GE Healthcare Life Sciences - Best use of contrast agents

The use of contrast media is a vital aid for radiologists seeking to distinguish certain organs during CT scans. However, misuse of these agents over sustained periods of time can result in complications further along in treatment. On behalf of GE Healthcare Life Sciences, Dr Judy Yee, professor and vice-chair of radiology and biomedical imaging at the University of California, San Francisco School of Medicine, discusses how best to deploy contrast agents to minimise incidences of acute kidney injury.

While computed tomography (CT) scans present a leap beyond the properties of a normal X-ray, ailments specific to certain organs are still hard to pinpoint without the use of an intravenous aid. This is often provided through the provision of contrast imaging, wherein ionic and nonionic compounds are injected into the patient to help distinguish different types of tissue during the scan. From their use in angiography to differentiate between certain blood vessels, to highlighting kidney tissue, these compounds - known as contrast agents - have proven vital in enhancing the accuracy of medical imaging across the board. However, their use brings certain implications for patients undergoing CT scans over a sustained period, especially for those suffering from impaired renal function.

Risk reduction

As professor and vice-chair of radiology and biomedical imaging at the University of California, San Francisco (UCSF) School of Medicine, Dr Judy Yee works at the cutting edge of research on new ways to deploy CT scans.

"These patients are often being evaluated for their responses to treatments such as chemotherapy or radiation therapy," she says. "As such, multiple CT scans may have to be performed because the patient has signs of a complication of the malignancy or therapy, such as an infection. Moreover, antibiotics used to treat infections are often nephrotoxic. As a result, these patients have a poor baseline health status, putting them at an even higher risk for contrast-induced acute kidney damage."

Older patients typically fall into this category, as they are the most likely to have multiple comorbidities during treatment. "In particular, older patients have higher incidences of diabetes mellitus and heart failure, which increases their risk for contrast-induced acute kidney infection," Yee explains. "Similarly, contrast-induced acute kidney injury has been found to occur more commonly within inpatients than outpatients. Additionally, we need to be aware of patients with thyroid cancer receiving iodine-131 treatment, since iodinated contrast, in general, will decrease the uptake by the thyroid, rendering the treatment ineffective."

Dial down the contrast

Ultimately, this does raise the question of whether the danger of incurring contrast-induced acute kidney injury places a significant burden on the oncology segment. After all, instances of the condition have been increasing. In this respect, Yee is in agreement.

"Certainly, acute kidney injury in oncology patients can be particularly devastating," she says. "There is a higher potential for bad outcomes, such as increased morbidity and mortality, as well as longer inpatient hospitalisation and concurrently high costs."

Efforts are underway at the UCSF School of Medicine to minimise dangers by establishing best-practice guidelines for the use of contrast agents. In particular, significant attention has been paid to the use of the compounds within the interventional oncology space. In renal cancer treatment, for example, there are cases where patients will undergo CT examinations pre and post-tumour ablation.

Yee says: "Really, you want to use the least-possibly nephrotoxic contrast agent, since the kidney undergoing tumour ablation can be particularly susceptible to contrast-induced acute kidney injury." To achieve this, Yee and her colleagues have put in place a series of specific protocols to minimise the risks associated with contrast media for higher-risk, renally impaired patients.

"We do not use N-acetylcysteine," she explains. "Most centres use nonionic contrast and either isosmolar or low-osmolar contrast agents. Ultimately, we consider it to be good practice to tailor hydration protocols to the particular patient, and their individual risk factors and fluid status."

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