Is My Thinking Flawed?

Esme12, ASN, BSN, RN · Jul 12, 2014

How much potassium how much Mag? but yes if you run each 25ml over one hour the total of 50ml can run over one hour and is equivalent. However I would be sure to cover it by calling pharmacy or the MD

MunoRN, RN · Jul 12, 2014

How much potassium how much Mag? but yes if you run each 25ml over one hour the total of 50ml can run over one hour and is equivalent. However I would be sure to cover it by calling pharmacy or the MD

I'm missing what the concern is, and I really can't see the MD caring if they even understand what you're talking about.

Esme12, ASN, BSN, RN · Jul 12, 2014

I'm missing what the concern is, and I really can't see the MD caring if they even understand what you're talking about.

Frankly I can't either...but I don't want to be the one to say go head...I don't know the patient. I don't know what dosage. I don't know enough information to make that determination. Check with your MD/pharmacy is my disclaimer.

jadelpn, LPN, EMT-B · Jul 12, 2014

If your order for your rate is 25mls an hour, then it is 25mls-

I wouldn't up it to 50 mls, unless it was ordered for 50 mls per hour.

I get that your point is that 2 25ml fluids equal 50, however, the ordered rate is the ordered rate. If you had 2 seperate sites you wouldn't put them at 50--you would run them each at 25 ml per hour as ordered.

If the MD orders the medication by grams per hour, then the rate could be something else entirely. But the addition of another medication, even if it is a change in volume, you do not add up that rate and run the entire thing according to the total.

Which hopefully makes sense.

I frequently ran banana bags--with all sorts of things in it--and the rate was the rate, didn't depend on each individual med.

MunoRN, RN · Jul 13, 2014

If your order for your rate is 25mls an hour, then it is 25mls-
I wouldn't up it to 50 mls, unless it was ordered for 50 mls per hour.
I get that your point is that 2 25ml fluids equal 50, however, the ordered rate is the ordered rate. If you had 2 seperate sites you wouldn't put them at 50--you would run them each at 25 ml per hour as ordered.
If the MD orders the medication by grams per hour, then the rate could be something else entirely. But the addition of another medication, even if it is a change in volume, you do not add up that rate and run the entire thing according to the total.
Which hopefully makes sense.
I frequently ran banana bags--with all sorts of things in it--and the rate was the rate, didn't depend on each individual med.

Sorry, but that's just wrong.

If you have two different infusions, both ordered to run in at 25ml/hr, and you combine them, then run that combination at 25ml/hr, you are now running each infusion at half the ordered rate (12 1/2 ml/hr). If you run two different infusions at 25ml/hr and then combine, such as y-site one into the other, the rate below that point is 50 ml/hr, even though each infusion is till running at 25ml/hr, the ordered rate. It makes no difference in the math involved if they are y-sited or combined in a buretrol. This basic math people.

Anonymous865 · Jul 13, 2014

40 mEq of potassium in a 100 ml bag- so over 4 hours at 25 ml/ hr- 10 mEq per hour. The mag bags are 4gms in 50 ml that we give over 2 hours when given separately. The doses weren't really vital to this question, since the ordered rate on both of these is 25 ml/hr.

I'm not a nurse, but from a purely math perspective, you would not be infusing at the desired rate if you set it at 50 ml/hr. 25 ml/hr won't give you the correct rate either. Here's why:

You are mixing 100 ml of K and 50 ml of Mag. Therefore your mixture is 1/3 mag and 2/3 K.

Total fluid is 50 Mag + 100 K = 150 ml

50 ml of mag / 150 total fluid is 1/3 of bag is mag.

100 ml K / 150 ml total fluid is 2/3 K

If your are infusing at 50 ml / hr them 1/3 of that 50 ml is mag. So you have infused 16.66 ml of Mag after 1 hour. After 1 hour 2/3 of that 50 ml is K. So you will have infused 33.33 ml of K after 1 hour.

After 2 hours you will have infused 33.33 ml of Mag and 66.66 ml of K.

After 3 hours you will have infused 50 ml of Mag and 100 ml of K.

So you gave the Mag slower than you wanted and you gave the K faster than you wanted.

Now if you set the pump at 25 ml / hour, then after 1 hour you will have given 8.33 ml of Mag and 16.66 ml of K.

After 2 hours - 16.66 of Mag and 33.32 of K

After 3 hours - 24.99 of Mag and 49.98 of K

After 4 hours - 33.32 of Mag and 66.64 of K

After 5 hours - 41.65 of Mag and 83.33 of K

After 6 hours - 50 of Mag and 100 of K

All this assumes that the Mag and K are evenly distributed in the liquid and they don't separate after you mix them.

