Ultrasound of the inferior vena cava for fluid therapy decisions: Strengths, limitations, and an integrated approach.

Accurate assessment of fluid responsiveness is critical in resuscitation; however, static indices often fail to predict it accurately. Inferior vena cava ultrasonography is valued for its simplicity and accessibility; however, its predictive accuracy in real-world settings remains uncertain. This narrative review examined the physiological rationale, limitations, and clinical utility of inferior vena cava ultrasonography. Although inferior vena cava ultrasonography leverages the Frank-Starling mechanism and heart-lung interactions, its measurements are susceptible to confounders (e.g. ventilator settings, spontaneous breathing, right-heart dysfunction, and intra-abdominal pressure) and operator-dependent variability. Evidence from heterogeneous cohorts has shown moderate accuracy, with reliable performance often limited to strictly controlled conditions. In lung-protective ventilation or mixed populations, its discriminative ability declines, raising the risk of misclassification. Consequently, inferior vena cava ultrasonography should not be used as a standalone tool for guiding fluid therapy. Its optimal role lies within a multimodal, iterative strategy incorporating passive leg raising, left ventricular outflow tract velocity-time integral, lung ultrasound, and venous excess ultrasound. In practice, inferior vena cava ultrasonography should inform but not decide fluid therapy; its safest role is as a contextual trend within a physiology-first, function-centered, and congestion-aware workflow.