Prediction of fluid challenge effect: filling pressure when left ventricular function is abnormal, diastolic volume when left ventricular function is normal.

Fluid resuscitation is a cornerstone of intensive care unit patient care, but prediction of the cardiovascular response remains difficult, despite many efforts in clinical research. The concept of responders and nonresponders illustrates such a difficulty. Many techniques have been tested, from strictly non-invasive to invasive, delivering various parameters related to the fluid challenge response. Considering the physical parameters available, such as pressure, volume and flow generated by right and left pumps circulating in elastic or compliant tubes, it sounds useful to go back to the basic knowledge to discuss the results of the present article. This published study tested in the postoperative period of cardiovascular surgery the prediction obtained with filling pressures and the diastolic volume. When left ventricular function (global ejection fraction) is adequate, the volume before fluid administration seems to predict well the fluid challenge response; whereas when the global ejection fraction is poor, the filling pressure seems more suitable. The present commentary discusses the main physiological issues related to these findings, with some methodological aspects.