Monitoring fluid responsiveness.
Functional hemodynamic parameters, such as stroke volume variation (SVV) and pulse pressure variation (PPV), are useful hemodynamic monitoring tools for the assessment of fluid responsiveness. These parameters are based on heart-lung interaction during positive mechanical pressure ventilation: Cyclic changes of intrathoracic pressure result in a reduced venous return and a decreased cardiac stroke volume after inspiration followed by a restoration of preload and stroke volume after expiration. Hemodynamic monitoring systems based on pulse wave analysis allow an automatic assessment of SVV and--at least for some of the devices--of PPV. Moreover, PPV is being integrated in the standard monitoring in the operating room and the intensive care unit, and the noninvasive plethysmographic assessment of fluid responsiveness has been recently introduced. These developments will result in a broader application of functional hemodynamic parameters in the near future. In contrast to traditional preload parameters (i.e. central venous pressure), SVV and PPV allow the prediction of fluid responsiveness and thus the determination of the actual position on an individual Frank-Starling curve or--in other words--the assessment of an individual preload reserve. Different studies in the last decade were able to prove the validity of this concept. However, to use these functional hemodynamic parameters in daily clinical practice, some limitations have to be considered. Arrhythmia and right heart failure, but also spontaneous breathing of a patient, or small tidal volumes may preclude reliable assessment. Based on these aspects, an ideal area of application of these parameters may be the use during perioperative hemodynamic optimization to improve patient outcome. However, only few studies on goal-directed therapy guided by these parameters have been published so far.