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Please note, these videos are intended for medical students, interns and other new clinicians on general medicine floors.

Transcript

What’s the difference between a midline and a PICC? And come on, can we really not just draw blood off of our peripheral IV? Well, today we’re going to go over all the questions that you’ve always wanted to know about IVs, but have been too afraid to ask on In the Nick of Time. So let’s look at five factors that are going to help determine what kind of IV we want.

One,  how long is the IV? Two,  how wide is the lumen? Three,  how many lumen do we need? Four,  how long are we going to need that IV for? And five,  are there any contraindications to specific types of IVs?  And stick around to the end when we’re going to go over some specific case examples of when to use different IVs.

Okay, so first thing, let’s take length. This is going to affect the function of our IV, its complication risk, and also its flow rate. Let’s start by looking at the shortest catheters, aka peripheral IVs. Now there is an upside to these smaller IVs. They’re pretty  easy to place. Unfortunately, that also means  they’re pretty easy to come out.

Which means that any medications that are going to be higher toxicity to the tissue around the vein, if they do come out, are really ones we  can’t give through these peripheral IVs. That means your  pressors,  your chemotherapy,  or your high osmolarity medications like TPN.  Unfortunately, you also can’t draw blood from these peripheral IVs.

Trust me, I wish you could. But unfortunately, when you apply suction into that small vein, it’s higher risk of blocking the catheter collapsing or irritating the vein, or just all that suction causing more hemolysis on the blood sample.  Now let’s take a look at some longer IVs. I’m specifically talking about ones that are long enough to reach the big central veins like the vena cava.

This can include peripherally inserted central catheters like PICCs or short term central catheters, like the triple lumen.

So there’s a lot of upsides to these longer central lines. They’re  more secure, so they  last longer because there’s less risk of them becoming displaced, you can give a lot of those  higher toxicity medications we talked about before, and you can draw blood from them with less risk of damage to the blood vessel or the catheter, and a lot less risk of hemolysis.

So that all sounds great, but unfortunately, central lines are not perfect. They come with a higher risk of quite a number of complications such as  clot or infection. If they do become malposition, they can cause complications such as  vascular or nerve injury, or they can cause  arrhythmia if they enter the atria.

So just remember that these complications are not rare. So we really try and stick to peripheral IVs when we can. So this is peripheral and central lines, but what about midlines? So midlines go further than a peripheral IV, but don’t make it quite to those central veins. They often stop in the axillary or subclavian vein.

That means that they are more secure than a peripheral IV, but we can’t give those high risk medications that we need a central vein for. And while there’s some variability, usually we can’t draw blood.  So that’s all helpful but we said there was one other reason why the length of an IV matters, and that’s how fast you can give medications and fluids through them.

Okay, let’s say your patient’s in septic shock. You need to give them fluids ASAP. But in order to give fluids quickly, you need a catheter with high flow rate. So what determines flow rate? Well, the walls of the catheter can actually lead to friction and that friction will resist the flow of fluids. So if we have a shorter catheter with less wall resistance, that means we’ll actually get a faster flow rate.

But length is not the only thing that affects flow rate. Remember our second factor width, also known as the gauge of a catheter. With higher gauges actually having a smaller width. But how is width going to affect our flow rate? Well, the wider catheter has less of the fluid interacting with the walls where there’s friction.

So we can give fluids faster, so a  wider catheter, otherwise known as a lower gauge, can give fluids faster. Whereas a  narrower catheter otherwise known as a higher gauge, will give fluids a little bit more slowly and width will actually affect your flow rate more than length because flow is related to length inversely, but it’s actually related to width to the fourth power.

So your width is going to have a huge impact on your flow rate. Okay, so here’s the summary of what we talked about so far. Now let’s look at the flow rate of some common types of IVs. So here’s a summary of some common types of IVs, their gauge, and the relative flow rates. So as we can see here,  as the gauge goes down on different types of IVs, in other words, as they get wider, the flow rate goes up.

So let’s say that you have a patient and you need to infuse two liters of fluids as fast as you can.  Okay. Let’s say that patient has a 22 gauge IV, a pretty common one on the floor. In order to give them two liters of fluids, it would take almost an hour. That’s a lot of time. But if you can get an 18 gauge IV in them, you cut that down to just 20 minutes.

