X-ray contrast media--an overview

Intravascular iodinated contrast media and the anaesthetist

The use of intravascular iodinated contrast media (ICM) in radiological investigations is common. Increasingly, anaesthetists and intensivists are involved in the care of patients undergoing these investigations. Whilst the use of ICM is generally safe there are important adverse effects that need to be recognised and measures instigated to prevent or treat these effects. In patients at risk of developing adverse reactions it is important to consider alternative modes of imaging so that ICM can be avoided. Strategies for the prevention of ICM nephropathy should be considered in all patients receiving ICM. Currently intravascular volume expansion with 0.9% saline has the strongest evidence base. The use of isotonic sodium bicarbonate combined with N-acetylcysteine appears promising in providing further benefits. Although the use of N-acetylcysteine alone has not been shown to significantly reduce the incidence of ICM nephropathy it is cheap, has few adverse effects and it would seem reasonable to continue its use in conjunction with intravascular volume expansion. The routine use of corticosteroid and antihistamine premedication is not always effective in preventing general adverse reactions.

Monitoring non-immediate allergic reactions to iodine contrast media

Non-immediate reactions to iodine contrast media (ICM) affect 2-5% of patients receiving these agents. We studied the immunological mechanisms involved in patients with a confirmed non-immediate reaction, maculopapular exanthema, after administration of ICM. The diagnosis was carried out by skin testing or drug provocation test. The immunological study was performed in sequential peripheral blood mononuclear cells taken from the onset of the reaction by flow cytometry and in skin biopsy by immunohistochemistry, with specific recognition by the lymphocyte transformation test (LTT) with different ICM. Flow cytometry showed an increase in the different activation markers [CD69, CD25 and human leucocyte antigen D-related (HLA-DR)] and the skin homing receptor [cutaneous lymphocyte-associated antigen (CLA)] in CD4 lymphocytes, whereas perforin was higher in the CD8 lymphocytes. The skin biopsy showed a perivascular mononuclear infiltrate composed of CD4 lymphocytes, expressing CD25, HLA-DR and CLA, with eosinophils. Intradermal skin tests and the LTT were positive to several ICM, including the culprit agent in four and three patients, respectively, with negative results in all 10 tolerant controls. We showed that a specific immunological mechanism was implicated in patients with non-immediate reactions to ICM. Moreover, the positive results in skin tests and lymphocyte proliferation tests indicated that an important cross-reactivity exists.

Formation of oxidation by-products of the iodinated X-ray contrast medium iomeprol during ozonation

The present work describes the investigation of the formation of oxidation by-products of the iodinated X-ray contrast medium (ICM) iomeprol during ozonation in water treatment. Bench-scale investigations revealed that ICM can be partly oxidized during ozonation processes, whereas the ionic diatrizoic acid showed the lowest reactivity. Iomeprol, as a representative of ICM, was not fully mineralized during ozonation. Thus, unknown oxidation by-products were formed. Aqueous solutions of iomeprol were treated by ozonation in order to assess the formation of oxidation by-products. The by-products were characterized by different liquid chromatography methods including detection of single-stage mass spectra, product ion mass spectra, and induced in-source fragmentation for analysis of iodine containing oxidation by-products. Aldehyde and carbonyl containing compounds were proposed to be among the stable by-products. A derivatization step confirms that the aldehyde and carbonyl moieties are major functional groups in oxidation by-products of iomeprol. Furthermore, oxidation by-products of iomeprol were detected at the outlet of an ozone reactor at a full-scale waterworks. However, the toxicological relevance of the by-products is a major future research tasks.

Contrast-induced nephropathy

Interventional radiological procedures involving anaesthesia are generally increasing. Contrast-induced nephropathy (CIN), usually defined as an increase in serum creatinine of 44 micromol litre(-1) (0.5 mg dl(-1)) or a 25% increase from the baseline value 48 h after intravascular injection of contrast media, is a common and potentially serious complication of the use of iodinated contrast media in patients at risk of acute renal injury. It is an important cause of hospital-acquired renal failure, may be a difficult differential diagnosis and the incidence does not appear to have changed over the last few decades. In the general population, the incidence of CIN is estimated to be 1-2%. However, the risk for developing CIN may be as high as 50% in some patient subgroups, such as those with diabetes mellitus and pre-existing renal impairment. The impact of CIN on clinical outcomes has been evaluated most extensively in patients undergoing percutaneous coronary intervention where it is associated with increased mortality both in hospital and at 1 yr. As treatment is limited to supportive measures while awaiting the resolution of the renal impairment, emphasis needs to be directed at prevention.

Cross-reactivity patterns of T cells specific for iodinated contrast media

BACKGROUND

Approximately 3% of patients exposed to iodinated contrast media develop delayed hypersensitivity reactions.

OBJECTIVE

We wanted to better understand the molecular basis of contrast media cross-reactivity.

METHODS

Cross-reactivity was assessed by skin testing and measurement of T-cell activation (CD69 upregulation) and proliferation ((3)H-thymidine uptake, 5,6-carboxyfluorescein diacetate succinimidyl ester staining) of PBMCs, T-cell lines, and T-cell clones of 2 patients with delayed hypersensitivity reactions to iohexol and iomeprol, respectively. Thirteen different contrast media and potassium iodide were compared.

