- I guess we can all agree that patient safety is paramount in the radiology department, in the vascular suite or otherwise. We're all very concerned about keeping the patient safe. That's why it's important to discuss
alternate contrast options. The use of contrast may present some safety concerns for certain patients, like the one we just talked about. Those with high risk for developing contrast-induced nephrotoxicity, and those who may have allergic reaction to contrast.
The American College of Radiology states in their manual on contrast media that patients who have had higher allergic- - [Audience Member] Can you speak into the microphone? - Sorry, is that better? - [Audience Member] Yeah.
- There's some background noise too. - According to the American College of Radiology, patients who have had a prior allergic or allergic-like reaction, or an unknown type of reaction, like those people who say that they're allergic to contrast but they can't articulate what that reaction may have been,
which I'm sure you have all run into, they're at a five times greater risk for having another reaction to contrast of the same type. So if they reacted to Omnipaque or Visipaque, something like that, they're at five times greater risk for reacting to contrast in the same category.
It's therefore conjectured that strategies to improve patient safety through the reduced risk of contrast-induced nephrotoxicity and anaphylactic reaction, while maintaining high quality images, includes the use of CO2 angiography.
This is just a little history of CO2 as a contrast agent.
In 1895 x-rays were discovered. Not that long afterwards room air was used with radiographs to visualize abdominal contents. Again, fairly soon after that, CO2 was introduced as a contrast agent. It was initially introduced to insufflate
the retroperitoneaum and CV structures and evaluate for masses. Room air was eventually abandoned as a contrast media because it became problematic. People were suffering air emboli. But CO2 remained viable.
In the '50s and '60s CO2 was used to visualize the right atrium to diagnose pericardial effusion. During the same period of time, animal studies demonstrated that CO2 was safe for venous injections and was generally well tolerated.
In the late '60s, CO2 was reported safe for injection into the IVC. Fast forward to the '80s and the development of digital subtraction angiography, CO2 becomes useful as a contrast media for vascular procedures.
In order to understand CO2 angiography, you need to understand the properties of CO2. CO2 is an odorless and colorless gas. It occurs naturally in nature. It occurs naturally within the body. There's no concern for allergic reaction,
no association with renal or hepatic toxicity. Viscosity is a measurement of the extent to which a liquid or gas resists flow. CO2 is much less viscous than iodinated contrast media. It's 1/400 as viscous as iodinated contrast media, which allows for it to be delivered
through much smaller access. It can actually be injected through needles as small as 27 gauge. It can also be injected through a catheter with the wire still in place using a Y adaptor. It's useful during procedures where it's preferable
to maintain a wire access, or in which you have to have smaller access. The solubility of a substance is the ability of the substance to dissolve in the solvent. CO2 has a very high solubility. It's much more soluble than oxygen.
It dissolves in the blood within two to three minutes after injection. When it's mixed with water, it creates carbonic acid, which is dissociated into bicarbonate and hydrogen ions, and then it's carried by the blood flow to the lungs, where the lungs break down the product
and it's exhaled. The buoancy of CO2 is its ability to float on water, air, or other fluid such as blood. Typically a gas will rise to the nondependent surface of the vessel. If all the blood is not displaced from the vessel
it will readily demonstrate interior structures, but potentially demonstrate smaller image of the larger feeding vessel. So when you're using CO2, it's imperative to displace as much blood as possible to generate a comparable image as using standard contrast.
CO2 is a gas which displaces the blood. It does not mix with the blood. It absorbs less radiation than the surrounding vessel wall, and therefore it's considered a negative contrast agent. With DSA, the density of the gas and the vessel wall is apparent.
Following venous injection, CO2 is carried by the blood to the lungs and eliminated in a single pass. The cost of CO2 is much less expensive than iodinated contrast media. It's about 3 cents per 100 cc of CO2.
This is an image of CO2 digital subtraction angiogram.
It looks pretty good, right? Not too bad. This is side by side. You can appreciate the negative and the positive contrast with the iodine on the left. This is probably what we're all used to looking at.
This is a normal aortoiliac angiogram with standard contrast.
- A lot of people are really familiar with the iodinated contrast. It's a liquid. It mixes with the blood.
So in comparison with CO2 where it's displaced, this one actually does mix with the blood when it's injected. We'll have a positive contrast. So in looking at the images you can see the positive versus the negative with the CO2.
