Fig. 4

Hypothetical effect of passive leg raising (PLR) on the venous return curve in function of the presence of fluid responsiveness. In the case of fluid responsiveness, PLR increased mean systemic pressure (Psm) to a larger extent than central venous pressure (CVP), because the operating point moved on the steep part of the Frank-Starling curve. This should lead to a significant increase in venous return and cardiac output. By contrast, in the case of fluid unresponsiveness, PLR increased Psm and CVP to a similar extent, because the operating point moved on the flat part of the Frank-Starling curve. This should not lead to a significant increase in venous return and cardiac output. CVP_B CVP at baseline, CVP_PLR CVP during passive leg raising, Psm_B PSM at baseline, Psm_PLR PSM during passive leg raising