r/IntensiveCare • u/swaggydoo29 • 6d ago
CRRT
How do nephrologist choose which bags to use for CRRT? 2k 4k 0k bags? im trying to understand how they decide which bags to use for a patient. and when do you actually decide to stop crrt? and which filter to use? ST150, oxiris, ST100. also how do they determine how fast the pre, dialysate, post filter runs? im really confused. can someone help me understand this? huhu
7
u/madipbar 6d ago
The ICU where I work we pick the bags based off of the patients labs. We almost always run citrate and then chose to add potassium, calcium and bicarb. based off of q6hr labs. We always run the same filter size. We don't have a proper dialysis unit at our hospital so if the kidneys don't improve after so many days we have to transfer the patient to a larger hospital that does once they are stable. Our ICU docs manage the crrt we don't have nephrology but I'm sure they consult them.
11
u/Particular_Dingo_659 RN, CCRN 6d ago
I can answer some of this:
The dialysate prescription is based on the lab values of the pt. For example, if the blood concentration of K, Ca, Na, etc. is higher than the concentration in the dialysate, then it’s taken out during dialysis.
The primary thing with the dialyzer is the surface area of the membrane. The “bigger” it is, the more particles are cleared from the blood.
In order to get better clearance, you have to increase the total blood volume cleaned, so you can increase the BFR, the time, or the dialyzer surface area/size.
3
u/MudJolly2951 5d ago
Honestly there’s way too many solutions offered by manufacturers. I’m a big fan of KISS - keep it simple stupid. Most hospitals are totally fine with just a 4K and 2K solution. I’m leaving citrate out the discussion as well as it’s technically still considered off label use.
Per KDIGO guidelines, goal delivered dose (which is the sum of the big bag rates + fluid removal/UF rate) is 20-25 mL/kg/hr. So they’ll usually overprescribe to around 30 mL/kg/hr to account for pauses in therapy.
Filters are like the bags. Too many for no reason (for adults!) peds needs varying sizes bc their patients are obv smaller. The ones you’re mentioning are Prisma. ST150 + HF1400 are the biggest. Biggest difference is ST150 has more adsorptive properties - think of the walls of the straws like your air filter in the furnace. It attracts more middle molecules (ie inflammatory mediators and cytokines), clogging up the filter faster which sucks for us but is a good indicator of effective therapy.
4
u/MudJolly2951 5d ago
Also important to add that nephrologists aren’t trained on the specific type of machine, but just CRRT in general. There are several CRRT machines, but the prisma is the only one that can do pre and poster filter replacement simultaneously without some rigged shady setup. If they didn’t have their training at a facility that utilizes prisma, they honestly may not fully understand it.
Pre filter replacement + post filter replacement are for convective clearance (middle to larger solutes)
Dialysate pump is for diffusive clearance (smaller solutes)
Filter selection determines if you get adsorptive clearanceThe distribution of the solutions at the bottom should be dependent on what’s going on with your patient- but generally they should start 50% diffusion and 50% replacement. So if those dose was 3,000 mL/hr, you’d have 750 PBP 1500 dialysate 750 post
3
u/Good_Tension_5660 5d ago
Couldn’t tell you about the pre and post filter stuff… but in terms of the bags, our nephrologists taught us to use the “Rule of 7s.” So if a patient had a K of 5, they’d most likely order a 2K+ bag to help bring it down (5+2=7). If the K was 3, they’d use a 4K+ bag to gently bring it up (3+4=7)… At least in our ICU they only really cared about the K+ bags since we replaced all the other electrolytes ourselves. Everything else… it was always “call dialysis”
1
1
u/Sufficient_Elk_941 2d ago edited 2d ago
It depends on if you are using diffusion or convection the doctor decides whether replacement fluid is given pre-dilution (before the filter) or post-dilution. With CRRT or In dialysis you are trying to correct the balance in the blood (ex an acid-base balance in metabolic acidosis) and remove/filter waste from blood. Thus you have to know what the goal of treatment is and what kind of molecules your trying to filter out of the blood and body (ex small molecules..uremia, creatinine, potassium vs moderate/large sized molecules like cytokines and inflammatory response mediators seen in sepsis) usually a standard sized filter is used but it is basically the weight of pt and the access/vascular/hemodynamic stability of the pt.. the prisma 150 is primarily use for