dosage calculation help

loveofrn, BSN, RN · Jul 7, 2014

A= (250/2.5hr)×(1hr/60min)*60 gtt = your answer in gtt per min

B=(20ml/1hr)*(30u/1000ml)= ypur answer in unit per hr

nurseprnRN, BSN, RN · Jul 8, 2014

My only caveat about DA (other than it is often much more complicated than necessary) is that so often I see students try to cram every possible bit of data in the question into an equation...and a lot of it is not needed for the answer. Examination writers know this and put distractors (wrong answers) that would result from doing that in the choices. Does make for a lot of confusion, and we see it here often.

Step back from every problem and ask what's really being asked, see if you can eyeball a possible answer range, and then determine how to solve for X in any way that works comfortably for you.

In your first question, you're being asked to figure out how fast to run an IV in drops per minute, but before that, you need to know how many cc per hour. Do this problem in two steps any you'll find it easier to figure out and really UNDERSTAND.

OK. So you have 250cc to give in 2.5 hours. Hmmm. Looks like if you ran it at 100cc/hour, that would be, umm, 100 cc+100cc +50cc. Bingo! Good. Now you need to figure out how many drops per minute is 100 cc/hour. Quickie cheat: with microdrop tubing (60gtts/cc) drops per minute AlWAYS equals cc per hour. Or you can figure that 100 cc = 100 x 60 gtts = 6000 gtts, and dividing that by 60 will give you how many gtts in one minute, 100 gtts.

In your second question, think about what's in the bottle. You have 30 units of pitocin in 1000 cc. So how many units of pitocin are there in one cc? 30/1000 = 3/100 of a unit in one cc. You're giving 20 cc per hour, so that's 20 x 3/100 units, or 60/100 units, or ... 0.6 units.

loveofrn, BSN, RN · Jul 8, 2014

My only caveat about DA (other than it is often much more complicated than necessary) is that so often I see students try to cram every possible bit of data in the question into an equation...and a lot of it is not needed for the answer. Examination writers know this and put distractors (wrong answers) that would result from doing that in the choices. Does make for a lot of confusion, and we see it here often.

Step back from every problem and ask what's really being asked, see if you can eyeball a possible answer range, and then determine how to solve for X in any way that works comfortably for you.

In your first question, you're being asked to figure out how fast to run an IV in drops per minute, but before that, you need to know how many cc per hour. Do this problem in two steps any you'll find it easier to figure out and really UNDERSTAND.

OK. So you have 250cc to give in 2.5 hours. Hmmm. Looks like if you ran it at 100cc/hour, that would be, umm, 100 cc+100cc +50cc. Bingo! Good. Now you need to figure out how many drops per minute is 100 cc/hour. Quickie cheat: with microdrop tubing (60gtts/cc) drops per minute AlWAYS equals cc per hour. Or you can figure that 100 cc = 100 x 60 gtts = 6000 gtts, and dividing that by 60 will give you how many gtts in one minute, 100 gtts.

In your second question, think about what's in the bottle. You have 30 units of pitocin in 1000 cc. So how many units of pitocin are there in one cc? 30/1000 = 3/100 of a unit in one cc. You're giving 20 cc per hour, so that's 20 x 3/100 units, or 60/100 units, or ... 0.6 units.

Thanks for that but did I solve the question because I haven't start med math yet. I am starting nursing school this August and I hope am in the right track in solving med math

Thanks again

Guests · Jul 9, 2014

a. Order: 250cc NSS over 2 ½ hours, available tubing: 60 gtts/cc. calculate in gtts/min

You're starting with a volumetric hour flow rate, right? That is, you're given a volume (250 mL) to be infused over 2.5 hours... so what's the rate?

[TABLE=width: 158]

[TR]

[TD=align: center]250 mL

[/TD]

[TD][/TD]

[/TR]

[TR]

[TD=align: center]----

[/TD]

[TD=align: center]=

[/TD]

[TD]100 mL/hr[/TD]

[/TR]

[TR]

[TD=align: center]2.5 hr[/TD]

[TD][/TD]

[/TR]

[/TABLE]

But there are two problems with this.... (1) they're looking for a minute flow rate, and (2) they're looking for a drip rate.

The key is recognizing the basic math principle that 60 gtt/mL means - mathematically speaking - that:

60 gtt = 1 mL...

do you see the difference? This (60 gtt/mL) is *not* an equation so you can't do math with it... math is predicated on *equations* so that you can substitute values. This is universally true and why I bristle at the notion of "DA" which (a) is not dimensional but rather "unit" analysis and (b) which people seem to think is some sort of magic... it's just based on simple EQUATIONS and SUBSTITUTIONS...

The other key is recognizing that 1 hr = 60 min

When I say that they're EQUAL I mean that they can be directly substituted for one another..

So, now that you've identified the simple equalities, do the substitutions...

[TABLE=width: 371]

[TR]

[TD=align: right](250)

[/TD]

[TD](60 gtt)[/TD]

[TD][/TD]

[TD=align: right](15000)

[/TD]

[TD](1 gtt)

[/TD]

[TD][/TD]

[/TR]

[TR]

[TD=colspan: 2, align: center]-------------

[/TD]

[TD]=[/TD]

[TD=colspan: 2]----------------

[/TD]

[TD] =

[/TD]

[TD]100 gtt/min[/TD]

[/TR]

[TR]

[TD=align: right](3)

[/TD]

[TD](60 min)[/TD]

[TD][/TD]

[TD=align: right](150)

[/TD]

[TD](1 min)[/TD]

[TD][/TD]

[/TR]

[/TABLE]

All that I did was to substitute "60 gtt" where I saw "mL" and "60 min" where I saw "hr"

i got so far: 60/1hr=x/2.5 hr x=150 minutes now what do i do with that new calculations,
250/150 x 60= 100gtts/min??? did i do it correctly??

