Contrast osmolarity does not affect renal impairment

The choice between a low-osmolar or iso-osmolar contrast agent makes no difference in terms of the rate of contrast-induced nephropathy, according to a study presented at the North American Society for Cardiac Imaging meeting this week in Las Vegas. The finding could result in considerable cost savings as the iso-agents are more expensive.

Contrast-induced nephropathy (CIN) is the acute deterioration of renal function following exposure to contrast media. Investigators at Massachusetts General Hospital in Boston sought to determine if there is a benefit from using one contrast medium over another for reducing CIN.

The prospective randomized double-blind multicenter trial compared Isovue 370 (low osmolar, Bracco) with Visipaque 320 (GE Healthcare). Dr. Dushyant Sahani, director of abdominal CT and intervention at MGH, reported the team's results.

All 166 patients had pre-existing renal impairment and were scheduled to undergo liver CT or CT angiography of the runoff vessels. Patients received equal amounts of iodine doses (40 gI) injected at 4 mL/sec.

Endpoints for contrast-induced nephropathy included increases in serum creatinine (? 25% or 0.5 mg/dL) or decreases in creatinine clearance ( ? 25%).

Researchers randomized 84 patients to the low-osmolar and 82 patients to the iso-osmolar arm. Several patients were excluded because of lab analysis problems or incomplete follow-up. Ultimately, 77 and 76 patients in the low-osmolar and iso-osmolar arms, respectively, had studies that could be evaluated.

Three patients in each study arm had serum creatinine increases greater than 25%. No patient in the low-osmolar arm and one patient in the iso-osmolar arm had a creatinine clearance decrease greater than 25%.

"The rate of CIN is low and similar in patients with moderate-to-severe renal impairment after the administration of iopamidol-370 or iodixanol-320 for contrast-enhanced MSCT," Sahani said.

Most of the data comparing low-osmolar and iso-osmolar contrast agents comes from interventional studies where the agent is injected intra-arterially. One interventional study found a clear advantage using iso-osmolar agents, but similar studies have reported no difference, Sahani said.

The current study is the first prospective randomized study comparing the two types of contrast agents during intravenous injection. Sahani said that it's more important to reduce contrast volume, give nephroprotective drugs, and ensure patients are well hydrated rather than focus strictly on the contrast agent.

"As more data emerges, we can devise a strategy as to whether one type of agent should be used or if there is a role for more than one," he said.

Using the same patient database, investigators also evaluated whether either of the two types of contrast media have an impact on heart rate. The study was an award-winning poster at the meeting.

Contrast media, which cause vasodilation, can result in a small increase in heart rate. Cardiac imagers strive to bring the heart to a manageable rate, lest images suffer from motion artifacts. Some clinicians say that higher osmolarity plays a role in heart rate effect and, consequently, they prefer the iso-osmolar agents.

"But this hypothesis is not backed up by science," Sahani said.

Researchers measured the heart rate of the 77 and 76 patients in the two study arms before and for five minutes after contrast medium administration. They found no statistically significant change in heart rate between the two agents.