adults and allows for more surface area for filtration of solutes and they tolerate a higher blood flow rate. Patients may need a lot of filtration (ultrafiltration to clear these molecules from the blood) the blood flow rate may need to be increased to avoid blood becoming to thick (hemoconcentration) and clotting off the filter but the blood flow rate is the amount of fluid being pulled from the blood (ultrafiltration) vs the amount of blood plasma entering the filter (this is your filtration factor usually kept below 25%) you have to increase the blood flow rate to dilute the blood entering the filter to prevent clotting the circuit… there’s more to it but this is my general understanding in what is happening. With specific bath concentration remember the principle of diffusion where molecules will cross the membrane from higher concentration to lower concentration (if you have high potassium you want a lower bath to pull out the excess potassium from the blood) the goal is to have clean blood with equal balance instead of an excess or deficit. Im not a doctor I’m a nurse so not claiming to know precisely but it’s my overview and your welcome to add to it or make me change my mind about it with your own Expirence and knowledge shared :) good luck on your journey into CRRT which happens to be one of my favorite kinds of ICU pts (gosh that’s an awful trait isn’t it…lol we are all sick in our own way-no pun intended) by the way we suck in healthcare in implementing CRRT…I mean we really do suck !! Or it’s never ordered or it should be started sooner rather than later to improve pt out comes and this is facts and one way we can fix this is to be aware and advocate for your patient…ask questions, understand what your doing…you are responsible for this patient so always ask yourself ? Is this safe for the patient? Do I understand the set up and function of the system and always have emergency equipment and an extra filter in immediate area. The biggest and almost most important part as a nurse for this treatment is to how to access properly and more importantly know how to return blood to your patients before filter clots off…you don’t want your patients to loose that blood volume that could be life or death for some..if you filter clots know how much blood and volume your patient just lost and what that means. Know the signs and symptoms of CRRT and dialysis complications and how your patients may react in these settings. Think about what you may need to do in emergencies and how you would get help the fastest. Adjust for the volume loss…anticipate what you may need or have on hand in an emergency. I can guarantee you will have to trouble shoot during this advanced ICU treatment and you own this process in the ICU if you mess up your pt could die think about acute blood loss and how much your body needs in it at all times before the body goes into hypovolemic shock and please ask your senior nurses charge nurses or educator for help..understand what you are doing if you don’t that could mean your license and someone’s life
35
u/Puzzleheaded_Test544 6d ago
Ok so a lot of thought should go into the details, but luckily you can simplify the end decision a bit. Ideally you should know how the kidney works to get an idea of what we are replacing. Vander's renal physiology is good for that. Then read up on how dialysis circuits work. Deranged physiology is good for that.
First
The question is really dialysis type.
For me, look for citrate contraindications- acute liver failure, cirrhosis (child's pugh C a hard no for me, everything else a solid maybe), 'we can't tolerate any bleeding complication' situarions (rare).
If you do citrate, ideally calcium and bicarb free. Usually a proprietary 'citrate bag'
Otherwise pick something normal. The various haemosol formulations are popular here. These roughly approximate ideal plasma concentrations often with a bit more buffer and no potassium so you can tailor your concentration.
Potassium.
If K high, make up the bags to be 4mmol/l or lower. How low- depends on how fast you need the patient's K to change.
If K low, do the opposite (or just give IV replacement all the time and fight the machine)
Sodium
Most solutions come with a physiological sodium concentration. This is a problem in severe hyponatraemia and your options are to either decrease dose or get make up some high risk custom formulation.
You might want a high normal sodium. You can add hypertonic sodium to the bags to bring the concentration up to achieve this.
Also if you decide to add more bicarb buffer for whatever reason (eg severe nagma) just be aware that will increase dialysate sodium concentration too. Best to avoid doing that.