IV Infusion Rate (mL per Hour)

The simplest arithmetic on the ward and the one most often done under interruption. A litre bag over eight hours runs at $1000/8 = 125$ mL/h, and that is the number typed into the pump. Solving the other way is just as common: 250 mL at 75 mL/h finishes in 3.33 hours, or 3 hours 20 minutes.

The mistakes are all unit mistakes. Time given in minutes and rate wanted per hour is the usual one, and it produces answers wrong by a factor of 60, which at least tends to look absurd enough to catch. The quieter error is forgetting that many medications arrive already diluted in a carrier, so the volume to be infused is the total bag volume rather than the drug volume, and that a piggyback line adds its own volume to whatever the primary is delivering.

Worth knowing that a volumetric pump has a real accuracy specification, typically within 5 percent, and that the specification assumes the set is loaded correctly and the fluid is not unusually viscous. For most fluids that error is irrelevant. For a vasoactive drug titrated to blood pressure, or for paediatric fluids where the total daily volume is small, it is not, which is why those infusions get checked against the patient rather than against the pump display.