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Indications, Techniques, and Complications of Dialysis

Definitions of Dialysis Procedures

Hemofiltration:

Hemofiltration is a continuous or intermittent renal replacement therapy. A filtrate is obtained from the blood through a semipermeable membrane with a defined pore size and replaced with a solution containing the desired electrolyte composition (Kierdorf et al., 2000).

CAVH:

CAVH stands for continuous arteriovenous hemofiltration. The blood pressure difference between an artery and a vein drives ultrafiltrate formation. This technique has largely been replaced by pump-driven venovenous procedures.

CVVH:

CVVH stands for continuous venovenous hemofiltration. A roller pump generates the pressure gradient in the blood circuit.

Hemodialysis:

Hemodialysis is an intermittent renal replacement therapy. Blood flows past a dialysate across a semipermeable membrane. Solute removal occurs primarily by diffusion, and fluid removal by ultrafiltration.

Hemodiafiltration:

Hemodiafiltration includes continuous venovenous hemodiafiltration (CVVHDF). Combining the above procedures increases the efficiency and speed of treatment.

Peritoneal dialysis:

Peritoneal dialysis involves infusing dialysate into the abdominal cavity and draining it after a dwell time that varies by technique. The peritoneum serves as the body's own dialysis membrane.

APD:

APD stands for automated peritoneal dialysis. A device repeatedly instills and drains dialysate, usually overnight.

CAPD:

CAPD stands for continuous ambulatory peritoneal dialysis. The patient manually infuses dialysate into the abdominal cavity and drains it after several hours. Usually, four exchanges are performed each day.

Epidemiology

In Europe in 2022, the incidence of renal replacement therapy was 152 patients per million population, and the prevalence was 1,074 patients per million population (8 % on hemodialysis, 12 % on peritoneal dialysis, and 5 % with preemptive kidney transplantation).

Technical Principles

Dialysis filter:

The dialysis membranes are housed in a casing with four ports: two for the blood circuit and two for the dialysate circuit. The membranes separate the two circuits.

Membrane:

The properties of a dialysis membrane include permeability (pore size), selectivity, and biocompatibility. Modern hemodialysis primarily uses synthetic high-flux membranes; cellulose membranes are now of historical interest only.

Capillary membrane: The membrane is arranged as a hollow fiber. The dialysis filter consists of thousands of hollow fibers.

Plate membrane: The membrane is arranged in multiple sheet-like layers within the dialysis filter.

Dialysis blood circuit:

Blood flow rates of 200–400 ml/min for hemodialysis and 100–250 ml/min for hemofiltration require a large-bore, double-lumen Shaldon venous catheter for acute dialysis. For chronic hemodialysis, an arteriovenous fistula in the arm is preferred. Alternatives include arteriovenous grafts and tunneled dialysis catheters.

Anticoagulation of the extracorporeal circuit depends on the procedure and the risk of bleeding. Unfractionated or low-molecular-weight heparin is usually used for intermittent hemodialysis. For continuous procedures, regional citrate anticoagulation is often preferred when there are no contraindications. Heparin-free dialysis may be necessary when the risk of bleeding is high.

Dialysate:

Buffered electrolyte solutions are used and can be adjusted as needed. Bicarbonate is usually used as the buffer.

Indications for Dialysis

Initiation of dialysis:

Indications include refractory hyperkalemia, acidosis, uremic symptoms, pericarditis, encephalopathy, bleeding tendency, or fluid overload. The GFR at which symptomatic uremia develops varies.

Indications for intermittent hemodialysis:

Intermittent hemodialysis is the preferred renal replacement therapy for mobile, clinically stable patients when extracorporeal dialysis is required.

Indications for continuous hemodiafiltration:

Continuous hemodiafiltration is the preferred renal replacement therapy for acutely ill patients who are hemodynamically unstable or fluid overloaded.

Indications for peritoneal dialysis:

Peritoneal dialysis is an equivalent dialysis modality for suitable patients and is particularly appropriate for those who prefer home dialysis, have residual kidney function, have difficult vascular access, are children, or prefer this modality. Relative contraindications include extensive intra-abdominal adhesions, inability to perform the procedure under sterile conditions, severe malnutrition, or unmanageable hernias.

Complications of Dialysis

Hypotension:

Hypotension is caused by rapid removal of extracellular volume, osmotic shifts, and autonomic dysregulation.

Dialysis disequilibrium syndrome:

Symptoms include headache, nausea, vomiting, visual disturbances, altered mental status, and seizures. The syndrome is caused primarily by rapid reduction of high urea concentrations, resulting in osmotic fluid shifts into the brain. It can be prevented with a gentle initial dialysis treatment of short duration and, if necessary, higher treatment frequency.

Bleeding:

The risk of bleeding is increased by anticoagulation of the extracorporeal circuit, platelet dysfunction following activation at the dialysis membrane, and uremia.

First-use syndrome:

First-use syndrome is an allergic to anaphylactic reaction during the first treatment, caused by intolerance to materials or sterilization residues. Risk factor: ACE inhibitor use, which prevents bradykinin inactivation.

References

Ifudu 1998 IFUDU, O.: Care of patients undergoing hemodialysis.
In: N Engl J Med
339 (1998), Nr. 15, S. 1054–62

Kierdorf 2000 KIERDORF, H. P.: [Current aspects of extracorporeal renal replacement therapy].
In: Internist (Berl)
41 (2000), Nr. 10, S. 1062–70

Pastan und Bailey 1998 PASTAN, S. ; BAILEY, J.: Dialysis therapy.
In: N Engl J Med
338 (1998), Nr. 20, S. 1428–37

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