Unifying Fluid Responsiveness and Tolerance With Physiology: A Dynamic Interpretation of the Diamond–Forrester Classification

Point of care ultrasound (POCUS) is a first-line tool to assess hemodynamically unstable patients, however, there is confusion surrounding intertwined concepts such as: “flow,” “congestion,” “fluid responsiveness (FR),” and “fluid tolerance.” We argue that the Frank–Starling relationship is clarifying because it describes the interplay between “congestion” and “flow” on the x-axis and y-axis, respectively. Nevertheless, a single, simultaneous assessment of congestion and flow via POCUS remains a static approach. To expand this, we propose a two-step process. The first step is to place the patient on an ultrasonographic Diamond–Forrester plot. The second step is a dynamic assessment for FR (e.g., passive leg raise), which individualizes therapy across the arc of critical illness.