is much like the screening for who is at risk for kidney injury from CT scans. Avoid gadolinium in patients on dialysis, acute kidney injury or chronic renal insufficiency with a depressed GFR. A GFR less than 30 scrubs the mission - do not inject.
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