Potential mechanisms behind contrast medium-induced nephropathy

How contrast medium-induced nephropathy (CIN) comes about is poorly understood, although CIN is a common cause of acute renal failure. Hitherto, the various studies performed have led to different interpretations and partially contradictory conclusions. This article aimed to review the mechanisms underlying CIN and to outline existing data obtained with the newer iodinated agents in patients with pre-existing renal failure. Osmolality, which has received considerable attention, is but one of several physico-chemical properties of contrast media (CM). The more recently developed iso-osmolar CM are dimers, not monomers as the widely used non-ionic low osmolar CM. Thus, in spite of them being iso-osmolar, they have physicochemical features different from other CM, e. g. in terms of viscosity (> 5 fold greater than plasma viscosity), which may be of considerable pathophysiologic and clinical importance. Many experimental studies provide evidence for greater perturbation in renal function with iso-osmolar CM compared with non-ionic lowosmolar CM. Conversely, some clinical trials indicate an advantage of the iso-osmolar CM, although others do not. In this review, the possible causes of CIN are highlighted, including altered rheological properties, perturbation of renal haemodynamics, regional hypoxia, auto-and paracrine factors (adenosine, endothelin, reactive oxygen species) and direct cytotoxic effects. It is concluded that caution must be taken to avoid a false sense of security with the use of iso-osmolar CM.