How do you use IVC collapsibility on POCUS to inform decisions for managing hypotension?

If a hypotensive patient is lying flat and spontaneously ventilating with a >50% collapse of the IVC (IVCmax - IVCmin/IVCmax x 100%) during a 'sniff' test then I would consider them 'volume tolerant'. They may not be responsive to IVF but it is unlikely that additional IVF will be harmful. Absolute diameter is less helpful but if it is small (<1.5 cm), it suggests they are more volume tolerant, and if it is large (>2.1 cm), it suggests they are less likely volume tolerant.