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Chapter: Medicine Study Notes : Renal and Genitourinary

Renal Replacement Therapy

For end-stage renal failure, characterised by: o Severe uraemia o Resistant pulmonary oedema o Uraemic pericarditis o Severe hyperkalaemia o Metabolic acidosis o Anaemia

Renal Replacement Therapy


·        For end-stage renal failure, characterised by:

o  Severe uraemia

o  Resistant pulmonary oedema

o  Uraemic pericarditis

o  Severe hyperkalaemia

o  Metabolic acidosis

o  Anaemia

o  Renal osteodystrophy


·        Usually required if: 

o   Cr is 500 – 1000 mmol/L (depending on patient‟s size)

o   Urea > 35 mmol/L

o   GFR < 10 mls/min

·        Wherever possible, the type of treatment is open to patient preference with the aim of home self-care


Principles of Diffusion in Dialysis


·        Replaces excretory function of the kidney. Residual kidney function reduces dialysis requirements – but this usually „dries up‟ over the first few years on dialysis


·        Blood is exposed to dialysis solution across a semi-permeable membrane ® movement of low molecular weight proteins by:


o   Diffusion

o   Ultra-filtration and convection due to pressure gradient carrying compounds passively in fluid




·        Indicated for:

o   Acute dialysis

o   Weight > 100 kgs

o   Patient preference

·        Contra-indicated: 

o   Profound hypotension: dialysis takes half a unit of blood out of the vasculature through the machine ® further hypotension

o   Cardiac failure: intermittent nature of dialysis (every 2nd or 3rd day) ® accumulating fluid in between times then rapid reduction in fluid. If heart function is dependent on pre-load, then a rapid reduction in circulating fluid ® frank failure 

o   Inability to establish long term vascular access: a particular problem with diabetics with vascular disease


·        Procedure: 3 times a week for 5 to 6 hours, with a dialysis machine, dialysis membrane and dialysate (buffer/electrolyte solution). Access is via an arteriorvenous fistula at the non-dominant wrist. There are other options if this fails. Vascular access can thrombose, become infected, lead to high-output failure, etc


·        Complications:

o   Hypotension

o   Muscle cramps 

o   Bleeding: due to blood loss in dialysis and the anticoagulation necessary to stop clotting in the machine

o   Arrhythmias: due to rapid changes in electrolytes

o   Infections: mainly staph in patients with temporary or tunnelled catheters

·        CVVHD = continuous veno-venous haemodialysis (used when BP too low for normal dialysis)


Peritoneal Dialysis


·        Dialysate introduced into the peritoneal cavity, with diffusion across the peritoneal membrane. Less efficient so requires longer period of dialysis. Good for dialysis while still some kidney function remaining. Easier to learn and lower cost than haemodialysis


·        Indicated if:

o   Severe cardiac disease: maintains more stable fluid levels in the body

o   Elderly or frail patients

o   Diabetic patients

o   Patient preference

·        Contraindicated if:

o   Previous extensive abdominal surgery: requires adequate peritoneal membrane

o   Greater than 100 kgs: not efficient enough

·        Types:

o   Continuous ambulatory peritoneal dialysis: 4 to 5 exchanges each day, each of 2 – 3 litres 

o   Automated Peritoneal Dialysis: Machine automatically exchanges through the night (good for kids and people who work through the day)

·        Complications:

o   Inadequate dialysis

o   Tenckhoff Catheter problems 

·        Infection at the exit site and peritonitis (abdominal pain and cloudy dialysis fluid). Usually staph. Intra-peritoneal antibiotics. If G –ive then ?intra-abdominal pathology

·        Hydrothorax

·        Hyperglycaemia: glucose is used in the fluid to encourage filtration

·        Malnutrition


Renal Transplantation


·        Treatment of choice.  If successful provides full excretory and hormonal function

·        95% of patients and 85% of grafts survival at 1 year.  Half life of a graft ~ 13 years

·        Not considered if significant co-morbidities

·        Types:


o  Cadaveric transplantation: donor and recipient must be ABO compatible with a negative direct cross match test (ie no recipient antibodies which might cause acute rejection)


o  Live Donor Transplants: 25% of transplants. Donors must be investigated to ensure good renal function. Good results due to well donors and better preparation of recipients


·        Life-long immunosuppressive therapy is required, using cyclosporin, mycophenolate and prednisone. Combination therapy allows ¯doses ® ¯complications


·        Acute rejection: oliguria, ­Cr, fever and swollen graft. May only be picked up biochemically. Most likely within the first 3 months, but can occur at any time. Treated with high dose corticosteroids


·        Long term complications:


o  Infections due to immune compromise, including opportunistic infections, eg CMV, EBV, PCP. Prophylaxis during the first 3 months common


o  Malignancy: ­ skin squamous cell, lymphoma, cervical and Kaposi‟s Sarcoma – not breast, lung or colon


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