r/emergencymedicine • u/baddadjokess Trauma Team - BSN • 1d ago
Discussion MTP: Trauma Line vs large bore peripheral IV.
Hello all.
I’ve been a trauma nurse for about a year, ER nurse for the better part of a decade. Not very long in a trauma role, but I’m doing my best at learning as much as my brain allows me to whenever I get the chance.
Today I was reading about poiseuille's law on a instagram post from a trauma surgeon somewhere in South America, where the post and most of the comments (from people who seemed to know what they were talking about) agreed that due to poiseuille's law, a large bore PIV (such as a 14g) was the preferred access using during MTP over a large bore, triple lumen CVC. They claimed that the length of the trauma line/CVC creates a significant amount of friction, considerably affecting the max flow rate of a viscous fluid like blood.
Since I started working trauma, I’ve always been taught that larger bore = higher flow, but that IG post peaked my interest and made me wonder if I could be making small changes in my practice that would lead to a better patient outcome.
I’m planning on discussing it with the surgeons at work, but I’d also love to hear your take on this topic.
Cheers.
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u/WhyDoYouPostGarbage Critical Care Physician 1d ago
Cordis with rapid infuser > 14G > 16G > Cordis gravity > 18G > 20G > 22G.
In reality, even a 16G can hit 180-220 mL/min, you rarely need more than that.
For a much more in depth explanation, would recommend reading the first chapter of Marino’s ICU Book.
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u/Aviacks 1d ago
Also look at the line itself and get an idea of the gauge and flow rating. We just had this fight with a random resident on off service GI rotation. GI has a blanket “patient must have two large bore IVs at all times” for literally every single patient, doesn’t matter if the hgb is literally 13.
Resident gets told to tell us we have to place an 18ga. We explain patient has a fistula on the left, has had multiple lines go bad on the right, and had a large bore triple lumen IJ placed by IR. With the largest lumen being rated for 10mL/sec and two lumens rated for 5mL/sec.
Mind you these ratings are for a thicker contrast, not just NS. Three days in a row we get asked to place an 18ga, hospitalist who was primary goes “literally fuck no” as they have superficial clots on the right arm already. Resident cites “PIV better than CVC for blood” on day three.
Like sure, in theory. But we can’t place bilateral 14s on everyone and keep them in place for two weeks while they’re inpatient. On average most IVs last 22-26 hours if you’re lucky. Meanwhile a triple lumen CVC capable of 10mL/sec flow under pressure in the proximal port will be more than enough for 99% of blood admin.
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u/Some_Caterpillar392 1d ago
People also tend to forget about vein size. Doesn't matter if you can get a 14g in a vein that is only good for a 20G, more than likely for it to extravaste and from my experience, you will achieve similar flow rates due to vein size.
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u/DaggerQ_Wave Paramedic 1d ago
If you really NEED the flow of a 14 gauge to keep up with losses, they’re probably capital F FUCKED
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u/baddadjokess Trauma Team - BSN 1d ago
Right. Agreed.
But if there’s a better, less restrictive option than what we’re doing now, why not implement it?
Like a fire extinguisher, I rather have it and not need it, than need it and not have it.
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u/DaggerQ_Wave Paramedic 1d ago
If you can get the 14 gauge, go for it! It’s just a tough line to get and easy to blow a vein with. I agree with the guy saying 16 gauge is all you need most of the time, with the added statement that you can cram a 16 gauge into way more vessels than a 14 g and cause a lot less vessel trauma
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u/baddadjokess Trauma Team - BSN 1d ago
Yeah I don’t disagree with them. We typically use 18s and 16s. Rarely 14s unless they’re sure shots. I rather have a 18/16 quickly than a 14 that takes 6-7 attempts.
But I may have not properly explained myself on my original post. I know things like line stability, any real need for such a high infusion rate, and time needed to place the line are to be considered in a real world scenario, but my question was that if ONLY considering poiseuille's law, would it be more beneficial to run MTP through a large bore CVC than a large bore peripheral line should a high rate of infusion be needed. Is the length of the LBCVC significant enough to make a real difference?
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u/Aviacks 1d ago
Yes, it’s a huge difference. Based on length alone and no other factors. Keep in mind also manufacturers play tricks with lumen diameter for CVCs. E.g. the IJs lumens might so “16ga” on them but flush like shit, it’s not the same 16ga measurement of your PIV.
Go flush the larger lumen on a PICC, then flush a 20ga in the forearm. It’ll become pretty clear how big of a difference it is. Some longer lines will get better flow rates because of higher pressure rating, but that isn’t really applicable to blood admin.
I place 10cm 18ga midlines a lot, compared to a short 18ga PIV they’ll often be a lot slower of a flush. But frequently they flow much better because they’re in a bigger vein and not being linked off. Vs shoving an 18ga in grandmas hand, you’ll likely not have the best flow.
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u/OldManGrimm Adult/Peds Trauma - RN 1d ago
At the risk of sounding dumb, what do you mean by midline? Femoral vein?
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u/Aviacks 1d ago
Your hospital may not use these or only use them inpatient? They’re a special kind of peripheral IV, inserted into the same veins in the upper arm as a PICC. Difference is they terminate in the axillary vein just before the shoulder goes into the chest wall.
Hospitals love them because it skirts CLABSIs while still giving a reliable IV that’ll outlast a regular peripheral IV by quite a bit. The CLABSI skirting leads to them being abuse by hospital systems, but they’re my go to for difficult IV access when we get called to the trauma / resuscitation bay in our ER. I can get an 8-10cm 18ga midline in the upper arm with ultrasound much faster than anyone starting a CVC or looking for an iv multiple times.
