You are in: eMedicine Specialties > Radiology > VASCULAR/INTERVENTIONAL Carbon Dioxide AngiographyArticle Last Updated: Jul 29, 2005AUTHOR AND EDITOR INFORMATIONSection 1 of 7
  Author: Kyung J Cho, MD, FACR, William Martel Professor of Radiology, Fellowship Program Director, Department of Radiology, Division of Interventional Radiology, University of Michigan Medical School Kyung J Cho is a member of the following medical societies: American College of Radiology, American Heart Association, American Medical Association, American Roentgen Ray Society, Association of University Radiologists, and Radiological Society of North America Coauthor(s): Irvin Hawkins, MD, Chief, Professor, Department of Radiology, University of Florida Editors: Anthony Watkinson, MD, Professor of Interventional Radiology, The Peninsula Medical School; Consultant and Senior Lecturer, Department of Radiology, The Royal Devon and Exeter Hospital, UK; Bernard D Coombs, MB, ChB, PhD, Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand; Douglas M Coldwell, MD, PhD, Professor of Interventional Radiology, Department of Radiology, University of Texas Southwestern Medical Center; Robert M Krasny, MD, Consulting Staff, Department of Radiology, The Angeles Clinic and Research Institute; Eugene C Lin, MD, Consulting Staff, Department of Radiology, Virginia Mason Medical Center Author and Editor Disclosure Synonyms and related keywords: CO2 angiography, negative contrast, vascular imaging, allergic reactions to contrast, contrast reactions, hypersensitivity to contrast, contrast material, contrast agent, contrast medium INTRODUCTIONSection 2 of 7
  Background Carbon dioxide (CO2) gas is used as an alternative contrast to iodinated contrast material. The gas produces negative contrast because of its low atomic number and its low density compared with the surrounding tissues. When injected into a blood vessel, carbon dioxide bubbles displace blood, allowing vascular imaging. Because of the low density of the gas, a digital subtraction angiographic technique is necessary for optimal imaging. The gas bubble can be visible on a standard radiograph and fluoroscopic image. Because of the lack of nephrotoxicity and allergic reactions, CO2 is increasingly used as a contrast agent for diagnostic angiography and vascular interventions in both the arterial and venous circulation. The gas is also used as a contrast agent for imaging of the nonvascular structures such as the bile duct, upper urinary tract, gastrointestinal tract, and peritoneal cavity. CO2 is particularly useful in patients with renal insufficiency or a history of hypersensitivity to iodinated contrast medium. CO2 should not be used as a contrast agent in the coronary and cerebral circulations because of the possibility of adverse effects secondary to a gas embolism. Physical properties CO2 is a colorless and odorless gas, and it cannot be visually distinguished from air. The incorrect application of technique may result in air contamination because (much less soluble in blood than CO2) contamination, which may result in serious complications. A thorough understanding of the unique physical properties of CO2 is necessary for safe and effective CO2 angiography. CO2 is approximately 20 times more soluble than oxygen. When injected into a vessel, CO2 bubbles completely dissolve within 2-3 minutes; however, if the gas is trapped in a large abdominal aneurysm, it may persist, allowing gas exchange between the CO2 and nitrogen in the blood. This exchange may result in colonic ischemia and the occlusion of the inferior mesenteric artery. Injections of CO2 should be separated by 2-3 minutes to prevent the localized accumulation of the gas bubbles, which may produce clinically a significant gas embolism, particularly in the pulmonary artery. CO2 is compressible during injection and expands in the vessel as it exits the catheter. Clear the fluid of the catheter by using 3 mL of CO2 before injection to reduce the explosive delivery. The explosive delivery is unlikely to cause vascular damage, but it may contribute to discomfort during the injection. The low viscosity and compressibility of the gas accounts for the greater sensitivity of CO2 as a contrast agent in detecting the source of bleeding compared with iodinated contrast material. CO2 is lighter than blood plasma; therefore, it floats above the blood. When injected into a large vessel such as the aorta or inferior vena cava, CO2 bubbles flow along the anterior part of the vessel with incomplete blood displacement along the posterior portion. Because of their anterior origin, the celiac and superior mesenteric arteries fill well with small volumes ( <30 mL) of CO2. Filling renal arteries may require rotation of the patient with the side of the renal artery elevated above the level of the table. If the renal artery remains unfilled, catheterization of the artery and selective injection is indicated. The buoyancy of the gas is not a problem when the vessel to be imaged is smaller than 10 mm in diameter because the gas bubbles tend to displace the blood in greater than 80% of the lumen. Elevation of the lower extremity to 15-20° with an intra-arterial injection of 100-200 µm of nitroglycerine improves gas flow