Colloid aliquots of 200 ml 6% hydroxy ethyl starch 130/ 0.4 (Voluven, Fresenius kabi, Deutschland GmbH, Bad Homburg, Germany) will be administered within 10 minutes and stroke volume response will be recorded .If stroke volume increase by more than 10 % for 20 minutes, the aliquot will be repeated. No further aliquots will be given once stroke volume failed to increase >10%. The last stroke volume without rise of > 10% will be defined as optimum stroke volume (SVopt).When stroke volume decreases by 10% below (SVopt), this will be defined as trigger stroke volume (SVT). Stroke volume will be followed every 30 minutes during surgery and every 4 hours for 24 hours postoperatively .