IVC collapsibility index (IVCCI) is assessed by measuring the maximum and minimum diameters of the inferior vena cava just below the hepatic vein confluence during quiet respiration or a sniff maneuver. A large IVC (>2.1 cm) that collapses less than 50% with inspiration suggests elevated right atrial pressure. A small IVC (<2.1 cm) that collapses more than 50% suggests low right atrial pressure and volume depletion. IVC assessment is widely used in point-of-care ultrasound (POCUS) for fluid responsiveness evaluation in emergency and critical care settings.