Colloid aliquots of 200 ml 6% hydroxy ethyl starch 130/ 0.4(Voluven) will be administered within 10 minutes and CVP response will be recorded. If CVP failed to rise sustainably for more than 2 mmHg for 20 minutes, the aliquot will be repeated. No further aliquots will be given once CVP increases more than 2 mmHg above the recorded one.The last CVP with sustained rise of>2 mmHg will be defined as CVP maximum (CVPmax).When CVP decrease below (CVPmax)by 3 mmHg, this will be defined as trigger CVP (CVPT).CVP will be followed every 30 min during surgery and every 4 hours for 24 hours postoperatively