Assessment of preload dependance in critical care: new insights and techniques

Fluid administration is a cornerstone in the management of hemodynamic instability, aimed at increasing cardiac output (CO) and improving tissue perfusion. However, only half of critically ill patients experience a meaningful rise in CO after fluid loading, underscoring the importance of identifying preload responsiveness to avoid unnecessary or harmful volume expansion. Traditional fluid challenges (350–500 ml) represent treatments rather than diagnostic tools, prompting the investigation of smaller-volume tests, such as mini-fluid challenges. These, however, require accurate CO monitoring to ensure reliability.This thesis explores two clinical studies developed during a PhD program, each targeting a different approach to preload responsiveness assessment. The first study demonstrates that calibrated pulse contour analysis reliably detects changes in CO following a 50 ml fluid bolus (micro-fluid challenge), supporting its use as a minimally invasive test of fluid responsiveness. The second study evaluates bioreactance, a non-invasive CO monitoring technique, in the same context. Results indicate that the current commercial version of the device lacks the sensitivity to detect hemodynamic changes following a micro-bolus, although previous work by our group suggests that optimized settings may enhance its performance. In an era of precision medicine, these studies collectively aim to expand the toolkit for hemodynamic monitoring in critical care, highlighting the need for tailored, responsive, and minimally invasive strategies to guide fluid management in high-risk patients.