Take, for example, potassium for infusion. As stated below, it should be infused at a maximum rate of 10mmol/hr.
For a patient requiring potassium containing fluid, potassium concentration is usually the limiting factor on infusion rate. For example, a patient requiring potassium phosphate, as in the PSA practice question, is to be given potassium phosphate concentrate in 1L glucose 5% solution.
The nominal potassium concentration of the concentrate is 30mmol/20mL.
Reason tells us the fastest infusion time is three hours because only 10mmol can be given per hour.
As it happen, NICE considers the addition of potassium to IV fluid bags dangerous practice.