# I can't figure out this calculation!

(it's not a school assignment I'm studying for nclex)

Q asks: prescribed is IV heparin 25,000 u in 500mL D5W.

After 6 hours at prescribed rate of 1300u/hr, the PTT is 44 sec. If it's 44 secs, then you increase infusion by 100 u/hr.

What rate in mL per hr should the RN set the IV infusion pump?

So...I'm having trouble just starting my calculation. Can anyone give me a hint please? I use ratio methods. TIA. (I got 2.8ml/hr on my first attempt...which I think is wrong)
2. ### About direw0lf, BSN, RN

Joined: Dec '14; Posts: 997; Likes: 1,064

3. The first step when doing dose calculations for liquid meds is to figure out how much drug is in each mL of solution. It should make a lot more sense once you do that.
If you already did that and are still stuck let me know!
4. Thanks! I did this:

1400u/1hour = 500ml/X

and got 2.8 ml/hr

do you know what I'm doing wrong?
5. OK, always start with what you're looking for. In this case, you want to know how many mL/hr to set the pump.

Look at the data you're given. You want mL at the top of your fraction and hours on the bottom. Which ratio are you given that has mL in the numerator? It's your heparin. Always start with the unit you need on top. You have 500 mL in every 25,000 units. Now, you initially set the IV pump to run at 1300 units per hour. Initially, your pump would be set at:

(500 mL / 25,000 units) x (1300 units/hour) = 26 mL/hr

Since you need to increase your dose by 100 units/hr, your equation now becomes:

(500 mL/ 25,000 units) x (1400 units/hour)