And when you’re resuscitating a patient, time matters. So you can see how important it’s to have the right type of IV.  Do you also notice that the triple lumen catheter is on this list twice? Well that’s because just like the name suggests, they have multiple different lumens, that can serve different functions.

And that’s actually the third thing that we want to look at when deciding a type of IV. And that’s the  lumens. So most catheters have just one lumen. You could probably guess that. And I mean, why complicate things, right?  So if you’re putting in a PICC, a midline, or a triple lumen, you have the option to have a catheter that has multiple lumen.

Why would you pick that? Well, let’s say that you want to give  multiple medications at the same time that aren’t compatible in the same lumen.  Or maybe you just want to give a  medication while you’re also using that catheter to draw blood.  Having multiple lumen allows you to do that. And that sounds great, but unfortunately there’s no free lunch here.

So more lumens, especially those long lumens that you have in a central catheter means a  higher risk for things like clots or infection. So make sure to only add those lumens if it’s clinically necessary.  So, okay, more lumens means just more lumens to work with, right? But remember that those lumens can actually differ in their function.

Okay? So notice how the triple lumen central catheter is made up kind of obviously of three different lines or three different lumens, and their different color is a hint that these three lumens are not all the same. For one, the width or gauge of these lumens can actually be different. One of them tends to be wider, and it varies a little bit with model, but it tends to be the distal brown port.

So, okay, we have one lumen that’s wider than the others. What could we use that for? Yeah, we could use that for resuscitation fluids. Wider lumen are able to give fluids faster, so that’s a great choice. Also, these lumen actually open up at different parts along the catheter. How does that help us? Well, if you want to draw blood, it might be a good idea to draw it from this proximal port.

That way, anything we’re infusing goes downstream of it and doesn’t contaminate our sample. Also, if you want to check central venous pressure, it might be a good idea to use the lumen that’s closest to the right atrium, the distal port.  Here’s some other common uses for the different lumens of a triple lumen catheter.

This can really vary, so it’s really just a starting guide, and you can find it in the show notes when it comes to lumens. The last thing to keep in mind is that these lumens can have actually very distinct functions from each other. A good example is dialysis or apheresis, where you want to have one lumen to take blood away from the patient and after it’s been treated or cleaned another lumen to bring blood back.

So this is exactly what you see in a dialysis or apheresis catheter. It’s made up of one lumen, usually red to bring blood away from the patient to the machine, and another lumen usually blue, to bring blood back to the patient after it’s been treated.

Keep in mind that these lumen are only used for these purposes, and if you want to use that catheter to draw blood or give other medications,  you need a third dedicated lumen that’s only available in certain models.

Okay, so more lumens lets us do more with the catheter, and those lumen may have distinct roles. But it also increases the complication risk. Speaking of complication, risk catheters tend to get more complications the longer they’re in. So for our fourth factor, let’s look at how long we’re going to need that IV for.

Now, peripheral IVs don’t last long. They generally have to be replaced every three to four days to avoid infection or inflammation, and oftentimes they just come out around that time. But remember, even though we’re replacing them often peripheral IVs are thought to account for about 23% of bloodstream infections.

So still consider taking them out if they’re not needed. Now temporary central lines are more secure, so they can last longer in theory. But remember that the longer they’re in, the higher that risk of    infection and blood clots. So still try to take them out as soon as you don’t need them anymore.

Okay, so what if you need a line for a few weeks, like you know, a patient being discharged in IV antibiotics? Well, here we’re often thinking about midlines, which are recommended for a week or two, or PICC lines, which can last several weeks, but which one of those are we gonna use?  Now, historically we’ve gone with a PICC anytime we need more than just a few days of antibiotics, but there was actually a recent study that found midlines to be a safe alternative when you need antibiotics for up to two weeks.

I mean, that’s great. There’s less complications with midlines. We’d love to be able to use them. Just keep in mind that midlines did have a higher rate of occlusion in that trial. And also some antibiotics like vancomycin actually have a higher complication rate with midlines. So for medications like that, we probably still need to use a PICC.

Are you still not sure exactly which catheter to use, midlines or PICCs?

Well, there’s this awesome guide called the Michigan Appropriateness Guide for Intravenous Catheters, or MAGIC, that can help you decide what catheter to use, depending on your clinical scenario.  Okay, so that’s a good start. But what if our patient needs a catheter for longer than that? I mean, think about people who need chemotherapy every few weeks or who need regular blood draws.

