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. Due to its high solubility rate and rapid diffusibility via the lungs, CO2 is safe for intravascular usage.
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
- allergy to iodinated contrast media
- poor renal function
- superior in:
- detection of bleeding
- opacification of small collaterals in occlusive disease
- arteriovenous (AV) shunting in tumors
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 AVF
-
relative
- COPD patients
- patients on nitrous oxide anesthesia: may increase the volume of the CO2 bubbles leading to pulmonary artery vapor lock which may be fatal
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