understanding SDN 120 concept

[Farcus]

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For 66.
Question: Magnesium sulfate is available as a 50% solution of
magnesium sulfate heptahydrate (7 waters of hydration).
What volume of this injection is needed for this formula?
Mg = 24, S = 32, H = 1, 0 = 16

The answer goes first part is "MgSO4 * 7 H2O = MW of 246 Mg is divalent, thus 246 mg = 2 mEq of Mg sulfate"

I dont understand this...

246mg = 1 mmoles of Mg, then mEQ = mmoles/valence so 1/2= should the mEQ be 0.5?



For 91
"91. What is the total osmolarity of the IV fluid being administered? Express your answer as milliosmoles,
rounded to the nearest whole number, per 1000 mL."

Answer part A) Since KCl —> two particles, then 1 millimole or milliequivalent = 2 milliosmoles
28.8 millimoles (from Que 90) (x) 2 milliosmoles per millimole = 57.6 milliosmoles for KCl

why would it be 57.6 when the whole TPN ask for 40meq? The question is using 28.8 meq/mmoles which relates to question 88, but 88 didn't use up all the amount of volume in the TPN. I think this is a mistake. Correct me if i'm wrong

Thats how I did 69. Na3PO4= 164mg = 3 mmoles of sodium in 1 mmole of Na3PO4.

The product wants 9 Na3PO4, so thats 27 mmoles, but the question ask for in mEQ so meq= mmoles/valence = 27mmoles/1 valence = 27 mEQ

for 101.

Information for questions 101 through 104. You are told to prepare a double strength Dopamine IV
drip because a patient is requiring large doses to obtain the drug's effects. The usual Dopamine drip
concentration is 400 mg in 250 ml. The patient weighs 176 pounds and needs the pressor dose level of
dopamine (10 mcg/kg/min). Dopamine Injection is available as 40 mg per mL in 10 mL vials. Answer
the following questions:
101. How many mL of the 40 mg per mL Dopamine Injection should be added to a 500 mg bag of IV
fluid to prepare the double concentration? (Ignore volume of the dopamine injection.)

Shouldn't the total volume be 40cc? since its asking to prepare double concentrated when the usual is 400mg/250ml
the answer provided is
x/500 = 400/250, x=800mg, but shouldn't this be 1600 though its asking for double the concentration.

 

[esulliv2]

I have another issue with the SDN problems:

Problems 30/31, the question says that the physician orders 1 liter of 3%NaCl. The answers for those 2 problems are based on you adding 23.4% to the 1L NS which ends up giving you a total volume of over 1L. Would you not remove some of the original NS to add in an equivalent volume of 23.4% to make the TOTAL volume 1L (as was originally ordered?)

 

[MUSIC2LOVE11]

66. The TPN formula will be run at 80 ml/hr, so the total volume required is 80 *24 =1920 ml. The total volume of TPN in that order is 960 ml, so you need 2 bags to last 24 hours. Double your number, and u get the correct answer

91. The formula has been running at 12 drops/mins for 15 hours so the total volume would be 720 ml, not 1000 ml.

101. You are correct, the final concentration should be 1600 mg/500 ml. However, since the original solution already had 800 mg of dopamine, so the amount of dopamine u need to add is 1600 mg -800 mg =800 mg which is 20 ml of the 40mg/ml dopamine injection

Happy studying 😉 I can't wait to be done with the boards!

Oops, didn't see the second post.

30/31. It really doesn't matter, the concentration is still 3%, so if the nurse sets it at a certain rate to be run for x hours, the pt still gets the 3% fluids. The remaining will be discarded.

 

[flo16]

Hi Farcus, trying to share my understanding of sdn problems.

1. problem 66. mgso4.7H20 - molecular weight is 246
since magnesium is divalent 2meq of mg = 246mg , 1 millimole of mgso4 contains 1milliosmole of mg.
so 1 mosmol of magnesium = 246mg.


1millimole = 1meq if it is monovalent ions such as sodium or potassium.but magnesium is a divalent


problem 91. it states osmolarity of total iv fluid being administered

though the the iv fluid has 40 meq of kcl, the patient used only 28.8meq as per problem 88 i,e patient got medication for 15 hours only (in which he received 28.8meq of kcl, not 40meq)

so 1millimole = 1meq since kcl is monovalent 28.8 millimoles = 28.8meq

since 1millimole kcl = 2milliosmoles ,(2 particles of kcl) so 28.8 * 2 = 57.6 milliosmoles

3. problem101.
usual strength of dopamine is 400mg, double strength is 800mg.
we have 40mg per ml of dopamine , so if 40mg is in 1ml then 800 mg will be in 20ml, so answer is 20ml ( do not consider 250ml or 500ml of iv fluid)...we are concerned only about strength of dopamine

Hope this helps..any suggestions are welcome..thanks flo16

 

[Ackj]

For 66.
246mg = 1 mmoles of Mg, then mEQ = mmoles/valence so 1/2= should the mEQ be 0.5?

mEq = mg present * valence / atomic mass

Stock solution is 50%, which is 50g/100mL, 50g = 50,000mg present
mEq = 50,000mg * 2 / 246mg
406 mEq in that 100mL
We want only 10mEq, so x ml/10meq = 100ml/406meq, x =2.46mL

66. The TPN formula will be run at 80 ml/hr, so the total volume required is 80 *24 =1920 ml. The total volume of TPN in that order is 960 ml, so you need 2 bags to last 24 hours. Double your number, and u get the correct answer

You got lucky by doubling it and getting the right answer, but you doubled for the wrong reason. The question asks how many ml you need to make the formula, not how many ml to make a whole days worth. For one bag, we are still basing everything off of the 960mL. You have to multiply by 2 for the valence, not for another bag.

 

[DrStreetCam]

Am I the only one tripped up by the fact that it says a 500 mg bag... not 500 ml?

"101. How many mL of the 40 mg per mL Dopamine Injection should be added to a *****500 mg***** bag of IV
fluid to prepare the double concentration? (Ignore volume of the dopamine injection.)"