The “power glide” brand of midlines from BD are rated for 325psi which lends them a very high flow rating despite that extra length, they’ll flow in CT much faster than a traditional 18ga on paper. But any trauma rapid infuser or pressure bag goes to 300mmHg, not PSI. Totally different ballparks of pressure you’ll never see outside of CT.
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u/herpesderpesdoodoo RN 1d ago
A RIC can be placed by seldinger-ing a 20g PIVC: get some peripheral access and expand it if you need. A trialysis or vascath catheter is also good if going central.
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u/baddadjokess Trauma Team - BSN 1d ago
Yeah we discuss the use of trialysis caths all the time but I have yet to see any of them put one in. One day, maybe.
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u/sbenno ED Registrar 1d ago edited 1d ago
Sometimes it's a balance between flow and security of the line.
An arrow rapid infusion catheter (5cm, 7fr pivc) will get you 600ml/min flow (edit: up to 1000mL/min according to LITFL) - can't be matched by a CVC of any type, but runs the risk of dislodgement and extravasation if its not well into a proximal vein.
An introducer sheath (edit: MAC sheath) doesn't get quite the same rate, and takes longer to place, but is rock solid and reliable. As others have also said, you don't often need 600ml/min as it is.
Plus showing off and putting an introducer sheath during your trauma resus is more glamorous than converting your 20g PIVC to a RIC.
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u/Davidhaslhof ED Resident 1d ago
In my experience the RIC is unmatched when it comes to resus transfusion. I placed one on a patient with a pelvis fracture and hypotension. It turned out he lacerated his internal iliac artery. We were able to hang 2 units of blood a minute on the rapid transfuser. In the OR he got 66 units of PRBC, 64 units of plasma, 56 units of platelets and an unknown amount of blood from the autotransfuser. We were going through units so fast that we couldn’t keep up with the supply from the blood bank during the initial resuscitation, though we didn’t see a systolic above 50 until his aorta was cross clamped.
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u/FungatingAss Trauma Team - Attending 1d ago
Bilateral 18G or greater is all you need for resus. Place the line later.
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u/Smirking_Greek_God 1d ago
So as per the explanation regarding Poiseuille's law, flow is inversely proportional to length, but also directly proportional to r4. In the setting of IVs most of them are of pretty similar length, so the larger the bore, the flow will be greater.
However in the setting of central lines, especially in a triple lumen, the length is quite a bit longer and the radius of each lumen is narrow. Therefore flow is reduced by two means. In the setting of an MTP it is therefore better to run it through a large bore short length IV (i.e. a peripheral IV) or through a very large bore central cannula (ex. a cortice).
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u/baddadjokess Trauma Team - BSN 1d ago
I can’t remember off the top of my head but I’m almost certain that the larger lumen of the three in our large bore cvc’s is larger than a 14g. I can confirm tomorrow. But even if that’s the case, would the length of it (16 or 20cm depending on what the use) cause enough friction where a 14g PIV would be a better choice between the two.
Obviously, I wouldn’t wait until the central line is placed to start transfusing. But once it’s in and secured, if MTP is still on going, is it worth moving from the current peripheral site, to the (large bore) central line?
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u/Aviacks 1d ago
If you have a 14 or 16ga PIV it’ll almost always be better for blood admin, especially under pressure. You can’t pressure infuse via Cordis, they aren’t pressure rated and if that softer tubing gets kinked from neck movement or tube movement it could be ugly lol.
That being said most larger even triple lumens can handle 10mL/second, keeping in mind that’s rated at 300PSI for those speeds from CT pressure injection.
16cm vs 20cm is negligible difference and not worth considering. 20 vs 30 vs 40cm are much bigger differences, some fem lines go to 30, and PICCs can be 30-55. Keep in mind also that your 14ga can still flow like shit if the veins suck or if they bend their arm or kink it in any way.
Just flush the lines and feel it out. You’ll feel pretty quickly if there’s goanna be a major difference. Me personally I’ll use the large bore PIV for as long as it works well, but I wouldn’t expect the line to last forever if it’s large bore and being used a ton. If it’s not flushing amazing because of location or shit veins then I’d switch to the CVC to have something more reliable.
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u/tallyhoo123 ED Attending 1d ago
You have to also take into consideration the drugs being used and what access is available.
A triple lumen CVC can be placed easily into the subclav and provide you 3 different lines of access for meds including blood during trauma. Which will allow for RSI meds / antibiotics / bloods.
A single 14g IVC will provide great flow but only a single line of access and when the patient is shocked or suffering limb injuries it is harder to find an appropriate vein to access.
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u/LoudMouthPigs 1d ago
DRILL BABY DRILL
Call me Nailin' Sarah Palin cause I'll put a spike in anyone who looks like shit. Radial over tibial, once their arms are in a solid position.
Central line is too fussy IMO. I'm not opposed to drop one once the patient is under control, but in a patient in extremis I'd rather spend time for line placement doing literally anything else.
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u/Vast_Bad_39 1d ago
yeah that’s pretty much my understanding too. short fat catheter usually wins over longer line even if the central line looks bigger.
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u/shaninegone 1d ago
The importance about Pouseilles law is the radius and the length of the line you place.
Short and fat = great flow
Long and thin = shit flow
14G cannulae are short and fat so they flow well but they are peripheral and at risk of dislodging more than central access. However can be inserted in seconds.
CVCs are relatively large bore but much longer which reduces the flow rate also take longer to place.
My ED commonly uses MAC sheaths for rapid infusion of blood products. It's basically and short and fat central line. Still more time consuming to place than a peripheral line but someone can be placing one while someone smashes in a decent peripheral line at the same time.