Carbon Dioxide Angiography - Indications, Procedure, and Limitations

What Is Carbon Dioxide Angiography?

Angiography is a diagnostic procedure used to evaluate and assess blood vessels. This procedure is usually done by injecting an iodine-based contrast medium into the vessel and then imaging them by using X-rays, computed tomography (CT), or magnetic resonance imaging (MRI). It helps identify many vascular problems such as blocks, blood clots, narrowing of the vessels, and others.

Carbon dioxide (CO2) angiography is a specialized angiographic technique where carbon dioxide is used as the contrast medium instead of iodinated contrast material. CO2 angiography has become a vital tool in patients who have allergic reactions to iodinated contrast material and those who have compromised renal functions.

What Are the Properties of Carbon Dioxide Gas?

• CO2 gas is colorless and odorless.

• It is highly soluble, and hence the CO2 bubbles completely dissolve within minutes when injected into any vessel.

• It has low viscosity, due to which CO2 can be injected even with the smallest needles or catheters and in smaller vessels.

• CO2 has high compressibility, which could result in an explosive delivery of the gas, causing greater discomfort during injection. In order to prevent this, a small amount of CO2 (3-5cc) should be injected first to clear the fluids and decrease the gas compression.

• It is an inexpensive gas.

• It is relatively safe, as no toxicity, allergy, or adverse issues are reported when appropriately used.

• CO2 gas is extremely buoyant and hence floats above the blood. This property helps in the filling of superficial vessels with ease however hinders easy fill of the deeper vessels.

• CO2 cannot be diluted as it does not blend with blood.

• Rapid diffusion through the lungs (usually dissipated within 30 to 45 seconds after administration).

What Are the Disadvantages of Using Carbon Dioxide?

• Since CO2 is extremely buoyant, the patient's position may influence the filling of the vessel. For a complete filling of arteries with a posterior course like lumbar or renal arteries, the patient should be in a more reclined position.

• Increased interobserver variability as CO2 has low radio opacity.

Where Is Carbon Dioxide Angiography Indicated?

CO2 angiography is usually used for peripheral vessels and arteries below the diaphragm. However, the venous system can be assessed throughout the body, excluding the cerebral vessels. It is indicated in the following condition:

• Patients with a known history of allergy to iodinated contrast medium.

• Patients with renal diseases are more susceptible to contrast-induced nephropathy.

• As CO2 is considered very safe, it is used in aortography, visceral angiography, and renal arteriography.

• It is used to aid in stent placement in procedures like angioplasty.

• Repair of a dialysis fistula.

What Is the Principle of Carbon Dioxide Angiography?

CO2 has low radio opacity when compared with iodinated contrast material. Hence CO2 is also known as a negative contrast medium. The difference in the radiation absorption coefficients would result in the contrast depicted. Since CO2 absorbs less radiation than iodine, the vessels look brighter as compared to iodine-based contrast materials, where vessels appear black.

CO2 once injected into the blood, converts into bicarbonate and reverts as CO2 before leaving the lung tissue. This chemical conversion is catalyzed by carbonic anhydrase. The entire CO2 can be dissipated in a single pass within 30 to 45 seconds from the administration of the first shot.

What Are the Preparations Required Before the Procedure?

• CO2 angiography requires sedation; hence the patient will be asked to fast for six to eight hours before the procedure.

• Patients can wear comfortable clothes and remove all jewelry, accessories, and other metallic objects.

• Patients should inform the doctor if they have any history of allergies.

• Patients who think they could be pregnant should also inform the doctor before the procedure.

• Doctors may prescribe blood tests to determine clotting time and other preoperative assays.

• The patient should keep the doctor informed if they are on Aspirin or other blood-thinning medications.

How Is Carbon Dioxide Angiography Done?

1. CO2 angiography can be conducted as an outpatient procedure.

2. The patient has to wear a hospital gown before the start of the procedure.

3. The patient will be made to lie on their back on the examination table.

4. An intravenous (I.V) line would be started on the patient’s arm to administer mild sedatives. No heavy sedatives or nitrous oxide should be used. It is done to prevent misdiagnosis of respiratory depression and hypotension caused by CO2 air contamination as side effects of sedatives.

5. The vitals such as pulse, breathing, and blood pressure would be monitored. An ECG machine would also be connected to monitor the patient’s heart.

6. Capnometer should be used to monitor ventilator and intravascular retention of CO2 in real-time.

7. The preferred site for catheter insertion is the arm or groin. The site would be shaved or trimmed of hairs and cleaned using an antiseptic solution.

8. The site would be anesthetized using a local anesthetic. The patient might experience a burning sensation.

9. A tiny incision is made in the vein through which a catheter is inserted. With the help of a fluoroscope, the catheter is carefully advanced up through the vein.

10. The CO2 contrast medium is usually delivered into the vessel either by a handheld syringe or a plastic bag system or with the help of a special portable CO2 delivery device known as a CO2mmander which in turn would be connected to the CO2 cylinder.

11. CO2 is never delivered straight from the cylinder as the gas is in high pressure; hence there is always a risk of injecting an excess volume of CO2.

12. A passive unidirectional flow of CO2 should be ensured, allowing the CO2 to expand and equalize with the atmospheric temperature.

13. Before injecting CO2, a small amount of CO2 (3-5cc) should be injected first to clear the fluids and prevent explosive injection.

14. The CO2 injection rates depend on the size, length, and flow of the vessel to be examined.

15. Co2 dissipates in 30 to 45 seconds; however, repeat injection should be timed two minutes apart and also after ensuring through a fluoroscope that the entire material is dissipated. The presence of CO2 beyond three minutes should induce suspicion of a trapped CO2 bubble or air contamination.

16. Once CO2 is injected, a digital subtraction angiography is used to obtain images.

What Are the Instructions After the Procedure?

• Patients are advised to lie flat on their back for a minimum of two hours after the procedure.

• Any respiratory or neurological disturbances should be reported to the doctor immediately.

• Patients are advised to refrain from smoking and alcohol for a few days after the procedure.

• Patients should avoid any form of physical strain for the next few days.

• They are advised to monitor the incision site for any unusual changes.

What Are the Limitations?

• CO2 is not recommended in arterial circulation above the diaphragm due to the possibility of cerebrovascular gas embolism and subsequent brain injury.

• Contraindicated with nitrous oxide sedation procedure as nitrous oxide prevents the proper excretion of CO2 from the blood.

• Possibility of increased intravascular pressure and hypertension. Hence extreme caution should be exercised while injecting in patients with vascular hypertension.

• Contraindicated in chronic obstructive pulmonary disease patients.

What Are the Adverse Effects Associated With the Procedure?

• Burning sensations, nausea, and pain at the injection site are usually temporary.

• Cerebral toxicity.

• Air embolism results in a stroke, paresthesia, myocardial infarction, or death.

• A possibility of bradycardia or hypotension.

Conclusion:

CO2 angiography has proven to be a vital tool in many diagnostic and interventional procedures. Though currently, it is considered an ancillary angiographic technique, the unique properties of CO2, its nontoxic nature, and easy disposal from the body can help it replace the traditional angiographic techniques completely. However, practitioners need to understand the nuances of this procedure better to employ them for better patient outcomes.