Renal Replacement Therapy

Renal Replacement Therapy

The aim of all renal replacement techniques is to mimic the excretory functions of the normal kidney, including excretion of nitrogenous wastes, maintenance of normal electrolyte concentrations, and maintenance of a normal extracellular volume.
Types of renal replacement therapy
1) Hemodialysis
In haemodialysis, blood from the patient is pumped through an array of semipermeable membranes (the dialyser) which bring the blood into close contact with dialysate, flowing countercurrent to the blood. The plasma biochemistry changes towards that of the dialysate owing to diffusion of molecules down their concentration gradients
Access for haemodialysis
Adequate dialysis requires a high blood flow.
The most reliable long-term way of achieving this is surgical construction of an arteriovenous fistula using the radial or brachial artery and the cephalic vein.
This results in distension of the vein and thickening ('arterialization') of its wall, so that after 6-8 weeks, large-bore needles may be inserted to take blood to and from the dialysis machine.
If dialysis is needed immediately, a large-bore double-lumen cannula may be inserted into a central vein - usually the subclavian, jugular or femoral.
Complications 1-Hypotension during dialysis is the major complication.
2-Very rarely patients may develop anaphylactic reactions
3-Other rare, complications include haemolytic reactions and air embolism.
4-Rapid correction of uraemia changes in plasma osmolality 'dialysis disequilibrium'. (vomiting, restlessness, and in severe instances seizures).

2)Haemofiltration

This involves removal of plasma water and its dissolved constituents (e.g. K+, Na+, urea, phosphate) by convective flow across a high-flux semipermeable membrane, and replacing it with a solution of the desired biochemical composition
Financial costs of disposable items are high and only a tiny minority of patients with end-stage renal failure are managed in this way.


3)Peritoneal dialysis
Peritoneal dialysis utilizes the peritoneal membrane as a semipermeable membrane, avoiding the need for extracorporeal circulation of blood. This is a very simple, low-technology treatment compared to haemodialysis. The principles are simple
Forms of peritoneal dialysis
Continuous ambulatory peritoneal dialysis (CAPD). Dialysate is present within the peritoneal cavity continuously, except when dialysate is being exchanged. Dialysate exchanges are performed three to five times a day, using a sterile no-touch technique to connect 1.5-3 L bags of dialysate to the peritoneal catheter; each exchange takes 20-40 minutes. This is the technique most often used for maintenance peritoneal dialysis in patients with end-stage renal failure.
Nightly intermittent peritoneal dialysis (NIPD). An automated device is used to perform exchanges each night while the patient is asleep. Sometimes dialysate is left in the peritoneal cavity during the day in addition, to increase the time during which biochemical exchange is occurring.
Tidal dialysis. A residual volume is left within the peritoneal cavity with continuous cycling of smaller volumes in and out.
Complication
1-Bacterial peritonitis is the most common serious complication
2-Infection around the catheter site
3-Failure of peritoneal membrane function is a predictable complication of long-term CAPD
RENAL REPLACEMENT IN ACUTE RENAL FAILURE
indications are as follows:
Increased plasma urea and creatinine.
Plasma urea > 180 mg/dl and creatinine> 6.8 mg/dl.
Hyperkalaemia.
A plasma potassium > 6 mmol/l is hazardous.
Metabolic acidosis.
Fluid overload and pulmonary oedema. In oligo/anuric patients.
Uraemic pericarditis/uraemicencephalopathy.; they are uncommon in ARF but are strong indications for RRT.
1)Intermittent haemodialysis
This modality offers the best rate of small solute clearance.
2)HaemofiltrationThis may be either intermittent, or continuous
3)Peritoneal dialysis
In ARF, this technique is rarely used. It is less efficient than haemodialysis, and seldom achieves adequate biochemical control in catabolic patients.


RENAL REPLACEMENT IN CHRONIC RENAL FAILURE
Of patients starting dialysis, 70% are treated by haemodialysis and 30% by peritoneal dialysis.
1)Intermittent haemodialysis
This is the standard therapy in ESRF.
Haemodialysis is started when the patient has symptomatic advanced renal failure but before the development of serious complications, often with a plasma creatinine of 6.8-9.0 mg/dl.
Haemodialysis is usually carried out for 3-5 hours three times weekly.
2)Continuous ambulatory peritoneal dialysis (CAPD)
Especially in children and old people with cardiovascular problems.

Renal transplantation

Renal transplantation offers the best chance of long-term survival in patients with end-stage renal disease.
All patients should be considered for transplantation unless there are active contraindications.

CONTRAINDICATIONS TO RENAL TRANSPLANTATION

Absolute
Active malignancy
Active vasculitis or anti-GBM disease, with positive serology
Severe ischaemic heart disease
Severe occlusive aorto-iliac vascular disease
Relative
Age - very young children (< 1 year) or older people (> 75 years)
High risk of disease recurrence in the transplant kidney
Disease of the lower urinary tract-in patients with impaired bladder function, an ileal conduit may be considered
Significant comorbidity
Management after transplantation
Immunosuppressive therapy is required to prevent rejection.
Different therapeutic regimens are used; a commonly used one is triple therapy consisting of prednisolone, plus ciclosporin or tacrolimus and azathioprine.