🔥Hemodialysis Kinetics 101🔥
Get to know the players 🧵
Q: What are the determinants of Blood Flow (Qb) in IHD?
#Tweetorial #Nephtwitter #Medtwitter @NSMCInternship
@SaynaNorouzi thank you for your help, you're a rock star
Get to know the players 🧵
Q: What are the determinants of Blood Flow (Qb) in IHD?
#Tweetorial #Nephtwitter #Medtwitter @NSMCInternship
@SaynaNorouzi thank you for your help, you're a rock star
1/ We're going to focus on factors related to Qb
🩸Qb is an active player in hemodialysis dose prescription. If we want to optimize dosing, we must know how Qb works in KT/V equation:
💺K =Dialyzer Clearance (ml/min)
🕒T = Time (min)
🧍♂️V = Distribution vol of Urea(ml)
🩸Qb is an active player in hemodialysis dose prescription. If we want to optimize dosing, we must know how Qb works in KT/V equation:
💺K =Dialyzer Clearance (ml/min)
🕒T = Time (min)
🧍♂️V = Distribution vol of Urea(ml)
2/ How do we get the Dialyzer Clearance (K)?
First, we need KoA
KoA is the maximum theoretical clearance of the dialyzer in mL/min for a given solute (urea) at INFINITE Qb and Qd
Provided by the manufacturer, is determined in vitro, and usually overestimates by about 20%
First, we need KoA
KoA is the maximum theoretical clearance of the dialyzer in mL/min for a given solute (urea) at INFINITE Qb and Qd
Provided by the manufacturer, is determined in vitro, and usually overestimates by about 20%
3/ After we choose the correct size of the filter, now we have our♨️KoA! ( 19H = KoA 1771)
Then, to obtain K we need specific values for:
🩸 Qb = Blood Flow (⬅️our player!)
💧Qd = Dialyzate Flow
Then, to obtain K we need specific values for:
🩸 Qb = Blood Flow (⬅️our player!)
💧Qd = Dialyzate Flow
4/ You can search in the manufacturer's manual 📒 or use this Equation to obtain K of a specific dialyzer given a specific value for Qb and Qd;
K = (1-exp(koa*(qb-qd)/qb*qd)))/(1/qb-1/qd*exp(koa*(qb-qd)/qb*qd)))
karger.com/Book/Home/2273…
K = (1-exp(koa*(qb-qd)/qb*qd)))/(1/qb-1/qd*exp(koa*(qb-qd)/qb*qd)))
karger.com/Book/Home/2273…
5/ Of course, there are calculators and apps for everything, and this time is not the exception😎:
If you have KoA and want to know K, given Qb and Qd:
👉touchcalc.com/calculators/di…
And if you don’t find the Dialyzer Maximum KoA;
👉@adequator_app
If you have KoA and want to know K, given Qb and Qd:
👉touchcalc.com/calculators/di…
And if you don’t find the Dialyzer Maximum KoA;
👉@adequator_app
6/ Now that we know where the values come from, let’s review the relationships between them
👉(📈)
⚠️Any possible mismatch between Qb and Qd distributions can create a significant reduction in the efficiency of the filter.
Our goal is Qb/Qd 1:2 ...but there is more
👉(📈)
⚠️Any possible mismatch between Qb and Qd distributions can create a significant reduction in the efficiency of the filter.
Our goal is Qb/Qd 1:2 ...but there is more
7/
🩸If Qb <200ml/min; K is linear to the Qb and is flow-limited so a high KoA or a high Qd does not matter.
🩸🩸If Qb >400ml/min; A bigger dialyzer or higher dialysate flow is helpful in improving K
🤓Now let's review the physics of fluid dynamics to understand more
🩸If Qb <200ml/min; K is linear to the Qb and is flow-limited so a high KoA or a high Qd does not matter.
🩸🩸If Qb >400ml/min; A bigger dialyzer or higher dialysate flow is helpful in improving K
🤓Now let's review the physics of fluid dynamics to understand more
8/ 🔥Our Equation;
Hagen-Poiseuille's equation (1840); 🇩🇪🇫🇷
⚡️The resistance to flow is directly related to length and inversely proportional to the fourth power of the catheter diameter;
Here is a video to understand better:
What does this mean?
