Overview of Carbon Dioxide Angiography
Before the discovery and use of carbon dioxide (CO2) as a contrast agent in medical imaging, room air was used for this purpose. A contrast agent helps doctors to see the structures inside the body more clearly. The first contrast used in people was a liquid, introduced in 1924. Much later, CO2 was studied for use in the arteries and veins of patients. It was first introduced through a needle and later through a tube called a catheter.
With advancements in medical imaging technology, specifically in digital subtraction angiography (DSA – a type of imaging that provides clear images of blood vessels), and with the approval of CO2 delivery systems by the Food and Drug Administration (FDA), CO2 angiography emerged as a viable alternative to the commonly used iodinated contrast. This is especially the case in situations where the patient is allergic to iodinated contrast or has kidney problems.
However, CO2 angiography does have certain limitations and risks. It’s important that doctors, especially those who are new to performing angiography, understand these clearly before using it.
Why do People Need Carbon Dioxide Angiography
CO2, or carbon dioxide, is used in a medical procedure called angiography that looks at your blood vessels. It’s especially helpful because it doesn’t harm your kidneys or immune system. Plus, it’s the cheapest option compared to other materials used in these procedures.
Here are some procedures where CO2 can be used:
Arteriography: This procedure looks at arteries, the blood vessels that carry oxygen-filled blood from your heart to the rest of your body. Specific arteries that can be examined are:
* Kidney arteries
* Arteries in the gut
* Arteries in the uterus
* Arteries in the arms and legs
Wedged portal venography: This procedure is done during certain liver processes. It allows doctors to look at the blood vessels in the liver.
Venography: This is a test to check veins, the blood vessels that carry blood back to the heart. It can be used in certain situations like:
* Placing a filter in a large vein in your abdomen, known as the inferior vena cava.
* Repairing a special connection, called a shunt or fistula, used for dialysis treatment.
* Checking the veins near your spine during specific procedures.
Because CO2 is thinner than other materials, it’s less likely to harm the tissues it touches. For instance, it can prevent a rupture, or a break, in the liver’s outer layer when it’s used to look at liver veins. However, there has been no specific trial yet to evaluate if there is a meaningful difference in patients’ outcomes when CO2 is used.
When a Person Should Avoid Carbon Dioxide Angiography
CO2, or Carbon Dioxide, should not be mixed with nitrous oxide, which is a type of anesthesia, due to a certain chemical reaction. When Nitrogen (N2) and CO2 mix, it makes it difficult for the CO2 to dissolve in the blood, which is an important process for its removal from the body.
Additionally, CO2 should not be used in arteriography, a type of imaging test, on structures located above the diaphragm, like the heart or lungs, as it can lead to a dangerous condition called a cerebral air embolism. This condition could lead to a stroke or even death. A cerebral air embolism can occur in two ways: either through a defect in the heart or lungs that allows blood flow to bypass the lungs (called a cardiopulmonary shunt), or from CO2 flowing back into arteries such as the carotid or vertebral arteries that supply blood to the brain.
In order to minimize this risk, it’s often recommended to position a patient in a slight Trendelenburg position, where the patient’s head is slightly lower than their feet, during the procedure if possible.
Interestingly, studies in animals have indicated that CO2 can be safely injected into coronary arteries, which supply blood to the heart, without any harmful side effects or backward flow into the brain. However, no instances of such kind of usage have been reported in humans yet.
Just like other dye substances used for imaging tests, CO2 can increase pressure in blood vessels, which could be harmful, especially in patients with pre-existing high blood pressure in specific regions, like pulmonary artery hypertension. Therefore, caution should be exercised while administering CO2, and measures like regularly monitoring these blood vessels using fluoroscopy, a type of real-time X-ray imaging, and measuring the blood vessel pressure, can be taken to ensure safety. Typically, the gas injected for imaging can be seen clearing off from the blood vessels in about 30 to 45 seconds after administration.
Equipment used for Carbon Dioxide Angiography
Capnography (ETCO2), which measures carbon dioxide (CO2) levels, lets doctors keep track of a patient’s breathing and the CO2 in the bloodstream in real-time during procedures that require a person to be in a semi-awake state. National guidelines recommend using capnography machinery and tubing for these kinds of procedures.