and filling of the arteries in the lower extremity. CO2 is approximately 400 times less viscous than iodinated contrast medium. The low viscosity permits manual gas injection with small-bore catheters between the catheter and guidewire. Doses of CO2 required for aortic imaging can be manually injected by using a 4F or 5F end-hole diagnostic catheter. The low viscosity accounts for better filling of collateral vessels in both arterial and venous occlusive disease and for portal vein after the wedged hepatic injection with CO2. Advantages of CO2 CO2 is less dense than iodinated contrast medium, and the overall quality of the CO2 vascular image is slightly less than that obtained with contrast medium. Usually, multiple hand injections are required, and the radiation exposure to the operator and patient can be increased. However, CO2 has several notable advantages compared with iodinated contrast medium. CO2 causes no allergic reaction. Because CO2 is a natural byproduct, it has no likelihood of causing a hypersensitivity reaction. Therefore, the gas is an ideal alternative to iodinated contrast medium in patients with a history of allergic reactions. No steroid preparation is needed when CO2 is used. CO2 causes no renal toxicity. Experimental and clinical findings indicate that the selective injection of CO2 into the aorta or into the renal artery is safe and causes no renal injury, even in patients with diabetes or compromised renal function. Therefore, the gas is the preferred contrast agent for renal artery stent placement. CO2 causes no hepatic toxicity. The authors have personally used CO2 as a contrast agent for celiac, splenic, superior mesenteric, and hepatic arteriograms in patients with a variety of diseases. No incidence of hepatic parenchymal injury has occurred after the injection of CO2. Unlimited amounts of CO2 can be used for vascular imaging because the gas is effectively eliminated by means of respiration. However, the operator should allow sufficient time for its clearance. A minimum of 2 minutes is needed for the first CO2 dose to completely dissolved before another dose is injected. CO2 is particularly useful in patients with compromised cardiac and renal function who are undergoing complex vascular interventions. Compared with nonionic contrast agents and gadolinium-based contrast medium (>$1/mL), CO2 is inexpensive ($0.005/mL). A 3 X 106-mL CO2 US Pharmacopeia cylinder costs approximately $600. Refilling the cylinder costs less than $100. TECHNIQUESSection 3 of 7
Patient preparation No specific patient preparation is required for CO2 angiography. The standard preparation for catheter angiography is used. Patients with a history of allergy to contrast material do not require steroid preparation. CO2 may be used as a contrast agent for outpatient angiography. Contraindications No absolute contraindications to the use of CO2 exist. Do not use CO2 in vessels above the diaphragm because of the risk of intracerebral propagation and stroke. Use CO2 with caution in patients with pulmonary insufficiency or pulmonary hypertension because diagnostic doses of CO2 can increase pulmonary arterial pressure. Do not use CO2 in patients with right-to-left shunts because of the possibility of paradoxical gas embolism. Sedation and analgesia Avoid heavy sedation during CO2 angiography. Respiratory depression and hypotension caused by air contamination may be mistaken for the adverse effects of the sedatives and/or analgesics. Patient monitoring Monitor all patients undergoing CO2 angiography with ECG. Monitor the O2 saturation levels, blood pressure, respiratory rate, and heart rate, and obtain capnograms if the patient is intubated. Check the blood pressure before and at 1, 2, and 3 minutes after CO2 injection. A significant change in any monitoring parameter suggests the inadvertent delivery of excessive doses of CO2 or air contamination. CO2 cylinder For CO2 angiography, use a US Pharmacopeia grade CO2 that is 99.99% pure. Do not connect the patient directly to the cylinder because of the potential risk of delivering excessive volumes of CO2. Delivery methods CO2 can be delivered into a vessel by using a 30- to 60-mL hand-held syringe, a closed bag system, or a dedicated CO2 injector. When using a syringe, fill it directly from a CO2 cylinder. Do not aspirate CO2 into the syringe because this technique may cause air contamination. After the syringe is filled with CO2, reduce its pressure to the atmospheric level by quickly opening and closing the stopcock. Do not leave the CO2-filled syringe with an open stopcock on the table before injection because the CO2 in the syringe (with a CO2 concentration of >99%) is rapidly replaced with air (with a CO2 concentration of 0.03%). The plastic bag delivery system (AngioDynamics, Queensbury, NY) is particularly useful when multiple injections are needed. An AngioFlush 111 fluid collection bag is filled with CO2 and connected to the reservoir port of the AngioFlush 111 Fluid Management System. The latter has airtight connections with the check valve, the injection port, the bleedback port, and the catheter port. Check the valves reduce stopcock manipulation, which may result in air contamination. The bag must be tightly connected to