Continuous Renal Replacement Therapies
Continuous Renal Replacement Therapies (CRRT)
CRRT is a routine therapeutic tool in intensive care settings with more than 100’000 treatments performed worldwide every year.
Slow Continuous UltraFiltration
SCUF
in case of
- Fluid overload
- Congestive heart failure
- Acute renal failure
SCUF is used to remove water from the body in case of fluid overload. Thus it allows to reduce the pressure within the body, especially on the heart, and to remove water that has cumulated within some organs, such as the lungs, and forms oedema there.
SCUF is usually performed from 4 to 24 hours, until the targeted water level within the patient is reached.
Technically speaking
In SCUF, blood is passed through a hemofilter which allows water to be filtrated, together with some other substances which are not of relevant importance in this case. The water is removed at a rate that is well tolerated by the patient and there is no compensation for the few undesired losses of other substances.
Continuous Veno-Venous Hemofiltration
CVVH
in case of
- Fluid overload
- Congestive heart failure
- Acute renal failure
- Crush syndrome
- Lactic acidosis
CVVH allows to remove all the substances that would normally be cleared by the kidneys such as water, urea, creatinin or salts, as well as medium size substances which result from an injury to body cells and are often nephrotoxic.
This therapy is usually performed continuously 24/24 until the renal function recovers, which may take from 2-3 days and up to 2-3 weeks.
Technically speaking
In CVVH, blood is passed through a hemofilter which allows water to be filtrated together with some other relevant substances , such as salts, urea, creatinin or other medium size substances, the resulting fluid being named ultrafiltrate. Ultrafiltrate is removed at a rate which allows the necessary clearances of desired substances. As this rate is often too important for other substances a substitution fluid is injected in the blood to compensate for undesired losses, such as that of water.
Continuous Veno-Venous HemoDialysis
CVVHD
in case of
- Acute renal failure
- Lactic acidosis
CVVHD allows to remove the substances that are the most commonly cleared by the kidneys such as water, urea, creatinine or salts. It has also some ability to remove the medium size substances which result from an injury to body cells however with less efficiency than CVVH.
It is a therapy that is usually performed continuously 24/24 until the renal function recovers, which may take from 2-3 days and up to 2-3 weeks.
Technically speaking
In CVVHD, blood is passed through a dialyzer while dialysate is circulated on the other side of the semi-permeable membrane across which the concentration differences of small substances will tend to equilibrate which is named diffusion or osmosis. In particular the substances to be removed from blood will migrate into the dialysate and the drained dialysate will take them away. The removal of water is added to the diffusion process by extracting more drained dialysate than the quantity of fresh dialysate injected, the difference of volume being water removed from the blood by filtration.
Continuous Veno-Venous HemoDiaFiltration
CVVHDF
in case of
- Fluid overload
- Congestive heart failure
- Acute renal failure
CVVHDF is a combination of hemofiltration and hemodialysis which can be preferred to these 2 methods. Reasons for this are, for example, the higher clearance of medium size substances when compared to hemodialysis or less dependence on blood flow when compared to hemofiltration.
It is a therapy that is usually performed continuously 24/24 until the renal function recovers, which may take from 2-3 days and up to 2-3 weeks.
Technically speaking
In CVVHDF, blood is passed through a hemofilter while dialysate is injected on the other side of the semi-permeable membrane. During treatment a significant amount of ultrafiltrate is also extracted from blood thus combining the filtration process and the dialysis one. In CVVHDF, substitution fluid must be injected in the blood to compensate for the filtration flow.
A bit ofHistory
CRRT is a routine therapeutic tool in intensive care ; its story has started during the seventies.
In 1977, Dr. Peter Kramer was the first one to describe such type of therapy in the literature. It was named CAVH (Continuous Arterio-Venous Hemofiltration) because the blood was moved from an artery to a vein through a hemofilter. Ultrafiltration rate was controlled by raising and lowering the drain bag which allows to modify the transmembrane pressure (TMP).
Because of the hypotension experienced by critically ill patients the blood flow of the AV method, where the difference of pressure between artery and venous vessels is used to create the flow, is low and limits the volume of ultrafiltrate which can be obtained.
In 1982 the US FDA (Food and Drug Administration) approves CAVH.
From the early 80’s a blood pump and a double-lumen catheter in a large vein are used to provide a consistent blood, and thus ultrafiltration, flow. This so called Veno-Venous technique has been since then adopted and improved to become the most standard in CRRT.
In the 90’s the first fully automatic machines are made and become immediately popular in intensive care settings.
Since the beginning of the millenium, technology has been improved to achieve better clinical outcomes and reach high safety levels for the patients. With this philosophy in mind, Infomed has designed devices which for example :
- Perform higher flows thus higher clearances
- Allow new therapies such as CPFA
- Optimise the blood flow,
- Display treatment values overtime on graphs
In 2002, the ADQI (Adequate Dialysis Quality Initiative) group gives the first consensus definition of ARF (Acute Renal Failure), the main reason to perform CRRT. Later the term AKI (Acute Kidney Injury) has appeared as a synonymous.
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