Follow-up evaluation after renal artery bypass surgery with use of carbon dioxide arteriography and color-flow duplex scanning

Physiology of Intraluminal Administration of Carbon Dioxide as a Contrast Medium

BACKGROUND

Carbon dioxide (CO2) exists in nature around us. In the middle of the 20th century, the intraluminal injection of CO2 demonstrated similar results to those of Digital Subtraction Angiography (DSA) with an iodinated contrast agent (ICA). Since then, the technology behind CO2 DSA has developed significantly.

OBJECTIVE

The aim of this study is to inform physicians about the unique properties of CO2 and its physiology after intraluminal injection.

METHODS

An extensive search for English literature on the properties of CO2 and the physiology of intraluminal administration was conducted using Pubmed.

RESULTS

There is sufficient literature on the properties of CO2 and the physiology of CO2 DSA. A review of this literature explains what happens to the human organism after the injection of CO2.

CONCLUSION

There is enough evidence that CO2 DSA is both effective, diagnostic and safe, but the properties of CO2 should be taken under consideration as complications occur, although rarely.

Carbon Dioxide in Vascular Imaging and Intervention

Angiography with iodinated contrast agents is bound up with the risks of contrast-induced nephrotoxicity and hypersensitivity, which led to the idea of using carbon dioxide (CO2) gas as a negative contrast medium to eliminate these drawbacks. During the last decade, refinements and experiences have proved carbon dioxide digital subtraction angiography (CO2-DSA) to be an accurate, safe, and clinically promising vascular imaging modality, with the advantages of no hypersensitivity and no nephrotoxicity as well as minimal patient discomfort. In this article, we have reviewed the history, physical and chemical aspects, techniques, and pathophysiologic changes with the use of CO2-DSA as well as some clinical trials. Applications of CO2 gas in vascular interventions and other imagings, and the advantages and limitations of using CO2 gas in DSA are also discussed.

Management of transplant renal artery stenosis

Transplant renal artery stenosis is the most frequent vascular complication of transplantation. Early detection and correction reduce patients' morbidity and allograft dysfunction. Although noninvasive imaging can detect an underlying stenosis, angiography with subsequent angioplasty or stenting, or both, provides definitive diagnosis and treatment. With the introduction of alternative contrast agents and newer catheter and stent technology, these procedures can be performed safely with little risk of contrast-induced nephropathy or allograft loss.

Renal artery stenosis: duplex US after angioplasty and stent placement

PURPOSE

To evaluate the hemodynamic outcome of technically successful percutaneous transluminal renal artery angioplasty and stent placement (PTRAS) with duplex ultrasonography (US).

MATERIALS AND METHODS

Eighteen patients who underwent PTRAS in 22 renal arteries were prospectively examined. All had abnormal preprocedural duplex US findings. Those who had significant renal artery stenosis (>70%) at angiography and underwent technically successful percutaneous interventions were enrolled. Standard intrarenal duplex US parameters (acceleration index [AI], acceleration time, waveform morphology grade, and resistive index) were compared before and after interventions.

RESULTS

A significant AI increase occurred after PTRAS (9.02 m/sec(2) +/- 4.85 [SD]), as compared with before intervention (2.34 m/sec(2) +/- 2.03; P <.001). Acceleration time significantly decreased from 0.084 second +/- 0.049 to 0.032 second +/- 0.008 (P <.01). There was also a significant resistive index increase from 0.69 +/- 0.12 to 0.79 +/- 0.12 (P <.01). Abnormal waveform morphology (modified Halpern waveform grade 3-6) was present in 19 (86%) of 22 intrarenal arteries prior to intervention, as compared with one (5%) after PTRAS (P <.001). In the instance in which an abnormal waveform persisted after intervention, waveform morphology improved from grade 6 to grade 3, with a concomitant AI increase from 0.96 to 5.1 m/sec(2).

CONCLUSION

The findings suggest an important potential role for duplex US in noninvasive assessment of the immediate hemodynamic outcome and long-term follow-up of PTRAS.

Carbon dioxide angiography for endovascular grafting in high-risk patients with infrarenal abdominal aortic aneurysms

Allergic reactions to contrast media, preexisting renal dysfunction, and hyperthyroidism are relative contraindications for angiography with conventional contrast medium. Carbon dioxide (CO(2)) angiography is an alternative method in high-risk patients because CO(2) is nontoxic, without allergic potential, and not iodic. CO(2)-related complications are extremely rare. Because renal insufficiency often occurs in vascular patients, this method will become increasingly important for endovascular surgery. We report on three consecutive patients with asymptomatic infrarenal aortic aneurysm and concomitant renal dysfunction or allergic reactions to standard contrast media. Aortic stent grafts were deployed under CO(2) angiographic control without complications or worsening of renal function.

