Continuous Renal Replacement Therapy (CRRT, dialysis)

Okay. In this lesson we’re going to talk about something called continuous renal replacement therapy or C R R. T. now CERT is slow dialysis. Now this is almost always done in the ICU, typically requires special training by an ICU nurse. And so I’m going to kind of gloss over a few things. I’m going to give you the basics and the best things that you need to understand really for anybody who’s receiving CRRT, anything you might see, whether it’s in school, or your first year as a nurse. If you end up in the ICU, you will get detailed training on how to take care of a client receiving CRRT. So CRRT, slow dialysis, and it usually uses one or both of these two processes. Hemodialysis, which is diffusion using a dialysate solution. And ultra filtration. Ultra filtration is when blood is actually forced through a filter to physically remove certain things from the blood. So indications, the reason why we do slow dialysis is typically hemodynamic instability. Remember with regular hemodialysis, we’re pulling off two to four liters in two to four hours. So we’re literally just ripping two to four liters of fluid out of their body. The chances of hypotension with that are actually really, really good. So if I have a patient who’s in kidney failure, needs dialysis, but has a low blood pressure already and is really unstable, typically we’re going to go with the slow dialysis route with the goal of removing one to two liters in 24 hours. And so we’re going to go real slow. We’re going to remove a couple of hundred milliliters an hour, and get that filtration happening. But without causing any more instability. Usually this is temporary. Again, this is a patient who is super sick, they’re in the ICU, they’re hemodynamically unstable and they need dialysis. So it’s temporary. Once we get them more stable, they can usually transition to regular hemodialysis. So again, preventing hypotension, giving us tight control of those exchanges.
Now, types of CRRT, I really just want to give you a general idea of what this looks like. Ultimately, the type that’s chosen is going to be determined by the nephrologist and it’s really just going to depend on the patient, their goals, the situation, and what’s going on. So there’s two main categories. There’s ones that involve filtration and there’s ones that involve dialysis and sometimes it involves both. So filtration or dialysis. First one is SCUF, slow, continuous ultrafiltration. So literally we’re just pulling the blood out of the body, forcing it through a filter and returning it to the patient. That’s it. That’s all we’re doing. A lot of times the purpose of this is just to remove volume and to filter out some of the smaller particles need to be filtered out.
Then you also have something called CVVH or continuous venovenous, meaning it comes out of a vein and back into a vein hemofiltration. So what we’re doing is the same thing. We’re forcing the blood out of the patient, forcing it through a filter and putting it back into the patient. But we’re also adding a replacement fluid. So we’re also adding this replacement fluid for two reasons. One is it helps a have a better balance in terms of electrolytes and things like that. We also have less overall volume removal. Really, we’re just trying to remove specific particles and waste products from the blood via filtration. Next one is CVVHD, so continuous venovenous. So again, uh, out of a vein back into a vein hemodialysis, C. V. V. H. D. this is going to remove that fluid by diffusion using dialysate.
So if you go back to the peritoneal dialysis and hemodialysis lessons, you’ll get some understanding of the purpose of dialysate, but really its major purpose is to create a concentration gradient so that I can remove certain fluid, I can remove certain electrolytes, certain waste products by that concentration gradient by diffusion. In CVVHD there’s no ultra filtration, so we’re not forcing anything through a filter and there’s no replacement fluid. We’re literally just pulling the blood out. We’re running it through, past a semi permeable membrane with dialysate on the other side. So we have certain things coming into the blood, certain things going out, and then we return that cleaned blood to the patient and whatever’s left over in this fluid, we pull out. Last one, CVVHDF. It basically combines all of these things together. So we have continuous venovenous hemodiafiltration, so it’s the same as CVVHD except it adds ultrafiltration.
So this semipermeable membrane is actually our filter. And not only do we pass the blood through here, but we’re also going to force some of it through these filters to be able to be ultra filtrated and then returned to the patient. And then of course we have that replacement fluid as well. Again, really just trying to achieve balance. We’re trying to achieve this homeostasis, which is the whole purpose of the kidneys, right? Is to create homeostasis. So that’s what we’re trying to accomplish. So the tightest control we can accomplish the most with CVVHDF and most CRRTs are actually going to be that. So just to recap, and some terms to remember. So you’re going to have, here’s your patient and here’s their catheter. Big thing to know is that CRRT must be done through a catheter. It’s actually pretty rare to be able to do it through a graft or fistula.
And we’ll talk about that in a second. So here’s our patient. The blood’s going to come off the patient. It’s going to go up through a pump. Sometimes it might get anticoagulated with either citrate or heparin. And the whole purpose of this anticoagulation is actually to prevent clots inside the filter. Most of the time we’re not actually causing any kind of anticoagulation in the patient themselves. So we’re going to possibly anti-coagulate, we’re going to go into the filter. This is where both diffusion and ultra filtration are happening. Filtration inside that filter. So from here, what you’re seeing is your dialysate solution being pumped in. So remember, dialysate is what creates our concentration gradient. Okay? So we pumped out into the filter. We allow for diffusion and ultra filtration to happen and that fluid that we’ve now created that has all the excess waste products, toxins, electrolytes, things that we don’t need, don’t want gets pulled out of that filter and gets excreted into this beautiful yellow bag. And we call that our effluent bag. It’s yellow because it has urea in it. It is basically the equivalent to urine. It just gets disposed of in the toilet just like urine would. And then what you’ll see is the cleaned blood comes out of the filter around, gets replacement fluid added and it gets put back into the patient. So it’s basically just one big cycle. We pass the dialysate by our blood, we remove all the toxins and things we don’t want and we give a replacement solution to bring it back into the patient.