The incidence of allergic reaction is pretty significant, from 0.7% to 3%, and severe anaphylaxis from 0.02% to 0.04%. But that's still pretty significant for patients. The excretion is mainly by glomerular filtration. I can never say that.
That's why renal function is really, really important. A lot of the patients that we see are already impaired renally with low GFRs, or they have other issues that might not make a contrast as desirable as CO2.
Indications for use of CO2 would be patients
with severe or anaphylactic allergy to ICM. If they did have the impaired renal function. Hemorrhage. It is reported that CO2 is 2.5 times more accurate and sensitive in detecting acute hemorrhage as compared to iodinated contrast.
You would want to use it in patients with peripheral artery disease, and with endovascular abdominal aneurysm repair, with interventional oncology, or anybody with a history or at high risk for contrast-induced nephropathy.
We're just gonna talk real quickly about contrast-induced nephropathy.
- Oh, it's back to me, okay. Contrast-induced nephrotoxicity is important. I'm sure you guys are well aware of it, well aware of the possible complications
that patients could suffer if they do in fact wind up with contrast-induced nephropathy. It's something that we need to discuss. This is just a little pathophysiology on contrast-induced nephropathy. It's commonly described as 25% or greater
increase in serum creatinine within 48 to 72 hours of the patient having received contrast media with no other identifiable cause for their bump in renal function. The Association for Radiological and Imaging Nurses practice guidelines mentions this
as the third leading cause of in-hospital renal failure. The incidence of hospital-acquired CIN is approximated at 7%. In a study which compared iodinated contrast media, gadolinium, and CO2 angiography in patients with renal insufficiency,
CO2 was the only agent noted to not demonstrate an elevation in creatinine. That study's a little bit old. It's from 2000. Some potential implications of increased morbidity and mortality, increased length of hospital stay,
increase in level of care, and increased cost of care may be attributed to contrast-induced nephropathy. Risk factors for developing this include but are not limited to patient history of chronic kidney disease, age over 75, GFR less than 60,
preexisting conditions which may alter kidney function, and administration of nephrotoxic medications. Other measures used to reduce the incidence of CIN include limiting your contrast volume and using a low-osmolar or iso-osmolar contrast. CO2 imaging can be used in conjunction
with limited diluted doses of iodinated contrast media to help maintain the quality of images, and to ensure a lower dose of iodinated contrast.
There are a few absolute contraindications for the use of CO2. Because there is a risk of embolic occlusion
and secondary ischemia, it should not be used above the diaphragm in patients who have right to left shunt or patent foramen ovale. It should never be administered with the patient in the prone position due to the risk for spinal ischemia.
Patients who are receiving nitrous oxide as part of general anesthesia should not receive CO2. That's because the nitrous oxide can diffuse into the CO2 bubble and increase the CO2 volume significantly. This may result in pulmonary artery vaporlock,
which is not a good thing. There are also some relative contraindications. It's not contraindicated to use this in patients with COPD. However, clearance can be decreased in these patients. Therefore it's suggested to allow more time
between injections. Recommended time is typically 30 to 60 seconds between injections. For patients with COPD, this time should be increased up to two minutes. There are some disadvantages to use.
Due to rapid dissolution of the CO2 bubbles in the bloodstream and the low density of CO2 as compared to iodinated contrast, there may be an increased radiation dose to the patient and to the operator. It is recommended that the frame rate
for acquiring CO2 images should be at 6 frames per second or more. A big disadvantage and what hinders most people is that they do need to learn to use the gas-based delivery system. There are a few on the market.
But that's a big hindrance. Because CO2 is invisible, colorless, and odorless, there's a lower comfort level for use as compared to the iodinated contrast. There's also a potential for the CO2 to fragment into random bubbles,
depending on how it's delivered. In order to avoid that, the catheter should be purged before delivery. Continuous and controlled delivery should be performed. It's preferred to use end-hole catheters to maintain a uniform bolus of the gas
and minimize that bubbling. When a blood gas interface is not present in an anterior structure such as an AAA, the CO2 can sit without dissolving and trap in that position. That trapping could lead to ischemia
manifested by pain. You'd have to check your patient. See how they're doing and if they're experiencing any pain. This doesn't happen all that often, but it is a possible complication.
