Thread by @adequator_app

1/16
Conventional Hemodialisis (HD)and continuous therapies (CRRT) both have blood pumps, filters, use catheters and are used in renal failure

But they are completely different treatments

Wonder Why? 👇🧵 get your calculator

2/ First we have to remember the concept of:

CLEARANCE (K)=Ratio of mass removal rate (N) to blood solute concentration (CB)

K= N/CB

✅ Practical definition: Volume of plasma completely cleaned from (X)

for this tweetorial (X) represent small molecules 40-100 daltons

3/ how HD & CRRT give CLEARANCE (K)?

Both expose blood 🩸 to a free of (X) fluid 💧 through a membrane In countercurrent direction

🩸————>
➖➖➖➖
<————💧

A fraction of (X) pases through the membrane from 🩸 to 💧 by a diffusion or convection mechanism

4/ but what’s the difference?

The relation of speed flow between the two fluids:

HD: 🩸 Qb / 💧 Qd 1 / 2
CRRT: 🩸 Qb / 💧 Qd 3 / 1

The inverse relation of flows, is the nature of the difference in clearance between both therapies

5/ What happens when you give a 4 hour HD?

100(X) ➡️🩸250ml/min ➡️ 30(X)
➖➖➖➖➖
70(X) ⬅️ 500ml/min💧⬅️ 0(X)

70% of Qb is completely cleared

(K) = 0.7*250 = 175 ml/ min
175*240 min = 42 L

6/ What happens when you give a 4 & 24 hour CRRT?

100(X) ➡️🩸100ml/min ➡️ 70(X)
➖➖➖➖➖
100(X) ⬅️ 30ml/min 💧⬅️ 0(X)

💧fluid is so SLOW that a 100% of it gets SATURATED with (X), meaning 💧 VOLUME=(K)

30*240=7.2 L
30*1440= 43 L

7/ (K) of different therapies

-HD 4 hrs = 175ml/min ——-42 L
-CRRT 4 hrs = 30ml/min——7.2 L

-CRRT 24 hrs =30ml/min—-43 L
-PD 24 hrs= 7ml/min———-10 L

-Kidney 24 hrs 100ml/min —144 L

Clearly HD is much more EFFICIENT than CRRT and PD

So, why bother with low efficiency?

8/ To understand the advantage of giving low efficiency to a therapy we need to know some concepts

📉1st ORDER KINETICS📈: amount of removal of (X) depends on the concentration of (X)

The more concentration the more you can remove and viceversa

9/ Concepts to determine a therapy’s characteristics, let’s review them:

-EFFICIENCY: Clearance (K)
-INTENSITY: Efficiency x time
-FREQUENCY: number of treatments per week
-EFFICACY: effective removal of a specific solute resulting from a given treatment in a given patient

10/ ⬆️ EFFICIENCY

✅
-Great for fast removal
-Enhanced with technical tricks (bigger filter & KoA, more Qd & Qb)

❌
-1st order kinetics: substance (X) will drop fast and then plateau, also (K)
-Bad for substance rebound
-If only using diffusion, no (K) of medium molecules

11/ ⬆️ INTENSITY

✅
-Steady state: removal=production
-1st O Kinetics: concentration is constant so removal is constant
-Great for substance rebound
-(K) of middle size molecules

❌
-Depends on time
-Bad for fast removal
-Only enhanced with more time
-Constant removal of PO4

12/EFFICACY
A patient particular clinical goal achieved by giving efficiency, intensity and frequency with a therapy

Some METRICS represent EFFICACY and try to generalize goals to all populations with a lot of controversy:

- KT/V 1.2
- PD weekly KT/V 1.7
- CRRT 20-25 ml/Kg/hr

13/ ✅ GOOD COMBINATIONS

-HD: high efficiency low intensity x3 frequency

-CRRT: low efficiency high intensity frequency as needed

-DP: very low efficiency high intensity high frequency

-SLED: low efficiency, high intensity frequency as needed

14/ ❌BAD COMBINATION

HIGH efficiency HIGH intensity:

- HD for 12 hours or more at normal flows
- CRRT at high doses 50-80 ml/kg/ hr to compensate down time and “catch up”

First order kinetics limits the efficiency RESULT = risk of “cleaning” the blood but not the patient

15/ FINAL THOUGHTS

✅Efficiency, intensity and frequency are tools to choose, adjust and get EFFICACY of a therapy
✅EFFICACY METRICS can be used to adequate therapies in a generalized manner
✅Knowing the nature and characteristics of therapies can help personalize them

16/
✅The relation between 🩸 and 💧 flows is the main difference
✅Being a low efficiency therapy, intensity is the priority in CRRT
✅In HD, efficiency and intensity can be changed to different goals (HyperK, SLED)
❌High intensity + high efficiency not a useful combination