I mean, we know keeping a central line in longer and longer increases the risk of things like clot and infection. So what do we do for these patients? Well, in cases like this, we can reduce the risk of infection by actually tunneling part of the catheter under the skin. These are called tunneled lines.

There’s tunneled central lines and tunneled dialysis catheters.  Finally, some people need a catheter for a long, long time, like years. This is when we use things called totally implantable venous access devices, where the whole catheter is under the skin. These are more commonly called ports.  Here’s a summary of all the types of catheters we talked about today, and this is gonna be available in the show notes for you to look at later.

The fifth and last thing to consider is whether there are any patient related factors that could make certain types of IVs contraindicated. Some of these are a little bit more straightforward. You know, avoid putting catheter in an area of skin abnormality like over a rash or infection, and try to avoid abnormal blood vessels.

Like, I wouldn’t recommend putting a catheter in a blood vessel that has a blood clot or a fistula.

Next, if the patient has a history of mastectomy and lymph node dissection, putting an IV in the same side is thought to increase the risk of lymphedema. Newer studies suggest that risk might be lower than we thought, although more studies are needed here.  If someone has a bloodstream infection, all those catheters become a nidus for infection.

So definitely avoid putting in any longer lines like a midline or central line, and talk to your infectious team about probably changing out any current IVs.  Finally, we have patients with chronic kidney disease. Now, in these patients, their arm veins are precious because we may need them to create a fistula or graft later.

So we can really only put peripheral IVs in the arms because other catheters could cause more damage to the veins. So if you have a patient with chronic kidney disease who may need a central catheter, you may need to place it elsewhere and always check with your renal team.

Let’s close out with some common clinical scenarios. As we go through, I want you to think about what type of IV you’d use. Let’s say we have a patient who needs rapid resuscitation, septic shock, hemorrhagic shock. We need fluids in quickly. What type of IV are you using?

You want an IV that’s short and wide to minimize friction on the wall, to increase flow rate and to get fluids into your patient.

The specific IV might vary, but a peripheral IV that’s 16 or 18 gauge might be a good one to choose. Okay. Now your page that phlebotomy has tried time and time again and they just can’t get blood on your patient. They’re asking you for a type of catheter for this. What are you gonna choose?

While sometimes a midline is able to draw blood, generally a central line is needed if we need to consistently be able to get blood from a patient using a catheter.

Again, only use this if you really can’t draw blood. Okay. Your patient’s post-op, they can eat. It’s been a long time. You’re gonna need to give TPN what type of catheter are they gonna need?

We’re gonna need a central line here again, TPN has a super high osmolarity, so it’s really irritating to peripheral veins.

Okay? You have a patient with stage four chronic kidney disease on the floor, on the internal medicine service. They can’t keep a peripheral IV in. It just keeps falling out. They need more stable access. What are you gonna get them?

Oftentimes we’re doing a midline pick here, but in a patient with chronic kidney disease, that’s generally not an option because we have to preserve those arm veins in case they need dialysis later.

So we try to avoid a central line as best we can try ultrasound guided IVs, but if ultimately they really need a central line, often that temporary central line has to go somewhere other than their arms. Okay. Your next patient, no chronic kidney disease. This time. They need about two more weeks of ceftriaxone after they leave the hospital.

Case management’s calling. We’re planning to discharge them tomorrow. How are you planning to give them that ceftriaxone?

Like we said before, for a patient who needs a few weeks of treatment, it’s the great midline versus pick debate. For this patient who just needs two weeks of treatment, they’re on ceftriaxone.

A midline might be appropriate, but you can talk to your IV and ID team to help you make the decision if you’re unsure. Your final patient for the day is just starting treatment for cancer. They’re gonna need blood draws and treatment for weeks to months, to maybe years. How are they gonna get that done?

Yeah to lower the risk of complications for this patient’s catheter, we may want it to go partially under the skin so it lasts weeks to months or completely under the skin. So it lasts months to years.  So the next time your patient needs a new catheter, remember the five factors we talked about here today by determining the right length, width, and number of lumens of that catheter, how long you’re gonna need it for, and whether there are any contraindications to placing it.

You’ll be on your way to picking the right catheter for your patient.