Carbon dioxide (CO2) is an excellent negative contrast agent which has been used for a variety of vascular interventions since the introduction of digital subtraction angiography. Small volumes can be rapidly eliminated by the lungs in a single pass, facilitating safe usage for certain vascular imaging indications 4.
Physical and chemical properties
CO2 is an inexpensive, highly compressible, and low-viscosity gas. Toxicity is not an issue when used correctly. It does not mix with blood and hence cannot be diluted, rather it pushes away the blood column within the vascular bed. Its extreme buoyancy helps to opacify the non-dependant vascular bed. Its very low viscosity allows injection via small (22G) needles/3F catheters even when there is a guidewire in situ, and results in filling of the smallest branches regardless of blood flow rate and degree of stenosis.
Indications
poor renal function
detection of bleeding
opacification of small collaterals in occlusive disease
arteriovenous (AV) shunting in tumors
Can be used in both arteriography (below diaphragm) and venography 4
Contraindications
-
absolute
CO2 has potential neurotoxic and cardiotoxic effects hence it should not be used for cerebral or coronary artery (above diaphragm aorta) angiograms.
prone position injection should be avoided due to possible spinal ischemia
arterial limb of dialysis arteriovenous fistula
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relative
COPD patients due to delayed CO2 absorption (higher baseline CO2 levels)
patients on nitrous oxide anesthesia: may increase the volume of the CO2 bubbles leading to pulmonary artery vapor lock which may be fatal
pulmonary hypertension
Considerations
angiography staff should be adequately trained prior to use of CO2 equipment
capnography for monitoring CO2 levels
may not be available in some institutions
time between injections may be longer than conventional contrast injections
patient positioning - Trendelenburg
Complications
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air embolism, leading to;
Stroke, myocardial infarction, paralysis, amputation, or death
venous obstruction when used in venography 4
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abdominal pain during mesenteric arteriography 4