Can passive leg raising be used to guide fluid administration?

Predicting fluid responsiveness has become a topic of major interest. Measurements of intravascular pressures and volumes often fail to predict the response to fluids, even though very low values are usually associated with a positive response to fluids. Dynamic indices reflecting respiratory-induced variations in stroke volume have been developed; however, these cannot be used in patients with arrhythmia or with spontaneous respiratory movements. The passive leg raising (PLR) test has been suggested to predict fluid responsiveness. PLR induces an abrupt increase in preload due to autotransfusion of blood contained in capacitance veins of the legs, which leads to an increase in cardiac output in preload-dependent patients. This commentary discusses some of the technical issues related to this test.