On the one hand, one might expect dialyzing away contrast to be a beneficial thing. There has been increasing data suggesting that residual renal function–even in patients on dialysis–can be a good thing. iv contrast is definitely of low enough molecular weight to allow it to be efficiently dialyzed.
HOWEVER–most of the actual data runs counter to this position. One particular study by Vogt et al performed a randomized controlled trial in which patients with a baseline Cr greater than 2.3 md/dL were randomized to receive either prophylactic hemodialysis or not immediately after iv contrast exposure. The creatinine was initially lower in the treatment group (as would be anticipated given the effect of dialysis on reducing creatinine levels) but by Day 6 there was no signficant difference between treatment and control groups–and there was even a suggestion that dialysis could be harmful. You can find studies reporting the opposite finding–that is, a potential beneficial effect of prophylactic dialysis on contrast nephropathy, such as this recent study by Lee et al–but in my opinion the suspected mechanism by which iv contrast causes renal injury would cast doubt on such a strategy. iv contrast’s toxicity is thought largely due to its high osmolar content, as evidenced by the appearance of intracellular vesicles in the renal tubular epithelium exposed to iv contrast. I would imagine that this tubular damage occurs rapidly after iv contrast exposure, and removal of contrast by dialysis would likely occur after the fact.
My own approach to the dilemma above: agree to dialyze the patient in order to get the test performed promptly. Evaluate the patient after the exam and see whether or not there is any objective reason to dialyze them earlier than their usual schedule would warrant. In rare instances, large amounts of iv contrast can cause volume overload/pulmonary edema. But in the majority of these instances, my suspicion is that prophylactic dialysis either to prevent contrast nephropathy in a patient with CKD or to preserve residual renal function in a patient with ESRD is not useful.