No well-defined protocols exist to guide fluid administration for prevention of contrast induced nephropathy in high risk patients undergoing coronary angiography. Long term hydration at routine speed(12h before and after procedure at 1ml/kg/h), as the most recommended adequate hydration, has been carried out to prevent contrast induced nephropathy in lots of clinical trials. Base on the data in the POSEIDON randomised controlled trial with haemodynamic-guided fluid administration, short term hydration at high speed(1h before and 4h after procedure at 3ml/kg/h) may not be inferior to the classic long term hydration, the speed should be reduced half of the intended speed in all the patients. We hypothesized short term hydration may not be inferior to the long one to reduced significantly the hospital stay and healthy cost.