The time course of fluid responsiveness.

Fluid responsiveness (FR) is a cornerstone concept in the hemodynamic management of critically ill patients, referring to the heart's ability to increase output in response to fluid administration. This review explores the time course of FR, emphasizing its dynamic and transient nature influenced by various patient-specific factors and treatments. We highlight that FR is not a stable, binary state but rather a continuum that requires repeated evaluations using appropriate tools. We examine into factors affecting the temporal profile of FR, including the stage of resuscitation, fluid infusion rate, norepinephrine use, mechanical ventilation settings, systolic function, spontaneous breathing, and the patient's health condition. Understanding the duration and decay of the hemodynamic response is crucial for individualizing fluid therapy, potentially reducing the risks of both fluid overload and under-resuscitation. This review underscores the necessity of frequent reassessment of FR in critically ill patients and integrating this knowledge into personalized resuscitation protocols to improve clinical outcomes.