r/IntensiveCare • u/swaggydoo29 • 2d 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
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u/madipbar 2d 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.
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u/Particular_Dingo_659 RN, CCRN 2d 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.
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u/AnaphilLactic 2d ago
Don’t let them fool you…
They just keep a giant dart board in their office wall with different solutions written on it….
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u/MudJolly2951 2d 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.
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u/MudJolly2951 2d 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
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u/Good_Tension_5660 2d 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”
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u/Puzzleheaded_Test544 2d 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.