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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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