Secondary IV infusions

Nurses General Nursing

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I'm a new nurse, and I have a couple questions about running secondary IV infusions:

When I hang a medication to be given via piggyback infusion, I usually use my IV pump to backprime the secondary tubing first, and then start the piggyback medication. This is the way I was taught. And it's also the way I was taught to back flush in between two different secondary medications. Anyway, I've noticed that some people also do this, but others prime the secondary tubing with the medication itself, then attach the secondary tubing to the secondary port on the pump cassette and start the pump. Thoughts?

The other part of my question has to do with VTBI. I always program my VTBI as exactly the amount that is in the secondary piggyback medication bag. But now I'm wondering, does the fact that I primed the secondary tubing with primary fluid mean that I'm not giving the patient the entire dose of medication? I assume that for the first few minutes of the secondary infusion, the patient is just receiving the fluid that was primed into the tubing. Even if I were to prime the secondary tubing with medication like some nurses do, the bottom half of the IV tubing that is common for the primary and secondary lines is filled with primary fluid and that's still what the patient is getting for the first few minutes. Not sure how much the tubing holds I will have to check the packaging but still. Do you see my confusion? So I'm wondering how you approach that.

If you're still with me.... I imagine there would be some residual in the secondary bag still. And the last part of my question goes off of that - I'm worried now that I might be always undermedicating my patients, because isn't there always residual secondary fluid? ie there is always some fluid left, if not in the minibag itself at least in the secondary line ie we don't run it dry. by this logic should we really be flushing the secondary line? but I've never heard of this...

One more thing. I see "overfill" listed on the label of some IV medications prepared by pharmacy. like the label will say 117 mL plus overfill. What do you program then? What's the rationale? How much overfill?? And therefore what do you set as the VTBI?

Not sure where to look for answers. Thanks for helping me think through this.

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Specializes in Critical care.

If I'm hooking up a new secondary line then I will prime with the med. I do it very carefully so I'm not wasting any. When I am using secondary tubing that has already been used I back prime a bunch into the old bag to clear the line (so I'm not worried about compatibility issues), then I clamp the line to stop flow and empty the drip chamber and then fill it some with the new med. It's important to always unclamp ASAP so you don't forget. I unclamp then program the pump. Some people unhook the secondary line to prime it with the new med, but I was taught not to do that for infection control purposes. The more times you unhook and open it up, the higher probability of contaminating the line.

I figure the residual left in the bag or tubing (as long as it's not a lot) is just some extra becaus it is known that most bags don't run dry. It drives me batty though when people hook up an antibiotic or similar med as a primary with no flush to run through. A hospital I used to work at told us the tubing holds 13mls of fluid so we need to run a 15ml flush afterwards to ensure the patient has gotten the full amount. If a 50ml bag of Zosyn is hooked up with nothing to run as a flush and 10ml of fluid is left in the tubing, that means the patient is not getting 1/5 (20%) of the med!

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Every single place that I have worked dispensed medication bags with a certain amount of overfill to prime the tubing. Even commercially filled ones. The correct way is to prime the tubing with the medication. Attach to the appropriate port on the tubing or the pump. Set the pump for the volume needed to administer the correct dose. Whatever remains in the line or the bag is the overfill. This way you can be confident you are giving your patient the dose that was ordered. I have never back-flushed a line from one bag to another. Was never taught to do it and do not see how it is a good idea having no idea how much fluid you may get into the medication bag thereby changing the concentration.

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Specializes in Critical Care.

The secondary tubing should be primed with the primary fluid, using the secondary medication to prime the tubing sort of misses the point of using a primary/secondary set up. This is particularly true of infusions after the initial set up, since then you would be disconnecting the secondary from the primary to prime the secondary tubing, which adds an unnecessary opening of an otherwise closed system.

Keep in mind that in a true primary/secondary set up the secondary volume you set the pump for doesn't mean the pump will only infuse from the secondary bag for that set volume, really you're just telling the pump to run at one rate for a certain volume, and then switch back to the primary rate. So if you set the secondary volume for 100ml but there are 120ml in the bag, and the secondary rate is 200 and the primary rate is 25, then the first 100ml of the secondary will infuse at 200ml/hr but the last 20 ml will take almost an hour to go in since the pump will switch back to the primary rate of 25.

The amount of residual medication depends on the height difference between the primary and secondary. What you're doing with a primary/secondary setup is creating a single fluid column with the secondary bag and usually at least part of the tubing above the top of the primary fluid. So long as the secondary bag is sufficiently above the primary, there will be minimal residual. If you really want to get it all in except for a miniscule amount, then you could backflush the secondary bag and allow that to infuse.

