How long can you use mdv and sdv?

We use any/all vials for 24 hours max. I work on a hospital IV Team as well as outpatient infusion suite (situated within the hospital.)

My first question would be to ask if you are pulling the flush solution out of a 50cc minibag of NS?
I am not sure about the 10 ml reconsitution.
Anyway, a MDV of saline (or heparin flush) has a preservative in it which if you pop the top and then label the vial and make it pt specific, it is good for 30 days. However, single dose vials are just that... single dose/use only. They Do Not have a preservative in them, therefore once you access them to withdraw a flush amount, you pitch it afterwards. Your (50, 100cc, and up) bags of fluids, DO NOT have preservatives in them either. SO, once they are spiked with the IV tubing, they must be thrown away after 24 hours regardless of how much fluid is left in them. Bacteria proliferate after 24 hours of hang time.
I also do not recommend you using them as a flush solution through-out the day as the numerous amount of entries increase substantially the chances of microbe introduction.

Okay, so you are drawing from a 50cc MDV of saline (0.9% sodium chloride) right?
So, that brings me to my next question... how much of this saline is being infused into your pts in a 24 hour period?
You see, because it is a MDV, in big bold red letters it says "warning-not for use in newborns"
that is because the preservative in it, benzol alcohol, is toxic to newborns. In addition, however, it is also toxic to your elderly pts. If you use more than 30cc of this MDV in a 24 hour period, neuro-toxicities could result.

That is why ideally, single dose medications, those without preservatives should be the diluent/flush of choice.

I also am on a hospital IV team. We only use a multi-dose vial for a single patient, and all at once. For example, when inserting a PICC, we'll draw up 3 syringes full of NSS from a multi-dose vial for use all at once. If any if left over, it is thrown out immediately. The same goes for Heparin. We do end up tossing a fair amount of solution, but it's worth the cost to prevent infections. Our hospital uses as many single dose vials as possible, and the multi-dose is only for us to draw up sterile-ly during insertions and such. The nurses on the floor never draw from a multi-dose vial. Also, our bags of NS are thrown out after 24 hours of continuous infusion or immediately upon d/c of bolus. Hope this helps!