[Daytonite]

Hi, poor25!

I would recommend that you do the same sort of thing our trigonometry instructor had us do to help us learn the measurements of the sides of right triangles and their trig functions. Make a table and memorize how to recreate it. As soon as you get the test, the first thing you do is draw that table from memory before you even attempt to do any of the problems on the test. So, look at the conversions you want to put on a table. Do you see any kind of pattern in the numbers (like a sequence) that might make it easier for you to remember when writing them down? Create this table of conversions for yourself. Then, copy it. Over and over. Every time of every day that you think about it. Do it so it only takes you a couple of minutes to draw and fill in the numbers on this table. Start now. By Saturday you should be able to copy this table onto to your test paper where it will be in black and white for you to refer to when you are under the pressure of having to perform the math on a test. This works. I guarantee it.

Welcome to allnurses!

[Woogy]

30 monkeys Laughed at 1 old zebra
8 dozen roses, 2Turkeys, 6 tums.
30 mL's = 1 oz. = 8 dr (drams) = 2 Tbs = 6 tsp
That's one that always sticks with me! They're all equivalent. So if you had that memorized and you had to answer how many ml's in 4 drams, just divide all numbers by 2. 4dr, 15ml, 1Tbs, 3 tsp.
As far as the metric, just memorizing the top middle and bottom figures, the rest can be figured out by simple math. Like memorize what 1gm equals, what 100mg equals, what 60mg equals, what 1mg equals. If you know what 1gm is (1000mg), then you can figure out what 500mg's equals without having to "memorize" it.

Good luck!

[Megsd]

One trick I learned to convert grains to milligrams is to think of a clock face (which is much easier if you can draw it, but bear with me).

At the top is 60 minutes (1 hr), on the right is 15 minutes, at the bottom is 30 minutes, and on the left is 45 minutes. 15 minutes is 1/4 hour, 30 minutes is 1/2 hour, 45 minutes is 3/4 hour, and 60 minutes is 1 hour.

1 grain = 60 mg, so
1/4 grain = 15 mg,
1/2 grain = 30 mg
3/4 grain = 45 mg

Thanks for the mnemonic for drams, tsps, etc. I avoided studying drams like the plague and luckily they weren't on THIS dosage test, but I'm sure it'll come up!

[Daytonite]

Originally Posted by emsjunkie2001

Pronestyl 4 g in 1000 ml D5W, infuse at 2 1/2 mg/ min..

I know the answer is 38 ml/hr. But can't figure out how to get this.

I am going to work this out by dimensional analysis for you, but let me also explain how I got the equation I am going to use for the dimensional analysis, or factor label method.

If you use the formula Dose Desired divided by Dose on Hand you will come up with the following complex fraction (a fraction in the numerator and a fraction in a denominator): 2.5 mg / 1 minute divided by 4 grams / 1000 mL. Remember that when you divide with a fraction that is in the denominator, you must multiple both the numerator and denominator by it's reciprocal fraction in order to clear the denominator of the fraction. That is going to leave you with the equation for the dimensional analysis that I am presented below. This is why 4 grams / 1000 mg now becomes 1000 mg / 4 grams in the equation below.




The object of using dimensional analysis is to manipulate the labels on all the terms in your equation and factor them out so all you are left with are the labels you want left on the final answer. In this case, the labels you want to be left with are: mL / hour.

2.5 mg / 1 minute (dose desired) x 1000 mL / 4 grams (dose on hand) x 1 gram / 1000 mg (conversion factor) x 60 minutes / 1 hour (conversion factor) = 37.5 mL / hour (after duplicate labels are cancelled out) = 38 mL / hour (final answer rounded up)

[LadyT618]

Originally Posted by trilli18

ok very frustrated thought I was getting this dosage calculation stuff and Im not. My professor suggested doing it as desired over have. I tried but am still coming up with wrong answer. Can some please help me
Here's the problem need to find desired dose:
ordered 1 1/2 teaspoon Zithromax 200mg/5ml PoQ6h
on hand 200mg per 5ml
If u could show me how to do this problem by solving it as desired over have I would appreciate it ---Thanks for ur help

Bear with me, I'm not good at setting problems up, but let me tell you how I would walk thru it. First I would figure how much of this drug is in 1ml. If you do the math, 200/5= 40mg/ml. Don't read too much into the question. Sometimes they give u more info than is needed. They already told u the concentration of the drug. They actually gave u the desired amount, u just have to convert that to a dose. All u have to know is conversion factors. 1tsp=5ml. So, 1.5 x 5ml = 7.5ml. So 7.5ml x 40mg = 300mg. There is your dose.
Remember, not all problems require desired over have. Hope I did not confuse u too much.