CO2 as a contrast medium in endoluminal treatment of high flow vascular malformations

PURPOSE

To evaluate the diagnostic usefulness of CO2 as a radiologic contrast medium in pre and post-embolization of hemodynamically active vascular malformations.

MATERIAL AND METHODS

Eight pre-and post-embolization angiographies were performed on five patients with hemodynamically active vascular malformations. In all cases sequentially iodinated contrast medium and CO2 were used. Procedures were performed using Philips Integris V equipped with specific software to process images obtained with CO2 as contrast medium and with a purpose-built gas injector pump. The images were assessed by three interventional radiologists who evaluated the findings by consensus. They were asked whether uptake of the malformations were better, worse or the same with iodinated contrast and CO2. The images were judged according to the following characteristics; quality, the filling in of the contrast in afferent artery of the HAVM, caliber and number of vessels and existence of pathologic communications in HAVM. These characteristics were assessed in all the patients of the study, both before and after embolization.

RESULTS

The CO2 angiographic results were compared to those obtained using iodinated contrast material. Iodinated contrast provided superior image quality in all performed studies. The filling of arterial afference of HAVM was well defined with both contrast media. In all performed cases with CO2, the malformations showed more vessels. No inmediate nor subsequent complications developed with CO2 injections, except in one female patient, who presented an intense sensation of cramps in the lower limbs.

CONCLUSION

CO2 is a useful diagnostic and assessment tool before and especially during the embolization of hemodynamically active vascular malformations. It improves quantification and uptake of the malformation's vascular architecture, detecting collateral circulation and arteriovenous shunts. It also detects residual post-embolization disease when iodinated contrast agent is unsuccessful.

Identification of the portal vein: wedge hepatic venography with CO2 or iodinated contrast medium

RATIONALE AND OBJECTIVES

The purpose of this study was to evaluate the utility of CO2 versus iodinated contrast medium for wedge hepatic venography in identifying portal vein anatomy during transjugular intrahepatic portosystemic shunt (TIPS) procedures.

MATERIALS AND METHODS

Wedge hepatic venograms obtained with CO2 or iodinated contrast medium and direct portograms of 43 patients undergoing TIPS procedures were analyzed retrospectively. Wedge venography was performed in 23 patients with CO2 and in 21 with iodinated contrast medium; direct portography was subsequently performed in 42 of 44 patients with iodinated contrast medium and in one with CO2. All cases were reviewed systematically to compare portal vein anatomy and completeness of anatomic identification between direct portography and wedge venography, and the results with CO2 were compared to those with iodinated contrast material.

RESULTS

On the basis of opacification of the main portal trunk, branches, or both, the portal vein appearance (definition of the portal bifurcation) was good to excellent in 21 of 23 patients imaged with CO2 but in only two of 20 patients imaged with iodinated contrast medium. Wedge venograms agreed with direct portograms in 91% (21 of 23) of the CO2 cases and in 10% (two of 20) of the iodinated contrast medium cases. The two patients with poor opacification using CO2 had poor delineation of the main portal trunk, branches, and varices. TIPS could not be created in three patients, In two, abnormal morphology was identified at CO2 venography; in the third, wedge venography was not performed.

CONCLUSION

Wedge hepatic venography with CO2 compared with iodinated contrast medium has a substantially higher likelihood of correctly and completely identifying the location and anatomy of the portal vein.

Angiography with carbon dioxide (CO2)

CO2 possesses many advantages over conventional iodinated contrast agents used for arteriography. It is nonallergic and lacks renal toxicity. Its unique properties permit use of smaller catheters in diagnostic and therapeutic angiographic procedures, allow optimal vascular imaging of various neoplasm, assist in detection of occult gastrointestinal bleeding, and facilitate TIPS procedures. With digital subtraction techniques and stacking programs, CO2 arteriography is as accurate as iodinated contrast studies in most patients and thus is the preferred arterial imaging technique in patients with contrast allergy and renal insufficiency. CO2 is also extremely inexpensive compared with available contrast agents. Understanding of the effects of buoyancy and compressibility is necessary for safe, controlled delivery of CO2 during arteriography, but only rare complications have occurred in our large experience with CO2 angiography. Thus, use of CO2 as an arterial contrast agent significantly expands the safety and utility of arterial imaging in patients with peripheral vascular disease.

