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. Some trials have reported superiority of sodium bicarbonate over saline in preventing CIN.185 188 Similarly, some have reported a benefit of N-acetylcysteine administration as adjunctive therapy to hydra- tion,185,189 whereas others have not.190,191 Thus, although the writing group found the evidence compelling for adequate hydration preparatory to angiography with contrast media, it found the evidence insufficient to recommend a specific regimen. With respect to limitation of contrast dose by renal func- tion, mounting evidence points to renal-function specific limits on maximal contrast volumes that can be given without significantly increasing the baseline risk of provoking CIN. In a contemporary study, Laskey et al studied 3179 consecutive patients undergoing PCI and found that a contrast volume to creatinine clearance ratio 3.7 was a significant and inde- pendent predictor of an early and abnormal increase in serum creatinine.166 In an earlier trial, administration of a contrast volume of 5 mL body weight (kg)/serum creatinine (mg/ dL), applied to 16 592 patients undergoing cardiac catheter- ization, was associated with a 6-fold increase in the likelihood of patients developing CIN requiring dialysis.167 Patients with CKD are consistently underrepresented in randomized controlled trials of cardiovascular disease.192 The impact of an invasive strategy has been uncertain in this group. 