The aim of the study is to analyze if blood protein concentration variation during continuous renal replacement therapy (CRRT) with fluid removal can predict a decrease of 15 % of cardiac index in intensive care unit (ICU) patients. Blood protein concentration, clinical data describing hemodynamic status (providing data from Pulsion medical system PiCCO2 ® monitoring), including preload dependency evaluation with passive leg raising, are collected at different times: before initiation of fluid removal, and after the first episode of hypotension or one hour after initiation of fluid removal.