10-minute Rounds: Calculations on CRRT (Filtration Fraction)

[@annychen5194]

I'm a med student and I just wanna thank you for those amazing videos you made. They helped me get a few good letter of recommendation from my attendings and I think I will do nephro in the future!!!!!!

[@akshartejasdesai]

Anny Chen I’m glad I could help Anny. Good luck in your career!

[@mikey6482]

@@akshartejasdesai We need more good renal fellows... welcome aboard Anny :)

[@ahmadraedtarakjimdfrcpc8201]

You should NOT include dialysate flow since it is NOT going through the blood compartment of the filter so it is NOT filtered out.

[@thmsdngsn]

Not sure why you plugged in the dialysate flow rate (you don’t thankfully in your final formula): the net dialysate volume doesn’t cross the membranes, so it would have nothing to do with clotting. Also, in reality the quality of the catheter (whether the flow is good or bad) and the overall condition of the pt (very septic pts and dying pts are much more prone to produce fibrin breakdown products and clotting factors) have much more to do with clotting than the filtration factor. As a long time acute dialysis nurse I find that the failure of the ICU teams responsible for catheter placement and replacement and the pts condx are the prime factors in clotting, not the BFR or UFR (though these are lesser causative factors). Also, considering the amt of fluids that go into very sick pts and concomitantly need to come out of them, your 20% is a bit of a pipe dream in practice. But I liked your presentation. It was pretty good for a physician.

[@dr.nadiaalharbi2463]

thank you for this informative video, just I had a question what is the program you used during the presentation which allows you to write without pen??

[@a.s.5169]

When you talk about QR (Replacement are you talking about pre-replacement fluid only? or pre and post? For example, in CVVH you're giving a rate for the PBP (pre-filter replacement) and for the Post-filter replacement. So, are you counting total replacement or just the pre-filter replacement? Thank you! Great video!

[@lpyne]

It is incorrect to include the Qd in the equation for filtration fraction. The dialysate and blood are different compartments. While effluent calculation for CRRT dose includes the Qd it does not make sense to include Qd in the equation for FF. The numerator should be water removal rate aka total UF rate. FF best thought of as fraction of water that is removed from the blood.

[@snapdoctor]

Very nice presentation. In order to solve the equation, do you convert the Qb into ml/hour or Qd into ml/min, as the units for both are different. Do you also have to convert UFR? Thanks

[@akshartejasdesai]

personally, i convert the QD into ml/min as well as the UFR. But it doesn't matter so long as all the flow rates are in the same units.

[@pauloandrepamplona7434]

Nice video, but I had the same question of Ahmad Read Tarakji.. You do not include dialisate flow cause it won't mix with blood flow, so you do not remove it from patient's blood directly

[@darshanru1]

What if the replacement is post filter? Then Qeff = Quf?

[@akshartejasdesai]

Thanks.

[@drgouth]

Good!

[@scottbieber4497]

I applaud you for working to educate people about nephrology and CRRT but there is a error in this video which can be confusing to trainees and it should be taken down. The equation for the filtration fraction for typical CRRT systems should reflect the ratio of the volume of fluid that is filtered through convection to the fluid entering the filter so it should not include the dialysate flow, which is not filtered. If you are referring to the flow fraction, as is used to understand NxStage technology, that is different and would include the dialysate flow.

[@raghaveshp]

What if patient is on CVVHDF. Do we have to add both the QD+QR to the numerator and denominator? Can u please explain? Thanks,

[@nephondemand]

+Pullalarevu Raghavesh In CVVHDF, you are both dialyzing against the dialysate (QD) and adding replacement fluid (QR). But the filtration fraction should still be the amount you remove from the blood compartment (numerator; Qeff = QR + UFR) divided by the amount you put into the blood compartment (QB*[1-hematocrit]). I do not believe you need to consider QD in the filtration fraction.

[@raghaveshp]

Thank u so much.

[@DrTahirZaman]

What about Post Filter Fluid, would this only be added to the numerator but not the denominator, thus reducing filtration fraction