Effects of selective angiography of the carotid artery with carbon dioxide on electroencephalogram somatosensory evoked potentials and histopathologic findings. A pilot study in pigs

RATIONALE AND OBJECTIVES

The authors investigate the cerebral effects of selective carotid angiography with carbon dioxide (CO2).

METHODS

In 6 pigs, CO2 was injected into the carotid artery with consecutively increasing doses. Cerebral function was monitored with two-channel electroencephalography and somatosensory evoked potentials (SEPs). After the experiment the brains were investigated histopathologically.

RESULTS

Initial doses led to reversible decreases in electroencephalograph power by 40% to 80%. Further doses result in partly nonreversible electroencephalographic changes. Somatosensory evoked potential latencies (n = 5) were not changed. Amplitudes were not affected in low dose ranges up to 40 mL CO2. Higher CO2 doses led to different changes. There were no SEP amplitude reductions (n = 1), as well as reversible (n = 2) and nonreversible (n = 2) SEP amplitude reductions. Histopathologically, edema (n = 6), edema necrosis (n = 2), and destroyed cells as a sign of ischemia (n = 2) were found.

CONCLUSIONS

Administering CO2 in brain supplying arteries impairs the cerebral function. Consecutive, increasing doses lead to partly nonreversible electroencephalographic and SEP changes and brain tissue damages.

1996 AUR Memorial Award. Densitometric analysis of eccentric vascular stenoses: comparison of CO2 and iodinated contrast media

RATIONALE AND OBJECTIVES

The authors compared the accuracies of CO2 and iodinated contrast material in the densitometric quantification of eccentric vascular stenoses.

METHODS

Five precision-machined eccentric phantom stenoses of 50%, 60%, 70%, 80%, and 90% cross-sectional area narrowing were integrated into a pulsatile ex vivo flow model, imaged with digital subtraction angiography (DSA), and analyzed with densitometry. Relationships between the actual and measured (densitometric) degree of cross-sectional area narrowing were evaluated by using linear regression analysis and paired Student t tests. Comparison measurements were obtained in en face and profile projections. In addition, the effect of iodinated contrast material concentration was evaluated over a range of dilutions (47-282 mg iodine per milliliter).

RESULTS

CO2 yielded significantly more accurate results than did iodinated contrast material (282 mg iodine per milliliter) in the 50%, 60%, and 70% stenosis models when imaging was performed en face (P < .005). The best overall correlation was observed with CO2 DSA when imaging in profile (slope = 0.91, intercept = 2.42% actual stenosis, r = .99). The accuracy of densitometric stenosis estimation was inversely related to the concentration of iodinated contrast material.

CONCLUSION

CO2 DSA densitometry, under the conditions of these experiments, yields quantitative measures of relative cross-sectional area narrowing that are comparable with, and under some circumstances surpass, those obtained with iodinated contrast material-based DSA. In this model, CO2 was more useful than iodinated contrast material in 50%-70% stenosis when imaging in the least-optimal plane of stenosis quantification, the en face projection.

Selection of patients for renal artery repair using captopril testing

BACKGROUND

Prediction of improvement following surgical or radiologic intervention in patients thought to have renovascular hypertension (RVH) is often unreliable. Use of the angiotensin-converting enzyme inhibitor captopril in conjunction with measurement of peripheral renin levels or radioisotope renograms is thought to detect patients with functionally significant renal artery stenosis. However, it is unclear whether these tests can identify patients whose hypertension will significantly improve after renal artery repair.

PATIENTS AND METHODS

The records of 52 consecutive hypertensive patients undergoing captopril studies followed by renal artery repair were reviewed. All patients had either renal artery stenosis > 75% or renal artery occlusion. Preprocedure evaluation included a captopril challenge test (measurement of peripheral renin levels after captopril ingestion) (n = 12) or a captopril renogram (determination of renal blood flow and glomerular filtration rate before and after captopril administration) (n = 40). Either renal artery bypass/nephrectomy (n = 41) or balloon angioplasty (n = 11) was done in all patients (18 bilateral/34 unilateral). No periprocedural deaths occurred. All surgically placed bypass grafts were shown to be patent by contrast or carbon dioxide arteriography before hospital discharge.