Whichever setup the doctor chooses must have a one-way flow process. This means that the CO2 from a pressurized tank must be allowed to flow into a system of IV-like tubes, and bags. As the CO2 moves through this process, it expands until it matches the pressure of the room, while also pushing any surrounding air out of the system. This is important because surrounding air, if it gets into a patient’s blood, won’t dissolve quickly and could possibly cause a dangerous air bubble in the blood (air embolus).
Currently, there is only one CO2 delivery system approved by the US Food and Drug Administration (FDA). This system has two main parts: a CO2 tank called the AngiAssist and a pressure control system called the K-valve. The AngiAssist tank stores up to 10,000 mL of CO2, enough for hundreds of procedures. The K-valve controls the flow and pressure of the CO2, and consists of:
- Valves that control the direction of the CO2 to keep it from mixing with room air,
- A 60-mL syringe that helps the CO2 to depressurise,
- A 30-mL injection syringe that allows for the safe delivery of CO2 into an angiographic catheter (a small tubelike device used in medical imaging).
Large, medical-grade CO2 tanks have also been used in certain imaging procedures for many years, but unlike the AngiAssist, they are not FDA-approved. Like medical oxygen tanks, these CO2 tanks have a metal diaphragm to keep the gas pure, a release valve, and a pressure gauge and regulator. Single CO2 tanks for medical use generally hold millions of milliliters of CO2 set to around 18 PSI (pressure per square inch). They require a separate setup, such as a homemade or purchased version of the K-valve system, to depressurise and purify the CO2 before it’s delivered to the patient. It is important to keep the entry and exit points of the system sealed until the doctor is ready to connect the system to a catheter.
Additionally, CO2 injection systems can also work with:
- An extra filter to purify the gas,
- A digital injector,
- A Y-shaped connector, which allows doctors to perform angiography (an imaging test that uses x-rays to view blood vessels) without having to remove the guide wire from the catheter.
Who is needed to perform Carbon Dioxide Angiography?
A medical professional, called an angiographic technologist, is an important part of the team that takes care of you during certain medical procedures. This person has special training on how to use a machine that delivers CO2 (a type of gas). This is very important for keeping you safe during the procedure.
Preparing for Carbon Dioxide Angiography
During certain medical procedures, like angiography, a special tube called an angiographic catheter is used. It’s crucial to keep this catheter clear of any fluid, including blood or saline, to avoid damaging your blood vessels. One way to do this is a method called the “stopcock and waste syringe technique.” Here’s how it works:
* A device known as a 3-way stopcock is set up. It has three ends: one is linked to the CO2 (carbon dioxide) source, another one is linked to a waste syringe, and the third one is connected to the catheter.
* The stopcock is adjusted to stop the flow of CO2, letting the patient’s blood flow back into the waste syringe.
* The flow to the waste syringe is then blocked.
* CO2 is carefully injected until it completely fills up the catheter. At this point, you generally feel a decrease in resistance when injecting.
To inject the CO2, if a syringe is used, then a bigger one (20-30 cc) is better. This reduces the chances of a strong, sudden delivery of CO2 into the artery or organ, which can be damaging. A smaller syringe (10 cc), usually used for injecting liquid contrast, is more likely to cause this issue.
It’s been found that using a catheter with only one opening at the end for CO2 injection usually provides the best results. This holds true even for major blood vessels where traditionally a different kind of catheter, a pigtail one, is used with liquid contrast.
How is Carbon Dioxide Angiography performed
When a doctor needs to get a clear picture of the vessels in your body, they may use a type of imaging called contrast imaging. This procedure involves injecting a special substance into your veins or arteries which helps make them visible on an X-ray or scan. The amount of substance (in this case CO2 or carbon dioxide) injected depends on the size of the vessel and the area of the body being examined.
For a large vessel like the abdominal aorta, your doctor will usually inject 30 to 40 milliliters (mL) of CO2. Sometimes, they might need to use up to 60 mL. In smaller arteries, such as those in the kidneys, liver, and intestines, your doctor might inject between 20 to 30 mL of CO2. In very small arteries or veins, the amount of CO2 needed can be as little as 5 to10 mL, sometimes up to 20 mL.
Your doctor will inject the CO2 slowly and carefully. It’s important to note that veins are injected more gently than arteries. Also, in a study using animals, it was found that there were no harmful changes in the heart or lungs when a dose of 1.6 mL/kg of CO2 was used. This means that a 70 kilogram person can safely receive about 112 mL, which is typically more than what’s needed for this procedure.
