Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Extracorporeal therapies > Principles of dialysis > Flashcards

Principles of dialysis Flashcards

1
Q

What’s the average length of treatment for IHD and CRRT?

A

IHD usually is 4-5h
CRRT is >24h

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

List 3 renal replacement modalities?

A

Extracorporeal: CRRT and IHD
Intracorporeal: Peritoneal dialysis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

The type of RRT is determined by…

A

The prescription and treatment type NOT by the type of machine selected

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Which of the RRT modality provides the most flexibility in terms of type of treatment that can potentially provide?

A

IHD

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Regarding the dialysis catheter there is an ‘arterial’ and a ‘venous’ line - what do they mean?

A

It has nothing to do with the type of blood processed as in dialysis (vs ECMO) it is always venous blood. It just indicates the direction ‘to’ (arterial) and ‘from’ the dialyser (venous).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

The hemodialysis apparatus is divided into _____ circuit and a _____ circuit. Both meet at the _____

A

blood
dialysate
dialyser

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What’s the main difference in terms of dialysate management between IHD and CRRT?

A

In IHD the dialysate is generated from purified water + acid concentrate + bicarbonate

In CRRT the dialysate is provided in sterile bags

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Briefly describe the process of water purification in IHD

A

From tap water the water purifier passes it through particulate filters, carbon sorbents for organic solutes, water softeners, deionization beds and ultimately performs reverse osmosis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is reverse osmosis?

A

It is the most important process of water purification in IHD machines. The process uses high pressure to push water through a semi-permeable membrane.
This membrane has tiny pores that only allow water molecules to pass through. Larger particles, like salts, bacteria, and other contaminants, are too big to go through and are left behind.

It’s called reverse osmosis because it works in the opposite way of natural osmosis. We apply pressure to push water in the opposite direction, from an area of high solute concentration (more impurities) to low solute concentration (clean water).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Some water purification processes uses an additional method by applying ‘ultraviolet light’ - what is the main risk entailed with this technique?

A

Ultraviolet light kills bacteria and although the bacteria themselves are too large to pass through the semipermeable membrane during the purification process, LPS released upon bacterial death can pass into the ‘clear water’ and contaminate the final dialysate.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is an ‘ultrapure dialysate’?

A

It is a dialysate that undergoeas an additional filtration process within the dialysis machine (NOT the water purifier)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

How can we manipulate the final solute concentration of the dialysate?

A
  • type of acid solution
  • amount of bicarbonate solution to be added to the dialysate
  • Na concentration can be directly programmed, however this will influence the dilution of the acid concentrate (higher sodium = lower dilution)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Which type of solute exchange mechanism is used by the native kidney?

A

Convection: hydrostatic pressure + solute drag

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Diffusion is a consequence of _____

A

random molecular movements (molecular kinetics) that follow the law of probability.

The velocity of a molecule in solution is inversely proportional to the molecular weight (smaller molecules are faster and have more chances to encounter a pore in the membrane)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Diffusion is mainly determined by ____

A
  • molecular size
  • concentration gradient
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is Ko?

A

Ko is the mass transfer coefficient derived from the ratio of D/X (diffusivity over membrane thickness)

It is an essential part of Fick’s law in the diffusion process

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is KoA?

A

mass transfer area coefficient

It is a theoretical number that describes the maximum clearance of a solute across the dialyser when the blood flow (Qb) and the dialysate flow (Qd) are infinite

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Formula to calculate KoA

A

KoA = [(Qb x Qd)/(Qb-Qd)] x ln [(1- (Kd/Qb) / 1- (Kd/Qd)]

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What is Kd and how can it be calculated?

A

Kd is the diffusive clearance of the dialyser

Kd = Qb x [(BUNin – BUNout)/BUNin]

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Extraction ratio formula (diffusion)

A

ER = (BUNin – BUNout)/BUNin]

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What is the KoA used for?

A

It is used to compare different dialyser.

KoA is specific for a certain solute AND a certain membrane/dialyser

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What is Ro?

A

It is the resistance (distance/diffusivity) a solute needs to overcome to get from the blood into the dialysate during DIFFUSION.

Ro = Rb + Rm + Rd

Rb = blood resistance
Rm = membrane resistance
Rd = dialysate resistance

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What is the most important component of Ro?

A

The thickness of the dialyser membrane followed by its diffusivity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

How can diffusion efficiency be improved?

