Fig. 1From: The haemodynamic effects of crystalloid and colloid volume resuscitation on primary, derived and efficiency variables in post-CABG patientsTwo situations of venous return curves intersecting with cardiac function curve after fluid resuscitation. CO is on y-axis and CVP is on x-axis. In the first situation, marked with subscripts 1 and 2, a volume bolus increases Pmsa from Pmsa1 to Pmsa2 and CVP from CVP1 to CVP2. The increase in return pressure (Δ (Pmsa − CVP)) is large. Compare this favourable situation with the situation marked with subscripts 3 and 4: an identical increase in Pmsa generates a larger increase in CVP and thus a smaller Δ (Pmsa − CVP). Relating Δ (Pmsa − CVP) to ΔPmsa (Evol) in the first instance yields a larger figure (app. 0.8) than in the second case (app. 0.25), indicating a better outcome of fluid resuscitation. This is formalised in Eq. (7). Heart efficiency, Eh, declines from app. 0.5–0.6 in the first instance to 0.39–0.36 in the secondBack to article page