[Daytonite]

Originally Posted by trilli18

ok very frustrated thought I was getting this dosage calculation stuff and Im not. My professor suggested doing it as desired over have. I tried but am still coming up with wrong answer. Can some please help me
Here's the problem need to find desired dose:
ordered 1 1/2 teaspoon Zithromax 200mg/5ml PoQ6h
on hand 200mg per 5ml
If u could show me how to do this problem by solving it as desired over have I would appreciate it ---Thanks for ur help

This is a situation where you are being asked to use a formula. You merely need to plug your known information into the parts of the formula. I think what is throwing you is that in this case you are already given the answer and one of the elements making up the formula is what you have to find. This requires using some algebra and doing some manipulation of the equation in order to find the solution.

The formula you are wanting to use is: Desired Dose divided by Dose on Hand equals the Dose to Give. You are being asked to determine the Desired Dose, so make that X. The Dose on Hand is 200mg / 5mL. The Dose to Give is 1.5tsp (teaspoons).



Plugging this information into the equation you get the following:

X / 200mg / 5mL = 1.5tsp (Note that your first term is a complex fraction with a fraction in the denominator)

Simplify the term on the left and clear the fraction out of the denominator by multiplying both the numerator and denominator by it's reciprocal 5mL / 200mg. You will now have the following equation:

(5mL)(X) / 200mg = 1.5tsp

Isolate X by multiplying both sides of the equation by the reciprocal fraction, 200mg / 5mL. You will now have the following equation:

X = (1.5tsp / 1)(200mg / 5mL)

Teaspoons, the label, need to be cleared from the equation. That is done by applying a conversion factor which will leave you with your answer, the Desired Dose:

X = (1.5tsp / 1)( 200mg / 5mL)(5mL / 1tsp) = 300mg

[Daytonite]

It occurred to me after I had posted the above, that I could have eliminated a couple of steps by simply altering the formula before plugging the given information into it. Duh!

So, in the formula Desired Dose divided by Dose on Hand equals Dose to be Given (DD/DH = DG), DD becomes X, the answer you are looking for. Isolating X gives you a new formula, X = (DG)(DH). Plug your given information into the formula and proceed from there. You still have to apply a conversion factor to clear the label for "teaspoons" out of the resulting equation and factor out the "mL" so you can be left with the label "gm" for the final answer.

[Nurse Education]

Originally Posted by minnielynn

I am in a desperate situation. I thought I was getting my calculations correctly and today I got back my math results and i got a 70% I am so disappointed I dont know what to do. On my first exam I received an 80%.

My professor said that if i get above 95% on my final (which is next week) I may be able to average a b+ or a- , but it will all depend on the overall average, if he curves grades or not. I went and bought 2 self help books on calculations .... My question is ..... do you think it is humanly possible to ingest all this info by next week (exactly a week from today)! I am having problems with the drips and the three step conversions. Is there a website that can help me? To top it off my professor sucks, so what I have learned, I have learned on my own. I am so frustrated, so much so, that it is getting harder and harder for me to pick up a book .....sorry for venting

Hello, sorry you're having a rough time. I found that the only way to get through math calculations was to memorize the formulas. I know of a website that has many nursing reference tools. Not sure if it will help, but it's called quick-reference.

[trilli18]

on IV's - got to calculate the original flow rate. then determine if an adjustment is necessary and calculate the adjusted flow rate. Adjustments can't exceed 25%

Ordered: 375mL RL over, 3h (10gtt/ml tubuing)
After 1h, 175ml has infused

please can someone help im going bonker been trying to figure this out for over an hour

[Daytonite]

The calculation, by dimensional analysis (factor labeling), to find the original flow rate would have been:

375 mL/3 hours (amount to infuse) X 10 gtts / 1 mL (drip factor of tubing being used) X 1 hour / 60 minutes (conversion factor) = 20.833 gtts/min = 21 gtts/min (rounded off)

After one hour you have 200mL of fluid left to infuse. (375mL minus 175mL = 200mL). You have 2 hours to infuse the remaining 200mL with 10gtt/mL tubing. To complete the calculation by dimensional analysis (factor labeling), keep in mind that you want an answer in gtts/min, so. . .

200 mL/2 hours (amount left to infuse) X 10 gtts/1 mL (drip factor of tubing being used) X 1 hour/60 minutes (conversion factor) = 16.666 gtts /min = 17 gtts/min (rounded off)

Somebody, or somehow, things got screwed up and for the first hour the infusion ran at 29 drops a minute, that's 175 mL an hour with 10 gtt per mL tubing.
You can see this formula at work here http://academic.cuesta.edu/nursing/math.htm Just scroll down to the section on IV therapy. I think this site may have already been posted on this thread, but it's worth a second posting.