so...exactly how fast is "wide open"? MAG in 250 cc experiment

[croaker260]

Just some of the random stuff I do at work when not running calls...

I was researching some infusion protocols for Mag sulfate and I realized that there was no clear estimates on how fast wide open would be if someone accidentlaly ran in a bag of mag (or any other drug). so, I did this little experiment.

Question: Can 5 GMS mag in 250 cc saline be safely run @ wide open and not exceed common safety parameters (i.e. < 1 gram/minute) in emergency situations?

Methods: Using a stop watch, time the infusion of 250 cc saline and 10 cc mag using two prosposed infusion methods (noted below).

Experiment #1: 250 cc saline + 10 cc (5 grams) mag elevated 30 inches above distal end, with 15 gtt set and saline extension set (93.5 inches total w/o cath) , run @ wide open, with 16 G 1 1/2 inch at distal end takes 5 minutes 26 seconds to run in. Estimated infusion rate 52 cc/minute

Experiment #2 250 cc saline + 10 cc (5 grams) elevated 30 inches above distal end, with 60gtt set "STAT II PUMPETTE and saline extension set (91.5 inches total w/o cath), run @ "Full OPEN" , with 16 G 1 1/2 inch at distal end takes 15 minutes 03 seconds to run in. Estimated approx 17.3 cc/minute

Conclusion: 5 GMS (10 cc) added to 250 cc saline run at the maximal possible infusion rate without a pressure infusion device (AKA wide open) at commonly accepted elevations and normal infusion equipment should not exceed safety parameters for emergency infusion using either commonly accepted infusion sets available in EMS.

Secondary conclusion: I am an EMS GEEK.

My challenge to you: Can you guys reproduce the same experiment with 18 G, 20 G and 14 G? And/or 10 gtt sets? (We dont use 10 gtt sets but some do...) I am sure if everyone takes one part and posts it, it would be very interesting. I am very interesting in the results with 18 and 20 G catheters.

Edited December 15, 2011 by croaker260

[DwayneEMTP]

Yeah, man, but I like your geekiness a lot...

Likely this experiment would be different if run into a patient. I'm guessing that you ran this onto the floor, or into a bucket which offers no vascular resistance, right?

I'm sure that there is some vascular resistance but am not at all sure what percentage difference it might make.

I would play but am at home now without access to those supplies.

Dwayne

[croaker260]

Yeah, man, but I like your geekiness a lot...

Likely this experiment would be different if run into a patient. I'm guessing that you ran this onto the floor, or into a bucket which offers no vascular resistance, right?

I'm sure that there is some vascular resistance but am not at all sure what percentage difference it might make.

I would play but am at home now without access to those supplies.

Dwayne

You are of course absolutely right, and I considered that as well. But I quickly came to two observations:

1- I have no equipment, nor accurate and useful parameters to simulate vascular resitance in this situation.

2- For this situation, vascular risistance is not a huge issue. I am trying to see what the maximum possible worst case scenario that could happen with a given combination of equipment if mag was left run at wide open, wich is one of the expressed concerns/reasons for our medical directorate wanting us to use a buretrol to give mag. So simulating vascular ristance is not that big of a concern. Incoperating vascular resstance would only make the estimate more conservative.

The interesting part of this experiment is that it could be extrapolated to "run away" lines on other infusions too, like dopamine, lidocaine, etc. So therefore it would be useful to reproduce in or discuss in a paramedic program or other class as well. I am hoping someone will reproduce this with an 18 and or 20 gauge here soon though. (hint hint pretty please)

Edited December 15, 2011 by croaker260

[DwayneEMTP]

...

1- I have no equipment, nor accurate and useful parameters to simulate vascular resitance in this situation...

You have veins, right? :-)

...2- For this situation, vascular risistance is not a huge issue...

Gotcha Brother...sorry, I lost track of your conclusion before posting...

I love the fact that you've tried to make this a group exercise! I hope some others step up to the plate. It's too seldom that we have threads that want to physically play with science instead of only theorizing about it. Though I believe that both are valuable, hands on doesn't happen often enough.

And also...use your spell check...great thread with horrible spelling.

Dwayne

[systemet]

I would urge caution with this. I think you are probably using quite a long 16.5 gauge catheter, and have something in the system that is restricting flow. The flow rates should be much faster, consider:

http://www.mcguffmed...V_Catheters.pdf

And think about how quickly we could get fluid into someone with that large a catheter, back when every real trauma got 20 - 40 ml/kg, even without pressure-infusing.

Even if your numbers end up good, they may be highly dependent on the particular secondary set and adaptors you're using. A change in the supply or brand used could result in a big change in these numbers.

Oh, and vascular resistance shouldn't matter that much. CVP is typically somewhere around 5-10 mmHg, or 6-13 cmH20. You're infusing from a pressure gradient of 75 cmH20, so you're looking at worst case a 20% or so decrease with the catheter in a vessel.

Edited December 15, 2011 by systemet

[croaker260]

I would urge caution with this. I think you are probably using quite a long 16.5 gauge catheter, and have something in the system that is restricting flow. The flow rates should be much faster, consider:

http://www.mcguffmed...V_Catheters.pdf

And think about how quickly we could get fluid into someone with that large a catheter, back when every real trauma got 20 - 40 ml/kg, even without pressure-infusing.