The CO2 dissolves in about 30 to 60 seconds after it’s injected. To make sure it’s completely gone, your doctor might wait about two to three minutes before injecting more CO2. If you still feel the effects of the CO2 after three minutes, your doctor will check for trapped CO2 or air in your body. If you have a lung condition called COPD, it may take longer for your body to absorb the CO2.
Your doctor will do their best to obtain the best quality images for the diagnosis. Adjusting the respiratory motion, stacking multiple images, and using software to create a comprehensive picture of your anatomy are a few techniques they might use. They might also use a medicine in your arteries to make them wider and make small arteries more visible on the image. This helps your doctor to better interpret the scan and diagnose your condition.
Possible Complications of Carbon Dioxide Angiography
When doctors use a medical treatment involving the bloodstream, there’s a small but dangerous risk that air could get trapped in the blood, called an air embolism. This could lead to serious health problems such as stroke, heart attack, paralysis, loss of a limb, or even death, though the risk is less than 1% when the treatment is managed by experienced doctors.
Sometimes, too much CO2 could gather in the blood vessels leading to your lungs or in the right side of your heart, which can slow down your heart rate and lower your blood pressure. If this happens, the doctor may move you to your left side to help the CO2 move away from the blood flow. Over time, and depending on the size of the gas bubbles, the gas will dissolve into your bloodstream.
People could also experience tingling feelings, a sense of needing to use the bathroom, or nausea, especially when the blood vessels are being actively examined (angiography) with high speed.
If you get abdominal pain during an exam of the blood vessels in your gut (mesenteric arteriography), it could be resolved if the doctor changes your position and massages your belly. Continuous belly pain, though, might indicate that gas is trapped in your arteries – a state referred to as ‘vapor lock’. This could damage your gut if it’s not resolved. In this case, the doctor may try to shift the gas bubble by changing your position, massaging, or using a catheter.
There hasn’t been any report of CO2 poisoning from such treatments; CO2 poisoning from other causes usually leads to low blood pressure and slow breathing.
What Else Should I Know About Carbon Dioxide Angiography?
Here’s what you need to know about a procedure that involves injecting a gas (CO2) into your blood vessels to view them better. This method has both pros and cons.
First, let’s delve into the problems that could crop up:
1) CO2 rises towards the top of your blood, so it might miss any issues towards the bottom of your blood vessels. This is only really a concern for your aorta (main artery from your heart) and IVC (a large vein that carries poor oxygen blood to your heart), and the big branches that come from them.
2) Certain arteries that run along your back, like lumbar (lower back) and some kidney arteries, may only fill with the gas when you’re positioned more on your side than on your back.
3) Compared to the traditional liquid markers or using intravascular ultrasound (an imaging technique), when CO2 is used, there might be inaccuracies in figuring out the size of your blood vessels. This method can also result in inconsistent observations between different healthcare providers about the size of your blood vessels.
4) CO2 is not as precise as a liquid contrast when it comes to depicting narrowings (stenosis) in your blood vessels. For instance, CO2 was only able to highlight about 86% of the concerning arteries and adequately illustrated the stenosis in only 85% of the arterial segments in a study on adult men’s lower extremities. The arteries below the knees were not seen well enough.
5) As CO2 passes through areas where your blood vessels divide, it can spread out and mimic a narrowing (a stenosis).
6) Since CO2 imaging may not be as good as liquid contrast, your doctor should always talk with you about whether you’re okay with them using a small amount of iodinated contrast (a different type of marker typically used in imaging) to spot stenosis or confirm if findings are unclear.
Now let’s focus on the advantages of this procedure:
1) CO2 is less thick than traditional liquid markers, which might make it easier to get out of the blood vessel and move along more inactive blood flow channels. This could potentially make it more efficient in spotting certain conditions. Here are a few examples:
* An arteriovenous fistula: an abnormal connection between an artery and a vein
* Slow blood leakage
* Sluggish blood flow in a vessel
* Endoleak: Type of leak within an aneurysm
* Abnormal vessels feeding a tumor
2) There have been instances in which gastrointestinal bleeding (bleeding from your digestive tract) and fistulae (abnormal connections between organs) were picked up with CO2 when liquid contrast didn’t detect the problem.
