▁not ▁actually ▁lost ▁by ▁the ▁patient , ▁for ▁this ▁volume ▁is ▁pur ified ▁and ▁redirect ed ▁into ▁the ▁patient . ▁ ▁On ▁the ▁other ▁hand , ▁hyper vo lem ic ▁hem od il ution ▁( H V H ) ▁uses ▁ac ute ▁pre oper ative ▁volume ▁expansion ▁without ▁any ▁blood ▁removal . ▁In ▁choosing ▁a ▁fluid , ▁however , ▁it ▁must ▁be ▁assured ▁that ▁when ▁mixed , ▁the ▁remaining ▁blood ▁behav es ▁in ▁the ▁micro cir cul ation ▁as ▁in ▁the ▁original ▁blood ▁fluid , ▁retain ing ▁all ▁its ▁properties ▁of ▁vis cos ity . ▁ ▁In ▁present ing ▁what ▁volume ▁of ▁AN H ▁should ▁be ▁applied ▁one ▁study ▁suggests ▁a ▁mathematical ▁model ▁of ▁AN H ▁which ▁calcul ates ▁the ▁maximum ▁possible ▁R CM ▁sav ings ▁using ▁AN H , ▁given ▁the ▁patients ▁weight ▁Hi ▁and ▁H m . ▁( See ▁below ▁for ▁a ▁gl oss ary ▁of ▁the ▁terms ▁used .) ▁ ▁To ▁maintain ▁the ▁norm ov ole m ia , ▁the ▁withdraw al ▁of ▁aut olog ous ▁blood ▁must ▁be ▁simultaneously ▁replaced ▁by ▁a ▁suitable ▁hem od il ute . ▁Ide ally , ▁this ▁is ▁achieved ▁by ▁is ov ole m ia ▁exchange ▁trans f usion ▁of ▁a ▁pl asma ▁substitute ▁with ▁a ▁col lo id ▁os m otic ▁pressure ▁( OP ). ▁A ▁col lo id ▁is ▁a ▁fluid ▁containing ▁particles ▁that ▁are ▁large ▁enough ▁to ▁ex ert ▁an ▁on c otic ▁pressure ▁across ▁the ▁micro - vas cular ▁memb rane . ▁When ▁deb ating ▁the ▁use ▁of ▁col lo