Acute and chronic
Haemodialysis

 

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A full range of haemodialysis services are available for the treatment of acute renal failure, end-stage chronic renal failure and poisoning or drug overdoses.

Haemo is the Greek word for blood and Dialysis means a filtering process.

Haemodialysis is therefore the process by which excess waste products and fluid are removed by using a dialyser. A dialyser is a bundle of hollow fibres made from a semi-permeable membrane. During dialysis blood is allowed to flow on one side of the membrane and dialysate solution on the other, and osmosis and diffusion takes place across the membrane. This is controlled and monitored by the dialysis machine.

Dialysis is required approximately 3 times per week with each session lasting 3-5 hours. Vascular access for chronic dialysis is obtained hrough one of the following:

  • Arterio-venous fistula
  • Arterio-venous graft
  • Temporary or permanent dialysis catheter inserted into a central vein

Acute renal failure - modes of therapy

There have been significant advances in the therapeutic options for renal replacement therapy over the last decade . For many years intermittent hemodialysis has been the standard form of dialysis to treat acute renal failure (ARF). Because of cardiovascular instability, sepsis, adult respiratory distress syndrome (ARDS), shock and multiorgan failure, many developed hypotension during the dialysis procedure . Continuous renal replacement therapies (CRTT) modalities have subsequently found widespread use and acceptance, in these circumstances.

Intermittent Hemodialysis

Still acceptable and standard form of treatment for ARF in both ICU and non-ICU settings. The vast majority of IHD is performed using single pass systems with countercurrent dialysate flow at rates greater than blood flow. Advances has been made with volumetric machines with precise ultrafiltration control.

The hemodynamically stable patient is better treated with IHD. In the indication of drug overdosage, IHD is a logical choice given its efficacy and rapidity of response.

Continuous venovenous therapies

Venous access is obtained by a dual-lumen catheter inserted in a central vein . A blood pump is used to provide sufficient blood flow and to create an adequate transmembrane pressure(TMP) for ultrafiltration . Alarms and safety features are built into the systems (venous bubble trap, air detector, arterial and venous pressure monitors) to avoid air emboli or bleeding from accidental disconnection. The use of a blood pump during continuous venovenous hemofiltration (CVVH) achieves a higher blood flow rate (100 - 200 ml/min ) compared with to CAVH . The replacement fluid is either administered before the filter (predilution) or after the filter (postdilution). Continuous hemodialysis uses a dialysate flow countercurrent to the blood flow through the dialyzer. Urea, creatinine, and potassium diffuse along a concentration gradient from blood to dialysate and lactate or bicarbonate passes in the opposite direction, thereby compensating for bicarbonate losses from plasma into dialysate.

Minimal technical requirements for venovenous therapies are a bloodpump, a dialysis membrane or haemofilter, arterial and venous pressure monitors, a venous air bubble chamber, an air detector and a balancing system for dialysate/replacement fluid with dialysate outflow/filtrate.

Indications and newer indications for CRRT

  • ARF and haemodynamic instability
  • ARF with multiple organ failure
  • ARF and sepsis
  • Oliguria + septic shock
  • Oliguria in ARDS
  • Oliguria in cerebral oedema
  • SIRS ( Systemic Immuno Response Syndrome)

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