If you were infusing equal quantities and at equal rates, then running it at 50 ml / hr should be the same as running 2 lines at 25 ml/hr.

MunoRN, RN · Jul 13, 2014

I'm not a nurse, but from a purely math perspective, you would not be infusing at the desired rate if you set it at 50 ml/hr. 25 ml/hr won't give you the correct rate either. Here's why:
You are mixing 100 ml of K and 50 ml of Mag. Therefore your mixture is 1/3 mag and 2/3 K.
Total fluid is 50 Mag + 100 K = 150 ml
50 ml of mag / 150 total fluid is 1/3 of bag is mag.
100 ml K / 150 ml total fluid is 2/3 K
If your are infusing at 50 ml / hr them 1/3 of that 50 ml is mag. So you have infused 16.66 ml of Mag after 1 hour. After 1 hour 2/3 of that 50 ml is K. So you will have infused 33.33 ml of K after 1 hour.
After 2 hours you will have infused 33.33 ml of Mag and 66.66 ml of K.
After 3 hours you will have infused 50 ml of Mag and 100 ml of K.
So you gave the Mag slower than you wanted and you gave the K faster than you wanted.
Now if you set the pump at 25 ml / hour, then after 1 hour you will have given 8.33 ml of Mag and 16.66 ml of K.
After 2 hours - 16.66 of Mag and 33.32 of K
After 3 hours - 24.99 of Mag and 49.98 of K
After 4 hours - 33.32 of Mag and 66.64 of K
After 5 hours - 41.65 of Mag and 83.33 of K
After 6 hours - 50 of Mag and 100 of K
All this assumes that the Mag and K are evenly distributed in the liquid and they don't separate after you mix them.
If you were infusing equal quantities and at equal rates, then running it at 50 ml / hr should be the same as running 2 lines at 25 ml/hr.

If you're volumes are different then the rates would be different, although the concentrations we use are 40meq/100 ml Kcl and 4 grams/100ml mag, so giving 40meq and 4 grams would be the same volume for each.

Anonymous865 · Jul 13, 2014

If you're volumes are different then the rates would be different, although the concentrations we use are 40meq/100 ml Kcl and 4 grams/100ml mag, so giving 40meq and 4 grams would be the same volume for each.

Yeah, but if you look at one of OP's later posts (I quoted it in my original post), they say they are giving 40 mEQ K in 100 ml at 25 ml/hr and mag is 4gms in 50 ml at 25 ml/hr. They said they are mixing those bags and giving them at 25 ml/hr. They were asking if it wouldn't be more accurate to give them at 50 ml/hr.

If you were using the concentrations you mentioned, then mixing them and infusing at 50 ml/hr would give them the correct rate. The concentrations they mentioned would not.

blondy2061h, MSN, RN · Jul 13, 2014

Yep, I figured that out in my third post in this thread. But still, our current practice is to run the 150 ml combined mixture at 25ml/hr, making it take 6 hours to go in, compared to 2 hours for the mag and 4 hours for the K when done separately. Wouldn't running the mixture over 4 hours (i.e., going with the longest necessary infusion) at 37 ml/hr be superior to running it at 25? It would get it done in 4 hours and be closer to the prescribed rate.

Anonymous865 · Jul 13, 2014

Yep, I figured that out in my third post in this thread. But still, our current practice is to run the 150 ml combined mixture at 25ml/hr, making it take 6 hours to go in, compared to 2 hours for the mag and 4 hours for the K when done separately. Wouldn't running the mixture over 4 hours (i.e., going with the longest necessary infusion) at 37 ml/hr be superior to running it at 25? It would get it done in 4 hours and be closer to the prescribed rate.

Well if you ran it at 37 ml / hr then you would have infused

12.33 (1/3 x 37) of mag and 24.66 (2/3 of 37) of K after 1 hour

24.66 of mag and 49.32 of K after 2 hours

36.99 of mag and 79.98 of K after 3 hours

49.32 of mag and 98.64 of K after 4 hours

You K would be going in at the desired 25 ml/hr. Your mag would be taking twice as long as ordered.

icuRNmaggie, BSN, RN · Jul 13, 2014

I have zero experience with pre term labor pts. I do believe that the Mag is given in OB to relax the uterus rather than as an electrolyte replacement. I could be wrong. Wouldnt it be better tolerated in a pt with pre term labor vs a critically ill hypovolemic pt? Just wondering.

Mr. Murse · Jul 13, 2014

The discomfort isn't an issue with central access.

I know, but did the OP ever specify they were referring only to central lines?