The use of CO₂ in peripheral angiography enables a contrast-sparing or Zero Contrast strategy for vascular procedures below the diaphragm, reducing exposure to iodinated contrast media in high-risk patients. This article is intended for vascular surgeons and interventional radiologists who want to move from general principles to practical decision-making, using objective image quality criteria and a planned fallback strategy with micro-iodinated contrast. The goal is to make CO₂-guided procedures more repeatable, traceable, and audit-ready, while preserving renal function when the risk of AKI/CIN is clinically significant.
CO₂ is a gaseous contrast agent used in angiography as an alternative to iodinated contrast media, particularly for peripheral and abdominal vascular interventions. The real value is not simply "using CO₂," but making the decision in advance whether to adopt a CO₂-first strategy (CO₂ as the default imaging modality with iodinated contrast used only when necessary) or a CO₂-only strategy (aiming for zero iodinated contrast), while establishing objective criteria for when to activate a fallback. Workflow automation and standardization (for example, with automated systems such as the Angiodroid CO₂ Injector) reduce operator-dependent variability, improve procedural safety, and increase traceability of injection parameters.
A CO₂-first strategy is generally the most robust option when the patient is at increased renal risk but the procedure includes specific steps where iodinated contrast may improve anatomical definition, reduce procedure time, lower radiation exposure, or increase diagnostic confidence (for example, a final endpoint confirmation). A CO₂-only strategy is appropriate when complete avoidance of iodinated contrast is the primary objective, such as in patients with advanced CKD, severe iodinated contrast allergy, or a history of contrast-induced AKI, provided that the anatomy and procedural target are suitable for CO₂ imaging. Micro-iodinated contrast should be considered a planned component of the workflow—not a rescue measure. It consists of small, targeted injections intended to answer a specific clinical question (for example, confirming a critical stenosis, verifying device positioning, or assessing the procedural endpoint), with the rationale clearly documented.
The five scenarios below represent situations in which the benefit-to-risk ratio of CO₂ is particularly favorable because iodinated contrast may increase morbidity through acute kidney injury, prolonged hospitalization, or adverse reactions. In every case, the essential clinical question is: "Can I obtain sufficient diagnostic information and procedural control with CO₂, and at which specific procedural steps should I plan targeted micro-iodinated contrast in advance?"
In patients with advanced chronic kidney disease, a CO₂-only strategy is appropriate whenever the procedure is performed below the diaphragm and the primary objective is morphological or hemodynamic assessment of the peripheral vasculature. CO₂ becomes the foundation of the workflow: mapping angiograms, roadmapping, and intermediate procedural assessments are all performed using standardized CO₂ protocols. Micro-iodinated contrast should be reserved exclusively for binary decision points—for example, confirming the procedural endpoint or clarifying an ambiguous finding—and should be limited to selective injections, with both the total volume administered and the clinical rationale carefully documented.
When the patient's medical history includes significant hypersensitivity reactions to iodinated contrast media, the most straightforward strategy is CO₂-first with the goal of achieving CO₂-only imaging. Before the procedure, the team should establish whether iodinated contrast is absolutely contraindicated or whether acceptable alternatives exist, such as CO₂ angiography combined with complementary imaging techniques. If the use of micro-iodinated contrast is considered acceptable based on multidisciplinary assessment and individual patient risk, it should be pre-authorized from both a clinical and informed-consent perspective and restricted to essential procedural steps. In these situations, multidisciplinary communication among the interventional radiologist, vascular surgeon, anesthesiologist, and allergist (when appropriate) minimizes improvised decision-making during the procedure.
In frail diabetic patients, the risk often extends beyond estimated glomerular filtration rate alone. It reflects the combined burden of dehydration, concomitant medications, intercurrent infections, repeated procedures, and previous iodinated contrast exposure. In this setting, a CO₂-first strategy provides the greatest clinical value by substantially reducing baseline iodinated contrast exposure while preserving the option of using targeted micro-iodinated contrast whenever it can accelerate clinical decision-making or improve diagnostic certainty. The practical measure of success is straightforward: reducing total iodinated contrast volume while minimizing uncertain procedural steps creates a workflow that is both more sustainable and easier to justify during clinical audits.
Lengthy infra-diaphragmatic procedures often result in a progressive increase in iodinated contrast volume due to repeated angiographic assessments. In this setting, the advantage of CO₂ lies in transforming serial imaging into low renal-impact evaluations. A CO₂-first strategy with predefined micro-iodinated contrast triggers is therefore the most rational approach. Practical triggers include persistent uncertainty regarding critical anatomy, failure to achieve diagnostic imaging despite optimized CO₂ technique, or the need for a single high-definition image at a key decision-making point. Defining these triggers before the procedure minimizes bias and prevents the unintended accumulation of iodinated contrast.
