A client receiving heparin infusion has 25,000 units in 500 mL D5W. If the order is 1,250 units per hour, how many milliliters per hour are administered?

A client receiving heparin infusion has 25,000 units in 500 mL D5W. If the order is 1,250 units per hour, how many milliliters per hour are administered?

• A. 15 mL/hr
• B. 25 mL/hr
• C. 35 mL/hr
• D. 45 mL/hr

Answer: (B)

The key idea is converting a prescribed units-per-hour dose into the corresponding milliliters-per-hour using the solution’s concentration. First find how strong the solution is: 25,000 units in 500 mL equals 50 units per milliliter (25,000 ÷ 500 = 50 U/mL). To deliver 1,250 units each hour, you need 1,250 units/hour ÷ 50 U/mL = 25 mL/hour. So the correct rate is 25 mL per hour. This also means 25 mL/hour provides 1,250 units each hour at 50 U/mL. If you used a smaller rate, you'd deliver fewer units per hour; a larger rate would deliver more units per hour, which would not meet the prescribed dose.

The key idea is converting a prescribed units-per-hour dose into the corresponding milliliters-per-hour using the solution’s concentration.

First find how strong the solution is: 25,000 units in 500 mL equals 50 units per milliliter (25,000 ÷ 500 = 50 U/mL).

To deliver 1,250 units each hour, you need 1,250 units/hour ÷ 50 U/mL = 25 mL/hour.

So the correct rate is 25 mL per hour. This also means 25 mL/hour provides 1,250 units each hour at 50 U/mL. If you used a smaller rate, you'd deliver fewer units per hour; a larger rate would deliver more units per hour, which would not meet the prescribed dose.