the reservoir port of the delivery system to prevent air contamination. The bleedback port near the catheter port allows sodium chloride solution, contrast medium, or CO2 injections. If CO2 is to be injected with a guidewire in the catheter, a Y-connector (Touy-Borst) should be connected to the injection port, or a 30-mL syringe is connected to the bleedback port filled with CO2 from the injection syringe before the guidewire is introduced. A dedicated CO2 injector is currently available (CO2 JET CO2 Angiographic System, AngioDynamics), which allows for the reliable, nonexplosive delivery of CO2. The system eliminates any possibility of air contamination or accidental injection of excessive quantities. The injector also includes an automatic system for flushing sodium chloride solution, an iodinated contrast injection capability, and a complete patient monitoring system (ECG, blood pressure, and O2 saturation). Study findings show that the automated injector is safe and easy to use for CO2 angiography, producing diagnostic images. In contrast to the plastic bag system, the CO2 injector reduces radiation exposure to the operator. The injector is not approved by the US Food and Drug Administration, but is available for use outside the United States. Injection factors The injection rate depends on the diameter, length, and flow of the vessels being imaged. For an aortogram or an inferior vena cavagram, 30-50 mL of CO2 is injected. When imaging aortic branches (celiac, superior mesenteric, renal arteries) or arteries of the lower extremity, 20-30 mL is used. Imaging Elevation of target vessels 15-20° above the level of the angiographic table and -the intra-arterial administration of 100-150 µg of nitroglycerin can improve filling of the distal arteries of the lower extremities. If available, use a 1024 X 1024 digital subtraction angiographic system and magnification technique. Stacking software for integrating a series of images has solved problems with CO2 bubble break up after injection. CLINICAL APPLICATIONSSection 4 of 7
CO2 is used widely as an intravascular contrast agent for imaging both the arterial and venous circulations, particularly in patients with renal insufficiency and a history of hypersensitivity to iodinated contrast medium. CO2 can be used as a contrast agent for various vascular interventions. A summary of the clinical applications of CO2 s a contrast agent for vascular diagnosis and interventions follows. Diagnostic applications CO2 may be useful in the following arterial procedures: abdominal aortography (aneurysm, stenosis), iliac arteriography (stenosis), runoff analysis of the lower extremities (stenosis, occlusion), renal arteriography (stenosis, arteriovenous fistula [AVF], aneurysm, tumor), renal arterial transplantation (stenosis, bleeding, AVF), and visceral arteriography (anatomy, bleeding, AVF, tumor). CO2 may be useful in the following venous procedures: venography of the upper extremities (stenosis, thrombosis), inferior vena cavography (prior to filter insertion), wedged hepatic venography (visualization of portal vein), direct portography (anatomy, varices), and splenoportography (visualization of portal vein). Interventions CO2 may be useful in the following interventional procedures: balloon angioplasty (arterial, venous), stent placement (arterial, venous), embolization (renal, hepatic, pelvic, mesenteric), transjugular intrahepatic portacaval shunt creation, and transcatheter biopsy (hepatic, renal). ADVERSE EFFECTS AND MANAGEMENTSection 5 of 7
The occurrence and severity of the adverse effects of angiography may be related to the dose or air contamination. CO2 aortography and celiac arteriography can cause nausea and pain lasting 2-3 minutes. No specific treatment is required. Placing the patient in a left or right side-up position may relieve the pain. A decrease in the doses of CO2 usually reduces the frequency and severity of pain. The injection of CO2 for runoff of the lower extremities may cause pain. Decreasing the amount of CO2 with selective injection and stacking technique helps in reducing the pain. The injection of CO2 into a peripheral vein for upper extremity venography may cause pain at the injection site. The mechanism of pain is probably the explosive delivery secondary to gas compression. Purging the injection tube with 3 mL of CO2 and administering 20-40 mg of lidocaine immediately before the injection of CO2 for venous imaging helps in reducing the pain. When CO2 is trapped in an aortic aneurysm, the gas bubbles may occlude the inferior mesenteric artery, resulting in colonic ischemia. Inadvertent injection of excessive volumes of CO2 or air contamination can cause vapor lock in the pulmonary artery, which results in severe hypotension. When air contamination occurs, fluoroscopy of the chest shows gas bubbles in the pulmonary artery that persist for longer than 30 seconds. If hypotension develops, place the patient in a Trendelenburg and left lateral decubitus position. If possible, aspirate the air in the pulmonary artery by using a catheter. MULTIMEDIASection 6 of 7
REFERENCESSection 7 of 7
Carbon Dioxide Angiography excerpt Article Last Updated: Jul 29, 2005 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