Even if your numbers end up good, they may be highly dependent on the particular secondary set and adaptors you're using.

First, thanks for that PDF. Very useful.

Second: The 16 G are quite short and I used the correct size. But yes, there is indeed something restricting flow,,, the size of the drip set You can have a 10 G in a vein but if you have a 60 gtt set on that, there is only so much volume that will flow through the needle in the drip chamber. Unless: (See point #3)

Third: The main way to increase infusion rates beyond these parameters is to add pressure infusion either via a pressure bag or via an infusion device (i.e. pump or rapid infuser). Neither of which I did because we don’t use pressure bags on med infusions.

You make excellent points regarding the equipment, etc. One thought though. RE; Trauma infusion rates- Most of that tubing (that we used back in the day of R Admas Cowley [R.I.P.] inspired trauma care) was 10 gtt tubing with oversized line (AKA repurposed blood tubing) and thus the laminar (sp) flow rates would be much higher.

On final point, anectdotally I think our IV lines used to be much shorter back then....but who knows really. I was surprised to see about 7 feet of line when I did this!

DWAYNE: Yes, I know, believe it or not I proof and MS word spell check usually, unfortunately I have issues typing, and further issues proofing on a computer screen. (This is why I print my charts to proof before I submit them, because I miss sooooooooo much when I try to proof on the computer screen). Its an issue I have struggled with for decades and short of multiple proofs, have never been able to completely lick. Ironically, I got straight A's in English, lit, journalism, and vocabulary, but this was before the age of computer screens in such common use in high schools and college. It is for simiar reasons I cant read (and I try to read a lot) on Kendles, Knooks, Xooms, or any of the other Ebook readers that are out there. Give me paper books any day! Perhaps I have some variant of deslexia (sp) ..who knows?

Edited December 15, 2011 by croaker260

[systemet]

Second: The 16 G are quite short and I used the correct size. But yes, there is indeed something restricting flow,,, the size of the drip set You can have a 10 G in a vein but if you have a 60 gtt set on that, there is only so much volume that will flow through the needle in the drip chamber. Unless: (See point #3)

Right. That's the flow-limiting point. I feel a little silly for not realising that.

Also, it turns out that the flow-rates that the manufacturers print on the side on the cannulae might not be accurate either.

http://www.anesthesi...108/4/1198.full

Wikipedia also has an ok entry on the Hagen-Poiesuille's equation/law for anyone interested: http://en.wikipedia....seuille%27s_law

McPherson D, Adekanye O, Wilkes AR, Hall JE. Fluid Flow Through Intravenous Cannulae in a Clinical Model. Anesth Analg. 2009 Apr;108(4):1198-202. PMID:19299786

Abstract

BACKGROUND: Predicting flow through an IV cannula is useful to clinicians if changes in flow are required and to guide selection of cannula. We sought the usefulness of manufacturers’ quoted flows in predicting actual flow and to characterize that flow.

METHODS: We built a vein model and inserted cannulae between 14 and 20-gauge. In the first experiment, we compared the manufacturer’s quoted flows using deionized water, Hartmann’s solution and Gelofusine. In the second experiment, we varied the pressure feeding the cannula and measured the resulting flow.

RESULTS: Flow through a cannula is not a simple ratio of the manufacturers’ quoted flow rate, even controlling for fluid type and feeding pressure. Flow is neither fully laminar, nor fully turbulent in the range of rates we have measured and in the International Organization for Standardization test. The Reynolds number is often below 2000.

CONCLUSIONS: Flow through cannulae is not laminar at the upper range of clinically used flows, therefore Poiseuille’s law is not useful in predicting flow and the effect of changing radius is less than commonly believed. The quoted maximum flows are also not useful. There are many conditions for laminar flow apart from Reynolds number. Further work would determine useful predictors of flow.

IMPLICATIONS: Flow through a cannula is not laminar at clinically used rates and not simply related to the quoted maximum. Neither Poiseuille’s law nor the quoted values can be used to predict the actual flow of IV fluid through an IV cannula.

Edit : I apologise for the leftover html tags, but I'm not going to remove them. Instead, I'm going to get some sleep.

Edited December 15, 2011 by systemet

[croaker260]

Wow, this is really shaping up to be an informative thread.

[DwayneEMTP]

I hear you croaker. It's one of the main reasons that I use Firefox, it spell checks everything.

I run it through FF, proof, preview and reread then post...and most often go back and edit for the crap that I swear popped in on it's own between proofing and submitting.

Not busting your chops Brother, just helping to look after you, like you do with me.

And this thread friggin' rocks. Any time you can get Systemet's attention and have him invested you're certainly in for a ride!

Dwayne

[croaker260]

Oh, and vascular resistance shouldn't matter that much. CVP is typically somewhere around 5-10 mmHg, or 6-13 cmH20. You're infusing from a pressure gradient of 75 cmH20, so you're looking at worst case a 20% or so decrease with the catheter in a vessel.

Quick question...where do you get the exact pressure gradient of 75 cm H2O? Not doubting you , just trying to figure it out. Thanks.

Edited December 16, 2011 by croaker260