ABSTRACT
In patients with acute circulatory failure, the decision to give fluids or not should not be taken lightly. The risk of over
zealous fluid administration has been clearly established. Moreover, volume expansion does not always increase cardiac
output as one expects. Thus, after the very initial phase and/or if fluid losses are not obvious, predicting fluid responsive
ness should be the first step of fluid strategy. For this purpose, the central venous pressure as well as other ―static‖
markers of preload has been used for decades, but they are not reliable. Robust evidence suggests that this traditional
use should be abandoned. Over the last 15 years, a number of dynamic tests have been developed. These tests are based
on the principle of inducing short term changes in cardiac preload, using heart–lung interactions, the passive leg raise or
by the infusion of small volumes of fluid, and to observe the resulting effect on cardiac output. Pulse pressure and
stroke volume variations were first developed, but they are reliable only under strict conditions. The variations in vena
caval diameters share many limitations of pulse pressure variations. The passive legraising test is now supported by
solid evi dence and is more frequently used. More recently, the endexpiratory occlusion test has been described, which
is easily performed in ventilated patients. Unlike the traditional fluid challenge, these dynamic tests do not lead to fluid
overload. The dynamic tests are complementary, and clinicians should choose between them based on the status of the
patient and the cardiac output monitoring technique. Several methods and tests are currently available to identify
preload responsiveness. All have some limitations, but they are frequently complementary. Along with elements
indicating the risk of fluid administration, they should help clinicians to take the decision to administer fluids or not in a
reasoned way.
Key words: Pulse pressure variation, Stroke volume variation, Pulse contour analysis, Heart–lung interactions,
Passive leg raising, Fluid responsiveness, Cardiac preload, Stroke volume, Volume expansion, Fluid therapy,
Haemodynamic monitoring, Critical care, Echocardiography, ICU, Operating room