RESULTS

Preprocedure captopril tests were positive (suggestive of RVH) in 39 patients (75%) and negative in 13 (25%). All patients with positive captopril tests had improvement in their RVH after intervention (17 cured, 22 improved) while 8 of 13 patients with negative captopril tests had no improvement in blood pressure control. Four of five false-negative tests were associated with a unilateral total renal artery occlusion, making detection of a postcaptopril effect impossible. If these 4 patients are excluded from analysis, preprocedure captopril testing was 98% accurate in predicting postprocedure outcome.

CONCLUSIONS

Preprocedure captopril testing permits extremely accurate selection of patients with renal artery stenosis who will benefit from renal artery repair.

Venography with carbon dioxide as a contrast agent

PURPOSE

The purpose of this study was to evaluate the feasibility, safety, and potential role of carbon dioxide (CO2) as a contrast agent for venography.

METHODS

Consecutive patients with contraindications to iodinated contrast agents or with unsatisfactory iodinated contrast studies underwent CO2 digital subtraction venography. The images were rated by three experienced angiographers. Image quality and complications were assessed.

RESULTS

Over a 14-month period, 66 vein segments were studied in 21 patients. There was good correlation between experienced angiographers on CO2 image quality (Ri = 0.80) and good agreement on diagnosis (k = 0.62). In 91% of the vein segments evaluated with C02 there was interobserver agreement on the diagnosis. Upper extremity veins were adequately imaged with CO2 alone in all (6/6) patients with contraindications to iodinated contrast. Following suboptimal iodinated contrast studies in six patients, CO2 produced significantly better quality upper extremity central vein images (p < 0.05). Pain following injection into peripheral veins was the only CO2-related complication. Inferior vena cava (IVC) filters were successfully deployed with CO2 alone in 78% (7/9) of patients; two required iodinated contrast.

CONCLUSIONS

Based upon initial experience, CO2 venography can be recommended in patients with contraindications to iodinated contrast or unsatisfactory iodinated contrast studies.

CO2 digital angiography: a safer contrast agent for renal vascular imaging?

Although the new nonionic contrast agents are safer than ionic agents, renal insufficiency and even death still occur occasionally. Therefore, we have explored the use of carbon dioxide (CO2) as an alternative angiographic contrast agent used in combination with digital subtraction angiography. Clinical observations have been made in over 800 patients. The images obtained are of equivalent diagnostic quality compared with those using conventional iodinated contrast agents. Recent advances in imaging, including "stacking," provide images comparable with iodinated contrast. Very small vessels, equivalent to third-order branches of the renal artery, can be imaged satisfactorily with CO2. Occasional studies with CO2 yield information not apparent with iodinated contrast agents, including excellent visualization of arteriovenous shunts, collateral circulations, malignant tumors, and minute amounts of arterial bleeding. Many of the advantages and disadvantages of CO2 derive from its special physical and chemical properties. The advantages include no allergic potentiation and no renal metabolism of CO2, because CO2 is cleared by the lungs and does not recirculate. Other advantages include delivery by very small catheters because of the low viscosity of CO2, minimal discomfort on injection, and very low cost. However, the low-density and compressibility of CO2 poses some special problems. Imaging requires digital subtraction angiography with electronic enhancement and injections require an experienced investigator and, ideally, a dedicated CO2 injector. The dedicated CO2 injector provides calculated, controlled dosing and rates for injection, while excluding the possibility of air contamination. The buoyancy of CO2 inhibits good filling of dependent vessels. Accordingly, CO2 does not normally produce good nephrographic images, although proximal renal arteries are normally shown clearly. Experimental studies in dogs, whose renal arteries have been injected repeatedly with very large doses of CO2, demonstrate only transient changes in renal blood flow and no endothelial cell damage. However, these studies also showed clearly that renal ischemia can occur due to a "vapor lock" phenomenon if the kidney is positioned vertically above the injection site, and recurrent injections are given without time for absorption of the arterially delivered CO2 boluses. Uncontrolled studies in over 800 patients have confirmed that CO2 likely has a very low renal toxicity. At the University of Florida, CO2 is the radiologic contrast agent of choice in patients with renal insufficiency, especially those with diabetes mellitus, and in those with pre-existing allergy to iodinated contrast agents. Further controlled clinical studies are required to define the true clinical utility and safety of CO2 compared with conventional radiologic contrast agents.