So big nursing responsibilities, again, ICU only they must have a catheter as opposed to a graft. Generally those grafts and fistulas are contraindicated for CRRT, but one study did show that only a third of the patient, I think it was about 48 patients that received CRRT through a graft, officially only about a third of them had complications. I have attached that article for you for interesting reading if you want to know, but just make sure you check with your facility about what kind of access they have to have.
So big things, nursing responsibility wise is strict intake and output. What we’re going to do is the nephrologist is going to give us a 24 hour net fluid removal goal. So for example, they might say let’s remove a 1200 milliliters in 24 hours. So you go, okay, I need to remove about 50 mls an hour, right?
So you’re kind of going to have a general hourly aim. But what’s going to happen is you’re going to have hourly monitoring. So let’s say you have a patient, and your hourly checking their I&O balance. So their total IV and PO in plus the total dialysate and replacement fluid that goes in minus their total out. So that could be a urine output, stool output, vomit, anything that is coming out of the patient themselves minus their total effluent. Okay, so that effluent bag is basically like their urine. That’s what we’ve put out through their dialysis. So total in IV and PO total in dialysis and replacement minus their total output, whatever it is, minus the total effluent bag, gives you your hourly balance. So this is what I’m talking about when I say minus 50 is we’re aiming for this. So every single hour we are calculating this.
We are looking at every single 10th of a milliliter that went in there, every single milliliter that they drank, every single milliliter that came out of them. Okay. Super, super strict I&O because we’re trying to accomplish this without causing further hypotension and instability. So that’s the second thing is we’ve got to be monitoring their vital signs. Again, most of these patients are going to be in the ICU, so they’re going to be on continuous monitoring. The other thing that’s unique with CRRT is we’ve got to monitor vascular access pressures really, really closely. Again, we want to keep that blood moving. So if pressures get too high, it could mean that you have a kink in your line somewhere. Especially patients that have like femoral access lines. If they bend their leg too much it kinks off, it’s really frustrating. But if the pressures are too low, you could have a disconnect somewhere or you could have a leak.
So really, really important that you’re watching those pressures. And then the other thing we’re gonna do is check lab values. A lot of times we’re checking lab values every four hours. We’re going to check a BMP that in a renal panel, we’re going to check an ionized calcium right? Check mag and phos, and then anything else special for that patient. So they might want, an ABG so they can check their acid base balance or they might want a lactic acid level. So whatever they order. And every four hours we call the nephrology team. We give them all of those numbers and they tell us if they want us to change anything. So we’re going to have specific settings and the nephrologist is going to control that. So it’s really, honestly, it’s probably one of the favorite things I’ve ever done in the ICU is actually take care of CRRT patients.
I think because I’m a super nerd and I like spreadsheets and I like numbers. It’s really a cool process. It’s really fun to be a part of. So if you ever get a chance to take care of a CRRT patient in the ICU, definitely take that opportunity.
So patient education, this is a CRRT machine. I know it looks all, you know, newfangled and fancy. If you’ll notice, it’s actually color coded. So again, yellow is urine, right? So that’s our effluent bag. We come in off the patient and then the blue goes back to the patient. So it’s really cool process. I really love doing it. Big thing to know though is a lot of times these patients are on bed rest. So we’ve got to make sure they know what their activity restrictions are, why they can’t get out of bed, what’s going on.
If they have any fluid and diet restrictions, again, it is dialysis. This is an ICU, so they might have some specific restrictions. Make sure they know that and then make sure you’re explaining the process and the equipment. As you can see over here in this image, this can be super overwhelming. This is really scary looking to be attached to this big old machine. and so make sure you’re explaining to them what’s happening while you’re doing the things that you’re doing. And it’s really just going to help ease the process for them. So major nursing concepts for a patient receiving CRRT – perfusion, again, if they’re getting CRRT, it’s because they’re hemodynamically unstable. So we’ve got to make sure we’re watching blood pressures, watching heart rates, fluid and electrolyte balance and elimination. Again, we’re replacing the functions of the kidneys.
So key points recap. CRRT is slow dialysis. It’s purpose is for hemodynamically unstable patients so that we can still give them the dialysis they need. It requires super, super close monitoring. A lot of times these patients are actually one to one. You don’t have any other patients monitor those. Super strict vital signs. Keep an eye on their vascular access pressures and the access itself and check your labs. You’re gonna work super closely with your nephrology team. Like I said, you’re going to call them with those lab results every four hours. Tell them exactly what your numbers are and they’re going to tell you if they want you to change anything. And then patient education. Remember this could be super overwhelming for them. The more you can give them, to ease their mind, the better. So I hope that was helpful. Like I said, CRRT is a specialized process that occurs in the ICU, but that doesn’t mean you’re not going to see it in nursing school and it doesn’t mean you’re not going to see it very quickly when you graduate. So we wanted to give you the basics and just understand what’s happening and why. So make sure you check out all the rest of the lessons on dialysis as well as the resources attached to this lesson. And I go out and be your absolute best selves today, guys. And as always, happy nursing.