The Nursing Math Thread  page 19
A member pm'd me the following question highlighted below. We created this thread for you guys to talk about math, solve math problems, and post math websites that you have found helpful. I was... Read More

Jan 20, '10I am working on IV Calculations and need help on one question. I think it's missing some information, but not 100% sure on these quite yet. Thanks for all your help and feel free to walk me through figuring these out. I'm most confused about mEq's!!! Any explanations are useful! I understand how to figure out the rate of flow, but it's the MEq's that confusing me! Thank You!
Your pt has an order to infuse 100 ml of D51/2NS with 10 MEq of KCl over the next thirty minutes. The set calibration is 10gtt/ml. What is the correct rate of flow for this pt?
Here's another one:
The order reads: "Over the next 4 hours, infuse 500 ml of 5% Dextrose in Normal Saline. Add 20 MEq of KCl to solution." You know that the IV tubing set is calibrated to deliver 10 gtt/ml. In drops per minute, what is the rate of flow. 
Jan 20, '10In the case of the first question, I would read that as the 10 mEq have already been added, and it's a straight driprate calculation: (100 mL x 10 gtt/mL) / 30 min = 33.3 gtt/min.
In the second question, it's a bit trickier, since the question seems to indicate that the D5 didn't come premixed with that 20 mEq. (Usually it does, hence the common report abbreviation "D5 1/2NS +20.") Since you don't know the concentration of the stock solution from which you added your 20 mEq, your final VTBI may be off by a few mL. Nevertheless, it's still a basic driprate problem: (VTBI x DF) / TI = DR, where VTBI = volume to be infused, DF = drop factor, TI = time of infusion, and DR = drip rate.
As for the mEq confusing you, all you're doing is adding a medication to an infusing IV; it's just that electrolytes such as potassium are frequently calculated in mEq/L rather than mg/L. 
Jan 20, '10Quote from mystyqueonethe meq could be mg or liters. they are not affecting the math to be performed for these problems unless there is an amount in ml for the 10 and 20 meq that the problem assumes you know is added to the iv solution. usually that amount is small (10ml or so). since it doesn't give you that amount i would just work with the main iv solution that the problem gives you. . .i am working on iv calculations and need help on one question. i think it's missing some information, but not 100% sure on these quite yet. thanks for all your help and feel free to walk me through figuring these out. i'm most confused about meq's!!! any explanations are useful! i understand how to figure out the rate of flow, but it's the meq's that confusing me! thank you!
your pt has an order to infuse 100 ml of d51/2ns with 10 meq of kcl over the next thirty minutes. the set calibration is 10gtt/ml. what is the correct rate of flow for this pt?
here's another one:
the order reads: "over the next 4 hours, infuse 500 ml of 5% dextrose in normal saline. add 20 meq of kcl to solution." you know that the iv tubing set is calibrated to deliver 10 gtt/ml. in drops per minute, what is the rate of flow.
your pt has an order to infuse 100 ml of d51/2ns with 10 meq of kcl over the next thirty minutes. the set calibration is 10gtt/ml. what is the correct rate of flow for this pt?
amount to be infused: 100 mlthe order reads: "over the next 4 hours, infuse 500 ml of 5% dextrose in normal saline. add 20 meq of kcl to solution." you know that the iv tubing set is calibrated to deliver 10 gtt/ml. in drops per minute, what is the rate of flow.
time to be infused: 30 minutes
drop factor of iv tubing: 10 gtts/ml
100 ml/30 minutes x 10 gtts/ml = 33.3 gtts/minute, rounded to 33 gtts/min.
amount to be infused: 500 ml
time to be infused: 4 hours
conversion factor: one hour = 60 minutes
drop factor of iv tubing: 10 gtts/ml
500 ml/4 hours x 1 hour/60 minutes (conversion factor) x 10 gtts/ml = 20.8333 gtts/minute, rounded to 21 gtts/min. 
Jan 20, '10Murphyle and Daytonite: Thank you very much. Now I know that I basically need to just ignore the added KCl because the amount is so little, that it won't effect the number of gtt too drastically. I just didn't know if I had to add it into the total amount to be infused or not. Now I know not to. Thank you both for your detailed explanations! A lot easier than I had thought!

