Thread by @adequator_app

1/ SECOND tweetorial in the CRRT SERIES

⚡️DOSE assessment in CRRT
⚡️Formation of “effluent” (E)
⚡️Modalities

Retweet if you like

To read the FIRST thread 👇

https://twitter.com/adequator_app/status/1209108776944619520?s=21

2/ Assessment of RRT dose in AKI

🤨Critical and AKI patients have characteristics that make RRT dose assessment challenging

✔️Constant change in volume status
✔️Unsteady metabolic state (catabolism, nutrition, inflammation)
✔️Modality options (H, HD, HDF, HDI, SLED)

3/ So how we assess dose in CRRT then?

✔️CRRT as we know it (Veno venous) & CRRT specific machines have being around for 20 years.

Since then, DOSE has been assessed as the effluent volume

🧐 But why this way?

4/To understand why, first we have to know what is effluent? 💧(E)

✅ The Waste product of any system giving CLEARANCE

Kidney = URINE
PD= fluid drained
HD= dialysate after the filter
CRRT= fluid after the filter

5/ Depending on the therapy, the effluent will get partially or completely saturated with small molecules (X)

Clearance will depend on the effluent volume and the amount of saturation

K = VOL *(sat %)

HD
-🩸 50 X
-💧 15 X
-VOL 120 L
-Sat 15/50 =30%
-K= 120*0.3
-K= 36 L

6/ In CRRT the effluent is produced so SLOWLY that it gets completely saturated and therefore every (ml) represents (K)

CRRT
-🩸 50 X
-💧 50 X
-VOL 50 L
-Sat 50/50 =100%
-K= 120*1
-K= 50 L

7/ EFFLUENT saturations with different RRT and modalities

-HD ➡️ 15-30%
-SLED ➡️ 60-70%
-PD ➡️ 80%

-CRRT
CVVH ➡️ 100%
CVVHD ➡️ 90-100%
CVVHDF ➡️ 90-100%

8/ How is effluent formed in CRRT?
It will depend in the modality used

✔️CVVH = hemofiltration
➡️🩸🩸🩸➡️
➖➖⬇️➖➖
E ⬅️💧💧

✔️CVVHD= Hemodialysis
➡️🩸🩸🩸➡️
➖➖➖➖
E ⬅️💧💧💧⬅️

✔️CVVHDF= Hemodiafiltration
➡️🩸🩸🩸➡️
➖➖⬇️➖➖
E ⬅️💧💧💧⬅️

9/Check how effluent is formed when using prismaflex with all the options activated

Remember: when giving convection every ml should be replaced with fluid in PRE filter, POST filter or both, so that fluid balance is 0

GIF 👇
CVVHDF
PRE + POST + Dialysate + fluid removal

10/ We can give the same dose and change the way the effluent is produced, only by changing modality IMAGE👇

🧐 If modality does not change the dose, why bother with different modality prescriptions?

11/ Three main reasons (in this order)

1. CRRT machine available 🎛

2. Technical aspects for circuit patency⚙️🔩

3. Type of transport needed (Convective or diffusive)

Lets review rationale for each one 🧐

12/ CRRT machines

⚡️The device available will be the most important variable on deciding a CRRT modality ⚡️

🧐Note: not necessarily the machine with more options is a better machine, there are other technical features that are not represented in the schema (other tweetorial)

13/ Circuit patency

⚡️Being an Intensity dependent therapy, circuit life should be the priority when choosing a modality⚡️

i.e.
-Using PRE RF to reduce FF will need a CVVH or CVVHD
-Using citrate as PRE dilution RF will need a CVVHDF

check the citrate thread 👇

https://twitter.com/adequator_app/status/1170152610537582593

14/ Type of transport

Until now we‘ve been talking about small size mol clearance(K)

But 🧐
-Medium size don’t saturate (E) to a 100% so (K) is ⬇️

-Convection will ⬆️ (K) of medium size mol by 30%~

-Small mol (K) will not change regardless of transport 👇

15/ Theoretically clearing middle (not measurable) “toxins” could improve outcomes & therefore using convection should do the job

🧐To this day there is no evidence that CONVECTION improves outcomes in the CRRT/AKI scenario & using it could lower ⬇️ circuit life

16/ To this point we know:

-(E) is used to dose CRRT because it represents (K) of small size molecules
-(E) forms depending on modality
-Modality choice depends on device availability, circuit life & type of transport

The next question will be

What dose?

17/ The recommended dose is 20-25 ml/kg/hr

This recommendation comes from a series of studies comparing high dose 40~ vs 20~, where no difference was found in mortality or adverse events

18/why not compare 20 vs lower dose? The reason is simple

CAVH studies demonstrated that 30~ ml/min urea (K) was needed to achieve metabolic control in catabolic well fed patients

✅20 ml/kg/hr is an EFFICIENCY metric that guarantees metabolic control to MOST patients (not all)

19/ Effluent ml/kg/hr is how CRRT is normally dosed, but are there other ways to do it ?

Absolutely, there are two interesting proposals that are based in urea clearance or urea kinetics that are worthy of mention 👇

20/ The first Proposed by @RClaure_nefro
Studied 6 Adequacy parameters
KB, KD, KtVB, KtVD, EKR, SRI & found that:

(K)(dialysis side) ml/min & Equivalent renal urea (K) were useful metrics to monitor & compare between dif treatments

dx.doi.org/10.5301%2Fijao…

21/ The second Proposed by Clark & Ronco

consist in measuring the Standard (daily) KTV & considering in the calculation two variables:

✔️Fluid overload
✔️Down time

doi.org/10.1159/000475…

21/ Conclusions

✅(E) is used to dose CRRT because it represents (K) of small size molecules
✅(E)forms depending on modality
✅Modality choice depends on device availability, circuit life & type of transport
✅CONVECTION clears middle size mol better than DIFFUSION

22/ conclusions

✅To this day No evidence of better outcomes with CONVECTION
✅20ml/kg/hr is an EFFICACY metric that guarantees metabolic control in catabolic well fed patients
✅No evidence for higher dose
✅Other efficacy metrics proposed are KD & Std daily KtV