[reidesert]

I have been practicing some dosage problems to get ready for the RN program in the fall. I found a work packet "Bonnie and Jill's Practical Approach to Dosage Calculations" but it does not have the answers to the problems. I was wondering if someone could tell me if I am on the right track on the process of finding the correct answer. I have been using dimensional analysis to find the answer and I think that it is working for me but I would really appreciate if someone could look over my answers to see if I am in fact doing it directly.

IV Problems Calculate flow rate.

Order: 1000ml D5N5 IV q8hr. The IV infusion set's drop factor is 15 gtt/ml.

15 gtt/ml X 1000ml/60 min X 1 hr/8hr=250/8=31.25 gtt/ml

Infuse 30 ml of 0.9% NS I.V. q1hr continuously. The drop factor is 60gtt/ml. How many gtt/min will deliver 30 ml/hr?

60gtt/ml X 30ml/60min = 30gtt/min

The order reads 1000ml LR I.V. Infuse from 0600-1400. The drop factor is 20gtt/ml. The flow rate is.

20gtt/ml X 1000ml/8(60min) =41.6 gtt/min

The order reads: Lidocaine dripat 2mg/min. You have D5W 500ml with 2 g of Lidocaine added. What is the flow rate in ml/hr?

2 mg/min X 60min/1 hr X500ml/2(1000)mg= 30ml/hr

A patient has an IV of D5W 500ml. The flow rate is 19 drops per minute. If the drop factor is 60gtt/ml, how many hours will it take for this infusion to finish?

60gtt/ml X 500ml/19gtt X 1 hr/60 min=26.3 hrs

If a patient has a Dopamine drip of 800 mg in 500ml of D5W, the concentration is:

800mg/500ml= 1.6 mg/ml

Drug Conversion Problems

The order is Lasix 80mg mg I.V. now. You have Lasix 100mg in 10ml of NS. What volume would you give?

80mg/x multiplied by 100 mg/10ml= 8 ml (How would I set this up to be a DA problem?)

How many kg does a 250 lb. man weigh?

250 lb X 1kg/2.2 lb = 113.6 or 114.

The order is for 4T. of MOM now. HOw many tsp is this?
4T X 15cc/1T X 1tsp/5cc=12tsp

[Daytonite]

Flow rates have to be expressed in terms of whole numbers, not fractions of numbers. If you are counting the drops in the drip chamber of IV tubing or setting a drip rate on an IV pump, you cannot count out or dial in 31.25 drops or 41.6 drops. While the math is correct, the reality of it is wrong and an instructor will probably mark your answer wrong.

The order is Lasix 80mg mg I.V. now. You have Lasix 100mg in 10ml of NS. What volume would you give?

You begin by setting it up using the formula dose desired divided by dose on hand, simplify the complex fraction and work out the math:

80 mg/100 mg/10 mL (dose desired divided by dose on hand which ends up as a complex fraction) = 80 mg/1 x 10mL/100 mg (the simplified equation, after being multiplied by the reciprocal of the denominator of the complex fraction now becomes two simple fractions that will be multiplied together conveniently leaving you with the label of mL that you need) = 8 mL

The order is for 4T. of MOM now. HOw many tsp is this?

Save yourself a lot of unnecessary extra steps here and use this conversion: 3 teaspoons = 1 tablespoon

[reidesert]

Thanks Daytonite! I really appreciate the help. I am stuck on one question. I think the fractions are throwing me off. I am not sure how to set it up. I know I must convert the gr to mg and I can do that but I am not sure what the question is asking.

Ok here is the question:
The order reads Phenobarbital gr 1/4; take gr 1/2 t.i.d. How many mg of Phenobarbital should the patient receive?

So this is what I think the order is for Phenobarbital 15 mg.
1/4 gr X 60mg/1 gr=15 mg

Is the question asking how many mg would you give it the patient takes half a dose three times a day?

15mg/2 = 7.5mg X 3day= 24mg???
I know this must be wrong b/c it isn't one of the answers lol. I am driving myself nuts here. I am thinking maybe I am just beating a dead horse. I don't know if I will ever be able to do this

[Daytonite]

Originally Posted by reidesert

Phenobarbital gr 1/4; take gr 1/2 t.i.d. How many mg of Phenobarbital should the patient receive?

The problem is telling you that a dose is grain 1/2 three times a day. All you need to do is determine how many mgs are in 1/2 a grain. The rest of the information is insignificant.

1 grain/2 (dose desired) x 60 mg/1 grain (conversion factor) = 30 mg for one dose

it might be clearer if this is written out as

0.5 grain (dose desired)/1 x 60 mg/1 grain (conversion factor) = 30 mg for one dose

If the problem said that the phenobarbital came in tablets of 15mg tablets and asked how many tablets you needed to give if the dose ordered was 1/2 grain, then the problem would be quite different.

0.5 grain (dose desired) x 1 tablet/15 mg (dose on hand) x 60 mg/1 grain (conversion factor) = 2 tablets (dose to give)