This is an image. This is a cross-table image of the CO2 sort of stuck in that aneurysm, lingering there. Can you appreciate that? Bowel gas and peristalsis can also impact the image quality, so that's a disadvantage to use as well.
Because vascular imaging is typically not as dense with CO2 as compared to standard contrast, patient motion can also seriously affect the image quality. Some of literature recommends general anesthesia for these patients so that they don't move.
However, you wouldn't be able to assess them for pain if you were using general.
Let's get back to our patients. Isn't she cute? - She's talking about the patient. - The patient.
But Cheryl's cute too. - You can see that the patient that we're discussing is a perfect candidate for CO2. She had, again just to recap, acute hypertensive crisis. She's on three antihypertensive medications,
including a calcium channel blocker and a diuretic without improvement. I mean, a lot of patients come in and they're on so many medications to begin with with the polypharmacy, it's amazing. With even the medications that they list
and they give to you when they come in, they're probably on 10 or 15 more that you don't even know about, especially in the elderly population. With her past medical history, with diabetes, CAD, stage 2 renal insufficiency, hyperlipidemia,
and prior allergic reaction, with elevated serum creatinine and a low GFR, and renal artery stenosis and lack of left kidney function. Patients come through all the time with this clinical picture. She went to the vascular suite and she underwent
a percutaneous transluminal renal angiolasty using CO2 in combination with limited doses of iodinated contrast. Even though she does have a sensitivity, along with CO2 you are able to give contrast in a very, very small dose. We found that the patient's renal function
and blood pressure then have improved. She tolerated the procedure without any adverse reactions, which is a great thing. The use of the combined contrast angiography and the CO2 angiography together reduced the reaction, or risk of allergic reaction,
or possibility of contrast-induced nephropathy. In the two in conjunction, in small doses, you can have successful outcomes.
Implications for practice. It's always about patient safety. Patients are the most important people
that we have to take care of. We want to improve the patient outcomes, and we want to reduce any risk of CIN or allergic reaction. But we also want to have a good quality image. You have to do a balance with the two.
Benefits to nursing practice: As advocates for our patients we can improve patient outcomes. By doing so we could probably be there for the patient. We want to assess for pain. We want to make sure that they have good ventilation
so that they can clear the CO2. Any way that we can minimize contrast would be a great thing for the patient.
And in conclusion. - Basically, in conclusion, the literature shows us that there's no association with allergic reaction,
nephrotoxicity or hepatic toxicity with the use of CO2 angiography. It may be preferred to standard iodinated contrast media in certain patient populations. Certainly not in every patient, but in specific patients for whom we would be concerned.
Additionally, unlimited quantities of CO2 can be utilized, given the operator allows ample time for clearance. As long as the patient is doing okay and they're breathing okay, and they don't have any respiratory limitations,
we should be able to use this in unlimited doses. Obviously, there were quite a few disadvantages to the use of CO2 gas as an imaging agent. They do include the possibility of embolic occlusion. It's not recommended to use CO2 angiography above the diaphragm, so we're looking at a small,
well not maybe a small, but a limited amount of cases that we can even consider this for. In patients have right to left shunt or patent foramen ovale, we shouldn't be using it. Due to the rapid dissolution of CO2 bubbles in the bloodstream and lower density of CO2
as compared to standard contrast, we also have to be aware that there may be increased radiation dose to the patient and to the people working on the patient in the room, especially those, obviously, closest to the imaging equipment.
However, the reduction in CIN and serious allergic reaction could reduce hospital stay and lower mortality rates in these high risk patients.
That's pretty much all we have to say about that. - [Audience Member] In your scenario, the patient had a contrast allergy?
- Yes, we actually, we neglected in the end, we neglected to say that we would have premedicated her for that allergy. But you all know. I mean, how many times do you get somebody who said, "Oh, it made me vomit," or "It made me feel hot."
you have to investigate the "allergy" and find out what it really is. - [Audience Member] So it was a true allergy and you did premedicate? - Yeah, we should have noted that. You're right.
But obviously if somebody comes in saying their allergic, you're gonna want to know what is that allergy, and you have to investigate that, just like you do every day. - As soon as they say allergy, it's a flag right there. - But so many of them will say
that they're allergic to shellfish or something. We know that that's not really relevant any longer. You have to educate that patient. I can send you the slides if you want. - [Audience Member] Just like all the references. - Yeah, I can definitely send it to you.
Just give me your email. We'll send it.
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