This is a randomised controlled trial to investigate the efficacy of preventive regimen of hydration with high dose oral N-acetylcysteine and intravenous sodium bicarbonate pretreatment in patients with stable advanced renal insufficiency (CKD stage 3 and 4:GFR 15-60ml/min/1.73m2 calculated by Modification of Diet in Renal Disease Study equation (MDRD formula)) undergoing elective percutaneous coronary intervention (PCI).