Beyond Access Flow: The FLASH Multiorgan Framework for Assessing High-Flow Arteriovenous Fistulas in Hemodialysis.

High-flow arteriovenous fistulas (AVFs) impose a continuous hemodynamic burden on patients receiving maintenance hemodialysis, yet access blood flow (Qa) alone does not determine their cardiovascular significance. High access blood flow, high-output physiology, and clinically relevant cardiovascular intolerance represent related but distinct states whose expression depends on the interaction among access-related hemodynamic exposure, systemic flow response, cardiovascular reserve, volume status, and downstream cardiovascular consequences. This review proposes a clinically oriented, multiorgan framework for evaluating patients in whom an AVF is suspected of contributing to cardiovascular deterioration. Assessment begins with the clinical and dialysis context and integrates five interconnected domains: FISTULA, characterizing access-related hemodynamic exposure; LOAD, evaluating the systemic circulatory response; ASSESSMENT OF EXTRAVASCULAR LUNG WATER, identifying pulmonary congestion; SYSTEMIC VENOUS CONGESTION, assessing systemic venous consequences; and HEART, evaluating cardiac adaptation and maladaptation. Integration across these domains may reveal overlapping clinical-hemodynamic patterns, including preserved tolerance despite high flow, predominantly hyperdynamic physiology, cardiac maladaptation, systemic venous- or pulmonary-predominant consequences, and multicompartmental involvement. Discordance between systemic venous and pulmonary findings may provide physiologically relevant information rather than represent conflicting evidence. Serial reassessment after ultrafiltration, clinical change, or access-flow modification further emphasizes the dynamic nature of these patterns. The framework is intended to support physiologic interpretation rather than establish AVF causality, define new diagnostic categories, or propose treatment thresholds. Ultimately, assessment should move beyond asking how much blood flows through the fistula toward determining how the individual patient responds to that flow.