Dialysis

What it is

Artificial replacement of the kidneys' filtering work when they have failed. In haemodialysis, blood is pumped from a vascular access through a filter where waste and excess water pass across a membrane into dialysis fluid, then returned, usually for four hours three times a week. In peritoneal dialysis, fluid is run into the abdomen through a permanent catheter and the peritoneum itself acts as the membrane, exchanged several times a day or overnight by a machine.

Why it is done

• End-stage kidney disease (eGFR under about 10, or symptoms of uraemia, fluid overload or high potassium that medication cannot control)
• Acute kidney injury with life-threatening potassium, acidosis, fluid overload or toxins
• Some poisonings (lithium, methanol, aspirin overdose)

Before the procedure

• Months of planning in advanced kidney disease: education, choosing the type, vaccination against hepatitis B
• Creating access: an arteriovenous fistula joining the radial artery and cephalic vein at the wrist (or a graft), which needs 6-12 weeks to mature; or a tunnelled catheter in the internal jugular vein for urgent starts
• For peritoneal dialysis, a catheter placed into the abdomen two weeks before use

Step by step

1. Haemodialysis: two needles in the fistula (or the catheter connected); blood flows at 300-400 mL/min through the dialyser; heparin prevents clotting; the machine removes a set volume of fluid; weight, blood pressure and bloods are monitored
2. Peritoneal dialysis: 2 litres of warmed glucose-based fluid drains into the abdomen, dwells for hours while waste and water diffuse across the peritoneum, then drains out; repeated 4 times a day (CAPD) or by a cycler overnight (APD)
3. Diet restricts potassium, phosphate, salt and fluid; phosphate binders, erythropoietin and vitamin D replace kidney functions dialysis cannot

Afterwards

• Tiredness and cramps after haemodialysis sessions are common
• Regular monthly bloods, adequacy checks and fistula care
• Assessment for a kidney transplant, which offers the best survival and quality of life

Recovery

Dialysis is ongoing rather than a one-off procedure; many people continue work and travel, with peritoneal or home haemodialysis giving more flexibility.