A nationwide Swedish survey181 of hospitaliza- tions for renal failure after coronary procedures in 57 925 patients found that this risk was paradoxically higher with iodixanol (1.7%) than ioxaglate (0.8%) or iohexol (0.9%; P 0.001). Although the result was observational, hence subject to selection bias, it persisted in analyses of high-risk patient subsets (patients with diabetes, prior history of renal failure), in multivariable analysis, and in hospitals crossing over from ioxaglate to iodixanol. Iodixanol s greater viscosity was speculated but not demonstrated to be a possible mech- anism for the observed effect. Thus, an overall summary of the current database, updated since previous guideline rec- ommendations,4 is that strength and consistency of relation- ships between specific isosmolar or low-osmolar agents and CIN or renal failure are not sufficient to enable a guideline statement on selection among commonly used low-osmolar and isosmolar media. Instead, the writing group recommends focusing on operator conduct issues shown to be important to protect patients, that is, 1) proper patient preparation with hydration, and 2) adjustment of maximal contrast dose to each patient s renal function and other clinical characteristics. With respect to patient preparation, the writing group re- viewed several trials addressing the optimal preparatory regimen of hydration and pharmacotherapy. The basic principle of hydration follows from experimental studies and clinical expe- rience, with isotonic or half-normal saline alone being the historical gold standards.164,165,182 184 More recently, sodium bicarbonate has been tested as the hydrating solution. 