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Indications, Techniques, and Complications of Dialysis

Different Techniques of Dialysis Procedures

Hemofiltration:

Hemofiltration is a continuous renal replacement procedure. A filtrate is obtained from the blood using a semipermeable membrane with a specific pore size, which is replaced by a solution with the desired electrolyte composition (Kierdorf et al., 2000).

CAVH:

CAVH stands for continuous arteriovenous hemofiltration. The blood pressure difference between the artery and vein is the driving force for the formation of the ultrafiltrate.

CVVH:

CVVH stands for continuous venovenous hemofiltration. The pressure difference is built up with a roller pump.

Hemodialysis:

Hemodialysis is an intermittent kidney replacement procedure. A dialysate flows around the blood, separated by a semipermeable membrane. The exchange of substances takes place exclusively by diffusion.

Hemodiafiltration:

Hemodiafiltration is also called continuous venovenous hemodiafiltration (CVVHDF). The combination of above-mentioned replacement procedures increases effectiveness and speed.

Peritoneal dialysis:

Peritoneal dialysis is the infusion of a dialysate into the abdominal cavity, which is removed after an exposure time.

APD:

APD stands for automated peritoneal dialysis. The dialysate is automatically inserted into and removed from the abdominal cavity several times; the technique is used at night.

CAPD:

In continuous ambulatory peritoneal dialysis, the dialysate is manually infused (by the patient) into the abdominal cavity and drained after several hours. Usually, four cycles are carried out per day.

Technical Basics of Dialysis

Dialysis filter:

The dialysis membranes are housed in a case with four connections, two connections for blood circulation and two connections for dialysate circulation. The dialysis membranes separate the two circuits.

Dialysis membranes:

Principal properties of the dialysis membrane are the permeability (pore size) and the selectivity of the membrane for passive diffusion. Cellulose membranes are used for hemodialysis, and synthetic polymer membranes (e.g., polyamide) with a pore size for molecules of 15,000 to 30,000 Daltons are used for hemofiltration.

• Capillary membrane: the membrane is a hollow fiber, the dialysis filter consists of thousands of hollow fibers.
• Plate membrane: the membrane is built into the dialysis filter in many layers.

Hemodialysis circuit:

The flow rate of the extracorporeal blood circulation is 200–250~ml/min for hemodialysis and 300–400~ml/min for hemofiltration, therefore solid vascular access is needed: thick two-lumen Sheldon venous catheter (acute hemodialysis) or a surgically created AV fistula (Chimino shunt), which is punctured twice for outflow and inflow.

Systemic anticoagulation with heparin is necessary for continuous hemofiltration. If there is a risk situation (after trauma or GI bleeding), heparin can be avoided during intermittent hemodialysis.

Dialysate:

The dialysate is a buffered electrolyte solution, which can be varied as required. Bicarbonate is usually used as a buffer in hemodialysis and lactate in hemofiltration.

Indications for Dialysis

Timing:

Indications to commence dialysis are therapy-resistant hyperkalemia, acidosis, uremic symptoms, pericarditis, or fluid overload. The level of GFR for symptomatic uremia is variable.

Indications for intermittent hemodialysis:

Intermittent hemodialysis is the renal replacement therapy of choice in mobile and clinically stable patients.

Indications for continuous hemodiafiltration:

Continuous hemodiafiltration is a renal replacement therapy for acutely ill and unstable patients in ICU. Hemofiltration is used in sepsis or burns to eliminate toxic metabolites.

Indications for peritoneal dialysis:

Vascular access failure, children, intolerance of hemodialysis, patients with diabetic retinopathy, severe heart insufficiency, patient with an active lifestyle.

Complications of Dialysis

Hypotension:

Hypotension during dialysis is caused by withdrawing extracellular volume and osmotically active metabolites.

Dysequilibrium syndrome:

Dysequilibrium syndrome is caused by an overly rapid correction of electrolytes and toxic metabolites in patients with significant uremia; the symptoms are headache, nausea, vomiting, visual disturbances, vigilance disorders, and convulsions. Gentle (short) initial dialysis treatment with a high (daily) frequency avoids dysequilibrium syndrome.

Bleeding:

The increased risk of bleeding is due to systemic heparinization and platelet dysfunction (due to false activation on the dialysis membrane and uremia).

First-use syndrome:

The first-use syndrome causes allergic symptoms during the first dialysis treatment caused by an intolerance to materials or residuals of the sterilization process. Risk factor: ACE inhibitor (prevents inactivation of bradykinin).

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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