RESULTS

Skin testing and analyses of PBMCs, T-cell lines, and clones showed broad cross-reactivity in both patients. Broad as well as more restricted cross-reactivity patterns were found in iohexol-specific and iomeprol-specific CD4(+) T-cell clones, whereas 1 iomeprol-specific CD8(+) T-cell clone showed no cross-reactivity at all. The reactivity to equimolar concentrations of iohexol and its dimer iodixanol was very similar, suggesting that the dimer was not more stimulatory than its monomer. Consistently low reactivity to iobitridol was found in both patients, but never to iodide. A frequency analysis of contrast medium-specific peripheral T cells gave values between 0.6 % (iomeprol) and 0.05 % (iobitridol).

CONCLUSION

Clinically observed cross-reactivity between different contrast media is a result of the presence of contrast media-specific T cells, some of which show a broad cross-reactivity pattern. Iodide ions, known to be present at low concentration in contrast media solutions, do not seem to be the causative moiety.

CLINICAL IMPLICATIONS

Detailed in vitro analysis might help identify noncross-reactive contrast media.

Adverse Events with Universal Use of Iodixanol for CT

OBJECTIVE

To evaluate the incidence of adverse events with the universal use of iodixanol for computed tomography (CT) and compare it with periods when iohexol was used exclusively.

METHODS

Iodixanol was used for CT in 15,142 consecutive patients and compared with 22,044 patients who received iohexol.

RESULTS

Adverse events were observed in 116 patients (0.77%) who received iodixanol and in 54 patients (0.25%) who received iohexol (P < 0.001). Immediate and delayed adverse events were seen in 76 and 40 patients (0.50% and 0.26%, respectively) who received iodixanol and in 52 and 2 patients (0.24% and 0.01%, respectively) who received iohexol, respectively (immediate, P = 0.002; delayed, P < 0.001). Adverse events with iodixanol and iohexol were as follows: mild, 89% and 98%; moderate, 10% and 2%; and severe, 1% and 0%, respectively.

CONCLUSIONS

Adverse events occurred in less than 1% of patients receiving either contrast agent. However, the incidence of immediate and delayed adverse events was significantly higher with iodixanol than iohexol.

Late skin reaction to iodixanol (Visipaque�): clinical manifestations, patch test study, and histopathological evaluation

Late reactions to iodinated contrast media are frequent. Cutaneous manifestations are the commonest, in which maculopapular exanthema, a type of cutaneous presentation, is widespread. Controversy exists about the utility of the skin test in the management of these reactions. The aim of this study is to analyse the clinical characteristics, the histopathological findings, and the results of the patch test in patients who developed a late skin reaction (LSR) to the nonionic, dimeric, iodinated contrast media Visipaque. We retrospectively reviewed the patients with LSR to Visipaque, seen in the Dermatology Department between 1999 and 2005. A total of 12 patients participated in this study (7 men and 5 women), ages ranging from 39 to 76 years (mean 56). 11 of the patients had significant medical history. All the patients developed a maculopapular exanthema between 2 hr and 3 days after the radiological examination, involving the trunk and proximal limbs, although some of the patients showed involvement of distal areas. The skin biopsy, performed in 6 patients, showed nonspecific findings consistent with drug reaction. In 3 patients, patch tests to Visipaque and iodixanol were positive. The most frequent manifestation of LSR to iodixanol is a maculopapular exanthema, involving the trunk and the limbs, although distal involvement can be seen. Histopathological findings are nonspecific and cannot be distinguished from other drug reaction. Patch tests have a limited value, and in cases where they were negative, reintroduction of the drug triggered a new LSR.

Current understanding of contrast media reactions and implications for clinical management

Iodinated contrast media (CM) are an integral part of modern diagnostic medicine. Although these agents are considered to be relatively safe, adverse effects in the form of allergy-like reactions occur in a significant number of exposed patients. These reactions may be divided into immediate and delayed responses. Immediate (within 1 hour of administration) anaphylactic reactions range from urticaria and angioedema to laryngeal oedema, hypotension and even death. Delayed reactions to CM occur from 1 hour to 1 week after administration and usually have mostly cutaneous manifestations. History of prior CM reactions and atopy predispose patients to CM reactions. Despite intense research into the pathogenesis of the immediate anaphylactoid responses, new evidence shows that true IgE type I hypersensitivity mediation occurs only in rare, severe cases. The aetiology appears to be multifactorial in most individuals. There is strong evidence to conclude that type IV hypersensitivity is responsible for the delayed reactions to CM. Although switching to non-ionic agents significantly reduces the incidence of immediate reactions to CM, there is little consensus regarding corticosteroid prophylaxis in high-risk individuals. Skin testing and provocative challenges also provide little security. Therefore, physicians must be better prepared to treat immediate anaphylactoid responses. Preventing delayed CM reactions is best performed with patch and delayed intradermal testing in those with a history of prior reactions, although false-negative results have been reported. Corticosteroids and antihistamines may be required for treatment. Until newer agents are developed that negate these issues, healthcare providers must strive to better understand the risk factors associated with CM reactions, as well as the available prophylactic and treatment options.