A

decreasing the resistance –> decreasing membrane thickness

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

High efficiency dialysers are characterised by _____

A

high urea KoA

however to be advantageous a high Qb is also needed as at low Qb the Urea Kd is almost the same for both high and low efficiency dialysers

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

Small MW = ____ D
Middle MW = _____ D
Large MW = _____ D

A

<500
500-15000
>15000

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

URR % formula

A

URR % = [(BUNpre - BUNpost)/BUNpre] x 100

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

Which is more important in the diffusion of particles, MW or membrane pore size?

A

MW

Most molecules can fit in the majority of membrane pores, however if larged MW = less velocity = less chances to encounter a pore

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

Difference between clearance and solute removal rate

A

clearance refers to the volume of plasma that is completely cleared from a solute

solute removal rate is a first order process which is directly proprotional to the solute concentration

30
Q

Since the solute removal rate depends on the initial solute concentration, with very high initial concentration the drop can be very sharp - how can we make the drop less dangerous?

A

It can be made safer by starting with a lower Kd (or Qb) and slowly increasing it during treatment

31
Q

What % of dogs presented for dialysis due to AKI are severely over hydrated?

A

Up to 50%

32
Q

Ultrafiltration

A

Movement of water across a semipermerable membrane. A transmembrane pressure (TMP) has to be generated to initiate ultrafiltration.

33
Q

What are the main determinants of the ultrafiltration rate?

A
  • TMP
  • hydrostatic permeability
  • surface area of the membrane
34
Q

Fick’s law - ultrafiltration

A

J = TMP / u x Rt

u = viscosity
Rt = total resistance

35
Q

What is Kuf?

A

Amount of fluid (mL) transferred per hour for each 1mmHg of transmembrane pressure

36
Q

Ultrafiltration rate formula

A

Ultrafiltration rate = TMP /Kuf

37
Q

What is the minimum TMP value to overcome plasma oncotic pressure?

A

25 mmHg

38
Q

Define ‘backflow’

A

Fluid shift from dialysate to blood.
It occurs when a negative transmembrane pressure develops.
Some hemodialysis machines will require a minimum amount of TMP and ultrafiltration to prevent backflow

39
Q

Ways of achieving ultrafiltration

A
  • pressure control - older and less reliable method which regulates ultrafiltration by modifying TMP
  • volumetric control - modern method which determines ultrafiltration by an ultrafiltration pump. UF is checked by measuring the volume of dialysate in vs volume dialysate out
40
Q

High flux vs low flux dialysers

A

High flux = high Kuf

41
Q

High flux refers to____
High efficiency refers to ____

A

ultrafiltration and Kuf
diffusion and KoA

42
Q

TRUE or FALSE
Rate of fluid removal is usually limited by Kuf

A

FALSE

In veterinary medicine Kuf rarely limits the rate of fluid removal. It is the patient size that determines the max safe fluid removal rate.

No more than 10ml/kg/h –> monitor parameters via critline to dectect early signs of hypovolemia

43
Q

According to Kopency et al. which are the main variables associated with ultrafiltration-related complications?

A
  • higher initial blood volume change (within 15-30 min)
  • lower initial venous oxygen saturation
  • lower nadir venous oxygen saturation
  • higher temperature prior to treatment
  • higher total extracorporeal circuit volume
  • lower post-treatment BUN
  • lower pre-treatment PCV
44
Q

Convection

A

Removal of solutes by solvent drag

45
Q

What is the max size of molecule removed via convection?

A

40K Dalton

46
Q

TRUE or FALSE:

Convection influences diffusive process

A

FALSE

No, it doesn’t as solutes moves together with the solvent

47
Q

Sieving coefficient

A

S = [x] filtrate/ [x] plasma

48
Q

Convective clearance (Kx)

A

Kx = Quf x Sx

49
Q

Hemodiafiltration

A

CRRT using both convection and diffusion

50
Q

According to a human metanalysis (Mostovaya et al. 2014) post-dilution HDF showed _____ compared to HD

A

reduction of all-cause and cardiovascular mortality and a dose-response relationship between convective volume and outcome

51
Q

What are the main limiting factors of IHD/CRRT?

A
  • lipid solubility
  • protein binding
  • volume of distribution
52
Q

What’s the significance of ‘effective MW’?

