MED MATH HELP ML/HR

[SN09]

I'm having so much trouble figuring out how to do ml/hr problems, can someone please help me out.

1. ordered: morphine sulfate 40mg in 25ml to infuse at 3 mg/h. How many ml per hr will the infusion run.

answer 18.75 ml/hr

2. Ordered: Lidocaine at 1 mg/min. The bottle is labeled Lidocaine 1 Gm in 500 ml. What is the flow rate in ml/hr.

answer 30 ml/hr

3. a 500 ml solution of D%NS with 20,000 units of Heparin is infusing at 20 ml per hr. The IV set delivers 60 gtts per ml. How many units of Heparin is the patient receiving each hour.

answer 800 unit/hr

Thank you

[Miss_TT]

1. 25mL/40mg x 3mg/hr = 1.875mL/hr. Rounding would give you 1.9 or 2 ml.

2. 1mg/1min x 1g/1000mg x 500mL/1g x 60 min/hr = 30 mL/hr

3. 20,000units/500mL x 20mL/hr = 800 units/hr

[SN09]

Thank you very much Miss TT...

[Smartferret]

In question #1 it would need to be 40mg in 250ml to get an answer of 18.75ml/hr.

[SN09]

I'm not understanding how to set up the problems,I use dimensional analysis and thought to line the equation up with the same units.

mg X mg

ml ml

[Miss_TT]

When using dimensional analysis, you use fractions or ratios. If a unit is in the numerator of one fraction, that same unit has to be in the denominator of the second fraction in order for it to cancel out.

For example, in your first problem-

25mL x 3g

40mg hr

hr is supposed to be below 3g. I don't know how to type the fraction.

since the question requires an answer in mL/hr, you have to cancel the mg out. Notice that mg is in the denominator of the first fraction and in the numerator of the second. This would cancel mg out, and you're left with mL/ hr. If both units of mg were on top, mg would not cancel out.

I hope I didn't confuse you.