Dialysis

Question 1

Are there any characteristics that you can list that influence clearance via the dialysis semi-permeable membrane?

Answer 1

1. pore size and number
2. thickness
3. membrane area
4. membrane charge!
5. hydrophilic/hydrophobic.

Question 2

How does diffusion work in the setting of dialysis?

Answer 2

This is how the SOLUTES are moved.

Basically, solutes move down concentration gradients, but the solVENT does not move.

The rate (or flux) is dependent on area available for transport and the concentration gradient.

We can influence the gradient by changing blood and dialysate flow rate

Question 3

How does convection work in the setting of dialysis?

Answer 3

When liquid is moved across the semi-permeable membrane, we call this ultra-filtrate.

Convection is the movement of solvent across the membrane. It brings dissolved solutes with it.

The fluid transfer rate is dependent on the permeability of the membrane AND the transmembrane pressure (which equals the hydrostatic pressure of blood - hydrostatic pressure of dialysate - oncotic pressure blood)

Question 4

Do you know of any measures of clearance (in setting of dialysis)?

Answer 4

Some centres use the Kt/V urea as a measure of dialysis adequacy.

This is the amount of solute removed from the blood, per unit of time, divided by the incoming blood concentration.

It is a way to represent the volumetric rate at which blood is cleared of solute.

Question 5

What is the term we use for removal of water via dialysis?

Answer 5

We call this ultrafiltration.

In some cases, we use oncotic pressure to drive it. e.g. peritoneal dialysis with high sugar in the bags.

In other cases we use a hydrostatic pressure gradient. e.g. haemodialysis.

Question 6

What is the strongest prognosticator for patients on dialysis?

What about “when high, what is associated with worst survival?”

Answer 6

Albumin is apparently the strongest predictor of mortality, however, it is worse when low.

In terms of “high” results, phosphate is bad news.

Question 7

Any absolute indications for dialysis?

Answer 7

Absolute Indications for Dialysis

1. Pericarditis
2. Fluid Overload Refractory to Medical Management
3. Electrolyte Disturbances Refractory to Medical Management
4. Accelerated Hypertension
5. Encephalopathy
6. Refractory Nausea and Vomiting
7. Declining Nutrition
8. Problematic Bleeding Diathesis (thought related to uraemic platelet dysfunction)

Question 8

Can you think of any reasons why haemodialysis would be chosen over peritoneal dialysis?

Answer 8

The College seems to have written a number of questions where PD is less favoured because of previous abdominal surgeries.

Question 9

What is the role of the peritoneal equilibrium test?

What does high, high average, low average and low mean in this setting?

Answer 9

Great question!

This relates to the ability of small solutes to transport across the membrane.

High transporters have quick movement of solutes (and glucose moves quickly into the serum), but this means poor ultrafiltration.

Low transporters have slow clearance of solutes, but good ultrafiltration.

Question 10

What does high and low transport mean for peritoneal dialysis prescriptions?

Answer 10

Low transporters do better with long “dwell”. Continuous ambulatory dialysis, for example.

High transporters do better with quick turnover, and therefore short dwells overnight.

Question 11

What is the measure of peritoneal dialysis adequacy?

Answer 11

We usually use Kt/V urea as a standard marker, but actually we rely on a number of features, including clinical features, dietary intake, potassium, fluid status.

(this question was from a past paper with the answer as potassium)

Question 12

What do we do to a PD fluid to increase the amount of ultrafiltrate?

Is there any side effects to this approach?

Answer 12

We have to increase the glucose concentration/osmolality.

The PD membrane becomes thick and fibrosed with exposure to lots of glucose.

Question 13

In a fluid-overloaded, tachypnoeic, oliguric patient, which of the following is the worst choice?

1. high dose fruse
2. decreasing oral intake
3. incr freq of dialysate bag change
4. incr strength of dialysate
5. incr volume of dialysate used

Answer 13

Probably increasing the volume of the dialysate would be worst. the risks are splinting of diaphragm and worsening dyspnoea.

The benefit obtained from stretching the membrane is relatively little FOR ULTRAFILTRATION

Question 14

What happens to a membrane that is heavily and repeatedly exposed to high levels of glucose?

Answer 14

This is chronic peritoneal membrane damage.

It can lead to sclerosing peritonitis (life threatening)

Question 15

How do we manage haemodialysis adequacy?

Answer 15

Kt/V urea is also used. The aim is >1.2

Urea reduction ratio > 65% is another target.
(urea reduct ratio = (serum urea pre-Dx - serum urea post-Dx)/serum urea pre-Dx)

Question 16

What are the major contraindications for haemodialysis?

Answer 16

1. access problems

2. haemodynamic instability

Question 17

In end stage renal disease, there are 2 different processes that affect the blood vessels. These are likely to both have an impact on mortality. Can you describe them?

Answer 17

Firstly, patients suffer garden variety atherosclerosis - abnormal endothelial function and narrowing/obstruction of the arterial lumen.

Secondly, patients experience vascular medial calcification with wall thickening and stiffening, leading to increased pulse pressure. This can also be contributed to by urea.

Question 18

How strong is the evidence for lipid lowering agents in ESKD?

Answer 18

A number of older studies demonstrated no benefit, however the SHARP study has shown that a combination of statin/ezetimibe have demonstrated benefit

Question 19

What about blood pressure in ESKD? How important is that as a CVD RF?

Answer 19

Interestingly there is only a MODEST association between hypertension post dialysis and mortality.

Question 20

Strongest CVD RF for ESKD patients?

Answer 20

Diabetes and smoking

Obesity is PROTECTIVE! (yup. weird, eh)

Question 21

What happens to the vascular smooth muscle cells when exposed to high phosphate?

Answer 21

They actually change from a vascular phenotype to a bone matrix phenotype. This happens once levels outside the normal range

Question 22

What are the best ways to minimise calcification in ESKD?

Answer 22

1. impecable PO4 control
2. aim for low-normal serum calcium
3. minimise the use of calcium containing PO4 binders
4. avoid using dialysate that has calcium that crosses into body
5. consider calcimimetics for hyperPTH when calcium product is high
6. avoid oversuppression of PTH (causes adynamic bone disease - not turning over normally)
7. perform a PTHectomy for severe hyper PTH (> 12 * normal level of PTH)

Question 23

What is the current target for Hb in ESKD?

Answer 23

The target is less than 120. We would not want to aim for normal levels. The risks of EPO include inc CV events and malignancy.

Question 24

What is the most common cause of mortality in dialysis patients?

What is the second?

Answer 24

Cardiovascular event

2nd: infection

Question 25

What is the strongest predictor of mortality in ESKD patients on HDx?

Answer 25

the malnutrition - inflammation syndrome is the strongest.
Albumin is a surrogate of above
serum phosphate is a major RF, but more about vessel calcification

Question 26

Does urea (in dialysis patients) have any sort of effect on mortality rates and reasons?

Answer 26

Low urea may be associated with mortality from poor nutrition