A

I.e. naproxen is a small molecule (MW 230g/mol) however due to the high protein-binding its effective MW includes albumin (68K dalton)

53
Q

What are the most important characteristics of a HP membrane?

A
  • biocompatibility
  • selectivity
54
Q

What’s the main difference between HD/CRRT and HP?

A

HD/CRRT remove free (unbound) substances vs HP can remove bound forms

55
Q

Van der Wall forces _____ adsorbs compounds

A

reversibly

i.e. if another substance with higher affinity to the compound bounded passes through the membrane this will release the compound once again into the plasma

This is why substances with <90% bind to albumin have extraction ratios of >80% but when the substance has >90% affinity with albumin the extraction ration falls

56
Q

Why is the HP filter sometimes followed by HD or CRRT?

A

The HP filter (especially if not a very selective resins) can bind other plasma substances like glucose, lytes, etc.
It is usefull to further process the blood with a dialysate that can correct these deficiencies

57
Q

What does a Vd>0.6L/Kg indicate?

A

Lipophilicity, protein or tissue binding

In people a Vd >1-2L/Kg is usually a deterrent otherwise extracorporeal removal

58
Q
A

If there is no saturation of the membrane, HP work as a 1st order kinetics

59
Q

Clearance formula for HP

A

Clearance = Qb (1-Hct) x [(Ca-Cv)/Ca]

Ca= pre-cartridge concentration
Cv = post-cartridge concentration

60
Q

One vs two compartments kinetics

A
61
Q

Clearance in IHD depends on ____ vs in CCRT depends on ____

A

Qb
Qd

62
Q

To achieve 100% clearance in CRRT ____

A

Qb > 3x Qd

If Qd > 1/3 of Qb it’s a waste of dialysate (which is very costly)

63
Q

Filtration fraction

A

Proportion of plasma filtered across the membrane

FF = Quf / Qp

Qp = Qb x (1-HCT)

64
Q

What’s the target FF?

A

Not >25%

65
Q

Clearance for:
- CVVH post-filter replacement
- CVVH pre-filter replacement
- CVVHD
- CVVHDF post-filter replacement

A
  • K = Quf
  • K = Quf / [1+(Quf/Qb)] ; correction factor
  • K = Qd
  • K = Quf + Qd ; if prefilter conside Quf with correction factor as in CVVH pre-filter
66
Q

Generally a poison is not considered removable by HD ir HF if the protein binding is >80%, however there are exceptions…

A

1) some substances at toxic concentrations have saturated all protein binding sites, therefore there is a high proportion which is unbound and liable to HD/HF (i.e. salicilates or valproic acid)
2) some substances have a high dissociation quotent (loose binding with albumin) so once the unbound pool has been cleared more dissociates from albumin
3) states of hypoalbuminaemia

67
Q

What are the major advantages and disadvantages of hemoperfusion vs hemodialysis?

A

Advantages:
- HP not influenced by molecular size or protein binding

Disadvantages:
- needs more systemic anticoagulation
- lower blood flow achievable due to high risk of hemolysis
- adsorbtion of platelets, WBC, calcium and glucose
- more costly and more difficult to get cartridges
- doesn’t correct metabolic derangements
- HP cartidges don’t absorb alchols or metals

68
Q

HD is usually preferred to CRRT for poisoned patients, why?
What advantages can CRRT still bring in a poisoned patient?

A
  • More rapid and efficient
  • Slower blood flow advantageous in CV unstable patients, lower chances of rebound effect
69
Q

Most common causes of acute on CKD in dogs

A

Mostly unknown, but suspected to be mainly inflammatory followed by pyelonephritis and ischemia.

Different from AKI where toxin exposure is a common feature

70
Q

Most common causes of acute on CKD in cats

A

Mostly unknown but presumptive pyelonephritis and ischemic events

71
Q

Short term prognosis vs long term prognosis indicators in ACKD in cats

A

Short term prognosis fair and related to serum phosphorus concentration

Long term prognosis poor (much worse than AKI) and related to IRIS stage and serum creatinine at time of discharge

72
Q

Short term prognosis vs long term prognosis indicators in ACKD in dogs

A

Short term prognosis fair and related to respiratoru rate, serum creatinine and CK activity.

Long term prognosis poor (much worse than AKI) but no specific predictive factor identified.

Extracorporeal therapies (2 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions