Q: What is large bore IV?

Answer: At least 16 gauge  and ideally 12-14 gauge.

As contrary to popular belief and practice central line is not a large bore or resuscitation line.

Rapid infusion of volume is based on basic physics of Hagen-Poiseuille equation. As per Hagen-Poiseuille equation just 2 fold increase in radius increase flow by 16 fold but 2 fold increase in length decrease flow by 50%.

Technically regularly available central lines (TLC or PICC line) is not ideal for IVF bolus due to longer length and smaller radius. 2 Large bore (say 16 gauge) peripheral IVs or one large bore central short IV (cordis) are real placements for aggressive resuscitation (due to bigger radius and shorter length).

Point is: Central line or two 18 G peripherals should not be labeled as large bore IVs.