Did you get the correct answer? Yes. Do you understand what you're doing? I don't know. You haven't carried any units through your calculations... you appear to have simply "forced" the desired units onto a magnitude at the end of your calculation.

Guests · Jul 9, 2014

Order: 30 units of Pitocin in 1000 ml D5W at 20 ml/hr.How many units of Pitocin is the client receiving per hour? _____units/hr
this one I am not so sure how to attempt it, 1000ml/x=20ml/1hr x=50hrs
50hrs/30units= 1.66 units/hr??????? is this set up correct

This is done in exactly the same manner... identify *equalities* and perform *substitutions* to solve for the unknown... that is, to solve for the rate of Pitocin administration

I'll just start identifying the equalities that I see...

"30 units of Pitocin in 1000 ml D5W" >>>> 30 units Pit = 1000 mL

[iI] "20 ml/hr" >>>> 20 mL = 1 hr

Those (and their inverses) are the *only* equations provided in the problem...

What do I mean by their inverses? Simply that the basic rules of algebra tell us (1) that we can freely multiply and divide both sides of an equation by the same value and maintain the equality, (2) that anything divided by itself equals one, and (3) that multiplying or dividing by one does not change the value of anything.

So, I know that I'm looking for a rate... (rate means how one thing changes as another thing changes... "this per that")... in this particular case, how does the amount of Pitocin change as time changes... or "units per hour"

Equation [1] relates amount of Pitocin to the volume of solution

Equation [iI] relates the volume of solution to an elapsed time

What I'm looking for is an equation that relates the amount of Pitocin to an elapsed time... and I only have two equations (and their inverses) with which to do it.

We can freely manipulate these equations following rules (1) - (3) in the paragraph above...

Knowing that relates amount to volume (units to mL) and that [iI] relates volume to time (mL to hr), I can see that I should seek to volume in with time from [iI]... meaning, where I see "mL" in , I want to substitute with "hr" (which equality is provided in [iI]...

[TABLE=width: 158]

[TR]

[TD=align: center]20 mL[/TD]

[TD=align: center][/TD]

[TD=align: center]1.0 hr[/TD]

[/TR]

[TR]

[TD=align: center]------[/TD]

[TD=align: center]=[/TD]

[TD=align: center]------[/TD]

[/TR]

[TR]

[TD=align: center]20[/TD]

[TD=align: center][/TD]

[TD=align: center]20[/TD]

[/TR]

[TR]

[TD=align: center][/TD]

[TD][/TD]

[/TR]

[TR]

[TD][/TD]

[/TR]

[TR]

[TD=align: center]1 mL[/TD]

[TD=align: center]=[/TD]

[TD=align: center]0.05 hr[/TD]

[/TR]

[/TABLE]

Substituting the inverse of [iI] into yields:

[TABLE=width: 265]

[TR]

[TD=align: center][/TD]

[/TR]

[TR]

[TD=align: center][/TD]

[/TR]

[TR]

[TD=align: center]30 units Pit[/TD]

[TD=align: center]=[/TD]

[TD=align: center]1000 mL[/TD]

[TD=align: center][/TD]

[/TR]

[TR]

[TD=align: center][/TD]

[TD=align: right]1 mL[/TD]

[TD=align: center]=[/TD]

[TD=align: center]0.05 hr[/TD]

[/TR]

[/TABLE]

[TABLE=width: 239]

[TR]

[TD=class: xl26, width: 96]30 units Pit[/TD]

[TD=class: xl24, width: 25]=[/TD]

[TD=class: xl25, width: 51](1000)[/TD]

[TD=class: xl27, width: 67](0.05 hr)[/TD]

[/TR]

[/TABLE]

[TABLE=width: 172]

[TR]

[TD=class: xl26, width: 96]30 units Pit[/TD]

[TD=class: xl24, width: 25]=[/TD]

[TD=class: xl25, width: 51, align: right]50 hr[/TD]

[/TR]

[/TABLE]

Which means that it takes 50 hours to infuse 30 units...

Since we now have an equation that relates amount of Pit to time, we can determine the rate (this per that) by dividing both sides by 50 hr

[TABLE=width: 229]

[TR]

[TD=align: center]30 units Pit[/TD]

[TD][/TD]

[/TR]

[TR]

[TD=align: center]----------[/TD]

[TD]=[/TD]

[TD]0.6 units/hr[/TD]

[/TR]

[TR]

[TD=align: center]50 hr[/TD]

[TD][/TD]

[/TR]

[/TABLE]

~~~~~~~

NOTE: This is *NOT* dimensional analysis!! This is basic algebra... Writing equations, performing substitutions, and using basic mathematical operators to isolate the desired values.

nurseprnRN, BSN, RN · Jul 9, 2014

Note that both both SongInMyHeart and I showed different ways to think about how to get the correct answer (0.6 units/hr) -- and the OP's answer (1.66 units/hr) was wrong.

brujacakes · Jul 9, 2014

When I first began nursing school, I was in a panic over med math. Practice a lot, use formulas that work for YOU and make sense to YOU, not everyone else and once you get med math down, you will learn to love it when you see it on exams because there is only ONE right answer to those questions ;-)