Renal replacement therapy

Question 1

What is the eGFR cutoff for dialysis? What is the first line choice for dialysis?

Answer 1

In general, patients with CKD require dialysis where GFR<10, but if asymptomatic GFR <6. Peritoneal dialysis should be offered as the 1^st choice in these patients as it can help to retain residual renal function and minimise haemodynamic instability.

Question 2

How long before requiring dialysis should patients be referred to the service? Why?

Answer 2

Ideally, patients with CKD are referred around 1 year before they are anticipated to require RRT. They should be given HBV vaccination and educated about dialysis, if required an AV fistula can be created

Question 3

What is the purpose of KT/V testing?

Answer 3

In medicine, Kt/V is a number used to quantify hemodialysis and peritoneal dialysis treatment adequacy.

K – dialyzer clearance of urea

t – dialysis time

V – volume of distribution of urea, approximately equal to patient’s total body water

Question 4

What is the principle of peritoneal dialysis?

Answer 4

Dialysis fluid contains electrolyte concentrations that draw electrolytes and urea/creatinine out of the blood for clearance by diffusion. Ultrafiltration of excess fluid is achieved by high glucose concentrations.

Question 5

What are the contraindications to peritoneal dialysis?

Answer 5

Peritoneal dialysis is contraindicated where there is no residual kidney function, intra-abdominal adhesions, abdominal wall stoma, respiratory disease, hernias, or intestinal disease.

Question 6

Peritoneal fluid can make what disease worse?

Answer 6

The glucose in dialysis fluid can worsen diabetic control

Question 7

There are two forms of peritoneal dialysis. How do they differ and how are they the same?

Answer 7

There are 2 forms of peritoneal dialysis, both tend to use 8 – 10L of fluid in 2L batches.

• CAPD. This involves the patient manually changing their fluid every 2.5 - 6 hours of dwell time, resulting in x4 fluid exchanges per day
  
  • It generally takes around 20 minutes to drain out, flush, and drain in dialysis fluid. The patient should inspect the fluid for any cloudiness, fibrin, or blood that could indicate infection
• APD. This is used overnight, an automated machine drains and replaces the fluid

Question 8

What test is used to demonstrate what type of transporter a patient is?

Answer 8

PET (peritoneum equilibrium test) can demonstrate if the patient is a high or low transporter, it is better for high transporters to have APD as they require shorter dwell times.

• The risk of leaving fluid in the peritoneum for longer than exchange is glucose passing into the blood. In the short term this draws water back out of the peritoneum and into the bloodstream, meaning no ultrafiltration takes place
  
  • Long term risks of this include hyperglycaemia and glycation damage to the peritoneum

Question 9

What is the major risk of peritondeal dialysis? How is it managed?

Answer 9

Peritonitis is the main risk with peritoneal dialysis, if the patient notices any clouding of fluid they should present immediately to hospital. This should be managed with intra-peritoneal broad-spectrum ABx (Vancomycin and an Aminoglycoside), there should be catheter removal if infection persists

• Common agents include S.aureus, coagulase negative staph, and pseudomonas

Question 10

Why is peritoneal dialysis only usually used for 5-8 years?

Answer 10

• Encapsulating peritoneal sclerosis can lead to bowel obstruction. Avoidance of this is why PD is generally only for 5 – 8 years

Question 11

What are the 4 main vascular access routes of haemodialysis?

Answer 11

1. Arterio-venous fistula, this formed through surgical anastomosis of an artery and vein at the wrist or elbow (radio/brachio-cephalic). Maturation of the fistula is required for at least 2 months prior to use
2. PTFE graft, this is a synthetic graft between an artery and vein
3. Tunnelled cuffed central venous catheter
4. Temporary central venous catheter, this should be in place for 2 weeks maximum

Question 12

What are the two functions of a haemodialysis machine?

Answer 12

Ultrafiltration (fluid removal) is one of the functions of the kidney and the hemodialysis machine. The other function that a hemodialyis machine is capable of is to perform dialysis (cleaning) of the blood in order to remove the toxins and built up wastes from the body. Hence the combination of dialysis and ultrafiltration constitute hemodialysis.

Question 13

What is the difference between haemodialysis and haemofiltration?

Answer 13

Haemodialysis removes solutes by diffusion. As such, it is relatively inefficient for solutes of high molecular weight as clearance by diffusion is inversely related to the molecular weight of the solute. Haemofiltration removes solutes by convection.

Question 14

Which RRT is favoured in intensive care of AKI?

Answer 14

Haemofiltration. The benefit of this is ­haemodynamic stability and is therefore used in critically ill AKI patients. This usually takes place as a continuous therapy in ITU.

Question 15

What is Haemodiafiltration (HDF)?

Answer 15

haemodialysis + haemofiltration è ­ haemodynamic stability alongside good clearance of small/middle molecules.

Question 16

In what ways must donor and receiver be matched?

Answer 16

Renal transplant grafts need to be matched in terms of blood group, exclusion of panel reactive antibodies and anti-HLA antibodies in the recipient, and ideally the graft and recipient are matched in major HLA antigens. The other factor to consider is the physical size of the donor kidney in relation to the recipient.

• HLA-A, HLA-B, and HLA-DQ are ideally all matched at both alleles (6 antigen match). Living donors can have x6 mismatches and still be transplanted, cadaveric donors can have a maximum of x2 mismatches, neither of which can be HLA-DQ

Question 17

What is the mechanism of direct and indirect acute organ rejection? What medications can be given to prevent this?

Answer 17

• Direct pathway donor cells present foreign MHC-I to recipient CD-8 T cells, this results in early (accelerated) graft rejection within a few days
• Indirect pathway donor proteins are shed from the graft, and engulfed by recipient macrophages. This leads to the generation of anti-graft antibodies and acute cellular rejection within 1 -3 weeks
  
  • IV Methylprednisolone and Plasma exchange can treat rejection in accelerated and acute forms

Question 18

What is the medication regime of a patient who receives an organ transplant?

Answer 18

• Induction of immunosuppression = Basiliximab (anti-IL2) infusion and high dose Prednisolone prior to surgery (¯ infection risk)
• Maintenance = combination of 3 medications:

1. Calcineurin inhibitors = Tacrolimus or Ciclosporin. S/E = renal fibrosis, ­BP, post-transplant diabetes, cosmetic
2. Anti-proliferatives = MMF/MPA. S/E = oral ulceration and bone marrow suppression
3. Prednisolone 20mg, gradually tapered down to a dose of 5mg maintenance

Question 19

What are the 4 main complications of organ rejection?

Answer 19

1. Graft rejection
2. Arterial/ venous thrombosis in the graft
3. S/E + risks of Immunosuppression = opportunistic infection, skin cancer, lymphoma
4. Recurrence of original disease within the graft. This is more common with FSGS, familial HUS, and IgA nephropathy (generally does not result in graft loss)