Jan 20, '10Here is another that I am having difficulties since it's sort of "backwards":
1000cc solution of D5NS with 20,000 units of Heparin is infusing at 20ml per hour. The IV set delivers 60 gtts per cc. How many units of Heparin is the pt receiving each hour?
I was figuring that there are 20 units of Heparin per cc (or ml) of D5NS, but how do I figure out the rest? Or do I just multiply the 20 by the gtt, 60, and then divide back with 60 to get the per hour? So, it would be 20 units per hour? Am I doing that correctly?
Thanks. 
Jan 20, '10the formula for solving this type of problem is: rate per hour x concentration per ml.
to solve the problem: 20 ml/hour x 20 units/ml = 400 units/hour.
i hope this information was helpful. 
Jan 21, '10Quote from MystyqueOneIf you set these up using dimensional analysis (factor label method) as chare did they will be much easier to solve. In doing nursing math like this you are always looking for 3 things:Here is another that I am having difficulties since it's sort of "backwards":
1000cc solution of D5NS with 20,000 units of Heparin is infusing at 20ml per hour. The IV set delivers 60 gtts per cc. How many units of Heparin is the pt receiving each hour?
I was figuring that there are 20 units of Heparin per cc (or ml) of D5NS, but how do I figure out the rest? Or do I just multiply the 20 by the gtt, 60, and then divide back with 60 to get the per hour? So, it would be 20 units per hour? Am I doing that correctly?
Thanks.
 the dose to be given (or ordered)
 the dose of the medication you have to work with
 the final amount you will give [usually the answer the question is looking for, but you could be given this figure and asked to solve for one of the other ones above]
 drip factors of IV sets for IV problems
 conversion factors (when you have to switch from things like liters to milliliters, killograms to pounds or hours to minutes

Jan 31, '10Here's a simple calculation that I'm wondering if it's right. It's basic math.
order: gr i 1/2
available 100 mg tablets
60mg to a gr
1.5 gr is 90mg
give: 9/10 of a tablet? is that right? can you do 9/10 of a tablet? 
Jan 31, '10Quote from scifihippieActually, 1 gr is 6065mg, so if you do it with 65 you get 97.5mg which you would probably round to 100 since you can't divide a PO med like that.Here's a simple calculation that I'm wondering if it's right. It's basic math.
order: gr i 1/2
available 100 mg tablets
60mg to a gr
1.5 gr is 90mg
give: 9/10 of a tablet? is that right? can you do 9/10 of a tablet? 
Feb 16, '10Order: Sodium Methicillin 750 mg IM
Label: Sodium Methicillin 1 g dry powder
Reconstitution: add 1.5 mL sterile water for injection to yield 0.5g/mL
How would you guys solve this. Please show me the steps. 

Feb 17, '10Quote from amaxiechrn2011it is important to remember when solving these problems that all of your units are expressed the same. this problem can be solved either using dimensional analysis or d/h * q = x formula.order: sodium methicillin 750 mg im
label: sodium methicillin 1 g dry powder
reconstitution: add 1.5 ml sterile water for injection to yield 0.5g/ml
how would you guys solve this. please show me the steps.
i would suggest that you use dimensional analysis, and show all of your calculations on paper when you first begin working medication math problems. initially, this might take a little longer, however you can easily visualize that you have made all of the necessary conversions. after you become familiar with this method and are comfortable with your abilities you can start using some of the shortcut methods.
to solve this using dimensional analysis:
750 mg * 1 g/1000 mg * 1 ml/0.5 g = x (mg and g cross cancel, leaving)this problem can also be solved using the d/h *q formula: d = desired dose, h = available concentration, and q = volume/quantity in which your available concentration is prepared. again remember, when you are using this formula you need to make your unit conversions as you set up the problem. this method is very similar to the dimensional analysis method, but you are making unit conversions mentally rather than including them in the formula.
750 * 1/1000 * 1 ml/0.5 = x
750 * 0.001 * 2 = 1.5 ml
to solve this using d/h * q:
750 mg/500 mg * 1 ml = x (mg cross cancels)i hope this information was helpful.
1.5 * 1 ml = 1.5 ml 