Logistical and reimbursement limitations dictate that most CT exams be performed on an outpatient basis, making it difficult to manage contrast-related reactions, especially in patients with renal insufficiency. Oral hydration may be as effective as intravenous fluids for preventing contrast-induced nephropathy in some instances, but further study is needed.

"The number of patients at risk for contrast-induced nephropathy is going to increase, primarily due to the increase in the number of patients with chronic kidney disease and diabetes. Administering routine IV fluids in the outpatient setting is challenging because of lack of staff and space," said Dr. Steven Weisbord, a staff nephrologist at the Center for Health Equity Research and Promotion at the VA Pittsburgh Healthcare System, at the 2008 Stanford International Symposium on Multidetector-Row CT in Las Vegas..

He referenced several studies that came to different conclusions on the feasibility of oral fluids. In one, 53 patients undergoing coronary angiography were randomized to either receive IV saline solution or drink as much fluids as possible before the exam (Nephron Clin Pract 2003;93(1):C29-C34). The incidence of contrast-induced nephropathy in the oral fluids group was 34.6% versus 3.7% in the IV group. These lackluster results caused the study to be stopped at midterm analysis, said Weisbord, who is also an assistant professor of medicine at the University of Pittsburgh School of Medicine.

In another investigation, 50 patients with chronic kidney disease — a quarter of whom had diabetes — underwent CT angiography. One group received IV fluids, and another was encouraged to drink one liter of water 12 hours preprocedure and two liters over 24 hours postprocedure. There was a 4% incidence of contrast-induced nephropathy in the water-drinking group, although serum creatinine levels returned to baseline within seven days in two of the patients. This effectively reduced the number of cases of clinically significant contrast-induced nephropathy in this series, Weisbord said (Clin Nephrol 2004;61:3:170-176).

Weisbord pointed out that it would be reasonable to conclude from these studies that water alone cannot provide the same protection as IV-administered saline solution. Another study, however, added oral salts to the mix (Nephrol Dial Transplant 2006:21:8:2120-2126). For this investigation, 312 patients received one of several types of IV fluids or were instructed to take salt tablets orally. Among the subjects who received IV fluids, 5.2% developed contrast-induced nephropathy, compared with 6.6% of those who took oral salts. The difference was not statistically significant, Weisbord said.

"Studies to date have been limited in size and scope, but oral fluids do not appear to be as effective as IV fluids," Weisbord said. "Oral salts may be as effective as IV saline, but that's really just based on one study. Future studies are clearly needed in this area."

Weisbord recommended using IV fluids for all inpatient imaging. Oral salts and water may be a reasonable alternative for outpatient imaging of low-risk patients (estimated glomerular filtration rate above 45). In patients with a higher risk (eGFR less than 45), IV fluids are preferable, but "very aggressive oral salts and water may be feasible," he said.

An audience member asked about using an electrolyte-balanced sports drink instead of water. Weisbord responded that sports drinks may more closely mimic saline, which enters the intravascular spaces in the body, versus water, which is delivered intracellularly. Dr. Robert Herfkens, director of MRI at Stanford University, however, cautioned that sports drinks are often loaded with sugar, which could be a problem for patients with diabetes.