Hagen-Poiseuille's equation (1840); 🇩🇪🇫🇷
⚡️The resistance to flow is directly related to length and inversely proportional to the fourth power of the catheter diameter;
Here is a video to understand better:
What does this mean?
9/ We need to know the variables in IHD so we can ⬆️ Qb 🌊🌊
A) (r) Diameter; French (Fr) in Catheters or Gauges (G) in the needles used for AVFs
B) (l) Catheter length
C)(P)Pressure in the system
D)(n) Blood viscosity
Now the relationship between them;
A) (r) Diameter; French (Fr) in Catheters or Gauges (G) in the needles used for AVFs
B) (l) Catheter length
C)(P)Pressure in the system
D)(n) Blood viscosity
Now the relationship between them;
10/ Vascular Access Characteristics (A and B)
It is not easy to find information related to Fr and Length in the literature or even the manufacturer's manual
I found a correlation of Qb with diameter but not with length or combining both.
It is not easy to find information related to Fr and Length in the literature or even the manufacturer's manual
I found a correlation of Qb with diameter but not with length or combining both.
12 /
What change the viscosity? ( D )
Temperature, Glucose, Hematocrit, Food, Ultrafiltration Rate, blood cell factors, plasma protein, blood volume and more
ncbi.nlm.nih.gov/pubmed/27767962
academic.oup.com/ajh/article/14…
What change the viscosity? ( D )
Temperature, Glucose, Hematocrit, Food, Ultrafiltration Rate, blood cell factors, plasma protein, blood volume and more
ncbi.nlm.nih.gov/pubmed/27767962
academic.oup.com/ajh/article/14…
13/ ⬆️ in Viscosity is compensated with:
-⬆️ BP or Vasodilation
-If BP is constant total peripheral resistance will necessarily increase, thereby ⬇️ blood flow
Consequently, blood viscosity has been established as a major determinant of the work of the ❤️
-⬆️ BP or Vasodilation
-If BP is constant total peripheral resistance will necessarily increase, thereby ⬇️ blood flow
Consequently, blood viscosity has been established as a major determinant of the work of the ❤️
14/Some Facts about Viscosity;
Atherosclerotic vessels cannot dilate sufficiently, so blood viscosity can only be compensated with a BP increase in such circumstances. ( Does this look familiar almost at the end of IHD in some patients with high UF?)
academic.oup.com/ajh/article/14…
Atherosclerotic vessels cannot dilate sufficiently, so blood viscosity can only be compensated with a BP increase in such circumstances. ( Does this look familiar almost at the end of IHD in some patients with high UF?)
academic.oup.com/ajh/article/14…
15/The higher blood viscosity at the dialysis fistula is directly related to increased kinetic force and shear stress on the vessel wall, which may be playing a role in increasing the risk of stenosis.
ncbi.nlm.nih.gov/pubmed/19670184
Viscosity plays an important role in CVD also.
ncbi.nlm.nih.gov/pubmed/19670184
Viscosity plays an important role in CVD also.
16/ Take Home points;
Qb is not just a number in HD, if we want to manage Qb in a proper way, we must know Hagen-Pouseuille's Equation variables. (especially #NephPed)
In practice; there is no reason to employ higher QBs or to use large dialyzers, as K will be limited by QD.
Qb is not just a number in HD, if we want to manage Qb in a proper way, we must know Hagen-Pouseuille's Equation variables. (especially #NephPed)
In practice; there is no reason to employ higher QBs or to use large dialyzers, as K will be limited by QD.
17/ Take home points 2
Best Steps to have better IHD dose:
1. Add Time ( Cost, Effective)
2. Higher Qd; 500 to 800ml/min if Qb >200
3. Higher Qb; Goal >400
4. Higher KoA
I hope you find this useful. 👋
Best Steps to have better IHD dose:
1. Add Time ( Cost, Effective)
2. Higher Qd; 500 to 800ml/min if Qb >200
3. Higher Qb; Goal >400
4. Higher KoA
I hope you find this useful. 👋