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The secondary tubing should be primed with the primary fluid, using the secondary medication to prime the tubing sort of misses the point of using a primary/secondary set up. This is particularly true of infusions after the initial set up, since then you would be disconnecting the secondary from the primary to prime the secondary tubing, which adds an unnecessary opening of an otherwise closed system.

Keep in mind that in a true primary/secondary set up the secondary volume you set the pump for doesn't mean the pump will only infuse from the secondary bag for that set volume, really you're just telling the pump to run at one rate for a certain volume, and then switch back to the primary rate. So if you set the secondary volume for 100ml but there are 120ml in the bag, and the secondary rate is 200 and the primary rate is 25, then the first 100ml of the secondary will infuse at 200ml/hr but the last 20 ml will take almost an hour to go in since the pump will switch back to the primary rate of 25.

The amount of residual medication depends on the height difference between the primary and secondary. What you're doing with a primary/secondary setup is creating a single fluid column with the secondary bag and usually at least part of the tubing above the top of the primary fluid. So long as the secondary bag is sufficiently above the primary, there will be minimal residual. If you really want to get it all in except for a miniscule amount, then you could backflush the secondary bag and allow that to infuse.

Why would you prime the secondary tubing with the maintenance fluid? Prime it with the secondary fluid when it's first hung and when it's done infusing it will be pre-primed for the next dose so you don't have to break into the system. Also, just curious about what pumps you are using? I'm having a difficult time picturing how your pumps work. I have not experienced pumps running the way you are describing.

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Why would you prime the secondary tubing with the maintenance fluid? Prime it with the secondary fluid when it's first hung and when it's done infusing it will be pre-primed for the next dose so you don't have to break into the system. Also, just curious about what pumps you are using? I'm having a difficult time picturing how your pumps work. I have not experienced pumps running the way you are describing.

I'm assuming they just have on secondary line for all meds, so it doesn't matter which fluid is in the secondary line because you will back flush between all meds. The only time I make separate secondary lines are for meds like dilantin. Printing with the primary infusion also reduces the chance of air bubbles. If you have extra in the secondary bag, you can program the pump to infuse the extra 10-15mls at the same rate as the secondary infusion

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I'm assuming they just have on secondary line for all meds, so it doesn't matter which fluid is in the secondary line because you will back flush between all meds. The only time I make separate secondary lines are for meds like dilantin. Printing with the primary infusion also reduces the chance of air bubbles. If you have extra in the secondary bag, you can program the pump to infuse the extra 10-15mls at the same rate as the secondary infusion

Hmmmm. Never done it that way. We have separate tubing for each med. Okay then, but if you set the pump to infuse the left over medication then aren't you actually giving a bigger dose than ordered? Most bags have at least 20ml of overfill.

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Specializes in Ambulatory Care-Family Medicine.

We use new secondary tubing for all different piggyback. We put caps on the ones not currently in use. Prime the secondary tubing with the med and hook it to the secondary port, just program the pump the run a flush of the primary fluid after the led is done to make sure the primary line is clear of the med to avoid compatibility issues. Not uncommon for a patient to have 2-3 different secondary setups handing with caps on the ones not currently in use.

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Hmmmm. Never done it that way. We have separate tubing for each med. Okay then, but if you set the pump to infuse the left over medication then aren't you actually giving a bigger dose than ordered? Most bags have at least 20ml of overfill.

Nope, because the dose is the same if I mix 40 mg pantoprazole in 100 mls or in 120 mls. It's still 40 mg

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Nope, because the dose is the same if I mix 40 mg pantoprazole in 100 mls or in 120 mls. It's still 40 mg

Too bad we don't have a pharmacist here to clarify because when I see a bag that says 100mg/50ml then I assume that it's a concentration of 100mg/50ml. Not 100mg/70ml. So I have to think that extra 20ml is an extra 40mg of the med that was never intended to be given to the patient which is why it's called overfill.

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Turns out I'm both right and wrong. Manufacturer filled bags DO have more medication in them than stated on the bag. The dose on the bag is the concentration not the total dose contained in the bag. However, there are some bags that are mixed as Triddin stated but those bags are supposed to be labeled with the total volume (med+overfill) to infuse in order to achieve the full dose and the flush required after administration. Which begs the question, in that case what's the point of the overfill?

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I honestly think that little extra or less would cause little harm to the patient to get either

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