During re-interventions, anatomical uncertainty is greater, making high-quality imaging essential for procedural safety. The most robust strategy is a CO₂-first approach, combined with a selective micro-iodinated contrast plan to clarify procedural steps in which CO₂ may be less conclusive, such as vessel overlap, complex collateral circulation, or endpoint assessment involving prosthetic material. In these cases, traceability becomes particularly important: documenting why iodinated contrast was introduced during a specific procedural step facilitates multidisciplinary case review and supports continuous improvement within the vascular team.
Before entering the angiography suite, determine whether the primary goal is to reduce iodinated contrast exposure (CO₂-first) or eliminate it entirely (CO₂-only), based on the patient's CKD stage, history of AKI/CIN, iodinated contrast allergy, and anticipated procedural complexity. Document this decision within the procedural plan so the entire team shares the same clinical objective.
Establish two to four objective triggers (for example, inability to confirm the procedural endpoint after optimized CO₂ imaging or persistent uncertainty regarding critical anatomy) and associate each trigger with a predefined action, such as selective micro-iodinated contrast, alternative imaging, or procedural reassessment. This prevents uncontrolled escalation of iodinated contrast use.
Prepare the delivery circuit, dedicated consumables, and injection system according to the manufacturer's Instructions for Use and institutional protocols. Coordinate injection timing and image acquisition to maximize diagnostic quality. When using an automated digital system (such as the Angiodroid CO₂ Injector), enable parameter recording to ensure repeatability and facilitate comparison between procedures.
For every acquisition, ask a simple question: does this image provide the information required to guide the next clinical decision? If the answer is yes, continue using CO₂. If not, perform one round of technical optimization (technique or acquisition). If uncertainty persists regarding a critical procedural decision, activate the predefined fallback strategy.
Record the imaging strategy, injection parameters, number of injections, fallback triggers, and total iodinated contrast volume administered. This documentation supports internal audits, multidisciplinary case discussions, and continuous improvement of CO₂ angiography protocols.
Choose a CO₂-first strategy when your goal is to substantially reduce iodinated contrast while anticipating one or two procedural steps in which a small amount of contrast may improve diagnostic confidence or speed decision-making (for example, final endpoint confirmation). A CO₂-only strategy is appropriate when iodinated contrast is clinically undesirable, such as in patients with advanced chronic kidney disease, a history of contrast-induced AKI, or severe iodinated contrast allergy, provided the vascular territory is suitable for CO₂ imaging. In both cases, the key principle is to predefine the indications and limits for using targeted micro-iodinated contrast.
Switch to micro-iodinated contrast when, despite optimized CO₂ imaging technique, the angiographic findings remain inconclusive for a critical clinical decision, such as target identification, lesion severity assessment, or procedural endpoint confirmation. A practical indicator is the inability to answer the next clinical question with a clear "yes" or "no." Micro-iodinated contrast should always be administered selectively, with both the rationale and the total contrast volume documented.
No. CO₂ is primarily indicated for vascular procedures performed below the diaphragm and should only be used in appropriate vascular territories by teams experienced in CO₂ angiography. Safe use depends on appropriate patient selection, the vascular territory being treated, procedural technique, and adherence to institutional protocols and the manufacturer's Instructions for Use. Whenever the anatomy or the clinical objective is not compatible with CO₂ imaging, an alternative imaging strategy should be planned in advance.
Traceability means systematically recording injection volumes, the number of injections, and—when available—additional parameters such as pressure and flow rate, together with the selected imaging strategy (CO₂-first or CO₂-only) and the reasons for activating the fallback strategy. This information supports clinical audits, multidisciplinary case discussions, protocol optimization, and continuous quality improvement. Automated digital systems simplify this process and ensure more consistent data collection.
Present the clinical indication (renal risk and/or iodinated contrast allergy), the selected imaging strategy (CO₂-first or CO₂-only), the estimated amount of iodinated contrast avoided, and the rationale for any targeted micro-iodinated contrast use. Include the traceability dataset (injection parameters, fallback triggers, and image quality assessment), together with immediate procedural outcomes such as technical success and complications. This structured format facilitates multidisciplinary discussion, supports protocol development, and contributes to defining institutional best practices.
Clinical and Compliance Note: The indications, contraindications, and technical settings for CO₂ angiography depend on the vascular territory being treated, the patient's clinical profile, and the specific device used. This guidance should always be integrated with institutional protocols, the manufacturer's Instructions for Use (IFU), and local safety policies.